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Arbuscular mycorrhizal fungi mitigate negative effects of combined drought and heat stress on tomato plants
Abstract
Arbuscular mycorrhizal (AM) symbiosis can alleviate drought and temperature stresses in plants, but it is unknown whether the benefits can be maintained when the plants are exposed to combined drought and heat stress. In this study, the impacts of AM fungi, Septoglomus deserticola and Septoglomus constrictum on tomato plant tolerance to combined drought and heat stress were investigated. No substantial differences in physiological parameters were found in all plants under non-stress conditions, except a higher expression of SlLOXD and SlPIP2.7 in plants + S. constrictum. Under drought, heat and drought + heat stress, both fungal symbionts could moderate oxidative stress by decreasing the lipid peroxidation, hydrogen peroxide level and improving leaf and root antioxidant enzyme activities, however better performance in plants + S. constrictum. Under drought and the combined stress, inoculation with S. constrictum enhanced stomatal conductance, leaf water potential and relative water content, elevated Fv/Fm and biomass production of the hosts as compared to non-inoculated plants whilst these improvements in plants + S. deserticola were not obvious. Under the combined stress inoculation of S. constrictum did not change the expression of SlNCED and SlPIP2.7 in roots as under heat stress. Expression of SlLOXD in root were upregulated in plants + S. contrictum under drought + heat stress as in mycorrhizal roots under drought stress. Altogether, our results indicated that AM inoculation, particularly with S. constrictum had a positive influence on the tomato plant tolerance to drought + heat stress. Further studies are essential to add some light on molecular mechanisms of mycorrhizal plant tolerance to this combined stress.
... Symbiotic microorganisms, like arbuscular mycorrhizal fungi (AMF), colonize plant parts in various habitats, enhancing mineral and water availability and environmental tolerance in plant-dwelling species. Additionally, AMF symbiosis changes the connection between plants and water in both drought-stressed and well-watered environments and AMF can even increase the productivity of colonized plants under sub and supra optimal temperature stress (Duc, et al. [1]). A number of machineries were displayed to be and by AM to water deficits in AMF plants, including improved stomatal conductance, enhanced water use efficiency, and lower oxidative damage due to higher enzymatic antioxidant activities and non-enzymatic antioxidant levels. ...
... It was also observed that AMF plants produced higher biomass when under heat stress in comparison to untreated counterpart (Duc, et al. [1]). Mycorrhizal plant diversity, intensity and proportion of colonized roots all increase with soil temperature (Heinemeyer,et al. [3]). ...
... By growing increasing the activity of antioxidant enzymes in the leaves and roots, both fungal symbionts Septoglomus constrictum and S. deserticola were able to lessen oxidative stress. However, similar benefits in plants that also contained S. deserticola were not immediately apparent (Duc, et al. [1]). The inoculation of AM fungus also boosted the activity of the enzymes superoxide dismutase (SOD), ascorbate peroxidase, and ascorbic acid in the leaves of heatstressed cyclamen plants, according to investigations (Matsubara, et al. [12,13]). ...
... (2010) [29] and Painawadee et al. (2009) [32] . Similar results were reported in tomato plants exposed to drought + heat stress by Duc et al. (2018) [16] and in rose plants exposed to drought stress by Salam et al. (2018) [36] . Soil application of Glomus mosseae and Gigaspora sps. ...
... (2010) [29] and Painawadee et al. (2009) [32] . Similar results were reported in tomato plants exposed to drought + heat stress by Duc et al. (2018) [16] and in rose plants exposed to drought stress by Salam et al. (2018) [36] . Soil application of Glomus mosseae and Gigaspora sps. ...
... The increase in relative water content of mycorrhizal groundnut may be due to the improved root conductance associated with alteration in root system induced by mycorrhiza (Kapoor et al., 2008) and greater water absorption by hyphae (Faber et al., 1991) [19] . AM plants could improve the water status under water deficit (Duc et al., 2018) [36] . Similar results were reported by Aliasgharzad et al. (2006) [1] in mycorrhizal sorghum plants. ...
... They also can stabilize soil aggregates, thus preventing erosion, through a combination of biophysical, biochemical and biological processes (Rillig and Mummey 2006). Finally, AMF hyphae can improve plant tolerance to biotic and abiotic stresses, including salinity, heavy metal exposure, heat stress and drought (Apple 2010;Duc et al. 2018), as well as pathogen tolerance (Jaiti et al. 2007). Thanks to these features, in desert soils with low nutrient and water availability, AMF are crucial symbionts which enable plants to establish and survive (Al-Whaibi 2009;Albaqami et al. 2018). ...
