No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Effects of various mixed salt-alkaline stresses on growth, photosynthesis, and photosynthetic pigment concentrations of Medicago ruthenica seedlings
Abstract
Soil salinization and alkalinization frequently co-occur in naturally saline and alkaline soils. To understand the characteristics
of mixed salt-alkali stress and adaptive response of Medicago ruthenica seedlings to salt-alkali stress, water content of shoots, growth and photosynthetic characteristics of seedlings under 30
salt-alkaline combinations (salinity 24–120 mM and pH 7.03–10.32) with mixed salts (NaCl, Na2SO4, NaHCO3, and Na2CO3) were examined. The indices were significantly affected by both salinity and pH. The interactive effects between salt and
alkali stresses were significant, except for photosynthetic pigments. Water content of shoots, relative growth rates of shoots
and roots and pigment concentrations showed decreasing trends with increasing salinity and alkalinity. The root activity under
high alkalinity and salinity treatments gradually decreased, but was stimulated by the combined effects of low alkalinity
and salinity. The survival rate decreased with increased salinity, except at pH 7.03–7.26 when all plants survived. Net photosynthetic
rate, stomatal conductance and intercellular CO2 concentration decreased with increased salinity and pH. M. ruthenica tolerated the stress of high salt concentration when alkali concentration was low, and the synergistic effects of high alkali
and high salt concentrations lead to the death of some or all seedlings. M. ruthenica appeared to be saltalkali tolerant. Reducing the salt concentration or pH based on the salt components in the soil may be
helpful to abate damage from mixed salt-alkaline stress.
Additional key wordsmixed salt-alkali stress–
Medicago ruthenica
–relative growth rate–root activity–photosynthesis–photosynthetic pigments–water content
... Mixed salinity and alkalinity stress often occurs naturally, and the effect of mixed salinity and alkalinity stress is very different from individual salt or alkali stresses due to the significant interaction between ion toxicity, osmotic effects, and high pH. Osmotic effects and ionic toxicity effects depend on salt concentration, while pH effects depend on buffer capacity [4]. This means that the higher the concentration of salt and alkalinity, the greater the buffer capacity. ...
... Under conditions of salinity stress, there is an increase in the activity of the enzyme chlorophyllase, leading to chlorophyll degradation. Consequently, as the stress level rises, there is a more pronounced reduction in the plant's chlorophyll content [4,29]. The decrease in chlorophyll content, induced by heightened chlorophyllase enzyme activity under salinity and alkalinity stress, is associated with the accumulation of specific ions. ...
... Iron deficiency can further contribute to a decrease in chlorophyll concentration. Iron, as a vital element, plays a crucial role in various metabolic and enzymatic processes, including chlorophyll biosynthesis, electron transport, photosynthesis, and nitrogen fixation [4]. ...
Background
This study explores the impact of various light spectra on the photosynthetic performance of strawberry plants subjected to salinity, alkalinity, and combined salinity/alkalinity stress. We employed supplemental lighting through Light-emitting Diodes (LEDs) with specific wavelengths: monochromatic blue (460 nm), monochromatic red (660 nm), dichromatic blue/red (1:3 ratio), and white/yellow (400–700 nm), all at an intensity of 200 µmol m⁻² S⁻¹. Additionally, a control group (ambient light) without LED treatment was included in the study. The tested experimental variants were: optimal growth conditions (control), alkalinity (40 mM NaHCO3), salinity (80 mM NaCl), and a combination of salinity/alkalinity.
Results
The results revealed a notable decrease in photosynthetic efficiency under both salinity and alkalinity stresses, especially when these stresses were combined, in comparison to the no-stress condition. However, the application of supplemental lighting, particularly with the red and blue/red spectra, mitigated the adverse effects of stress. The imposed stress conditions had a detrimental impact on both gas exchange parameters and photosynthetic efficiency of the plants. In contrast, treatments involving blue, red, and blue/red light exhibited a beneficial effect on photosynthetic efficiency compared to other lighting conditions. Further analysis of JIP-test parameters confirmed that these specific light treatments significantly ameliorated the stress impacts.
Conclusions
In summary, the utilization of blue, red, and blue/red light spectra has the potential to enhance plant resilience in the face of salinity and alkalinity stresses. This discovery presents a promising strategy for cultivating plants in anticipation of future challenging environmental conditions.
... Therefore, alkaline salt causes more serious effects than neutral salt stress on plants. Soil alkalization can reduce soil osmotic potential, and cause ion imbalance, disrupt physiological processes, inhibit the growth and development of plants, leading to a serious decline in the yield and quality, and even the death of plants (Yang et al., 2011). Saline-alkali stress leads to leaf wilting and chlorosis , fewer pods, seeds and lower 100-seed weight , inhibited nodule development and other phenomena (Chen et al., 2018) of soybean, resulting in soybean growth retardation, and eventually lead to a serious decline in soybean yield . ...
... Soil salinization and alkalization can reduce soil osmotic potential, and cause ion imbalance, disrupt physiological processes, inhibit growth and development of plants, leading to a serious decline in its yield and quality, and even the death of plants (Zhu, 2001;Yang et al., 2011). Soil salinization and alkalization frequently co-occur, but in the saline-alkaline land in mainland China, the soil salinization caused by alkali salts such as NaHCO 3 and Na 2 CO 3 is more serious than that caused by neutral salts such as NaCl and Na 2 SO 4 (Yang et al., 2008(Yang et al., , 2011. ...
... Soil salinization and alkalization can reduce soil osmotic potential, and cause ion imbalance, disrupt physiological processes, inhibit growth and development of plants, leading to a serious decline in its yield and quality, and even the death of plants (Zhu, 2001;Yang et al., 2011). Soil salinization and alkalization frequently co-occur, but in the saline-alkaline land in mainland China, the soil salinization caused by alkali salts such as NaHCO 3 and Na 2 CO 3 is more serious than that caused by neutral salts such as NaCl and Na 2 SO 4 (Yang et al., 2008(Yang et al., , 2011. In general, the stress factors of neutral salts are mainly the ion stress of Na + and osmotic stress of low water potential caused by high salt concentration, but for the alkaline salts, there is an added factor of high pH (Shi et al., 1998). ...
Alkaline soil has a high pH due to carbonate salts and usually causes more detrimental effects on crop growth than saline soil. Sodium hydrogen exchangers (NHXs) are pivotal regulators of cellular Na⁺/K⁺ and pH homeostasis, which is essential for salt tolerance; however, their role in alkaline salt tolerance is largely unknown. Therefore, in this study, we investigated the function of a soybean NHX gene, GmNHX6, in plant response to alkaline salt stress. GmNHX6 encodes a Golgi-localized sodium/hydrogen exchanger, and its transcript abundance is more upregulated in alkaline salt tolerant soybean variety in response to NaHCO3 stress. Ectopic expression of GmNHX6 in Arabidopsis enhanced alkaline salt tolerance by maintaining high K⁺ content and low Na⁺/K⁺ ratio. Overexpression of GmNHX6 also improved soybean tolerance to alkaline salt stress. A single nucleotide polymorphism in the promoter region of NHX6 is associated with the alkaline salt tolerance in soybean germplasm. A superior promoter of GmNHX6 was isolated from an alkaline salt tolerant soybean variety, which showed stronger activity than the promoter from an alkaline salt sensitive soybean variety in response to alkali stress, by luciferase transient expression assays. Our results suggested soybean NHX6 gene plays an important role in plant tolerance to alkaline salt stress.
... As a result, the accumulation of these pigments is considered to be related to photosynthetic functions of leaves. Many previous studies reported different effects of salt stress on chlorophylls, depending on plant species and the salinity level [7,[30][31][32]. In our study, the results showed that the chl a and chl b accumulations were maintained under the salinity, even enhanced (as for chl a) under the extreme saline condition (400 mM NaCl) (Figure 4). ...
... The similar pattern of change in the accumulation of chlorophylls was reported for a halophyte Kalidium foliatum under high salinity [31]. It is proposed that salt stress increases the chlorophyllase activity that promotes the degradation of chlorophylls and reduces the chlorophyll content in plants, and the effect degree depends on the salt tolerance of plants [31,32]. However, the accumulation of chlorophylls was maintained, and even the salt-induced increase in the chl a accumulation occurred in the P. nodiflora shoots under the 400 mM NaCl treatment ( Figure 4). ...
Phyla nodiflora is a valuable medicinal plant growing in coastal areas, hypothesizing its adaptability to salinity; however, it has not been investigated. This study, for the first time, elucidated responses in the growth of the shoots and its physiology to different soil salinity of 50–400 mM NaCl. The data showed that the shoot’s dry biomass was not affected by the salinity levels up to 100 mM, and it only decreased 33.50–56.33% compared to the control under 200–400 mM NaCl, indicating that P. nodiflora is a salt-tolerant plant that could survive under high salinity. In addition, the plant also had physiological responses which indicated its salt-induced injuries and adaptation to the salt stress. The chlorophyll a content was increased while the chlorophyll b remained unchanged under the salt stress. The proline and salt accumulation increased under the salinity, but the K+ and NO3− accumulation decreased. Moreover, increases in malondialdehyde and electrolyte leakage were observed, indicating salt-induced membrane damages. These responses suggested that the plant might evolve adaptive mechanisms to salinity. Our findings are useful information for further research in order to elucidate the salt-tolerant mechanisms and develop this plant for saline agriculture.
... The alkalization of soil has become a global environmental problem and is portant factor limiting agricultural productivity [44]. Using biological safety com to improve plant productivity and quality has recently received much attention. ...
... The alkalization of soil has become a global environmental problem and is an important factor limiting agricultural productivity [44]. Using biological safety compounds to improve plant productivity and quality has recently received much attention. ...
Citation: Youssef, S.M.; Abdella, E.M.M.; Al-Elwany, O.A.; Alshallash, K.S.; Alharbi, K.; Ibrahim, M.T.S.; Tawfik, M.M.; Abu-Elsaoud, A.M.; Elkelish, A. Integrative Application of Foliar Yeast Extract and Gibberellic Acid Improves Morpho-Physiological Responses and Nutrient Uptake of Solidago virgaurea Plant in Alkaline Soil. Life 2022, 12, 1405. https://
... The ecological management and amendment of saline-alkaline land is of great importance for enhancing the stability of ecological systems, improving soil productivity, and promoting the utilization efficiency of resources. In addition, the area of saline-alkali land has consistently grown by (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15) × 10 6 hm 2 per year [3,4]. Salinealkali soil, as one of the dominant soil types in ecologically fragile areas of China, is widely distributed, especially in the northwest, north, and northeast regions of China and coastal areas [5], and other countries such as the USA and Spain [6,7].Saline-alkali soils are found in most of the cultivated land in these areas [8]. ...
... With respect to China, a total of 8.18 × 10 7 hm 2 of cultivated land is classified as saline-alkali land, and 1.77 × 10 7 hm 2 of cultivated land has a potential saline-alkali risk [9,10]. The saline-alkalinity of soil is a growing problem throughout the world due to a shortage of fresh water, rapid evaporation, and excessive irrigation and fertilization [11][12][13]. ...
The effective and safe use of FGD gypsum in agricultural land is still debated in some countries even though its effectiveness in soil management has been reported in many studies. Thus, the changes in the levels of soil salinity, alkalinity, crop yield, and other physicochemical properties in different soil types and crops after reclamation and planting with FGD gypsum over four years are evaluated in this paper. The main aim of this paper is to review the effects of six treatment technologies in addressing soil salinity and sodicity and crop production in soils, with a focus on the basic theory, key technologies, and industrialized applications. This paper also shows that soil conditions can be improved and crop yields can be increased by using FGD alone or in combination with humic acid or fertilizer. FGD gypsum plus K–Zn–Mn fertilizer increased the yield of rice by 135%. In alkaline, salinized, and secondary salinized soils, FGD gypsum combined with organic fertilizer or organic plus chemical fertilizer increased the yield of rice by 21.2% and 60.4%, the yield of sunflower by 2.4% and 23.6%, and the yield of medlar by 18.81% and 20.78%, respectively. The application of FGD gypsum also increased the salt tolerance of salt-tolerant plants. Combined with drainage, laser field levelling and tillage decreased soil salinity by more than 63.76% and increased the yield of oil sunflower by up to 96.96%. This study provides convincing evidence of the benefits of the application of the six treatments to reclaim saline–alkali soils. It is suggested that comprehensive measures should be taken to improve saline–alkaline soil.
... Saline-alkali heterogeneity is one of the most important soil chemical properties affecting plant growth. Soil salinization has become an increasingly serious global environmental problem because of the large-scale degradation of grasslands (Munns and Tester, 2008;Yang et al., 2011). Salinity is always heterogeneously distributed in local habitats, especially on degraded grasslands. ...
... Two neutral salts (NaCl and Na 2 SO 4 ) and two alkaline salts (NaHCO 3 and Na 2 CO 3 ) were selected for this experiment to simulate the salt components in the soil of the Songnen Plain in Northeast China (Yang et al., 2011). Four salts were mixed at a molar ratio of 1:1:1:1, and according to different concentrations: no salinealkali (0 mmol L −1 , pH = 7.20, EC = 63 μs cm −1 ), low-saline-alkali (100 mmol L −1 , pH = 8.97, EC = 523 μs cm −1 ), or high-saline-alkali (200 mmol L −1 , pH = 9.70, EC = 1209 μs cm −1 ). ...
Soil salinity is well known heterogeneous and various within natural soil environment. In Songnen grassland of Northeast China, grazing aggravates the saline-alkali heterogeneity in soil habitat, which led to dominant clonal plant species forming a variety of adaptive strategies. However, based on the previous studies of morphological plasticity and clonal integration in clonal plants, there was a lack of mechanism research on the spatial expansion strategy of clonal plants population subjected to clipping in saline-alkali heterogeneity soil patches. To address this knowledge gap, we carried out an experiment by applying different clipping intensities (0%, 35%, 70% of the above-ground biomass removed) to explore the spatial expansion strategy and morphological plasticity of Leymus chinensis and their belowground rhizomes in different heterogeneous saline-alkali patches. We found that, clipping significantly decreased the plant average height and above-ground biomass in homogeneous patches, especially heavy clipping had a significant adverse impact on plant belowground (rhizome, fine root) biomass and leaf area. However, there was no significant difference in the biomass, average height, and leaf area among the clipping treatments in low saline-alkali heterogeneous patches. In addition, the number of leaves, daughter plants and rhizome internode buds were significantly affected by saline-alkali heterogeneity alone, and low saline-alkali heterogeneity had a positive effect on these parameters. Biomass accumulation and rhizome expansion were gradually inhibited by the increasing of clipping intensity in a homogeneous environment, but the inhibitory effect of clipping was not significant in saline-alkali patches soil. We concluded that L. chinensis can respond to grazing or mowing disturbance by increasing tiller and daughter-plant numbers in a saline-alkali heterogeneous environment. The saline-alkali patches promoted clonal plant population spatial expansion more than grazing or mowing disturbance did. This study emphasizes saline-alkali heterogeneity distribution patterns in grassland soil environment were the primary and important driving factor promoting the spatial expansion of L. chinensis.
... The alkalization of soil has become a global environmental problem and is portant factor limiting agricultural productivity [44]. Using biological safety com to improve plant productivity and quality has recently received much attention. ...
... The alkalization of soil has become a global environmental problem and is an important factor limiting agricultural productivity [44]. Using biological safety compounds to improve plant productivity and quality has recently received much attention. ...
Alkaline soils have fertility issues due to poor physical qualities, which have a negative impact on crop growth and output. Solidago is used in flower arrangements, bouquet filler, and traditional medicine. The possible biological fertilizers’ eco-friendly and cost-effective nature favours farmers because of the vital role in soil productivity and environmental sustainability. A field experiment was performed during two successive seasons to explore the effect of applying yeast extract (YE) at (0, 0.5, 1.0, and 1.5 g/L) and/or gibberellic acid (GA3) at (control, 100, 200, and 300 ppm) on the morpho-physiological parameters, macronutrients, and biochemical constituents of Solidago virgaurea. The results emphasize that YE (1.5 g/L) and/or GA3 (300 ppm) treatments show the highest significant increase in plant growth (i.e., plant height, no. of branches, fresh and dry weight of shoots); photosynthetic efficiency (i.e., chlorophyll (a), chlorophyll (b) and total carotenoids); macronutrient content (i.e., N, P, and K); and biochemical constituents (i.e., total soluble sugars, total phenolic, total flavonoids, and total glycosides). The study results recommend using YE and GA3 in combination at concentrations of 1.5 g/L and 300 ppm, respectively, to improve Solidago production sustainability under alkaline soil conditions.
... Salt, alkali, and drought are important abiotic stressors that threaten crop yield [4][5][6]. Soil salinization and alkalization can reduce soil osmotic potential, and cause ion imbalance, disrupt physiological processes, and inhibit the growth and development of plants, leading to a serious decline in its yield and quality, and even the death of plants [6,35]. It is also known that under drought stress, soybean yield will be significantly reduced [36]. ...
... Overexpression Can Improve the Tolerance of Soybeans and Arabidopsis to NaHCO 3 , NaCl, and Mannitol Stresses Salt, alkali, and drought are important abiotic stressors that threaten crop yield [4][5][6]. Soil salinization and alkalization can reduce soil osmotic potential, and cause ion imbalance, disrupt physiological processes, and inhibit the growth and development of plants, leading to a serious decline in its yield and quality, and even the death of plants [6,35]. It is also known that under drought stress, soybean yield will be significantly reduced [36]. ...