... However, we could expect that plants growing in extreme desert conditions (e.g. extreme drought, low soil nutrients, discontinuous vegetation cover, high heat and soil alkalinity in the AlUla region) might greatly benefit from this mycorrhizal interaction feature which can help plants mobilize water and nutrients and survive heat stress (Duc et al. 2018;Harkousse et al. 2021;Madouh and Quoreshi 2023). Another example of such plant adaptations in extreme environments was reported in the highly polymetallic soils in New Caledonia, where Cyperaceae plants (known as non-mycorrhizal) were found to unexpectedly develop mycorrhization (Lagrange et al. 2011), which is in line with our observations in AlUla, where AMF were detected in Cyperus conglomeratus. ...
... Environmental conditions, e.g., biotic stress, climate and soil nutrient content, are important factors underlying the establishment of AMF mutualistic symbiosis (Muthukumar et al. 2004;Lagrange et al. 2011), plant taxonomy alone may not be discriminant enough to know the true mycorrhization potential of a plant species. For example, salinity, heat and drought can affect plant mycorrhization (Diatta et al. 2014;Duc et al. 2018). Land use, pH and geological parent material also of soils under date palms in farms (Bouamri et al. 2006). ...
Hot deserts impose extreme conditions on plants growing in arid soils. Deserts are expanding due to climate change, thereby increasing the vulnerability of ecosystems and the need to preserve them. Arbuscular mycorrhizal fungi (AMF) improve plant fitness by enhancing plant water/nutrient uptake and stress tolerance. However, few studies have focused on AMF diversity and community composition in deserts, and the soil and land use parameters affecting them. This study aimed to comprehensively describe AMF ecological features in a 5,000 km² arid hyperalkaline region in AlUla, Saudi Arabia. We used a multimethod approach to analyse over 1,000 soil and 300 plant root samples of various species encompassing agricultural, old agricultural, urban and natural ecosystems. Our method involved metabarcoding using 18S and ITS2 markers, histological techniques for direct AMF colonization observation and soil spore extraction and observation. Our findings revealed a predominance of AMF taxa assigned to Glomeraceae, regardless of the local conditions, and an almost complete absence of Gigasporales taxa. Land use had little effect on the AMF richness, diversity and community composition, while soil texture, pH and substantial unexplained stochastic variance drove these compositions in AlUla soils. Mycorrhization was frequently observed in the studied plant species, even in usually non-mycorrhizal plant taxa (e.g. Amaranthaceae, Urticaceae). Date palms and Citrus trees, representing two major crops in the region, however, displayed a very low mycorrhizal frequency and intensity. AlUla soils had a very low concentration of spores, which were mostly small. This study generated new insight on AMF and specific behavioral features of these fungi in arid environments.
... Arbuscular mycorrhizal fungi can improve nutrient and water transport to their host plant roots, enhancing stress tolerance [10][11][12]; therefore, mycorrhizal inoculation is becoming a common practice in the sustainable production of horticultural crops. At the same time, AMF, as important microbes of the soil ecosystem, can form synergistic and even antagonistic relationships with other microorganisms, bacteria, and fungi. ...
... Trichoderma spp. and AMF interactions in the tomato have been intensively studied [11,14,28,29] with various results. In some cases, inhibition of the mycorrhizal colonization of roots caused by Trichoderma was recorded [30], and many experiments showed no inhibition or enhancement in the colonization level [31]. ...
... However, many studies have reported an increase in colonization with the combined application of mycorrhizae and Trichoderma due to their synergistic effect [28,32]. The effects on the plant development, yield, enzyme activity, or nutrient content of fruits also differed significantly [11,12]. ...
Sustainable plant production requires less use of synthetic chemicals in plant nutrition and protection. Microbial products are among the most promising substitutes for chemicals. With the increasing popularity and availability of such products, it has become obligatory to use different microbes together. The effect of this has been tested in several studies, but their results have sometimes been contradictory depending on the microbial strains tested and the mode of application. We tested the effect of two commercially available antagonists and Funneliformis mosseae alone and in combination on tomato. Mycorrhizal treatment increased plant growth and yield, both alone and combined with the antagonists; however, mycorrhizal root colonization was not influenced by the antagonist. This treatment also led to a slight decrease in the occurrence of Trichoderma spp. on tomato roots but did not impede the colonization of roots by the applied Trichoderma strain. Our result confirmed that Trichoderma asperellum (T34) and Streptomyces griseoviridis (K61) can be safely combined with arbuscular mycorrhizal fungi (AMF), namely with F. mosseae.
... This nutrient uptake is essential for maintaining plant health when plants are subjected to high salinity [99,103,104]. PGPR treatments reduce electrolyte leakage in plants under saline stress, which indicates better membrane stability and less cellular damage [100,105,106]. A study conducted by [101] revealed that plants treated with PGPR presented lower levels of oxidative stress markers, including malondialdehyde and hydrogen peroxide. ...
... All these activities increase the rates of photosynthesis, chlorophyll content, stomatal conductance, and carotenoid content. The colonization of these plants improves nutrient assimilation and metabolism and promotes recovery from heat stress [106]. Similarly, AMF also helps mitigate saline stress via osmotic regulation and the maintenance of cellular integrity, turgor pressure, and cellular functions [120][121][122]. ...
Strawberry (Fragaria ananassa) is well known among consumers because of its attractive color, delicious taste, and nutritional benefits. It is widely grown worldwide, but its production has become a significant challenge due to changing climatic conditions that lead to abiotic stresses in plants, which results in poor root development, nutrient deficiency, and poor plant health. In this context, the major abiotic stresses are temperature fluctuations, water shortages, and high levels of soil salinity. The accumulation of salts in excessive amounts disrupts the osmotic balance and impairs physiological processes. However, drought reduces fruit size, yield, and quality. Similarly, heat and cold stresses directly affect the rate of photosynthesis. Plants respond to these changes by producing growth-promoting hormones to ensure their survival. In the context of these abiotic stresses, beneficial microbes support plant growth. Among these fungi, the most extensively studied are plant growth-promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungi (AMF). When applied as bioinoculants, they are associated with roots and subsequently improve soil health, fruit quality, and overall crop yield. This review highlights the impacts of abiotic stresses on strawberry roots, growth, and hormonal pathways. Moreover, it focuses on the role of beneficial soil microbes in the mitigation of these responses.
... Drought stress causes the extreme generation of ROS like H 2 O 2 , mostly in the chloroplast and mitochondria of plant cells, due to the disruption in physiological events like photosynthesis and photorespiration. Eventually, plants suffer from oxidative stress, such as cellular damage, including EL, and lipid peroxidation, which is indicated by higher MDA content upon stress exposure [48,49]. Similar to Duc et al. [48] and Chitarra et al. [50], this study showed the seedlings suffering from drought-accumulated higher MDA and excessive EL, with an elevated level of H 2 O 2 compared to the control as an indication of ROS-generated lipid peroxidation. ...
... Eventually, plants suffer from oxidative stress, such as cellular damage, including EL, and lipid peroxidation, which is indicated by higher MDA content upon stress exposure [48,49]. Similar to Duc et al. [48] and Chitarra et al. [50], this study showed the seedlings suffering from drought-accumulated higher MDA and excessive EL, with an elevated level of H 2 O 2 compared to the control as an indication of ROS-generated lipid peroxidation. However, drought-mediated H 2 O 2 and MDA accumulations were lowered in VA-pretreated seedlings, which proved the protective role of VA in decreasing oxidative stress markers in tomato seedlings under water deficit. ...
Vanillic acid (VA) regulates various plant physiological and biochemical processes upon different environmental stresses to enhance their tolerance. This study aimed to evaluate the protective effect of VA on growth and physiology, including osmoprotection, and antioxidant defense systems for enhancing higher tolerance by lowering oxidative damage against water deficit stress in tomatoes (Solanum lycopersicum L. cv. BARI Tomato-16). Hydroponically grown tomato seedlings (8 d old) were pretreated with 50 µM VA for 2 days followed by water deficit stress (imposed by water withdrawal and 12% polyethylene glycol; PEG-6000) for 4 d. Drought stress inhibited the seedlings’ growth by reducing water content and photosynthetic pigments contents, alleviating oxidative stress induced by a reactive oxygen species and methylglyoxal. A significant enhancement in growth, biomass accumulation, and photosynthetic pigment content was observed in VA-pretreated stress conditions. In addition, there was an improvement in the water status and proline content, along with modulated activities of the antioxidant responses, including both non-enzymatic and enzymatic components in leaves of VA-pretreated seedlings upon the water deficit. Vanillic acid significantly reduced the reactive oxygen species generation and decreased cellular membrane damage in drought-affected tomato seedlings. Methylglyoxal detoxification was ensured to a great extent in VA-pretreated stressed tomato seedlings by strengthening the glyoxalase enzymes’ activities. Therefore, VA can be effective for protecting tomato seedlings by inducing a plant antioxidant defense and the methylglyoxal detoxification system and osmoregulation under drought stress.