Soybean [Glycine max (L.) Merri.] is an important oilseed and food crop. In recent years, environmental degradation has accelerated soil alkalization, salinization, and water deficit, which have seriously threatened the soybean quality and yield. Chaperone DNAJ proteins play important roles in plant response to a number of abiotic and biotic stresses. Here, we investigated the function of a soybean DNAJ gene, GmDNAJC7, in plant tolerance to abiotic stresses. GmDNAJC7 gene expression was induced by alkaline-salt, salt, and drought treatments in soybean roots, suggesting its possible role in soybean response to these stresses. GmDNAJC7 overexpression improved the alkaline-salt tolerance of soybean composite plants, which showed a higher SPAD (Soil and Plant Analysis Development) value for chlorophyll content and leaf relative water content than the control plants after NaHCO3 treatment. Moreover, the GmDNAJC7 overexpressing Arabidopsis had a higher germination rate and average root length than the wild type and dnajc7 mutant, under NaHCO3, NaCl, and mannitol stresses, indicating that the ectopic expression of the GmDNAJC7 gene enhanced the alkaline-salt, salt, and drought tolerance in Arabidopsis. These findings suggest that GmDNAJC7 is involved in the alkaline-salt, salt, and drought tolerance in Arabidopsis and soybean. This study provides new insights into the role of DNAJ proteins in plant tolerance to abiotic stress.
... Moderate potassium supplementation promotes chlorophyll synthesis and stability, while excessive potassium supply negatively impacts chlorophyll synthesis by burdening the plant, resulting in reduced chlorophyll content [35,36]. In this study, chlorophyll a, b, and total chlorophyll content of P. chinensis seedling leaves exhibited an initial increase and subsequent decrease with increasing potassium application levels, reaching the highest content at K4 (160 mg·K·plant −1 ), applied with N and P. ...
Parashorea chinensis, an endemic tree species in China’s tropical rainforests, holds ecological and economic importance. Challenges like low resistance, poor quality, and low survival rates hinder its successful cultivation. This study explores the potential of autumn potassium fertilization on Parashorea seedlings from two provenances (Napo and Tianyang). The treatments included no fertilizer (CK-1), a single application of 160 mg K·plant−1 (CK-2), and various potassium levels K1, K2, K3, K4, K5, and K6 (corresponding to 0, 40, 80, 160, 320, and 640 mg·K·plant−1, respectively) combined with nitrogen (200 mg·plant−1) and phosphorus (80 mg·plant−1) fertilization. The findings indicate that autumn potassium application, in conjunction with nitrogen (N) and phosphorus (P) fertilization, significantly enhances seedling height and biomass in both provenances, resulting in an average increase of 101% and 89% under the K4 treatment compared to CK-1 and CK-2, comparatively. Both Napo and Tianyang provenances exhibited distinct responses in photosynthetic rate (2.70 μmol·m−2·s−1 and 1.97 μmol·m−2·s−1, respectively) and stomatal conductance (0.042 mol·m−2·s−1 and 0.029 mol·m−2·s−1, respectively) to the K4 treatment, which proved most effective. The chlorophyll content was significantly higher for Napo provenance with the K3 treatment (74.31%, 58.99%), while for Tianyang, it was higher with the K4 treatment (41.48%, 17.36%), compared to CK-1 and CK-2, respectively. Antioxidant enzymes activity, osmoregulatory capacity, and malondialdehyde content all exhibited variations with potassium application levels, with the K4 treatment offering significant benefits. In Napo provenance, lignin (199.82 mg·g−1) and cellulose (252.38 mg·g−1) peaked at K4, while Tianyang exhibited variation, higher lignin (184.25 mg·g−1) at K3, and cellulose (257.73 mg·g−1) at K4. Nutrient content analysis demonstrates that the K4 treatment enhances nutrient absorption and storage, increasing total N (21.56 mg·kg−1), P (4.69 mg·kg−1), and K (13.49 mg·kg−1) content. A comprehensive analysis reveals that the K4 treatment yields the highest quality scores (1.87, 1.85) and membership values (0.82, 0.68) for both Napo and Tianyang seedlings, with Napo seedlings outperforming their Tianyang provenance. Thus, treatment K4 underscores the effectiveness of autumn potassium applications for robust seedling cultivation and adaptation, offering valuable insights for sustainable cultivation practices.
... This will also produce a large amount of reactive oxygen species (ROS) in the plant, causing damage to the plant cell membrane system, and thereby affecting the physiological and biochemical reactions in the cells [3][4][5]. Alkaline soil can do more damage to plants than a saline soil because of its higher pH, which can affect the ion balance and nutrient absorption [6]. To overcome the harm caused by salinity-alkali stress, plants will also carry out a series of mechanistic adjustments to maintain normal growth, such as the accumulation of osmoregulatory substances, the enhancement of antioxidant systems, and the transport of numerous toxic ions to the vacuoles [7][8][9][10]. ...
Syneilesis aconitifolia is a potential ground cover and decorative material in gardens, which exhibits a strong salt-alkali tolerance, and also has medicinal value. In this study, the arbuscular mycorrhizal (AM) fungi community in the soil surrounding S. aconitifolia roots in the Songnen saline-alkali grassland was used as the inoculation medium for a pot cultivation experiment. After normal culture for 90 days, NaCl and NaHCO3 solutions were applied to subject plants to salt or alkali stress. Solution concentrations of 50, 100, and 200 mmol/L were applied for 10 days, and mycorrhizal colonization, biomass, relative water content (RWC), chlorophyll concentration, malondialdehyde (MDA) concentration, antioxidant system activity, and osmomodulator concentration were determined to identify the effects of AM fungi on root colonization status and salinity tolerance in S. aconitifolia. There were three key results. (1) Compared to the controls, the intensity and rate of colonization decreased under saline-alkali stress, and the adaptability of AM fungi under low concentration alkali stress was higher than that under salt stress. (2) The AM fungi could increase the biomass, RWC, and chlorophyll concentration, and decrease the MDA concentration of S. aconitifolia to some extent. With an increase in the salt or alkali solution concentration, AM fungi not only upregulated the activity of the antioxidant system, but also increased the concentration of osmotic regulatory substances. (3) A multivariate analysis of variance (ANOVA) and radar map analysis showed that the mechanisms of resistance to salt and alkali stress were not the same in S. aconitifolia. In the salt treatment, AM fungi mainly regulated salt stress through osmotic regulatory substances such as soluble sugars, soluble proteins, and proline. In the alkali treatment, AM fungi mainly regulated alkali stress through glutathione (GSH), soluble sugars, and MDA. The results showed that the colonization rate of S. aconitifolia under low concentration alkali stress was higher than that under salt stress, and the inoculation of AM fungi could significantly reduce the MDA concentration of S. aconitifolia plants under salinity and alkali stress, and improve the antioxidant enzyme activity and osmoregulatory substance accumulation, thereby improving the salinity tolerance of S. aconitifolia.
... Medicago ruthenica (L.), as a perennial legume forage (Small and Marcel, 1989), is closely related to alfalfa (Medicago sativa), which is an excellent germplasm material for cross breeding of Medicago genus (Guan et al., 2009;Yang et al., 2011). M. ruthenica is highly adaptable to drought, low temperature, high temperature, salinealkali and other harsh environment, so it is considered as a valuable forage for both artificial and natural grasslands (Campbell et al., 1997;Campbell et al., 1999). ...
Medicago ruthenica is closely related to Medicago sativa, a commonly cultivated forage. Characterized by its high tolerance to environmental stress, M. ruthenica is a valuable genetic resource. However, low yield limits its large-scale utilization. Leaf morphology, an important agronomic trait, is closely related to forage yield and photosynthetic efficiency. In the presented study, “Correlation of Leaf Morphology and Photosynthetic Performance with Forage Yield in Medicago ruthenica: The Underlying Molecular Mechanisms,” comprehensive data analysis revealed a significant positive association between leaf width and leaf area with forage yield in Medicago ruthenica (p < 0.05). The specific cultivar “Mengnong No.1 (MN No.1) had a large leaf area, and its physiological parameters related to photosynthetic characteristics were superior. Anatomical examination revealed that the leaves of MN No.1 had strong palisade tissue and compact cell structure. Subsequent investigations, utilizing small RNA and transcriptome sequencing, discerned critical miRNA-target gene networks that underpin the high photosynthetic efficiency in M. ruthenica. A total of 63 differentially expressed miRNAs (DEMs) were identified, inclusive of several well-characterized miRNAs such as miR408, miR171, and miR398. These miRNAs were predicted to target 55 genes (mRNAs), of which 6 miRNA-target gene pairs, particularly those involving miR408and miR171, exhibited inverse expression patterns. Among the six postulated miRNA-target gene pairs, the targeted cleavage of LACCASE5 (LAC5) by miR408 was conclusively validated through degradome sequencing, with the cleavage site pinpointed between the 9th and 10th nucleotides from the 5′end of miR408 via the 5′-RLM-RACE assay. Therefore, it is posited that the miR408-MrLAC5 module constitutes a central mechanism in fostering high photosynthetic efficiency in M. ruthenica. Moreover, these findings also provide valuable information for further study of the regulatory genes and miRNA functions of forage yield in legume forage.
... Salt stress environments have been reported to reduce the contents of the photosynthetic pigments. For example, salt stress destroys Chl, resulting in a decrease in photosynthetic pigments such as Chl a and band C ar ; the effect is attributed to the increased content of the toxic cation Na + (Pinheiro et al., 2008;Yang et al., 2011). C ar is essential for the photoprotection of photosynthesis and plays an important role as a signaling precursor during plant development under abiotic and biotic stresses and has significant potential to improve nutrient quality and plant yield (Ashraf and Harris, 2013). ...
Cherry tomato (Lycopersicon esculentum var. cerasiforme) is a relatively salt-tolerant fruit and vegetable widely planted worldwide. In this study, the growth and physiological responses and the different regulatory of cherry tomatoes under high, low salinity, and partial root zone salinity conditions were investigated. Cherry tomatoes grown under nonuniform salinity (0/20, 0/100 mM NaCl) conditions in a split-root pot were compared with seedlings grown under uniform salinity (20, 100 mM NaCl) conditions, and their growth and physiological parameters were determined. Our results showed that the growth was not hindered under a low salinity (20 mM NaCl), and the fruit quality was improved without a yield reduction; this was caused by promoted root growth and better leaf function maintenance. The relief effects under the higher salt stress (100 mM NaCl) conditions were more significant than those under a lower salt stress condition (20 mM NaCl). Compared with uniform high salinity conditions, nonuniform salinity conditions could improve photosynthetic characteristics and maintain better leaf function. The apparent quantum efficiency (AQE), carboxylation efficiency (CE) and light saturation irradiance (LSP) increased, while the light compensation point (LCP) and CO 2 compensation point (CCP) decreased; this enhanced the light energy and CO 2 utilization. Chlorophyll content (Chl), including Chl a and b and the carotenoids (Car), and the chlorophyll fluorescence parameters, including the maximum quantum efficiency of photosystem II (PSII) reaction centers (F v /F m), the quantum efficiency of PSII (Y(II)) and electron transport rate through PSII (ETR), were increased; this significantly promoted the net photosynthetic rate (P n) and water use efficiency (WUE). Compared with a uniform high salt stress treatment, the leaf relative water content (RWC) and water potential (Ψ) increased by 22.57% and 13.71%, respectively, the electrolyte leakage rate decreased by 36.13%, and the final yield increased by 2.89 times under a nonuniform high salinity treatment. These results indicated that nonuniform salinity conditions regulated the leaf water relations and the antioxidant system and maintained better anatomical structure to improve photosynthesis in cherry tomato under a high salinity environment. Finally, our results can aid in the improvement of tomato productivity from salt-affected lands.
... Medicago ruthenica (L.) Trautv. seedlings partially or completely died in response to the synergistic effect of high salt concentration (24-120 mM NaCl) and high alkali content, and the water content of aboveground organs, the relative growth rate of aboveground organs and roots, and pigment concentration decreased, as did root viability in the high salinity treatment, whereas low salinity promoted root viability (Yang et al. 2011). G. divaricata formed roots normally in response to a low concentration (50-100 mM) of NaCl, showing no obvious differences with the control group, and even promoted some growth indicators, which may be due to the ability of low salt concentration to stimulate photosynthesis (Kurban et al. 1999). ...
Soil salinity is a major environmental stress that restricts agricultural production worldwide. Gynura divaricata is widely cultivated on tropical islands in China and has both edible and medicinal value. NaCl stress and growth indicators, antioxidant enzyme activity, as well as MDA, proline, and soluble sugar content, were determined. Based on the transcriptomic data of G. divaricata tissue-cultured plantlets grown in control (0 mM NaCl) and (50 and 200 mM) NaCl stress conditions, the expression patterns of responsive genes were explored. KEGG enrichment analysis of differentially expressed genes indicated that plant hormone signaling, the MAPK signaling pathway, and starch and sucrose metabolism pathways, were significantly enriched, allowing the main biological pathways and salt stress-responsive genes of G. divaricata to be identified, and providing a molecular basis for breeding salt-tolerant varieties.
... Under stress, plants must maintain a high concentration of K + in epidermal cells and guard cells to regulate stomatal opening and closing. The combined use of straw and nitrogen fertilizer has been shown to increase the K + concentration in rice tissue and alleviate stomatal closure caused by saline-sodic stress [64]. This promotes the improvement of net photosynthetic rate and transpiration rate in plants. ...
Soil salinization is a prevalent global environmental issue that significantly hampers crop growth and yield. However, there has been limited research on the impact of nitrogen fertilization and various management practices in alleviating saline-sodic stress in crops. In order to examine the impact of combined straw and nitrogen fertilizer application on the physiological and photosynthetic characteristics of rice in saline-sodic paddy fields, a three-year field experiment was conducted in Jilin Province, China. The experiment was conducted as a split-zone trial, where the main zone consisted of straw (S) and the secondary zone consisted of nitrogen fertilizer (N). Two levels of straw were 0 t ha−1 (B) and 7 t ha−1 (T). Four nitrogen treatments were applied: 0, 150, 250, and 350 kg ha−1, denoted as N0, N1, N2, and N3, respectively. The results show that the combination of straw and nitrogen fertilizer has been found to effectively reduce the Na+/K+ value, malondialdehyde content, and the relative electric leakage of rice leaves in saline-sodic soil. Furthermore, it increases leaf water potential, relative water content, and chlorophyll content, thereby promoting rice photosynthesis and improving rice yield. The rice yield exhibited the greatest positive effect when straw and nitrogen fertilizer were combined at a rate of 250 kg ha−1. The effectiveness of this combination improves over time. However, it is important to avoid excessive application of nitrogen fertilizer when using straw returning. This approach not only ensures stable rice yield in saline-sodic fields, but also has positive effects on the economic impact of fertilizer application and soil environment preservation.
... Chlorophyll can directly affect the photosynthetic efficiency of plants, and the content of chlorophyll provides a measure of the ability of the stress tolerance of plants [31]. Previous studies have shown that the chloroplasts of plants are damaged by saline-alkaline stress, and this leads to the degradation of chloroplast pigments, which results in an imbalance in the photosynthetic system and affects normal plant growth [32]. ...
Grafting the wine grape variety Cabernet Sauvignon onto salinity-tolerant rootstocks can improve salinity tolerance and grape yields in regions with high salinity soils. In this experiment, the effects of different rootstocks and rootstock combinations on the saline–alkaline stress (modified Hoagland nutrient solution + 50 mmol L−1 (NaCl + NaHCO3)) of Cabernet Sauvignon were studied. Correlation and principal component analyses were conducted on several physiological indicators of saline–alkaline stress. Salinity limited biomass accumulation, induced damage to the plant membrane, reduced the chlorophyll content and photosynthetic capacity of plants, and increased the content of malondialdehyde, sodium (Na+)/potassium (K+) ratio, and antioxidant enzyme activities (superoxide dismutase, peroxidase, and catalase). Significant differences in several indicators were observed among the experimental groups. The results indicate that the saline–alkaline tolerance of Cabernet Sauvignon after grafting was the same as that of the rootstock, indicating that the increased resistance of Cabernet Sauvignon grapes to saline–alkaline stress stems from the transferability of the saline–alkaline stress resistance of the rootstock to the scion.
... Saline-alkali soil is mainly caused by sodium carbonate (Na 2 CO 3 and NaHCO 3 ), which increases the pH and Na + concentration, decreases the water potential, and results in drought [2][3][4][5]. Thus, land saline alkalization has become an increasingly serious problem, as it can decrease the osmotic potential of soil, disrupt ion homeostasis, disturb physiological processes, inhibit the growth and development of plants, lead to declines in quality and yield, and even result in the death of plants [6,7]. Therefore, study of the mechanisms underlying the responses of plants to saline-alkali stress will aid the use of biotechnology to breed plants with improved saline-alkali tolerance. ...
The pH of saline–alkali soil is high because of carbonate salts, and the deleterious effects of saline–alkali soil on the growth of plants are greater than those of saline soil. Few studies have examined the saline–alkali tolerance of Betula platyphylla at the molecular level. To clarify the regulatory mechanism underlying saline–alkali tolerance in B. platyphylla, RNA sequencing analysis of B. platyphylla seedlings treated with NaHCO3 was conducted. Differences in gene expression in the roots of B. platyphylla seedlings under saline–alkali stress (induced via NaHCO3) for 3 h and 6 h were characterized, and a total of 595 and 607 alkali stress-responsive genes were identified, respectively. Most differentially expressed genes were involved in stress, signal transduction, secondary metabolic process, regulation of jasmonic acid, and the abiotic stimulus signaling pathway. The single nucleotide polymorphism loci in the differentially expressed genes were associated with the alkaline-salt tolerance in birch germplasm. In addition, birch plants overexpressing WRKY70 and NAC9 were obtained using the A. tumefaciens-mediated transient transformation method, and these two genes were found to play key roles in saline–alkali tolerance. Additional study revealed that WRKY70 and NAC9 can increase resistance to saline–alkali stress by enhancing reactive oxygen species scavenging and inhibiting cell death in birch plants. The results of this study enhance our understanding of the saline–alkali stress tolerance of B. platyphylla at the molecular level, and provide several key genes that could be used in the breeding of birch plants in the future.