... For instance, the synthesis of enzymes that degrade ROS, such as superoxide, catalase, peroxidases, and dismutase, can improve heat stress tolerance in plants. This enhancement can be observed in plants colonized by beneficial bacteria like Pseudomonas and Bacillus, as well as mycorrhizal fungi like Septoglomus deserticola and Septoglomus constrictum [77]. Some available biostimulants contain P. fluorescens and P. aeruginosa, which contribute to improving soil quality and heat stress tolerance, working as bioremediators and phytostimulators and enhancing soil fertility [67]. ...
... Diverse inoculants may emerge as a more environmentally benign alternative, as implied by studies on AMF or Bacillus spp. [77]. ...
The increasing global demand for food caused by a growing world population has resulted in environmental problems, such as the destruction of ecologically significant biomes and pollution of ecosystems. At the same time, the intensification of crop production in modern agriculture has led to the extensive use of synthetic fertilizers to achieve higher yields. Although chemical fertilizers provide essential nutrients and accelerate crop growth, they also pose significant health and environmental risks, including pollution of groundwater and and other bodies of water such as rivers and lakes. Soils that have been destabilized by indiscriminate clearing of vegetation undergo a desertification process that has profound effects on microbial ecological succession, impacting biogeochemical cycling, and thus the foundation of the ecosystem. Tropical countries have positive aspects that can be utilized to their advantage, such as warmer climates leading to increased primary productivity and, as a result, greater biodiversity. As an eco-friendly, cost-effective, and easy-to-apply alternative, biofertilizers have emerged as a solution to this issue. Biofertilizers consist of a diverse group of microorganisms able to promote plant growth and enhance soil health, even under challenging abiotic stress conditions. They can include plant growth-promoting rhizobacteria, arbuscular mycorrhizal fungi, and other beneficial microbial consortia. Bioremediators, on the other hand, are microorganisms that can reduce soil and water pollution or otherwise improve impacted environments. So, the use of microbial biotechnology relies on understanding the relationships between microorganisms and how they affect their environment, and, inversely, how abiotic factors influence microbial activity. The more recent introduction of genetically modified microorganisms into the gamut of biofertilizers and bioremediators requires further studies to assess potential adverse effects in various ecosystems. This article reviews and discusses these two soil correcting/improving processes with the aim of stimulating their use in developing tropical countries.
... While the alleviating effects of AM fungi under cold stress have frequently been examined [9][10][11], their effect at high temperatures has rarely been observed [12][13][14]. With the increase in the global mean annual temperature [15] and the increasing frequency of heat waves, improving our knowledge in this field is becoming increasingly important to avoid economic losses in agriculture and guarantee food security [16]. ...
... On the other hand, the leaf water potential decreased significantly under heat stress, and AM fungal symbiosis did not provide any benefit, as there was no difference between H and HAM plants. This is in accordance with the findings of Duc et al. [12]; however, it is inconsistent with those of other studies, as AM fungi have consistently been shown to improve the water status of plants under different stress conditions, such as heat stress, salt stress, and water deprivation [14,51,52]. In addition to the physiological parameters, the general stress status of tomato plants was observed by measuring the H 2 O 2 and MDA levels, as these molecules, depending on their cellular level, activate defence responses or initiate cell death after a critical level [53]. ...
In this study, we report the interaction between an arbuscular mycorrhizal fungus, Septoglomus constrictum, and tomato plants under heat stress. For the first time, this interaction was studied by Illumina RNA-seq, followed by a comprehensive bioinformatic analysis that investigated root and leaf tissue samples. The genome-wide transcriptional profiling displayed fewer transcriptomic changes in the root under heat-stress conditions caused by S. constrictum. The top 50 DEGs suggested significant changes in the expression of genes encoding heat-shock proteins, transporter proteins, and genes of phytohormone metabolism involving jasmonic acid signalling. S. constrictum induced the upregulation of genes associated with pathways such as ‘drought-responsive’ and the ‘development of root hair’ in the root, as well as ‘glycolipid desaturation’, ‘intracellular auxin transport’, and ‘ethylene biosynthesis’ in the leaf. The pathways ‘biotin biosynthesis’ and ‘threonine degradation’ were found in both investigated tissue types. Expression analysis of transcription factors showed 2 and 11 upregulated transcription factors in heat-stressed root and leaf tissues, respectively. However, we did not find shared transcription factors. Heat-stressed arbuscular mycorrhizal plants suffered less oxidative stress when exposed to high temperatures. Colorimetric tests demonstrated less accumulation of H2O2 and MDA in heat-stressed mycorrhizal plants. This phenomenon was accompanied by the higher expression of six stress genes that encode peroxidases, glutathione S-transferase and ubiquitin carboxyl-terminal hydrolase in roots and leaves. Our findings provide a new perspective on elucidating the functional metabolic processes of tomato plants under mycorrhizal-heat stressed conditions.
... Drought Augmentation in both the dry weight of roots and shoots. Additionally, there was an increase in stomatal conductance, relative water content, and the activities of antioxidant enzymes (Duc et al., 2018) 3. ...
... Temperature Resulted in a reduction in lipid peroxidation and hydrogen peroxide levels, while enhancing the activities of antioxidant enzymes in both leaves and roots. (Duc et al., 2018) 12. ...
In order to meet the rising need for food around the world, more sustainable agriculture practices need to be created. These practices should ensure increased production and yield stability. Adverse abiotic conditions can result in significant reductions in crop yields, posing a significant challenge to agriculture. To address this issue and meet the growing global food demands, it is crucial to enhance crop’s ability to withstand multiple stress factors and reduce the negative impacts of abiotic stressors. The association between plant and microbial biostimulants helps in plant growth and soil health under abiotic stress conditions. Several different microorganisms can be used as biostimulants to mitigate abiotic stresses. The use of biostimulants is a cost-effective and environmentally beneficial approach to increase immune system. The biostimulant abilities demonstrated by arbuscular mycorrhizal fungi (AMF) constitute a sustainable method to mitigate the negative effects of adverse conditions. The stresses that rising salt content, drought, heavy metals, and other conditions often place on global agriculture limit plant growth and production, degrade the quality of the soil, and pose a serious threat to the world’s ability to feed itself. AMF promotes the nutrition of plants by absorbing and distributing mineral nutrients outside of the plant rhizosphere’s depletion zones (biofertilizers), and they also alter secondary metabolism to produce better nutraceutical chemicals. The fruitful interdependence and useful connection between the plant and AMF could develop adequate defensive regulatory mechanisms to guard against the threats of stresses.
... A significant increase in the total soluble protein contents was recorded i.e. 34.053 mg g -1 tissue which was an increase of 20.8467% over control (Table 2 & 3). The findings recorded by Duc et al., (2018) demonstrated that total soluble protein contents increased as a result of drought heat stress in tomato plants which was in accordance to our results. This increase in the total soluble protein contents might be due to the increase production of heat shock proteins which ultimately enhanced the total soluble protein contents in the plant. ...
... In a controlled experiment on S. lycopersicum, inoculation with Septoglomus deserticola and Septoglomus constrictum at transplant was assessed for its ability to alleviate combined drought (50% field capacity) and heat stress (42 • C for 6 h). AM inoculation was achieved by applying 30 (Duc et al., 2018) . Beyond AM fungi, also plant growth promoting rhizobacteria (PGPR) may modulate key biochemical and molecular pathways to increase plant resilience to enviromental stresses. ...
The study examines how biostimulants can support plant adaptation to drought and high temperatures, focusing on key Mediterranean crops. Rather than offering a miraculous solution, biostimulants enhance the plant’s natural resilience by modulating key physiological and biochemical pathways. This underscores the importance of continued research into the endogenous defense strategies of plants, as well as the need to design tailored biostimulants that specifically amplify these existing protective mechanisms. Advancing this knowledge will be essential for optimizing sustainable agricultural practices in the face of climate change.