... Salt stress can result in significant decreases in growth, chlorophyll degeneration, water status imbalance, changes in stomatal movement, ion disequilibrium, and many other consequences (Al-Ashkar et al., 2019). The concentration of photosynthetic pigments decreases in certain stressful conditions, such as salt stress, which has the potential to break down chlorophyll; this effect is linked to an increase in the poisonous cation, namely Na + (Yang et al., 2011). When plants are exposed to salt stress, their response is mediated at least in part by an increase in the production of active oxygen species, particularly in chloroplasts and mitochondria, which induce lipid peroxidation and membrane damage as well as protein breakdown and enzyme inhibition (Safdar et al., 2019). ...
Salinity is a significant abiotic element that lowers agricultural production globally. With a projected loss of 30% of arable land over the next 25 years and 50% by 2050, increased salinization of arable land is predicted to have catastrophic worldwide effects. Leguminous crops like faba beans are severely hampered in their development and output by salinity. Numerous physiological and metabolic mechanisms are involved in the response of plants to salt stress. In this work, we evaluated the effects of foliar application of zinc oxide nanoparticles (ZnONPs), zinc nanoparticles (ZnNPs), zinc (Zn), and moringa leaf extract (MLE) on faba bean (Vicia faba L.), cultivars (Giza 716 and Sakha 4), and salt tolerance. 60 to 90 days after planting, morphological, biochemical, and molecular characteristics of plants cultivated in saline environments (50 and 100 mM NaCl) were evaluated. RT-qPCR was used to ascertain the expression patterns of the plant defence genes polyphenol oxidase (PPO) and peroxidase (POX) in faba bean leaves collected at 0, 3, 6, and 9 hours after being sprayed with 10 mL of ZnONPs (50 mg mL-1). The Sakha 4 cultivar was much more affected by salt stress than the Giza 716 cultivar in terms of growth characteristics, photosynthetic pigments, proline, minerals, total phenol, and enzyme activity. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and UV-Vis spectroscopy were used to characterise the structural properties of ZnoNPs and ZnNPs. ZnoNPs and ZnNPs both had a peak in their UV spectra at wavelengths of 370 and 371, respectively. SEM analysis verified that ZnONPs and ZnNPs had average sizes of 220 nm and 240 nm, respectively. The FTIR analysis verified the presence of phenols, proteins, carboxyl, and hydroxyl groups, which serve as reducing and stabilising agents, on the surfaces of green synthesis ZnONPs. Additionally, the TEM images of the green synthesis ZnONPs showed that the ZnONPs had a flower-like pattern and the ZnNPs had an uneven form. On faba beans grown in salt-stressed conditions, foliar spraying of ZnoNPs, ZnNPs, Zn, and MLE significantly increased growth parameters like shoot length, number of leaves, relative water content, shoot, root fresh and dry weights, proline, minerals like Na+, K+, Ca2+, and Zn2+, total phenol, and enzyme activities like polyphenol oxidase (PPO), peroxidase (POX), cat The (Vf PPO) gene's expression rose considerably (P 0.05) at the 9th and 12th hours for 100 mM NaCl and ZnONPs + NaCl, respectively, while the (Vf POX) gene's expression increased significantly (P 0.05) at the 6th and 9th hours for both treatments. This demonstrated that both genes activate genes in plants that defend them against salt stress. Furthermore, there was no discernible difference between the treatments at a 100 mM NaCl concentration. Based on these results, it is possible that MLE, ZnONPs, and ZnNPs applied by foliar spraying might lessen the deleterious effects of salinity on faba bean development, photosynthetic efficiency, and biochemical and molecular properties.
... With the increase in global temperatures, stronger evaporation and constant salt accumulation on the soil surface are becoming more obvious, and the increasing salinity level in the natural environment and on cultivated land is becoming an important factor influencing plant growth and agricultural production [1,2]. Overgrazing, intensive cultivation, and unscientific irrigation have led to the accumulation of salt in the soil [3]. Approximately 20% of the world's irrigated agricultural land is affected by high salinity levels [1,2]. ...
To investigate the amelioration of salt-induced damage on Paeonia ostii ‘Fengdan’ by exogenous silicon, we analyzed the photosynthetic and physiological characteristics of 1.5-year-old ‘Fengdan’ seedlings under NaCl stress by applying exogenous silicon (0, 0.75, and 1.5 mmol/L). Our results showed that the contents of the photosynthetic pigments chlorophyll a, chlorophyll b, and carotene, the transpiration rate, stomatal conductance, and intercellular CO2 were significantly enhanced under salt stress when silicon treatment was applied, implying that the net photosynthetic rate was greatly improved. In addition, the plant height, stem thickness, and above-ground dry biomass of tree peony seedlings were effectively increased under salt stress with low-concentration silicon (0.75 mmol/L) treatment, along with osmotic substance (SS, SP, and Pro) content, total polyamine (TP) contents, and the activities of antioxidant-related enzymes (SOD, POD, and CAT) and polyamine-related synthetases (ADC, ODC, and SAMDC). In the low-concentration silicon treatment, malondialdehyde (MDA), hydrogen peroxide (H2O2), and superoxide anions (O2−) were transformed quickly, which eventually reduced cell oxidative damage and improved seedling tolerance. This is an important finding in the understanding of how exogenous low-concentration silicon can alleviate salt-induced damage and promote the growth of tree peony seedlings, thus providing a new perspective on tree peony cultivation.
... Abiotic stresses such as salt stress, have evolved a variety of physiological, transcriptomic, and proteomic responses in plants due to their sessile nature. Stress caused by salinity stress increases the Na + ions, while it inhibits the availability of minerals in the soil, such as K + , Mg 2+ , Ca 2+ , and H 2 PO À 4 , by causing precipitation (Yang et al., 2011;Noor et al., 2022). Various metabolic pathways are impaired by high Na + and low mineral nutrient acquisition in plants (Ullah et al., 2019). ...
Wheat plays a significant role in the provision of food and nutrition. However, rapid soil salinization poses a severe threat to its production worldwide. Salt stress stunts wheat growth and quality, resulting in low grain yields. The adaptation of wheat to salinity involves complex physio-biochemical and molecular mechanisms. This study aimed to identify the genetic approaches concerning salt stress-responsive proteins and protein pathways in wheat roots under controlled (0 mM) and NaCl stress (250 mM) solution using label-free proteo-mic quantification analysis. We found a significant accumulation of Na + in the leaf and root compared with the controlled condition. Besides, we identified 2436 proteins enhanced under salt stress, with 198 differentially abundant proteins (DAPs), including 170 up-regulated and 28 down-regulated proteins. Many of these proteins were involved in salinity tolerance, including heat shock proteins, glutathione S-transferase, dehy-drin, peroxidase, potassium channel beta subunit-type H +-ATPase, superoxide dismutase (Cu-Zn), 14-3-3 protein, peroxidase, malate dehydrogenase, and heat shock proteins. The abundance of a V-type H + ATPase and 14-3-3 protein was also enhanced, facilitating Na + compartmentalization in the vacuole through the salt overly sensitive (SOS) pathway. Additionally, many antioxidant enzymes, including peroxidase, glutathione-S-transferase, and thioredoxins, were up-regulated, playing a vital role in detoxifying reactive oxygen species (ROS) in salinity-stressed wheat roots. Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) enrichment analyses showed that salinity stress enhances the abundance of proteins in several metabolic pathways, such as the citrate cycle, ribosome, oxidative phosphorylation, glycolysis, carbon metabolism, and cytoplasm. We anticipate that the identified proteins under salinity conditions will provide us with a deeper understanding of their application in agriculture biotechnology.
... The chloroplast is the binding site for photosynthesis, in which light and dark reactions occur. Salt stress can break down chlorophyll (Chl), the effect ascribed to an increased level of the toxic cation, Na + [58][59][60][61]. Under salinity and multiple heat and salinity stress conditions, the YNU31-2-4 genotype shows a higher Chl accumulation (Figure 2 and Tables A3 and A4). ...
The yield-reduction effect of abiotic stressors such as salinity and heat stresses with the growing world population threatens food security. Although adverse effects of salinity and heat stress on plant growth and production parameters have been documented, in nature, abiotic stresses occur sequentially or simultaneously. In this study, the stress tolerance and yield capacity of Yukinkomai, YNU31-2-4, and YNU SL rice genotypes tested under control (26 ◦C, 0 mM NaCl), salinity (26 ◦C, 75 mM NaCl), heat (31 ◦ C, 0 mM NaCl), and heat and salinity (31 ◦ C, 75 mM NaCl) stress combinations at vegetative and reproductive stages with six different scenarios. The results show that salinity and the heat and salinity combination stresses highly reduce plant growth performance and yield capacity. Heat stress during reproduction does not affect the yield but reduces the grain quality. The YNU31-2-4 genotype performs better under heavy salt and heat and salinity stress then the Yukinkomai and YNU SL genotypes. YNU31-2-4 genotypes accumulate less Na+ and more K+ under salt and multiple stresses. In the YNU31-2-4 genotype, low Na+ ion accumulation increases photosynthetic activity and pigment deposition, boosting the yield. Stress lowers the glucose accumulation in dry seeds, but the YNU31-2-4 genotype has a higher glucose accumulation.
... The combination of straw and nitrogen fertilizer increased the K + concentration in rice tissue and alleviated stomatal closure caused by saline-sodic stress (Fig. 2d, e, f). It promoted the improvement of net photosynthetic rate and transpiration rate of plants (Yang et al. 2011). It is also possible that the combined application of straw and nitrogen fertilizer reduces the content of Na + in plant tissues and maintains the integrity of the membrane (Fig. 2a, b, c), which not only ensures the smooth progress of chlorophyll synthesis, but also provides a favorable place for the smooth progress of photosynthesis. ...
Aims salinisation severely limits crop growth and yield. In recent years, the effect of nitrogen fertilisation and different management practices on the mitigation of saline-sodic stress in crops has been less studied. Therefore, we conducted a three-year field experiment in Jilin Province, China, to investigate the effects of combined straw and nitrogen fertilizer application on the physiological and photosynthetic characteristics of rice in saline-sodic paddy fields.
Methods The experiment was designed as a split-zone trial, with straw (S) as the main zone and nitrogen fertilizer (N) as the secondary zone. The amount of straw returned was 0 t ha⁻¹ (B) and 7 t ha⁻¹ (T). Nitrogen treatments of 0, 150, 250 and 350 kg ha⁻¹ were recorded as N0, N1, N2 and N3, and each treatment was repeated three times.
Results Straw combined with nitrogen fertilizer can effectively reduce the Na⁺/K⁺ value, malondialdehyde content and relative electric leakage of rice leaves in salt-alkali soil, and ensure the integrity of cell membrane. At the same time, the leaf water potential, relative water content and chlorophyll content were increased, which promoted rice photosynthesis and improved rice yield. In addition, it was found that straw combined with nitrogen fertilizer had the greatest positive effect on rice yield at 250kg ha⁻¹.
Conclusions Straw combined with nitrogen fertilizer can improve the physiological and photosynthetic characteristics of rice in saline-alkali paddy field and provide a theoretical basis for rice yield increase in this area
... These results were consistent with studies that reported similar trends in Cl − content in citrus (Carrizo citrange) [45], spring wheat (Triticum aestivum), and winter barley (Hordeum vulgare) [46] caused by mycorrhiza. We also found that alkaline stress reduced the content of SO 4 2− in H. bogdanii, which is consistent with the findings of Yang et al. [47]. The SO 4 2− content of E+ was higher than that of E− when endophytic fungi infected H. bogdanii, indicating that endophytic fungi increased the accumulation of SO 4 2− in host plants. ...
Plants cope with abiotic stress in several ways, including by collaborating with microorganisms. Epichloë, an endophytic fungus, has been shown to improve plant tolerance to extreme external environments. Hordeum bogdanii is a known salt-tolerant plant with the potential to improve alkaline lands. NHX1 plays a key role in the transport of ions in the cell and is overexpressed in plants with increased salt tolerance. However, the expression levels of HbNHX1 in Epichloë endophytic fungal symbionts in H. bogdanii have not been elucidated. We used Hordeum bogdanii (E+) with the endophytic fungi Epichloë bromicola and H. bogdanii (E−) without the endophytic fungi and compared the differences in the ion content and HbNHX1 expression between the shoots and roots of E+ and E− plants under alkaline stress. The absorption capacity of both K+ and Na+ of H. bogdanii with endophytic fungi was higher than that without endophytic fungi. In the absence of alkaline stress, endophytic fungi significantly reduced the Cl− content in the host H. bogdanii. Alkaline stress reduced SO42− content in H. bogdanii; however, compared with E−, endophytic fungi increased the content of SO42− in E+ plants. With an increase in the alkaline concentration, the expression of HbNHX1 in the roots of H. bogdanii with endophytic fungus exhibited an upward trend, whereas the expression in the shoots exhibited a downward trend first and then an upward trend. Under 100 mmol·L−1 mixed alkaline stress, the expression of HbNHX1 in E+ was significantly higher than that in E−, indicating that endophytic fungi could increase the Na+ region in vacuoles. The external environment affects the regulation of endophytic fungi in H. bogdanii and that endophytic fungi can play a key role in soil salinization. Therefore, the findings of this study will provide technical support and a theoretical basis for better utilization of endophytic fungi from H. bogdanii in saline land improvement.
... Chlorophylls (Chl) and carotenoids (Car) are the main photosynthetic pigments that play an important role in photosynthesis [51]. Salt stress can affect the Chl and Car contents, as the changes depend on the amount of salt and the plant species [34,52]. Some authors use the changes in the pigment amount as a sensitive indicator for the salt-sensitivity of the plants [23,53]. ...
The present study shows the effect of salinity on the functions of thylakoid membranes from two hybrid lines of Paulownia: Paulownia tomentosa x fortunei and Paulownia elongate x elongata, grown in a Hoagland solution with two NaCl concentrations (100 and 150 mM) and different exposure times (10 and 25 days). We observed inhibition of the photochemical activities of photosystem I (DCPIH2 → MV) and photosystem II (H2O → BQ) only after the short treatment (10 days) with the higher NaCl concentration. Data also revealed alterations in the energy transfer between pigment–protein complexes (fluorescence emission ratios F735/F685 and F695/F685), the kinetic parameters of the oxygen-evolving reactions (initial S0-S1 state distribution, misses (α), double hits (β) and blocked centers (SB)). Moreover, the experimental results showed that after prolonged treatment with NaCl Paulownia tomentosa x fortunei adapted to the higher concentration of NaCl (150 mM), while this concentration is lethal for Paulownia elongata x elongata. This study demonstrated the relationship between the salt-induced inhibition of the photochemistry of both photosystems and the salt-induced changes in the energy transfer between the pigment–protein complexes and the alterations in the Mn cluster of the oxygen-evolving complex under salt stress.
... Accumulated cytotoxic molecules can damage the photosynthetic apparatus and downregulate the production of photosynthetic pigments leading to photo-inhibition. High salt stress is found to inhibit chlorophyll production and promote its degradation (Yang et al. 2011). Similarly, high salt stress decreases β-carotene level, which is converted into zeaxanthin for protection against photo-inhibition (Banerjee and Roychoudhury 2016). ...
Pulses are climate-smart grain legumes important to nutritional security and sustainable agriculture. Abiotic stresses take a heavy toll in pulse production, and genetic engineering offers a solution to add adaptive traits in the germplasm. Abiotic stresses being mostly polygenic are difficult to manipulate and require a thorough understanding of the underlying mechanism. Impact of abiotic stresses in eight different pulses, genetic mechanism involved, and transgenics approach adopted for enhancing the stress tolerance in those pulses are discussed. Traits engineered in chickpea (drought and salt tolerance), pigeon pea (salt tolerance), mung bean (salt and cold tolerance), urdbean (salt and drought tolerance and aluminum toxicity), cowpea (salt tolerance), field pea (salt, frost, and heat tolerance), common bean (drought tolerance), and lentil (cold and freezing tolerance) and resulting phenotypes are also discussed. Currently, only two transgenic pulses for biotic stress (insect resistance for cowpea and golden mosaic virus in common bean) are commercialized. Climate change poses various challenges, and genetic engineering and emerging genome editing techniques for abiotic stress-adaptive traits shall play a crucial role in abiotic stress management.
... Researchers found that the number of Triticum aestivum leaves decreased and the maturity period was advanced when plant suffered from salt stress . And Mitsuya et al., conducted the experiment on Ipomoea batatas showed that salt and alkali stress affected the plant cell structure, destroyed the chloroplast structure and affected the photosynthesis (Mitsuya et al., 2000;Yang et al., 2011;Cheng et al., 2015). Meanwhile, soil salt-alkalization will interfere with the dynamic balance of ions of plant cell (Ruiz et al., 2016;Zhang et al., 2020), and increase the permeability of cell membrane (Dinneny, 2015). ...
... According to several studies, a branching root system is more cold resistant than a single taproot. 8 In the QTP, the frigid climate, low temperature, and strong ultraviolet radiation during the winter and spring seasons cause the accumulation of reactive oxygen species (ROS) in the plants and also affect the normal physiological metabolism. 9 Low temperature results in the accumulation of ROS that damage the membrane system, proteins, and nucleic acids by disrupting the balance between the production and degradation of ROS in the plants. ...
BACKGROUND
The roots are the main functional organs involved in the overwintering adaptability of alfalfa (Medicago sativa). However, it is still unclear how the roots are involved in the cold resistance in the high‐altitude area of the Qinghai–Tibet Plateau (QTP). In this study, three winter‐surviving 2‐year‐old alfalfa varieties (M. sativa Zhongmeng No.1, M. sativa Chiza No.1, and M. sativa Gongnong No.1) planted at two different altitudes (2812 m and 3109 m) in the northeast edge of the QTP were used to explore the cold‐resistance mechanism.
RESULTS
At low altitudes (2812 m), the overwintering rate, taproot length, root area, root surface area, and root average diameter, plant height, fresh yield and hay yield of M. sativa Zhongmeng No.1 were significantly higher (P < 0.01) than for the other two varieties. At high altitude (3109 m), lateral root length, number of lateral roots, main root dry weight, and lateral root dry weight of M. sativa Chiza No.1 were higher (P < 0.01) than the other two varieties. At low and high altitudes, the activities of peroxidase and catalase were higher (P < 0.05) in M. sativa Chiza No.1 during post‐winter and pre‐winter respectively. At low altitude, higher soluble sugar (P < 0.05) and proline (P < 0.01) contents were recorded during the pre‑ and post‐winter periods. Membership function analysis showed that M. sativa Zhongmeng No.1 has the strongest cold resistance. The structural equation model showed that the overwintering rate of alfalfa was mainly affected by the morphological characteristics of roots and the physiological characteristics of roots, with contribution rates of 0.54 and 0.75 respectively, and the physiological characteristics of roots had the greatest effect on the overwintering rate.
CONCLUSIONS
This study is of great significance to effectively solve the overwintering of alfalfa, the lack of high‐quality legume forage resources, and promote the development of animal husbandry in the alpine areas of the QTP. © 2022 Society of Chemical Industry.
... Medicago ruthenica is an allogamous, diploid (2n = 16) perennial legume forage. It is widely distributed in alpine and desert grasslands and has the advantages of resistance to cold, drought, salt, and alkali, trampling [21,22]. Its drought resistance was reported to be better than alfalfa (Medicago sativa) and other legume forages. ...
Background
Drought is one of the main causes of losses in forage crop yield and animal production. Medicago ruthenica (L.) cv. Zhilixing is a high-yielding alfalfa cultivar also known for its high tolerance to drought. We analyzed the transcriptome profile of this cultivar throughout drought stress and recovery and we were able to describe its phased response through the expression profiles of overlapping gene networks and drought-specific genes.
Results
The ABA and auxin signal transduction pathways are overlapping pathways in response to drought and drought recovery in forage crops. Medicago ruthenica (L.) cv. Zhilixing adopts different strategies at different degrees of drought stress. On the 9th day of drought, transcriptional regulations related to osmoregulation are enhanced mainly through increased activities of carbohydrate and amino acid metabolism, while photosynthetic activities were reduced to slow down growth. With drought prolonging, on the 12th day of drought, the synthesis of proline and other stored organic substances was suppressed in general. After recovery, Medicago ruthenica synthesizes flavonoids through the flavonoid biosynthesis pathway to remove accumulated ROS and repair the oxidative damage from water stress. In addition, the regulation of circadian rhythm seems to accelerate the drought recovery process.
Conclusions
Medicago ruthenica adapts to drought by regulating the osmoregulatory system and photosynthesis, which appears to involve the ABA and auxin signaling pathways as key regulators. Furthermore, the synthesis of flavonoids and the regulation of the circadian rhythm can accelerate the recovery process. These results enriched our knowledge of molecular responses to drought and drought recovery in Medicago ruthenica and provide useful information for the development of new legume forage grass varieties with improved adaptability to drought stress.
... Stomatal factors decreased Ci, while non-stomatal factors increased it 33 . When both factors were present, the direction of the change in Ci depends on the dominant factor 34,35 . The results showed that the Pn, Gs, Tr, and Ci of the two rice varieties decreased under NaCl stress at the stage of 2.5th leaf, indicating that the decrease of Pn in rice seedling leaves was peimarily the result of stomatal limitation. ...
Brassinolide (BR) is a sterol compound, which can regulate plant seed germination, flowering, senescence, tropism, photosynthesis, stress resistance, and is closely related to other signaling molecules. This study aimed to evaluate the ability of soaking with BR to regulate growth quality at rice seedling stage under salt stress. Results demonstrated that salt stress increases the contents of ROS, MDA, Na ⁺ and ABA, reduces the the SPAD value, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), maximum fluorescence (Fm), variable fluorescence (Fv), the effective photochemical efficiency of PSII (Fv/Fo) and the maximum photochemical efficiency of PSII (Fv/Fm), reduces the biomass production and inhabits plant growth. All of these responses were effectively alleviated by BR soaking treatment. Soaking with BR could increase the activities of superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, and the contents of ascorbic acid, glutathione as well as soluble protein and proline, while BR soaking treatment inhibited the accumulation of ROS and reduced the content of MDA. BR soaking significantly reduced the contents of Na ⁺ and increased the contents of K ⁺ and Ca ²⁺ , indicating that soaking with BR is beneficial to the excretion of Na ⁺ , the absorption of K ⁺ and Ca ²⁺ and the maintenance of ion balance in rice seedlings under salt stress. BR also maintained endogenous hormone balance by increasing the contents of indoleacetic acid (IAA), zeatin (ZT), salicylic acid (SA), and decreasing the ABA content. Soaking with BR significantly increased the SPAD value, Pn and Tr and enhanced the Fm, Fv/Fm and Fv/Fo of rice seedlings under NaCl stress, protected the photosythetic system of plants, and improved their biomass. It is suggested that BR was beneficial to protect membrane lipid peroxidation, the modulation of antioxidant defense systems, ion balance and endogenous hormonal balance with imposition to salt stress.
... Both chlorophyll a chlorophyll b fell significantly under intermediate and high saline stress similar to other research in salt-stressed plants [52][53][54][55]. As a response to salt stress, chlorophyllase activity increases, which leads to a decrease in chlorophyll concentrations as salt-stress levels increases with the extent of the decline in salt stress varying between plant species [56]. ...
Background
Alhagi sparsifolia (Camelthorn) is a leguminous shrub species that dominates the Taklimakan desert’s salty, hyperarid, and infertile landscapes in northwest China. Although this plant can colonize and spread in very saline soils, how it adapts to saline stress in the seedling stage remains unclear so a pot-based experiment was carried out to evaluate the effects of four different saline stress levels (0, 50, 150, and 300 mM) on the morphological and physio-biochemical responses in A. sparsifolia seedlings.
Results
Our results revealed that N-fixing A. sparsifolia has a variety of physio-biochemical anti-saline stress acclimations, including osmotic adjustments, enzymatic mechanisms, and the allocation of metabolic resources. Shoot–root growth and chlorophyll pigments significantly decreased under intermediate and high saline stress. Additionally, increasing levels of saline stress significantly increased Na⁺ but decreased K⁺ concentrations in roots and leaves, resulting in a decreased K⁺/Na⁺ ratio and leaves accumulated more Na + and K + ions than roots, highlighting their ability to increase cellular osmolarity, favouring water fluxes from soil to leaves. Salt-induced higher lipid peroxidation significantly triggered antioxidant enzymes, both for mass-scavenging (catalase) and cytosolic fine-regulation (superoxide dismutase and peroxidase) of H2O2. Nitrate reductase and glutamine synthetase/glutamate synthase also increased at low and intermediate saline stress levels but decreased under higher stress levels. Soluble proteins and proline rose at all salt levels, whereas soluble sugars increased only at low and medium stress. The results show that when under low-to-intermediate saline stress, seedlings invest more energy in osmotic adjustments but shift their investment towards antioxidant defense mechanisms under high levels of saline stress.
Conclusions
Overall, our results suggest that A. sparsifolia seedlings tolerate low, intermediate, and high salt stress by promoting high antioxidant mechanisms, osmolytes accumulations, and the maintenance of mineral N assimilation. However, a gradual decline in growth with increasing salt levels could be attributed to the diversion of energy from growth to maintain salinity homeostasis and anti-stress oxidative mechanisms.
... The H 2 O 2 level was determined at the absorbance at 415 nm according to the standard curve plotted with a known concentration, while the O 2 − content was calculated per gram of fresh mass of leaves at 530 nm. The accumulation of H 2 O 2 and O 2 − was examined by histochemical staining with 3,3 -diaminobenzidine (DAB) and nitro blue tetrazolium (NBT) respectively [41]. Briefly, tomato leaves were placed in a solution of 1 mg mL −1 DAB (pH 3.8) for 8 h under light to analyze the H 2 O 2 and in 0.5 mg mL −1 NBT for 8 h in the dark to analyze the O 2 − . ...
Basic leucine zipper (bZIP) transcription factors of the ABA-responsive element binding factor/ABA-responsive element binding proteins (ABF/AREB) subfamily have been implicated in abscisic acid (ABA) and abiotic stress responses in plants. However, the specific function of ABF/AREB transcription factors under saline–alkaline stress is unclear. Here, we identified four ABF/AREB transcription factors in tomato and found that SlAREB1 strongly responded to both ABA and saline–alkaline stress. To further explore the function of SlAREB1 under saline–alkaline stress, SlAREB1-overexpressing lines were constructed. Compared with wild-type plants, SlAREB1-overexpressing transgenic tomato plants showed reduced malondialdehyde content, increased the relative water content, and alleviated the degradation of chlorophyll under saline–alkaline stress. Importantly, SlAREB1 directly physically interacted with SlMn-SOD, which improved the activity of antioxidant enzymes and increased the scavenging of excess reactive oxygen species. Overall, the overexpression of SlAREB1 increased the antioxidant capacity of the transgenic tomato under saline–alkaline stress.
... The MicroRNA397a-LACCASE17 module regulates lignin biosynthesis in Medicago ruthenica (L.) Introduction Medicago ruthenica (L.) is an allogamous, diploid (2n = 2x = 16) perennial legume forage of the Medicago genus (Small and Jomphe, 1989). Compared to other Medicago species, M. ruthenica has enhanced tolerance to environmental stresses, and making it a valuable resource for the resistance breeding of Medicago sativa (alfalfa) (Wang D. K. et al., 2008;Guan et al., 2009;Yang et al., 2011). Due to its adaptability to harsh environments, M. ruthenica is widely distributed in northern China, particularly in the Mongolian Plateau, where it is an important forage legume in cultivated and natural grasslands. ...
Mechanical strength is essential for the upright growth habit, which is one of the most important characteristics of terrestrial plants. Lignin, a phenylpropanoid-derived polymer mainly present in secondary cell walls plays critical role in providing mechanical support. Here, we report that the prostrate-stem cultivar of the legume forage Medicago ruthenica cultivar ‘Mengnong No. 1’ shows compromised mechanical strength compared with the erect-stem cultivar ‘Zhilixing’. The erect-stem cultivar, ‘Zhilixing’ has significantly higher lignin content, leading to higher mechanical strength than the prostrate-stem cultivar. The low abundance of miRNA397a in the Zhiixing cultivar causes reduced cleavage of MrLAC17 transcript, which results in enhanced expression level of MrLAC17 compared to that in the prostrate-stem cultivar Mengnong No. 1. Complementation of the Arabidopsis lac4 lac17 double mutants with MrLAC17 restored the lignin content to wild-type levels, confirming that MrLAC17 perform an exchangeable role with Arabidopsis laccases. LAC17-mediated lignin polymerization is therefore increased in the ‘Zhilixing’, causing the erect stem phenotype. Our data reveal the importance of the miR397a in the lignin biosynthesis and suggest a strategy for molecular breeding targeting plant architecture in legume forage.
... Salt stress causes osmotic injury and ion toxicity in plants, whereas alkali stress exposes them to high pH levels. On subjecting Medicago ruthenica seedlings to mixed saline-alkali stress (MSAS), Yang et al. (2011) observed a significant decrease in photosynthetic characteristics, such as net photosynthetic rate, stomatal conductance, intercellular CO 2 concentration, and chlorophyll content, with an increase in salinity and pH. MSAS is not just a simple superposition of salt and alkali stresses, but there is a certain synergistic effect that causes complex, serious damage to plants. ...
Soil salinization–alkalization is a major hindrance to agricultural development globally. Tea crabapple is widely used in China. However, little remains known regarding the molecular mechanisms used to withstand mixed saline–alkali stress (MSAS). Herein, we exposed tea crabapple seedlings to MSAS, and RNA-seq was performed for the transcriptome analysis of roots. Between 43.26 million and 43.37 million clean reads were thus obtained. In comparison with the control group (day 0), 2931, 2335, and 3746 genes were differentially expressed at day 1, day 3, and day 6 of MSAS exposure, respectively, and 1022 genes were common in the three comparison groups. On functional annotation, we observed that numerous differentially expressed genes were involved in “global and overview maps”; “carbohydrate metabolism”; “folding, sorting, and degradation”; “biosynthesis of other secondary metabolites”; “environmental adaptation”; and “signal transduction.” Heat shock proteins, cytochrome P450s, disease-resistant proteins, non-specific lipid-transfer proteins, pectate lyase, and beta-glucosidases were also induced in response to MSAS, in addition to nitrogen, phosphorus, and potassium absorption and metabolism-related genes. Transcription factor-coding genes appear to regulate the response of tea crabapple roots to MSAS by participating in, for example, plant hormone signal transduction and heat shock response. We also performed quantitative real-time PCR to validate the expression of six differentially expressed genes. Our findings provide new insights into the molecular mechanisms used by tea crabapple to cope with MSAS.
... A large number of experimental studies have shown that salt stress could lead to the weakening of photosynthesis, mainly including the reduction in net photosynthetic rate (Pn), stomatal conductance (Gs), and transpiration rate (Tr) and photosynthetic pigments of plants. This is closely associated with a reduction in biomass and yield under salt and alkali stress [6], and alkalinity stress often has more damage to the plant photosynthesis than salinity stress at the same concentration [7]. The excessive salt in the soil could lead to the reduction of the soil water potential and make it difficult for plants to absorb water from the soil [8]. ...
Salinity and alkalinity stress are two major constraints on plant growth and crop production, limiting sustainable agriculture production. Wheat is a vital cereal crop. It is very important to ensure food security; however, its growth and yield usually are adversely affected by salinity and alkalinity stress. To investigate the differential effects of neutral and alkaline salt stress on the seedling growth of wheat, we set a wheat hydroponic culture experiment, CK neutral salt (NaCl:Na2SO4 = 9:1 pH = 6.5), neutral salt with high pH value (NaCl:Na2SO4 = 9:1 pH = 8.9), alkaline salt (NaHCO3:Na2CO3 = 9:1 pH = 8.9), all treatments at the same Na+ concentration. Alkaline salt inhibited seedling growth more than neutral salt and neutral salt with high pH value. The results showed that the salt and alkali stresses decreased chlorophyll contents in leaves of wheat seedlings, inhibited photosynthesis and induced osmotic stress oxidative stress and ion toxicity to wheat seedlings. Finally inhibit the growth of wheat seedlings, while the alkali salt caused a stronger injurious effect than the neutral salt neutral salt with high pH value in wheat seedlings. Our study results show that alkaline salt inhibits wheat seedlings more significantly than neutral salt and neutral salt with high pH value. And, the main factor affecting seedling growth is not pH alone.
... tonnes (Statistical of Tamil Nadu, 2020). The suitable climate for the cultivation of green gram should be warm humid and within a temperature range of 25 0 C -35 0 C, with moderate rainfall [2][3][4][5]. Green gram accounts for about 65 and 64% of world acreage and production, among that India is the largest producer and consumer in the world. It thrives well in drought prone areas, it is cultivated in more than 6 million ha in the tropical regions of the world [6]. ...
Pulses play an important role in Indian diet due to higher protein content. Among the pulses, green gram (Vigna radiata L.) is one of the leguminous crops with high nutritional value, short growing period and soil fertility restoration by biological nitrogen fixation. Drought stress is one of the major constraints for pulse production which negatively affects its growth and production. The present experiment was performed with the objective of studying the seedling germination traits differences in five mung bean genotypes namely, MH421, VBN2, VBN4, CO8 and CO(Gg)912 under water deficit environment. It was done at laboratory conditions using various concentration of PEG 6000 as 5%, 10%, 15%, 18%, 21%. Using this level of moisture stress, 5 green gram genotypes were screened for their drought stress and the following parameters such as radicle length, shoot length, plant height, germination percentage and seed vigour were noted. By observing physiological traits of different genotypes under stress condition and founded that VBN 2 has drought tolerant ability.
... tonnes (Statistical of Tamil Nadu, 2020). The suitable climate for the cultivation of green gram should be warm humid and within a temperature range of 25 0 C -35 0 C, with moderate rainfall [2][3][4][5]. Green gram accounts for about 65 and 64% of world acreage and production, among that India is the largest producer and consumer in the world. It thrives well in drought prone areas, it is cultivated in more than 6 million ha in the tropical regions of the world [6]. ...
Pulses play an important role in Indian diet due to higher protein content. Among the pulses, green gram (Vigna radiata L.) is one of the leguminous crops with high nutritional value, short growing period and soil fertility restoration by biological nitrogen fixation. Drought stress is one of the major constraints for pulse production which negatively affects its growth and production. The present experiment was performed with the objective of studying the seedling germination traits differences in five mung bean genotypes namely, MH421, VBN2, VBN4, CO8 and CO(Gg)912 under water deficit environment. It was done at laboratory conditions using various concentration of PEG 6000 as 5%, 10%, 15%, 18%, 21%. Using this level of moisture stress, 5 green gram genotypes were screened for their drought stress and the following parameters such as radicle length, shoot length, plant height, germination percentage and seed vigour were noted. By observing physiological traits of different genotypes under stress condition and founded that VBN 2 has drought tolerant ability.
... Herein, salt stress reduced the chlorophyll content of Arabidopsis leaves. Yang et al. (2011) showed that salt stress reduces chlorophyll content in plants through the disruption of Na + ion balance and activity of some proteases. Tulay et al. (2015) also found that salt stress increases the activity of chlorophyllase in Spergularia marina (Caryophyllaceae), decreases the content of Mg 2+ ions, accelerates the degradation of chlorophyll, inhibits the function of pigment protein complex, and the leaves become yellow or even fall off. ...
MYB transcription factors (TFs) mediate plant responses and defenses to biotic and abiotic stresses. The effects of overexpression of MYB37, an R2R3 MYB subgroup 14 transcription factors in Arabidopsis thaliana, on chlorophyll content, chlorophyll fluorescence parameters, reactive oxygen species (ROS) metabolism, and the contents of osmotic regulatory substances were studied under 100 mM NaCl stress. Compared with the wild type (Col-0), MYB37 overexpression significantly alleviated the salt stress symptoms in A. thaliana plants. Chlorophyll a (Chl a) and chlorophyll b (Chl b) contents were significantly decreased in OE-1 and OE-2 than in Col-0. Particularly, the Chl a/b ratio was also higher in OE-1 and OE-2 than in Col-0 under NaCl stress. However, MYB37 overexpression alleviated the degradation of chlorophyll, especially Chl a. Salt stress inhibited the activities of PSII and PSI in Arabidopsis leaves, but did not affect the activity of PSII electron donor side oxygen-evolving complex (OEC). MYB37 overexpression increased photosynthesis in Arabidopsis by increasing PSII and PSI activities. MYB37 overexpression also promoted the transfer of electrons from QA to QB on the PSII receptor side of Arabidopsis under NaCl stress. Additionally, MYB37 overexpression increased Y(II) and Y(NPQ) of Arabidopsis under NaCl stress and decreased Y(NO). These results indicate that MYB37 overexpression increases PSII activity and regulates the proportion of energy dissipation in Arabidopsis leaves under NaCl stress, thus decreasing the proportion of inactivated reaction centers. Salt stress causes excess electrons and energy in the photosynthetic electron transport chain of Arabidopsis leaves, resulting in the release of reactive oxygen species (ROS), such as superoxide anion and hydrogen peroxide, leading to oxidative damage. Nevertheless, MYB37 overexpression reduced accumulation of malondialdehyde in Arabidopsis leaves under NaCl stress and alleviated the degree of membrane lipid peroxidation caused by ROS. Salt stress also enhanced the accumulation of soluble sugar (SS) and proline (Pro) in Arabidopsis leaves, thus reducing salt stress damage to plants. Salt stress also degraded soluble protein (SP). Furthermore, the accumulation of osmoregulation substances SS and Pro in OE-1 and OE-2 was not different from that in Col-0 since MYB37 overexpression in Arabidopsis OE-1, and OE-2 did not significantly affect plants under NaCl stress. However, SP content was significantly higher in OE-1 and OE-2 than in Col-0. These results indicate that MYB37 overexpression can alleviate the degradation of Arabidopsis proteins under NaCl stress, promote plant growth and improve salt tolerance.
... Ci was decreased by stomatal factors and increased by nonstomatal factors. When both factors are present, the trend of Ci depends on the dominant factor (Steduto et al., 2000, Yang et al., 2011. It was found that Pn and Ci decreased and Ls increased gradually under NaCl stress at the stage of 2.5 leaves, suggesting that the decrease of Pn at the stage of 2.5 leaves under NaCl stress was mainly due to stomatal limitation. ...
In order to explore the effects of NaCl stress on the growth and physiological characteristics of rice seedlings and the mitigation effects of brassinolide (BR), a pot experiment was conducted with rice cultivar “IR29” under 3 g·L⁻¹ NaCl stress. The effects of soaking with BR on the growth and physiological characteristics of rice seedlings at the 2.5 leaves stage and 4.5 leaves stage under NaCl stress were studied. The results showed that NaCl stress inhibited the growth and development of rice, and had adverse effects on the photosynthesis and resistance physiology of rice seedlings. The inhibition of NaCl stress on the seedling growth of rice could be alleviated in different degrees by soaking with BR. Compared with a single NaCl treatment, the stem base width, aboveground dry weight, and underground dry weight of rice seedlings at different stages were increased after soaking with BR at 0.1 mg·L⁻¹. Soaking with BR increased the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and phenylalanine ammonia-lyase (PAL) as well as the levels of ascorbic acid (AsA) in the leaves of rice seedlings under NaCl stress were increased. It inhibited the accumulation of reactive oxygen species (ROS), reduced the content of malondialdehyde (MDA), and increased the soluble protein content. The MDA and H2O2 contents in rice leaves decreased by 23.6%, 10.8% and 19.9%, 1.4%, respectively. Treatment of soaking with BR increased the chlorophyll content and Pn of rice seedlings at the 2.5 leaves stage and 4.5 leaves stage under NaCl stress, the Pn increased by 27% and 10.06%, respectively. In summary, exogenous BR effectively improved the salt tolerance of rice seedlings, mainly because BR can improve the osmotic adjustment and antioxidant capacity, removed excess ROS, and alleviated oxidative damage and osmotic stress, thereby improving the photosynthesis of rice seedlings and alleviating the damage of NaCl stress to rice seedlings.
Syneilesis aconitifolia, with medicinal value and salt-alkali tolerance, is a potential ground cover and decorative material in gardens. To investigate the influence of arbuscular mycorrhiza (AM) fungi on the colonization and salt-alkali tolerance of S. aconitifolia, a pot experiment was conducted and the AM fungi community existing in Songnen salt-alkali grassland was selected as the inoculation. After 90 days of cultivation, NaCl and NaHCO3 solutions (50 mmol/L, 100 mmol/L, and 200 mmol/L) were applied for 10 days, subsequently, the mycorrhizal colonization, biomass, relative water content, chlorophyll content, malondialdehyde content, antioxidant enzyme activities and the level of osmotic regulation were measured. The results showed that the colonization rate and intensity decreased under saline-alkali stress, and the adaptability of AM fungi in low-concentration alkali stress was higher than that of salt stress. AM fungi could increase the biomass, relative water content, and chlorophyll content, and decrease the malondialdehyde content of S. aconitifolia to some extent. With the increase of salt or alkali solution concentration, AM fungi not only upregulated the activity of the antioxidant system, but also increased the content of osmotic regulatory substances, which indicated that AM fungi could improve the saline-alkali tolerance of S. aconitifolia. Multivariate analysis of variance (ANOVA) and radar map analysis showed that the mechanisms of resistance to salt stress and alkali stress were not the same in S. aconitifolia. In addition, the regulation of AM fungi on salt-alkali resistance of S. aconitifolia was also different. The results provided a scientific basis for the symbiosis between the local AM fungal community and S. aconitifolia, as well as data support for the restoration of saline habitat using S. aconitifolia with high medicinal value.
Introduction:
Safflower (Carthamus tinctorius L.) is an important oilseed crop grown throughout the semiarid regions in many parts of the world. It has been cultivated for its oil and flowers and as a meal. Alkaline stress is caused by alkaline salts such as Na2CO3 or NaHCO3 in the soil. Alkaline stress, is widespread environmental constraint affecting crop productivity ,which can inhibit absorption of inorganic anions such as Cl–, NO3 – and H2PO4–, greatly affect the selective absorption of K+-Na+, and break the ionic balance. However, under alkali stress, accumulation of compatible solutes, such as betaine, proline and soluble sugar into the vacuole are considered as the basic strategies for plant re-established cellular homeostasis. Some reports have clearly demonstrated that alkaline salts (NaHCO3 and Na2CO3) are more destructive to plants than neutral salts (NaCl and Na2SO4). Moreover, the salt-alkali stress can directly damage plant growth, alter the availability of nutrients and disrupt the balance of ions and mineral nutrition. The objective of this study was to investigate the effects of alkaline stress on growth and some physiological characteristics of safflower.
Materials and Methods:
This study was conducted in a greenhouse in Vali-e-Asr University of Rafsanjan as factorial arrangement in completely randomized design with three replications. Experimental factors included alkaline stress in 7 levels (0, 10, 20, 30 , 40, 50 and 60 mM) and two varieties of safflower (Sofeh and 411). Seeds were planted in pots filled with perlite and cocopite (1:1). The pots were irrigated with a nutrient solution with half strength Hoagland's solution. After the fourth true leaves appeared, alkaline stress in the pot was created by adding NaHCO3, to half strength Hoagland’s solution. Control plants were only irrigated with half strength Hoagland’s solution. Plants were harvested after 40 days of seed sowing. After forty days, shoot and root height, shoot and root dry weight, Fv/Fm, PI, proline, total carbohydrate, malondialdehyde content, cha, chb, total chlorophyll, cartonoied content, potassium, sodium content and sodium to potassium rate were measured.
Results and Discussion:
Result showed that with increasing alkaline stress, decreased shoot and root height, shoot and root dry weight. A similar result had observed previously in sugar beet. Researches have indicated that plants respond to elevated NaHCO3 concentrations in soil or in growing medium solution with decreased shoot and root growth. This could be due to either HCO3 − or Na+. Many of the data test showed high pH as a key factor in limiting plant growth and development under alkaline conditions. 411 variety showed superiority compared to Sofeh cultivar in mentioned characteristics. Also, Fv/Fm and PI decreased under alkaline stress condition, whereas proline, total carbohydrate and malondialdehyde content increased. Also, the increases in proline and total carbohydrate content were reported in wheat under alkaline stress condition. Baghre and Roosta (2012) reported that Fv/Fm values and PI reduced under alkalinity stress. In the present experiment, alkaline stress decreased cha, chb and total chlorophyll whereas it increased cartonoied content. Yang et al., (2009a) concluded that in alkalinity stress, the contents of Chl and Car in the barley plants decreased sharply with increased stress in comparison to salinity stress. They also stated that high pH might decrease contents of photosynthetic pigments. Potassium content decreased under alkaline stress condition whereas sodium and sodium to potassium rate increased. Also, Zhang and Chun-Sheng (2009) reported that with increasing alkaline stress, potassium content decreased in Lathyrus quinquenervius whereas, sodium content and sodium to potassium rate increase. In wheat stems, a decrease in potassium content and potassium to sodium rate and an increase in sodium content were also observed. A high-pH environment surrounding the roots can cause metal ions and phosphorus to precipitate, with loss of normal physiological functions of roots and destruction of root cell structure.
Conclusions:
Result showed that alkaline stress decreased shoot and root height, shoot and root dry weight, whereas proline, total carbohydrate and malondialdehyde content increased. Also, with increasing alkaline stress Fv/Fm, PI, cha, chb, total chlorophyll and potassium content decreased whereas cartonoied content, sodium and sodium to potassium rate increased. 411 variety showed superiority compared to Sofeh cultivar in growth characteristics, cha, total chlorophyll. Also, both cultivars showed same reaction under alkaline stress.
There is a dearth of rootstock studies on how salinity stress imparts tolerance to the scion cultivar in citrus [Citrus sinensis (L.) Osbeck]. The impact of sodium chloride on sweet orange cv. Pusa Sharad (PS) grafted on 11 different rootstocks i.e. Jatti khatti (JK), X–639 (X9), CRH–12 (C12), NRCC–1 (N1), NRCC–2 (N2), NRCC–3 (N3), NRCC–4
(N4), NRCC–5 (N5), Troyer citrange (TC), CRH–47 (C47) and Cleopatra mandarin (CM) was evaluated at the nursery unit of ICAR-Indian Agricultural Research Institute, New Delhi, during 2019–22. Irrigation water containing 30 and 60 mM of sodium chloride (NaCl) was applied to scion/rootstock combinations in comparison to control (without NaCl) till the onset of salt injury symptoms i.e. 42 days. Under salinity stress, the PS scion grafted onto CM, X9, C47, N1, and N3 rootstocks exhibited minimum reduction in the scion height, leaf area ratio, root to shoot ratio, total chlorophyll content, total carotenoid content, transpiration rate, photosynthesis rate, internal CO2 concentration and stomatal conductance as compared to PS scions grafted onto JK, C12, N2, N4, N5, and TC rootstocks under 60 mM NaCl stress. Results showed that specific rootstock can enhance salt-tolerance potential by increasing pigment content and strengthening the photosystem. PS scions grafted onto CM, C47, X9, N1, and N3 demonstrated greater NaCl tolerance compared to those grafted onto JK, C12, N2, N4, N5, and TC and hence recommended for areas having salinity level up to 60 mM.
The process of soil salinization and the preponderance of saline water sources all over the world represent one of the most harmful abiotic stresses to plant growth. In nature, soil salt and alkali coexist, and the interaction of salt and alkali is an important feature of saline-alkali stress. Halostachys caspica is a salt-tolerant halophyte belonging to Amaranthaceae and widely distributed in arid and saline-alkali areas in Xinjiang, Northwest China. This paper studied the response of the germination of the desert halophyte Halostachys caspica to different types of salt stress, aiming to provide a theoretical basis for development and utilization of halophytes growing in saline-alkali soils. The results showed that the seed germination of Halostachys caspica was not significantly inhibited when the salt concentration was low (≤ 200 mmol/L), but with the increase of salt concentration, the germination rate of seeds dropped sharply, and the recovery germination rate at high concentration was higher than that at low concentration, when salt was removed. Step-by-step regression analysis showed that at the same concentration, the alkaline salt inhibited seed germination more severely than the neutral salts; the inhibitory effect of the mixed salt and mixed alkali on seed germination is heavier than that of the mono-salt and mono-alkali; under mixed salt alkali stress, the higher the alkaline salt content, the higher the degree of inhibition on seed germination; indicating that alkaline salt play a major role in mixed saline-alkali stress.
Background
Medicago ruthenica, a superior leguminous forage, is strongly drought-resistant and has wide adaptability. It is closely related to Medicago sativa (a commonly cultivated forage). Characterized by its high tolerance to environmental stress, M. ruthenica is a valuable genetic resource. However, its low yield limits its large-scale promotion and utilization. Leaf morphology, an important agronomic trait, is closely related to forage yield and photosynthetic efficiency.
Results
In this study, leaf width and leaf area were found significantly positively correlated with forage yield in M. ruthenica. Specifically, the cultivar M. ruthenica ‘Mengnong No.1’ (MN No.1) with a larger leaf area had higher photosynthetic efficiency. Furthermore, the key miRNA-target gene networks associated with high photosynthetic efficiency of M. ruthenica were identified using small RNAs and transcriptome sequencing. Totally, 63 differentially expressed miRNAs (DEMs) were identified, including some known miRNAs (miR408, miR171, and miR398, etc.). These known miRNAs corresponded to 55 target genes; 6 miRNA-target gene pairs had negatively correlated expression patterns. Degradome sequencing analysis further confirmed the authenticity of miR408-targeted cleavage of LAC5; namely, the miR408-LAC5 module may mediate the mechanism of high photosynthetic efficiency formation in M. ruthenica.
Conclusions
This study for the first time proposed that leaf morphology as a key trait affecting the high-yielding plant type of M. ruthenica. The key gene modules screened in this study may provide new insights into the elucidation of photosynthetic efficiency mechanism and the bio-design breeding of legume forages in the future.
Drought stress is a major environmental stress that affects on plants Therefore, it is necessary to know the mechanism that plant shows in encounter of stress. The selection of drought-resistant ecotypes is known as an effective strategy for the continued growth and survival of species exposed to drought stress and the assessment of genetic diversity in castor beans plays a vital role in identifying superior genotypes to use in plant breeding programs. This study aims to investigate the genetic relationships and differentiation of 22 castor ecotypes using ISSR markers Also, morphological, biochemical, antioxidant and miRN expression changes in response to drought stress were investigated. For this purpose, first, the diversity and genetic relationship of 22 castor ecotypes were investigated. Out of 26 screened primers, 19 primers that produced the most polymorphic bands were used. Totally, these primers generated 188 bands, of which 180 bands (95.58 %) were polymorphic. The studied ecotypes were divided into two separate group’s using cluster analysis. The highest similarity was observed between ecotypes 4 and 5 (collected from Sari) and the lowest similarity was observed between ecotypes 1 and 14 (Sari and Babolsar).The highest Nei's genetic diversity (H) and Shannon index (I) were observed in population No. 2 including 12 ecotypes. According to the genetic structure of populations performed by Structure software, ecotypes were divided into two subpopulation clusters. The molecular analysis of variance showed that 37% of genetic variation attributed to between group's and 63% to within group's, which can be used in its breeding programs. In order to evaluate the effect of drought stress on physiological, biochemical and Antioxidant traits of castor plant, a factorial experiment was conducted in a completely randomized design with three replications in Sari Agricultural Sciences and Natural Resources University in 1397-8. The first factor was 22 castor ecotypes and the second factor was drought stress with 5 levels, full irrigation, four levels (irrigation was cuted at the primary of spike growth) (11, 22, 33, 44 days after Irrigation cut off). In this study, traits including superoxide dismutase (SOD), Catalase, Ascorbate peroxidase, Guaiacol peroxidase chlorophyll a, chlorophyll b, total chlorophyll, carotenoids, phenol, flavonoids and protein, Proline, malondialdehyde content as well as morphological traits such as plant height, leaf area index, Stem diameter and number of leaves were measured. The results showed that activity of superoxide dismutase (SOD), Catalase, Ascorbate peroxidase, Guaiacol peroxidase, Malondialdehyde biochemical biomarker activity, proline and protein, phenol and flavonoid content increased significantly with increasing the intensity of stress while the amount of photosynthetic pigments and carotenoids as well as plant height, leaf area index, number of leaves and stem diameter showed a significant decrease with increasing level of stress. According to the results of cluster analysis under drought stress, castor ecotypes were divided into three clusters. According to the results, ecotypes 2, 3, 5, 8 and 19 were introduced as resistant ecotypes for future breeding. Programs. In order to investigate the changes in the expression of miRNAs of three ecotypes (sensitive, semi-tolerant and tolerant) from the previous experiment, the expression pattern of 3 miRNAs (miR393, miR166, mi159) and miR168 (considered as a reference gene) were selected in leaf tissues under control conditions and drought stress levels were investigated using qRT-PCR method. Changes in miRNA expression compared to control conditions at each level of stress was variable that can for the difference between the target cell and the cellular miRNA that is expressed, so represents a complex regulatory network of miRNA.
Salt stress has detrimental effects on the growth and development of rice seedlings. In the present study, we assessed salt-responsiveness of three coastal rice landraces namely Nona-morchi, Kalihytta and Nara. We conducted two factors pot trial that included five rice genotypes (three candidates coastal rice landraces, Binadhan-10 as tolerant check and BRRI dhan48 as sensitive check) against three salinity levels e.g., control (tap water), 6 and 12 dSm-1 of sodium chloride. Study revealed that, at 12 dSm-1 of salinity, Binadhan-10 showed the lowest reduction in shoot length (14.62%), shoot fresh weight (30.04%) and shoot dry weight (33.71%) which was followed by Nona-morchi, Kalihytta, Nara and BRRI dhan48. Two stress tolerance indices e.g., relative water content (RWC) and electrolyte leakage (EL), also support salt-induced responses of these five rice genotypes. At the highest level of salinity (12 dSm-1), the lowest RWC reduction was observed in Nona-morchi (8.20%) which is followed by Binadhan-10 (11.38%), Kalihytta (38.93%), BRRI dhan48 (36.30%) and Nara (36.51%). And, the highest EL increased in Nara (40.06%) which is followed by BRRI dhan48 (22.06%), Kalihytta (21.12%), Binadhan-10 (8.64%) and Nona-morchi (5.87%) compared with their respective controls. Importantly, photosynthetic pigments profile (chlorophyll a, chlorophyll b, total chlorophyll) were increased in Nona-morchi (24.48, 15.22 and 21.87%, respectively) and Binadhan-10 (13.75, 12.50 and 13.41%, respectively) and reduced in Kalihytta (7.89, 19.42 and 11.08%, respectively), Nara (27.76, 31.32 and 28.76%, respectively) and BRRI dhan48 (32.73, 36.97 and 34.02%, respectively) at 12 dSm-1 salinity compared with their respective controls. It is to noteworthy that at 6 dSm-1 of salt stress, shoot length significantly decreased in the sensitive check BRRI dhan48 by 23.07%, Kalihytta by 17.32% and Nara by 11.54%. While, no significant effect of 6 dSm-1 of salt stress was observed in Binadhan-10 and Nona-morchi in case of shoot length, root length, shoot fresh and dry weight, EL and RWC. Among the three coastal rice landraces, Nona-morchi found as highly tolerant and Kalihytta were found as moderately tolerant while Nara was identified as sensitive against salt stress (12 dSm-1). In the future, these identified salt tolerant rice genotypes might be the ideal resource for breeding new salt tolerant rice varieties.
Elucidating the effect of γ‐aminobutyric acid (GABA) on seed germination and seedling growth of Medicago ruthenica under low‐temperature could provide a reference for alleviating the harmful effects of low temperatures on legumes in alpine meadows. We set up different temperatures to screen three low temperatures that inhibit seed germination of Medicago ruthenica, and six aqueous concentrations of GABA (0, 0.1, 0.5, 1, 5, 10 mM) were set up to screen out the best GABA seed soaking concentration that can promote the seed germination at low‐temperature. The three temperatures of 10 °C, 20/5 °C and 15/5 °C inhibited seed germination of Medicago ruthenica. Soaking seeds with 1 mM GABA could significantly increase seed germination rate of Medicago ruthenica at low‐temperature (10 °C). Soaking seeds only with 0.1 mM GABA could promote germination of Medicago ruthenica at 20/5 °C, but there is no significant difference compared with distilled water soaking. Whereas, all GABA seed soaking concentrations delayed seed germination time and inhibited seed germination at 15/5 °C. Pre‐spraying seedlings with 1 mM GABA at 10 °C reduced the production of superoxide anion, hydrogen peroxide and malondialdehyde content, and increased the activities of catalase, peroxidase, superoxide dismutase and ascorbate peroxidase in leaves of Medicago ruthenica on days 7. Simultaneously, Pre‐spraying seedlings with 1 mM GABA at 10 °C significantly increased the net photosynthetic rate and decreased intercellular CO2 concentration. These data suggest that GABA could enhance the cold tolerance of Medicago ruthenica by promoting seed germination, regulating the antioxidant system, and increasing photosynthetic efficiency. However, the mitigation effect of GABA on low‐temperature is only applicable to a certain temperature. The mitigation effect of GABA on low temperature will be weakened as the low temperature of plants is less than 10 °C
One of the sustainable and the most effective methods for controlling wind erosion is protecting the ground surface by mulching and vegetation cover. This study was done to assess the effect of organic and inorganic mulches and also compaction levels on soil properties and growth characteristics of caper plants, as one of the important shrubs to combat desertification in hot-humid areas. Results suggested that sugarcane bagasse and palm waste compost mulches significantly increased soil organic carbon (OC), nutrients (available nitrogen, phosphorus, and potassium), and moisture, and decreased soil electrical conductivity (EC), pH, and temperature. Petroleum mulch increased soil penetration resistance (69.50 kPa) and temperature (25.50). Petroleum and cement-slag mulch, and also their combination (petroleum-cement mulch) decreased soil moisture to the minimum extent. For either compaction level, using petroleum mulch increases penetration resistance. Compaction decreased soil moisture by 0.96% and increased total neutralizing value (TNV) and bulk density (BD) by 1.52% and 0.31 g cm⁻³, respectively. For either compaction level, soil porosity increased with the application of sugarcane bagasse mulch and palm waste compost. Using sugarcane bagasse mulch and palm waste compost increased stem length, leaf number, above ground and root weight, and shoot to root ratio of caper plant. Soil temperature (a = −0.70, R² = 55.70%, P ≤ 0.001), EC (a = −0.87, R² = 42.49%, P ≤ 0.001) and penetration resistance (a = −1.32, R² = 17.03%, P ≤ 0.01) decreased with increasing soil moisture. BD (a = −1.20, R² = 37.08%, P ≤ 0.001) decreased with increasing soil OC. Findings suggested the significant effect of organic mulches on improving some soil properties and growth characteristics of caper plants.
This paper discusses whole-plant responses to salinity in order to answer the question of what process limits growth of non-halophytes in saline soils. Leaf growth is more sensitive to salinity than root growth, so we focus on the process or processes that might limit leaf expansion. Effects of short-term exposure (days) are considered separately from long-term exposure (weeks to years). The answer in the short term is probably the water status of the root and we suggest that a message from the root is regulating leaf expansion. The answer to what limits growth in the long term may be the maximum salt concentration tolerated by the fully expanded leaves of the shoot; if the rate of leaf death approaches the rate of new leaf expansion, the photosynthetic area will eventually become too low to support continued growth.
A glasshouse experiment examined the effect of water stress on the growth of
Lupinus angustifolius L. and
Lupinus pilosus Murr. grown on an acid sandy soil, a
limed sandy soil and an alkaline clay soil. Decreasing soil water content
decreased the stomatal conductance and photosynthetic rate, and reduced plant
growth. The responses of both species to water stress were generally similar
in the sand and limed soils, but in the alkaline soil,
L. angustifolius grown with limited water had markedly
lower conductances and photosynthetic rates than the plants in the other soils
at equivalent soil water contents. In adequately watered plants, the lupin
species differed substantially in their growth response to soil types. Whereas
the growth of L. pilosus was unaffected, the shoot dry
weight of L. angustifolius grown on the limed and
alkaline soils for 25–44 days was reduced by 32–54 and
44–86%, respectively, compared with the growth in the acid soil.
The poor growth of L. angustifolius appeared to be
primarily due to its poor root growth. In the alkaline soil, water stress
reduced rather than stimulated root growth. The results suggest that, in the
field, the limited root growth of L. angustifolius on
alkaline soils will exacerbate water deficits when the topsoil dries out in
the latter part of the season.
Eight-week-old seedlings of Puccinellia tenuiflora were stressed by exposure to 1 : 1 molar ratio mixtures either of the two neutral salts NaCl and Na2SO4 or of the two alkali salts, NaHCO3 and Na2CO3. To identify the physiological mechanisms involved in this plant’s resistance to alkali stress, the relative growth rates, the quantities and compositions of organic acids accumulated and secreted through the roots into the rhyzosphere, the concentrations of inorganic ions, proline and other solutes accumulating in the shoots were measured. The results show that the organic acid constituents in the shoots and roots were much the same. These were predominantly malic acid, oxalic acid, citric acid and succinic acid. The total concentration of organic acids in the shoots increased strongly with increasing alkali stress. However, these either did not increase or they decreased slightly with increasing salt stress. Of the four organic acids, the concentration difference between salt- and alkali-stressed plants was most striking for citric acid. This became the dominant organic acid component under alkali stress. Results show that proline is the main organic osmolyte, whereas the contribution of betaine to osmotic adjustment is insignificant under either salt or alkali stress. The main organic acid accumulated was not only an important organic osmotic regulator, but also an important negative charge contributor, playing important roles in ionic balance and pH adjustment. The concentrations of Na+, K+, Cl− and of organic acid were 80.7% of all solutes under salt stress. The concentrations of Na+, K+, Cl− and of organic acid were 85.4% of all solutes under alkali stresses. The ionic balance was disrupted by the strong increase in Na+ content under alkali stress. This perhaps explains why large amounts of the organic acids were accumulated. The organic acid concentration in the roots was lower than in the shoots. The roots secreted citric acid into the rhyzosphere only under alkali stress, secretion of the other organic acids was not detected. Therefore, citric acid secreted from the roots probably plays an important role in pH adjustment in the rhyzosphere of P. tenuiflora.
As a traditional Chinese medicinal plant, Lyciumbarbarum is of high economic value and has attracted many considerable interests in recent years. The plant is a perennial halophyte grown under extreme conditions, especially under highly saline soil. A pot experiment was carried out to quantify the responses of L. barbarum plants to soil salinity applied at 100 and 200 mM NaCl. The results demonstrate that 100 mM NaCl soil improves the growth of L. barbarum seedlings. Because the 100 mM NaCl soil enhanced plant height and dry matter by 20% and 30% compared with the nonsalinised soil, it is considered suitable, and the 200 mM NaCl soil showed negative effects, too extreme for the growth of L. barbarum. The leaf cations and betaine content increased significantly under salt stress. The leaf chlorophyll, gas exchange, photochemical efficiency, leaf area and soluble sugar contents showed a significant decrease under 200 mM NaCl stress compared with the nonsalinised and the 100 mM NaCl-affected soil. The results do not provide a basic mechanism for the observed growth stimulation; however, they suggest that L. barbarum may be an economic species for cultivation in moderately saline areas such as northwest China.
Kochia sieversiana (Pall.) C. A. M., a naturally alkali-resistant halophyte, was chosen as the test organism for our research. The seedlings
of K. sieversiana were treated with varying (0–400mM) salt stress (1:1 molar ratio of NaCl to Na2SO4) and alkali stress (1:1 molar ratio of NaHCO3 to Na2CO3). The concentrations of various solutes in fresh shoots, including Na+, K+, Ca2+, Mg2+, Cl−, SO42−, NO3−, H2PO3−, betaine, proline, soluble sugar (SS), and organic acid (OA), were determined. The water content (WC) of the shoots was calculated
and the OA components were analyzed. Finally, the osmotic adjustment and ion balance traits in the shoots of K. sieversiana were explored. The results showed that the WC of K. sieversiana remained higher than 6 [gg−1 Dry weight (DW)] even under the highest salt or alkali stress. At salinity levels >240mM, proline concentrations increased
dramatically, with rising salinity. We proposed that this was not a simple response to osmotic stress. The concentrations
of Na+ and K+ all increased with increasing salinity, which implies that there was no competitive inhibition for absorption of either in
K. sieversiana. Based on our results, the osmotic adjustment feature of salt stress was similar to that of alkali stress in the shoots of
K. sieversiana. The shared essential features were that the shoots maintained a state of high WC, OA, Na+, K+ and other inorganic ions, accumulated largely in the vacuoles, and betaine, accumulated in cytoplasm. On the other hand,
the ionic balance mechanisms under both stresses were different. Under salt stress, K. sieversiana accumulated OA and inorganic ions to maintain the intracellular ionic equilibrium, with close to equal contributions of OA
and inorganic ions to anion. However, under alkali stress, OA was the dominant factor in maintaining ionic equilibrium. The
contribution of OA to anion was as high as 84.2%, and the contribution of inorganic anions to anion was only 15.8%. We found
that the physiological responses of K. sieversiana to salt and alkali stresses were unique, and that mechanisms existed in it that were different from other naturally alkali-resistant
gramineous plants, such as Aneurolepidium chinense, Puccinellia tenuiflora.
Seedlings of Chloris virgata were treated with varying (0–160 mM) salt-stress (SS; 1: 1 molar ratio of NaCl to Na2SO4) or alkali-stress (AS; 1: 1 molar ratio of NaHCO3 to Na2CO3). To compare these effects, relative growth rates (RGR), stored energy, photosynthetic pigment contents, net photosynthetic
rates, stomatal conductance, and transpiration rates were determined. Both stresses did not change significantly the photosynthetic
parameters of C. virgata under moderate stress (below 120 mM). Photosynthetic ability decreased significantly only at high stress (160 mM). Thus C. virgata, a natural alkali-resistant halophyte, adapts better to both kinds of stress. The inhibition effects of AS on RGR and energy
storage of C. virgata were significantly greater than that of SS of the same intensity. The energy consumption of C. virgata was considerably greater while resisting AS than while resisting SS.
The ABA concentrations of leaves, roots, soils and transport fluids of chickpea and lupin plants growing in acid (pH=4.8) and alkaline (pH=8.0) soils and an acid soil with an alkaline subsoil and an alkaline soil with an acid subsoil were measured with the aim of explaining the poor growth of narrow-leafed lupins in alkaline soil. The ABA concentration in the leaves was higher in lupin than chickpea, but did not differ when the plants were grown in alkaline compared to acid soil. The ABA concentration of the roots and xylem sap of lupin did not differ significantly when grown in acid or alkaline soil. Chickpea roots and xylem sap had, however, lower ABA concentrations in acid soil. The ABA concentration in the soil solution was higher in the acid than in the alkaline soil. Roots of lupin and chickpea showed no suberization of the hypodermis or exodermis whether grown aeroponically or hydroponically and the pH of the cytoplasm did not change significantly when root cells of lupin and chickpea were exposed to external pHs of 4.8 or 8.0. The chickpea roots had greater suberization of the endodermal cells adjacent to radial xylem rays and maintained a slightly higher vacuolar pH than lupin in both acid and alkaline external media, but these small differences are insufficient to explain the reductions in lupin growth in alkaline soil.
We compared the effects of salt-stresses (SS, 1: 1 molar ratio of NaCl to Na2SO4) and alkali-stresses (AS, 1: 1 molar ratio of NaHCO3 to Na2CO3) on the growth, photosynthesis, solute accumulation, and ion balance of barley seedlings, to elucidate the mechanism of AS
(high-pH) damage to plants and the physiological adaptive mechanism of plants to AS. The effects of SS on the water content,
root system activity, membrane permeability, and the content of photosynthetic pigments were much less than those of AS. However,
AS damaged root function, photosynthetic pigments, and the membrane system, led to the severe reductions in water content,
root system activity, content of photosynthetic pigments, and net photosynthetic rate, and a sharp increase in electrolyte
leakage rate. Moreover, with salinity higher than 60 mM, Na+ content increased slowly under SS and sharply under AS. This indicates that high-pH caused by AS might interfere with control
of Na+ uptake in roots and increase intracellular Na+ to a toxic level, which may be the main cause of some damage emerging under higher AS. Under SS, barley accumulated organic
acids, Cl−, SO4
2−, and NO3
− to balance the massive influx of cations, the contribution of inorganic ions to ion balance was greater than that of organic
acids. However, AS might inhibit absorptions of NO3
− and Cl−, enhance organic acid synthesis, and SO4
2− absorption to maintain intracellular ion balance and stable pH.
The seedlings of wheat were treated by salt-stress (SS, molar ratio of NaCl: Na2SO4 = 1: 1) and alkali-stress (AS, molar ratio of NaHCO3: Na2CO3 = 1: 1). Relative growth rate (RGR), leaf area, and water content decreased with increasing salinity, and the extents of the reduction under AS were greater than those under SS. The contents of photosynthetic pigments did not decrease under SS, but increased at low salinity. On the contrary, the contents of photosynthetic pigments decreased sharply under AS with increasing salinity. Under SS, the changes of net photosynthetic rate (P
N), stomatal conductance (g
s), and transpiration rate (E) were similar and all varied in a single-peak curve with increasing salinity, and they were lower than those of control only at salinity over 150 mM. Under AS, P
N, g
s, and E decreased sharply with rising salinity. The decrease of g
s might cause the obvious decreases of E and intercellular CO2 concentration, and the increase of water use efficiency under both stresses. The Na+ content and Na+/K+ ratio in shoot increased and the K+ content in shoot decreased under both stresses, and the changing extents under AS were greater than those under SS. Thus SS and AS are two distinctive stresses with different characters; the destructive effects of AS on the growth and photosynthesis of wheat are more severe than those under SS. High pH is the key feature of the AS that is different from SS. The buffer capacity is essentially the measure of high pH action on plant. The deposition of mineral elements and the intracellular unbalance of Na+ and K+ caused by the high pH at AS might be the reason of the decrease of P
N and g
s and of the destruction of photosynthetic pigments.
Sunflower seedlings were treated under 30 different conditions of alkalinity and salinity, which were established by mixing NaCl, NaHCO3, Na2SO4, and Na2CO3, at various proportions. The treatments included a salt concentration range of 50–250 mmol and pH values from 7.12 to 10.72. Several physiological indices of seedlings stressed—including relative growth rate (RGR), leaf area, electrolyte leakage rate, proline content, citric acid content, and contents of Na+ and K+—were determined to analyze the characteristics of the stresses due to the salt–alkali mixes and their main stress factors.
This study examined the effects of salinity and climate on instantaneous CO2 exchange rates and daily carbon balance for two populations of Phragmites australis. Plants propagated from seeds collected in Denmark (=Danish population) and Spain (=Spanish population) were grown at salinities of 0, 5 and 10‰ at outdoor experimental plots situated at a nemoral growth site (Denmark, 56°N) and at a mediterranean growth site (Spain, 41°N). In situ measurements of shoot CO2 exchange were made under different meteorological conditions. Maximum CO2 uptake rates were 24 and 19 μmol m−2 s−1 in Spain and Denmark, respectively, and were only reached under conditions of full sunlight. On sunny days, CO2 uptake was reduced less by salinity at the Spanish site than at the Danish site. Photosynthetic photon flux densities saturating shoot photosynthesis were much lower in Spain (ca. 600 μmol m−2 s−1) as compared to those in Denmark (ca. 1300 μmol m−2 s−1). This affected the period of maximum CO2 uptake rates which was 2–3 h longer at the Spanish growth site, despite shorter day length at this site (15 h) than at the Danish site (17 h). Dark respiration rates of shoots were higher at the Spanish growth site (2–8 μmol CO2 m−2 s−1) as compared to the Danish site (less than 2 μmol CO2 m−2 s−1). Salinity was observed to accelerate rates of dark respiration only at the Spanish site. Integrals of shoot CO2 exchange rates over a 24 h period indicated lower total daily carbon gain at the Danish site, which under clear sky conditions was 65–80% of that at the Spanish site. Cloud cover was found to reduce net photosynthetic CO2 uptake considerably and could even cause a net loss of carbon during periods, which in absence of clouds could confer maximum uptake rates. The salt tolerance and productivity of P. australis is therefore strongly related to the ratio of realised to potential sun hours. This ratio may override the importance of other environmental factors such as temperature. This study also evaluated the effects of moderate salinity stress (0–15‰ salinity) on in situ P. australis transpiration. Daily transpiration rates were 30–75% higher at the Spanish site (0.38–0.56 g H2O cm−2 day−1) as compared to the Danish site (0.22–0.38 g H2O cm−2 day−1). Rates were equally affected by salinity at both the growth sites. Since water loss is an important factor behind P. australis salt tolerance it is speculated that salt tolerance may increase under conditions favouring high transpiration, contrary to most other halophytes.
This study estimated the effects of Danish (temperate nemoral) and Spanish (mediterranean) climatic conditions on the salt tolerance of two Phragmites australis (Cav.) Trin. ex Steud. populations. Plants propagated from seeds collected in Denmark (=Danish population) and Spain (=Spanish population) were exposed to salinity levels ranging from 0 to 30‰ at outdoor experimental plots situated in Denmark (56°N) and Spain (41°N). Plants were measured for growth rate, mortality, below-ground/above-ground ratio, water content, ash content, nitrogen content, C:N and ions (K+, Na+, Mg2+, Ca2+, Cl−). Growth was significantly enhanced at the Spanish growth site, especially for salinity levels ranging from 10 to 20‰. In this interval, growth rates of both the Danish and the Spanish population were 20–100% higher than at the Danish growth site. These growth data point to higher salt tolerance at the Spanish site when using relative salt tolerance and absolute salt tolerance as criteria. Salt tolerance is ascribed to two important mechanisms, cation adjustment and water loss. Despite higher transpiration at the Spanish site, plants were able to maintain or improve K+/Na+ ratios of leaf laminas, indicating enhanced cation adjustment under the Spanish climatic conditions. Primarily, this was due to higher K+ accumulation at the Spanish site (305–378 mmol kg−1) as compared to the Danish site (220–268 mmol kg−1), while a climatic effect on Na+ level only was evident for the Danish population. Climatically induced differences in water content may also have contributed significantly to the higher salt tolerance observed for plants at the Spanish site. Shoot water content was lower at the Spanish site (1.9–2.4 g water g−1 DW) than at the Danish site (2.6–4.0 g water g−1 DW), suggesting that water loss is an important mechanism contributing to osmotic adjustment. Water loss may act by concentrating solutes in the cell sap, thereby reducing the need for synthesis of metabolically expensive organic osmotica as well as reducing the need for Na+ uptake for osmotic adjustment. This study also showed that P. australis populations differ in salt tolerance. A relatively higher salt tolerance observed for the Danish population was related to lower mortality, lower leaf Na+ and Cl− content, higher leaf K+/Na+ ratio, higher leaf nitrogen content, higher below-ground/above-ground ratio and lower ash content of below-ground parts and is discussed in relation to partitioning.
The volume identifies how stressful conditions affect plants. Various stresses, such as drought, salinity, waterlogging, high and low temperatures, can have a major impact on plant growth and survival - with important economic consequences in crop plants. This book examines some of the more important stresses, shows how they affect the plant and then reviews how new varieties or new species can be selected which are less vulnerable to stress. The wide-ranging and important consequences of stress should ensure that the volume is widely read by plant biologists at the graduate and research level.
Irrigated agriculture has faced the challenge of sustaining its productivity for centuries. Because of natural hydrological and geochemical factors, as well as irrigation-induced activities, soil and water salinity and associated drainage problems continue to plague agriculture. The problems have extended far beyond the farmlands, where saline soils and waters impair crop production. Practices based on the presumption that saline drainage waters will somehow, somewhere, be discharged are now being challenged. New and extended regulations on the discharge of nonpoint source pollutants in agricultural drainage waters are expected in the United States. This chapter presents an overview of the nature of salinity in soils and waters, its extent from global to regional scales, the reactivity of salts and salt flows, and the concerns of agriculture and other sectors of society.
Iron dynamics in plants start by complex interactions between plants and the rhizospheric microflora, which determine the amount of available iron for uptake by root transporters. Under iron-deficient conditions, two types of high affinity transport systems are activated, depending on the plant family considered. In nongrass plants, Fe(III)-chelate reduction is followed by Fe(II) uptake, whereas in grasses, Fe(III) chelated to secreted phytosiderophores (PSs) is taken up by roots. Long distance allocation of iron between organs and tissues, as well as its subcellular compartmentation and remobilization, also involve various chelation and reduction activities, associated to transporters and to soluble proteins storing and buffering this metal. This iron trafficking at the whole plant, cellular, and subcellular levels, is a highly regulated process starting to be characterized at a molecular level. To maintain iron homeostasis is an important determinant to build up prosthetic groups such as heme and Fe-S clusters, and to assemble them into apoproteins. Such processes require complex protein machineries which are located in mitochondria and plastids. An essential and plant-specific role of these iron dynamics is evidenced by the strong iron requirement for the photosynthetic reaction to take place.
Plants of chick-pea (Cicer arietinum L. cv. ILC1919) inoculated with Mesorhizobium ciceri strain ch-191 were grown in a controlled environmental chamber, and were administered salt (0, 50, 75, and 100 mM NaCl) during
the vegetative period. Four harvests (4, 7, 11, and 14 d after treatment) were analysed. The aim was to ascertain whether
the negative effect of saline stress on nitrogen fixation is due to a limitation on the photosynthate supply to the nodule
or a limitation on the nodular metabolism which sustains nitrogenase activity.
Plant growth was affected only by the highest NaCl concentration, whereas nitrogenase activity was affected from 50 mM. At
the first harvest, Rubisco, PEPC and MDH activities in leaves rose with salt, but fell during the following harvests. The
increase of PEPC and MDH in nodules at the two first samplings was clearly related to salt concentration. While 50 mM NaCl
increased GS and GOGAT in nodules at some harvests, 100 mM strongly inhibited these activities at all the harvests. The accumulation
of proline, amino acids and carbohydrates was clearly related to salt especially in the leaves, whereas in the nodules the
protein content was boosted by salt. Although photosynthesis declined with NaCl, the response of nitrogen fixation to salt
was more pronounced. This situation, together with carbohydrate accumulation, suggests that the lack of photosynthate does
not cause the inhibition of nitrogenase activity under this type of stress. The similar trend observed for the PEPC-MDH pathway
and the ARA support the hypothesis concerning the limitation in the supply of energy substrate, mainly malate, to the bacteroids.
The accumulation of compatible sol
utes is more a consequence of damage produced by salt stress than of a protective strategy.
Medicago ruthenica (L.) Ledebour has long been recognized as a potential new forage crop, which may also have potential as a source of genes for improving abiotic stress tolerance in cultivated alfalfa (M. sativa L). This study was designed to assess the genetic variation among 50 M. ruthenica accessions, collected in Inner Mongolia in 1991 from 15 environments ranging from sand dunes to lush grassland, and to assess the agronomic potential of the species in the humid eastern USA. Accessions were evaluated in the held at Beltsville, MD, in 1993 and 1994 on an luka sandy loam (coarse-loamy, siliceous, acid, thermic, Aquic Udigluvent; pH 6.4) in boron and potassium deficient soil. Stand retention was only 47% (compared with 94% for M. sativa checks) after the winter of 1993, indicating that the species is not well adapted to the humid eastern USA. Significant variation was noted for reaction to environmental stress (possibly boron deficiency), days from seeding to tillering, dry matter yield, growth habit, leaf shape, and plant height and width. No disease symptoms were noted; however, a detailed pathological examination was not conducted. A positive relationship was noted between plant width and yield, and between uprightness and narrow leaves. The more procure-bent plants with broader leaves may have been less susceptible to winter damage under Beltsville conditions. Some of the most agronomically desirable accessions could have resulted from genetic shifts due to selection. Analyses indicate that M. ruthenica may have the potential to become a new forage crop, perhaps for low input systems, and that semi-erect (for hay production) or procumbent (grazing tolerant) populations with improved seedling vigor and yield could be developed. Considering the antiquity and isolation of M. ruthenica, its harsh native environment, and the stress tolerance and yield of elite accessions under low-input conditions, M. ruthenica may provide genes that could be of considerable value to cultivated alfalfa.
We evaluated the effect of salinity on rice at the reproductive phase. From flag leaf stage to dough stage, potted rice plants were irrigated twice a week with saline water (0, 25, 50, 100, and 200 mM NaCl) at a volume of 1.5 times that of the soil. Photosynthesis and leaf biochemical constituents were measured at flowering (15 days after treatment establishment, DATE) and milking stage (25 DATE). Samples for grain dry matter and biochemical analysis were collected at milking (25 DATE) and dough (37 DATE) stages. Reduction in photosynthesis in the salinized plants depended not only on a reduction of available CO2 by stomatal closure, but also on the cumulative effects of leaf water and osmotic potential, stomatal conductance, transpiration rate, relative leaf water content, and biochemical constituents such as photosynthetic pigments, soluble carbohydrates, and protein. The cumulative effects resulted in low concentrations of assimilates in the leaves. These low concentrations and poor translocation of assimilates from the source reduced grain dry matter. Grain growth was less sensitive to salinity at milking stage. This suggests that the plant is able to escape stress when the duration of salinity is short.
Forage grasses and turfgrasses are increasingly being subjected to salinity stress, due to accelerated salinization of irrigated agricultural lands worldwide, and to increased use of reclaimed and other secondary water sources for irrigating turfgrass landscapes. The objective of this study was to examine salinity responses of a number of important forage and turfgrass genera in the subfamily Chloridoideae in attempt to gain understanding of salinity tolerance mechanisms operating in this subfamily. Grasses were exposed to salinities up to 600 mM NaCl in solution culture. Salinity tolerance decreased in the following order: Distichlis spicata var. stricta (Torr.) Beetle > Sporobolus airoides (Torr.) Torr. > Cynodon dactylon (L.) Pets. = Zoysia japonica Steud. > Sporobolus cryptandrus (Torr.) A. Gray. > Buchloe dactyloides (Nutt.) Engelm. > Bouteloua curtipendula (Michx.) Torr. Relative root length (RL) and relative root weight (RW) increased under saline conditions, relative to control, in salt tolerant grasses. Leaf sap osmolality, Na+, Cl-, and proline concentrations were negatively correlated and glycinebetaine was positively correlated with salinity tolerance. Bicellular salt glands were observed on leaves of all species. Salinity tolerance was positively correlated with Na+ and Cl- salt gland secretion rates. Within the subfamily Chloridoideae, salinity tolerance was associated with saline ion exclusion, facilitated by leaf salt gland ion secretion, and with accumulation of the compatible solute glycinebetaine.
We tested wheat (Triticum aestivum L.) seedlings under five different saline and alkaline stress (9:1 molar ratio of NaCl/Na(2)SO(4) and 9:1 molar ratio of NaHCO(3)/Na(2)CO(3), respectively) regimes of differing severity for 7 d, comparing growth, germination, and ionic balance of wheat seedlings, to elucidate the mechanism of alkaline stress (high pH) damage to wheat, and it physiological adaptive mechanism to alkaline stress. We found that alkalinity had a more severe effect on wheat seedlings than salinity, preventing germination before and after recovery, and severely inhibiting shoot and root growth. Plants responded to both saline and alkaline stress by accumulating Na(+) at the expense of K(+), and by accumulating soluble osmolytes, but these effects were more pronounced under alkaline stress than saline stress. Alkaline stress also induced several specific responses such as the inhibition of fructan synthesis (fructan levels increased in response to salinity), the accumulation of organic acids, the accumulation of Ca(2+) and the depletion of H(2)PO(4)(-). The results suggest that specific damage caused by alkaline stress might reflect a massive influx of Na(+), resulting in a severe deficit of negative charge. The plants respond by trying to restore the osmotic balance and synthesizing organic acids as counter-ions to address the intracellular ion imbalance. These data provide important leads in the development of engineered wheat plants with improved stress tolerance.
Glasshouse trials, using trickle irrigation and increasing levels of NaOH-induced alkalinity, identified species that could be expected to tolerate the high-pH conditions of bauxite processing waste residue sites. Of 29 taxa tested, the most tolerant were Casuarina obesa, Melaleuca lanceolata, M. armillaris, M. nesophila, Eucalyptus loxophleba, E. halophila, E. platypus, Tamarix aphylla, and a particular clone of E. camaldulensis; E. spathulata, E. tetragona, E. preissiana, E. gomphocephala, E. diptera, and E. occidentalis proved to be relatively sensitive to severe alkaline conditions. Tolerance appeared to relate to an ability to maintain root membrane function, nutrient uptake balance, and ultimately root tissue structure while under increasing levels of alkalinity stress. Species normally inhabiting alkaline soils tended to have increased growth rates in nutrient irrigation conditions between pH 8 and 10 compared with control plants irrigated with nutrient solutions of pH values near 7.4. However, once the irrigation solutions reached pH 12 and the buffering capacity of the soil appeared to be exceeded, the condition of susceptible plants rapidly declined and death followed. Sensitive plants initially showed symptoms related to nutrient deficiency, followed by wilting and death as the root systems failed. Field trial conditions in the bauxite residue impoundments at Kwinana, Western Australia, include soils with pH values as high as 11.00. In general, the relative survival and growth of seedlings after eight months were predicted by the response under glasshouse trial conditions. Appropriately designed stress trials can be important ecological techniques in choosing species most capable of surviving difficult environmental conditions in the rehabilitation of damaged landscapes.
Halosarcia pergranulata(P. G. Wilson) subsp.pergranulatais a member of the Salicornioideae and is native to Australia. Salt tolerance inH. pergranulatasubsp.pergranulatawas assessed by growing plants for 83 d at seven NaCl concentrations from 10 to 800 mol m−3. Shoot biomass was greatest for plants grown at 10 to 200 mol m−3NaCl, while at salinities of 300 mol m−3or higher it was inhibited. There was little increase in succulence in response to NaCl, and it even declined at the highest salinities. The K+:Na+molar ratio in succulent shoot tissues decreased from 0.30:1 in plants grown at 10 mol m−3NaCl to 0.02:1 in plants at 600 mol m−3, due to a three-fold increase in tissue Na+concentration and a five-fold decline in tissue K+. The osmotic potential of sap (πsap) in the expanding shoot tissues remained −1.7 to −2.5 MPa below the πof the root medium. Na+plus Cl−contributed 56 to 80% of the πsapin plants grown at 10 to 800 mol m−3NaCl. These findings show thatH. pergranulatasubsp.pergranulatahas a high degree of NaCl tolerance, and that studies on solute compartmentation at the cellular level are required to elucidate the mechanisms by which this species tolerates very low tissue K+:Na+ratios.
A sodium bicarbonate (NaHCO3)‐buffered hydroponic growth system was developed that simulates alkaline soil growth conditions necessary to screen sugar beet genotypes for iron (Fe) efficiency character. Three genotypes (NB1, NB4, and F, hybrid, NB 1xNB4) with differing capacities for Strategy I Fe responses were phenotyped successfully using this system. Genotypes NB1 and NB1xNB4 are Fe efficient, while NB4 is Fe inefficient. It was demonstrated that 5 mM NaHCO3 provided buffering within an optimal range (pH 7.3 ‐ pH 6.3) for the duration of ‐Fe treatments, promoted enhanced H extrusion, and increased the in vivo capacity for Fe‐chelate reduction (Fe‐chelate reductase [FCR] activity), especially in the roots of the Fe efficient genotypes. The same concentrations of NaHCO3 did not interfere with Fe supply to +Fe control plants of any genotype. The in vivo capacity for Fe‐chelate reduction increased over fivefold in both Fe efficient genotypes (NB1 and NB 1xNB4), but just under twofold in the Fe inefficient genotype (NB4). Localization and duration of enhanced Fe‐chelate reduction capacity were dependent upon the Fe efficiency character of each genotype.
The genus Medicago has recently undergone extensive taxonomic changes. At least two dozen species not previously accepted as belonging to it have been added. Moreover, the circumscription, infraspecific taxonomy, and nomenclature of many of the species placed in Medicago have been altered recently, and the circumscription and nomenclature of the sections of the genus have also changed. Adding to the need for a synopsis is the fact that many of the species are very difficult to identify. This conspectus presents a key to the 12 sections and eight subsections of the genus, a comprehensive illustrated key to the 83 species (and 18 infraspecific taxa) of Medicago, and brief notes on their geography, ecology, and possible confusion with similar species.
Seedlings of two forage sorghum genotypes (Sorghum bicolor (L.) Moench) differing in salt tolerance were subjected to 0 and 100 mM NaCl and shoot development, leaf elongation, and organic and inorganic solutes contents in leaves were measured. Salt stress reduced both shoot development and leaf elongation and enhanced leaf senescence and injury. It also led to accumulation of toxic ions (Na ' and Cl (), organic solutes (carbohydrates, amino acids and proline), and reduction of K ' content in leaf blades. Toxic ion accumulation was higher in the basal zone of the leaf blade and occurred during the period of intense leaf growth while organic solutes accumulation, mainly proline, was higher in the apical zone and occurred when the leaves practically had reached their final size. All these changes were more conspicuous in the sensitive than in the tolerant genotype. The latter also retained more toxic ions in leaf sheath tissue than the former. It is suggested that the reduction in shoot development and leaf elongation were related to toxic ion accumulation and depletion of K ' ions in the leaf blades. The accumulation of organic solutes in leaves did not appear to be related to salt tolerance. Proline accumulation appears to be a reaction to salt stress damage and not a plant response associated with salt tolerance. # 2002 Elsevier Science B.V. All rights reserved.
Despite a wealth of published research on salinity tolerance of plants, neither the metabolic sites at which salt stress damages plants nor the adaptive mechanisms utilized by plants to survive under saline conditions are well understood. As a result, there are no well-defined indicators for salinity tolerance available to assist plant breeders in the improvement of salinity tolerance of important agricultural crops. Although plant breeders have successfully improved salinity tolerance of some crops in recent decades, using plant vigor or seed yield as the main selection criteria, selection may be more convenient and practicable if the crop possesses distinctive indicators of salt tolerance at the whole plant, tissue or cellular level. Thus, there is a need to determine the underlying biochemical mechanisms of salinity tolerance so as to provide plant breeders with appropriate indicators. In this review, the possibility of using these biochemical characteristics as selection criteria for salt tolerance is discussed. It is concluded that although there are a number of promising selection criteria, the complex physiology of salt tolerance and the variation between species make it difficult to identify single criteria. Progress is more likely if biochemical indicators for individual species rather than generic indicators can be determined.
Throughout arid regions of the world, groundwater is extracted for human population centres. In the Great Basin and Range region of the USA, we lack basic information regarding some plant communities detailing the extent to which vegetation is threatened by groundwater extraction. This is particularly true for alkali meadow vegetation, which is restricted to zones of shallow groundwater yet is not a riparian plant community with obligate wetland properties.
To increase our understanding of the relative importance of groundwater and precipitation in maintaining alkali meadow vegetation cover, we used a 16‐year record of plant cover derived from satellite data of Owens Valley, California, USA, in conjunction with concurrent depth‐to‐water and precipitation measurements, to analyse vegetation response to anthropogenic and climatic changes in water availability.
Groundwater decline varied from 0·5 to 5·0 m throughout the study area, with the largest changes occurring at sites closest to pumping wells. The entire region experienced a 6‐year drought (1987–92), during which annual precipitation remained below the 50‐year median.
Meadow plant cover over the 16‐year study period was correlated with groundwater depth, but plant cover was generally unresponsive to annual precipitation variability. Sensitivity to groundwater decline was greatest for plots with a higher cover of herbaceous perennials.
The results showed that this plant community is groundwater dependent, and that this characteristic buffers the system from the effects of drought. However, at sites with extensive groundwater decline, the remaining plant cover became weakly correlated with precipitation only after groundwater declined below a threshold depth located at 2·5 m, representing the average plant rooting depth.
Synthesis and applications . Sustainable water development that seeks to pump groundwater without adversely affecting vegetation cover and plant assemblages must recognize the maximum rooting depth of groundwater‐dependent plant species. When groundwater is within the root zone, management decisions can be made to either increase or decrease vegetation cover through modification of groundwater depth. When groundwater is below the root zone, vegetation cover is low and susceptible to changes in precipitation. Quantitative satellite measurements of vegetation cover might aid the monitoring and sustainable management of water resources.
Defining root death in studies of root dynamics is problematic because cell death occurs gradually and the resulting effects on root function are not well understood. In this study, metabolic activity of grape roots of different ages was assessed by excised root respiration and tetrazolium chloride reduction. We investigated changes in metabolic activity and patterns of cell death occurring with root age and changes in root pigmentation. Tetrazolium chloride reduction of roots of different ages was strongly correlated to respiration (R2 = 0.786). As roots aged, respiration and tetrazolium chloride reduction declined similarly, with minimum metabolic activity reached at six weeks. Tetrazolium chloride reduction indicated that the onset of root browning corresponded to a 77% reduction in metabolic activity (P < 0.001). Anatomical examination of roots at each pigmentation stage showed that even though some cells in brown roots were still alive, these roots were functionally dead. The effect of using different definitions of root death in relation to root survivorship was determined in a study of ‘Concord’ grapes with two pruning treatments, using three criteria for root death: browning, blackening or shriveling, and disappearance. There was no effect of vine pruning on root life span when life span was defined as the time from first appearance to the onset of browning. However, if death was judged as the point when roots either became black or shriveled or disappeared, vine pruning decreased root life span by 34% and 40%, respectively (P < 0.001), and also increased the decay constant for root decomposition by about 45% (P < 0.001). We conclude that the discrepancy among determinations of root life span assessed with different definitions of death might be partly caused by the latter evaluations of root life span incorporating a portion of root decomposition in definitions of root death.
The stress conditions of salt-alkalinized soil were simulated to investigate the features and acting factors of salt-alkaline mixed stress, using a natural salt-alkaline tolerant grass Aneurolepidium chinense (Trin.) Kitag. According to the features of salt-alkalinized soil in the northeast of China, various salt-alkali conditions with different salinities and pHs were established by mixing NaCl, NaHCO3, Na2SO4, and Na2CO3, in various proportions. The treatments included a salt concentration range of 50 to 350mM and pH values from 7.14 to 10.81. Seedlings of A. chinense were stressed under these salt-alkali conditions. Several physiological indices of seedling stress were determined, including survival rate, tillering rate, number of rhizomes, relative growth rate (RGR), proline content, electrolyte leakage rate, and Na+ and K+ content, in order to analyze the characteristics of the stresses due to the salt-alkali mixes and their main stress factors.The results showed that the survival rate, tillering rate, number of rhizomes, RGR, and K+ content of A. chinense decreased with increasing salinity and pH (or alkalinity). Proline and Na+ content and electrolyte leakage rate increased with increasing salinity and pH (or alkalinity). The deleterious effects of a high pH value or salinity alone were significantly less than those of high pH in combination with salinity. This result suggested that for a salt-alkaline mixed stress, a reciprocal enhancement between salt stress and alkali stress was a characteristic feature, and it was most evidently reflected in the survival rate. When salinity was below 125mM or pH was below 8.8, survival rates were all 100%. However, when salinity was above 125mM and pH was above 8.8, survival rates sharply declined with the increasing of either salinity or pH.The buffer capacity of the treatment solution was taken as a stress factor in order to simplify the stress factor analysis. The results of the statistical analysis showed that for the stress factors of the salt-alkaline mixed stress, [CO32–] and [HCO3–] could be fully represented by the buffer capacity, and [Na+] could be fully represented by salinity, whereas [SO42–] was negligible. Therefore, four factors, salinity, buffer capacity, pH and [Cl–], could reflect all of the stress factors. Perfect linear correlations were observed between all physiological indices and four or three stress factors by a stepwise regression analysis. However, the effects of the four stress factors on the physiological indices were significantly different in magnitude. Buffer capacity and salinity were dominant factors for all physiological indices. Thus, it is reasonable to consider the sum of salinity plus buffer capacity as the strength value of salt-alkaline mixed stress. Furthermore, the relationships between different physiological indices and various stress factors were shown to be different.
Sunflowers were treated with mixing proportions of NaCl, Na2SO4, NaHCO3, and Na2CO3. Effects of salt and saltalkaline mixed stress on growth, photosynthesis, chlorophyll fluorescence, and contents of inorganic
ions and organic acids of sunflower were compared. The growth of sunflower decreased with increasing salinity. The contents
of photosynthetic pigments did not decrease under salt stress, but their contents decreased sharply under salt-alkaline mixed
stress. Net photosynthetic rates, stomatal conductance and intercellular CO2 concentration decreased obviously, with greater reductions under salt-alkaline mixed stress than under salt one. Fluorescence
parameters showed no significant differences under salt stress. However, maximal efficiency of PSII photochemistry, photochemical
quenching coefficient, electron transport rate, and actual PSII efficiency significantly decreased but non-photochemical quenching
increased substantially under salt-alkaline mixed stress. Under salt-alkaline mixed stress, sunflower leaves maintained a
low Na+- and high K+ status; this may be an important feature of sunflower tolerance to salinity. Analysis of the mechanism of ion balance showed
that K+ but not Na+ was the main inorganic cation in sunflower leaves. Our results indicated that the change in organic acid content was opposite
to the change of Cl−, and the contribution of organic acid to total charge in sunflower leaves under both stresses decreased with increasing salinity.
This may be a special adaptive response to stresses for sunflower. Sunflower under stress conditions mainly accumulated inorganic
ions instead of synthesizing organic compounds to decrease cell water potential in order to save energy consumption.
Additional keywordssalt stress-salt-alkaline mixed stress-chlorophyll fluorescence-photosynthesis-inorganic ions-organic acids
The effect of salinity on some agro-physiological parameters in plants of five multigerm varieties of sugar beet has been investigated. Plants were submitted to four salt treatments, 0, 50, 100 and 200 mM NaCl, for 30 days in a sand culture and the physiological responses were measured. Salinity affected all of the considered parameters. Thus, high NaCl concentrations caused a great reduction in growth parameters such as leaf area, and fresh and dry weight of leaves and roots, but the leaf number was less affected. These changes were associated with a decrease in the relative water content and the K+ concentrations, but Na+ and Cl− contents were highly increased in the leaves. The solute leakage and proline content were also increased, but nitrate reductase activity was found to decrease in leaves of all of the tested varieties. Varietal differences were evident at the highest NaCl concentration for almost all of the considered parameters. The significance of inorganic ions and proline accumulation in relation to osmotic adjustment was discussed. In contrast to proline, inorganic ions seem to be involved in osmotic adjustment.
Soil salinization and alkalinization frequently co-occur in nature, but very few studies focus on the interactive effects of various salt and alkali stresses on plants. A study quantifying the effects of various salt and alkali stresses on growth, organic solutes, and cation accumulation in a halophyte Spartina alterniflora was conducted. The experiment consisted of six levels of salinity (100, 200, 300, 400, 500, and 600 mM) in each of six pH levels: A (pH 7.1 ± 0.02), B (pH 8.1 ± 0.17), C (pH 8.8 ± 0.14), D (pH 9.8 ± 0.14), E (pH 10.4 ± 0.08), and F (pH 10.8 ± 0.10). Survival rate, relative growth rate (RGR), tiller rate, rhizome number, leaf chlorophyll content, root activity, electrolyte leakage rate (ELR), and content of proline, soluble carbohydrates, Na⁺, and K⁺ were determined.
The physiological response of the herbal edible perennial Plantago coronopus (L.) to the four major constraints of salinity (leaf gas exchange, water (and ion) relations and osmotic adjustment) was studied in hydroponically grown plants exposed to 6 weeks of various salt levels [0, 25, 50, 75 and 100% seawater salinity (sws)]. The salinity threshold of P. coronopus (L.) was reached at 25% sws and growth was strongly depressed by higher salinities. Also gas exchange properties such as net photosynthesis and water use efficiency were affected strongly by NaCl-saline conditions and this was related to stomatal conductance. The apparent quantum yield and the dark respiration decreased, which may reflect a relative increase in alternative processes for electron consumption. There was also an increase in the carotenoid/chlorophyll ratio and of the LAR leading to a reduction of the flow of electrons through the photosystems (reduction of photosynthetic efficiency) altogether diminishing the risk of photoinhibition. Leaf water potential and osmotic potential decreased after salinity stress was imposed. Predominantly Na+ and Cl− contributed to the salt-induced changes in leaf osmotic potential (juvenile and adult). In response to such stress conditions the concentrations of the major essential ions (such as Ca, K, Mg and nitrate) transiently decreased. This biphasic development could be related to the growth of the plant and not to ion imbalance because the minimum value of the abovementioned nutrients was reached at the maximum yield. Osmotic regulation by organic solutes was also determined. Sorbitol was the most abundant sugar (alcohol) in most organs. The results suggest, that sorbitol serves as a compatible solute and osmoprotectant at various levels of root zone salinity. We conclude that salt-induced water stress primarily controlled gas exchange of salt-treated P. coronopus (L.) leaves, whereas the salt load and the ion imbalance in the leaves did not cause irreversibly damage to the photosynthetic apparatus.
Physiological behavior and antioxidant responses to salinity were studied in Crithmum maritimum, a local halophyte naturally growing on rocky coasts. The plant growth was significantly improved at moderate salt levels (50 mM NaCl), but was drastically reduced at 200 mM NaCl. The stimulation of biomass production at 50 mM NaCl was associated with enhanced root length and leaf number. Tissue hydration seemed unaffected by salinity, despite Na+ and Cl− were largely accumulated in shoots. The highest salinity (200 mM NaCl) induced mineral nutrition disturbance within the plant shoots, as their Ca2+, Mg2+, and K+ concentrations significantly declined. However, C. maritimum displayed high uptake selectivity for the latter. Monitoring lipid peroxidation showed that both root and shoot malonyldialdehyde (MDA) contents of plants cultivated at the optimal salt concentration (50 mM NaCl) were lower than control ones. This was related to enhanced activities of antioxidant enzymes, like superoxide dismutase (SOD) (EC 1.15.1.1), catalase (EC 1.111.1.6), and peroxidase (EC 1.111.1.7), especially in shoots. The limitation of the plant growth at 200 mM NaCl was concomitant with lesser efficiency of these protective enzymes, but MDA levels in both roots and shoots remained close to control ones.
Suaeda fruticosa (L.) Forssk plants grown in saline conditions (200 to 400 mol m−3NaCl) had greater fresh and dry weights than those grown in non-saline controls, and 600 to 1000 mol m−3NaCl inhibited growth. Gibberellic acid and kinetin both alleviated some of the inhibitory effects of salinity at 800 mol m−3NaCl on shoot growth of S. fruticosa while root growth was promoted by kinetin. Tissue water content increased in up to 200 mol m−3NaCl but decreased with a further increase in salinity. Water potential and osmotic potential of plants became more negative with an increase in salinity. Leaf Ca2+, Mg2+, and K+concentration decreased with increasing salinity, while both Na+and Cl−increased and reached 1391 and 1673 mmol kg−1dry weight, respectively. Total glycinebetaine content of shoots was highest at 600 to 1000 mol m−3NaCl.
The effects of salinity on growth, water relations, glycinebetaine content, and ion accumulation in the perennial halophyte Atriplex griffithii var. stocksii were determined. The following questions were addressed: (1) What effect does salinity have on growth responses at different ages? (2) Is A. griffithii an ion accumulator? (3) Does A. griffithii accumulate glycinebetaine in response to salinity? Atriplex griffithii plants were grown in pots at 0, 90, 180 and 360 m m NaCl in sand culture in a plant growth chamber and plants were harvested after 30, 60 and 90 d. Plant total dry weight was significantly inhibited at 360 m m NaCl. Root growth showed a substantial promotion at 90 m m NaCl. The water potential and osmotic potential of shoots became more negative with increasing salinity and time of growth. The Na+and Cl−content in both shoots and roots increased with increases in salinity. Increased treatment levels of NaCl induced decreases in Ca+, K+and Mg2+in plants. Atriplex griffithii accumulated a large quantity of ions, with the ash content reaching 39% of the dry weight in leaves. Inorganic ion accumulation is significant in osmotic adjustment and facilitates water uptake along a soil-plant gradient. Glycinebetaine concentration was low in roots, and in stems it increased with increases in salinity. Total amounts of glycinebetaine in leaves increased with increases in salinity, and its concentration increased substantially at 360 m m NaCl. Copyright 2000 Annals of Botany Company
Iron is essential for plants but is not readily accessible and is also potentially toxic. As plants are a major dietary source of iron worldwide, understanding plant iron homeostasis is pivotal for improving not only crop yields but also human nutrition. Although iron acquisition from the environment is well characterized, the transporters and reductases involved in plant organellar iron transport and some of the transcription factors that regulate iron uptake have only recently been discovered. Here, we discuss newly characterized molecular players, focusing on Arabidopsis. Localization of iron to the right compartment and accessibility of iron stores are proving crucial for maintaining proper iron homeostasis and will need to be considered in biofortification efforts currently underway.