This is the link to the article: https://www.sciencedirect.com/science/article/pii/S2667064X25000673?via%3Dihub
... The AM symbiosis also improves plant osmoregulation, which entails actively decreasing plant water potentials to create a gradient that promotes turgor, stomatal opening, and photosynthesis (Ruiz-Lozano 2003;Wu et al. 2017;El-Samad and El-Hakeem 2019). Additionally, associating with AM fungi protects against drought-induced oxidative damage (Ruiz-Lozano 2003;Duc et al. 2018;Zou et al. 2021;Tereucán et al. 2022). AM fungi also alter root morphology by increasing lateral root growth (Gutjahr and Paszkowski 2013) which may benefit plants during drought by increasing the volume of soil for water uptake. ...
Under drought conditions, arbuscular mycorrhizal (AM) fungi may improve plant performance by facilitating the movement of water through extensive hyphal networks. When these networks interconnect neighboring plants in common mycorrhizal networks (CMNs), CMNs are likely to partition water among many individuals. The consequences of CMN-mediated water movement for plant interactions, however, are largely unknown. We set out to examine CMN-mediated interactions among Andropogon gerardii seedlings in a target-plant pot experiment, with watering (watered or long-term drought) and CMN status (intact or severed) as treatments. Intact CMNs improved the survival of seedlings under drought stress and mediated positive, facilitative plant interactions in both watering treatments. Watering increased mycorrhizal colonization rates and improved P uptake, particularly for large individuals. Under drought conditions, improved access to water most likely benefited neighboring plants interacting across CMNs. CMNs appear to have provided the most limiting resource within each treatment, whether P, water, or both, thereby improving survival and growth. Neighbors near large, photosynthate-fixing target plants likely benefited from their establishment of extensive hyphal networks that could access water and dissolved P within soil micropores. In plant communities, CMNs may be vital during drought, which is expected to increase in frequency, intensity, and length with climate change.
Supplementary Information
The online version contains supplementary material available at 10.1007/s00572-025-01181-z.
... In turn, mycorrhizal symbiosis favors stomatal regulation and optimizes Water Use Efficiency (WUE) when there is water deficit (Augé et al., 2015). AMF reduce peroxidative damage due to increased activity of antioxidant enzymes (Chang et al., 2018;Duc et al., 2018) and induce morphophysiological changes in some organs and tissues of mycorrhizal plants, making them tolerant to water stress (Begum et al., 2019). Other authors report that mycorrhizal symbiosis could regulate a variety of physio-biochemical processes in plants such as, increased proline accumulation (Yooyongwech et al., 2015); increased growth and photosynthesis due to the regulation of the antioxidant system and increased levels of glutathione, one of the main antioxidant metabolites used by plants to tolerate various biotic and abiotic stresses (Rani, 2016). ...
... New technologies are now available to enhance the resilience of the agricultural industry to mitigate the detrimental impacts of drought and heat stress on crop output. Biofertilizers can be effectively utilized as a way to enhance plant tolerance to many stress conditions (Duc et al., 2018). Additionally, more advanced cultivars of the crop can be utilized to enhance agricultural practices. ...
... Moreover, BSs based on extracts or by-products are often degraded by the plant into bioactive signals capable of initiating beneficial processes against stress, so if BS treatments are not synchronous/proximal with the stress, the plant response may turn weak or ineffective [19]. In tomato crops, BSs consisting of arbuscular mycorrhizae showed increased resilience to excessive salinity [20] and induced higher tolerance in heat-stressed tomato plants or mitigated negative effects combined with drought [21]. Non-arbuscular fungi improved tolerance to imposed thermal and water deficit stress, acting on antioxidant metabolism [22,23]. ...
Rising temperatures due to climate change may affect the quality of open-field cultivated processing tomatoes by altering the nutrient content. Bioinoculants are growing in popularity as a nature-based strategy to mitigate these environmental stresses. Untargeted quantitative NMR spectroscopy was leveraged to characterize the metabolome of tomato fruits exposed to abiotic stress during the year 2022, which was marked by unexpected high temperatures and low rainfall compared to the year 2021 with average conditions. This study was conducted at growing sites in Tarquinia and Viterbo, comparing untreated plants to ones treated with a Trichoderma-based bioinoculant. The hotter year affected the water-soluble fraction (28 compounds), causing an increase in amino acids, citrate, and formate contents while decreasing carbohydrates together with a significant drop in β-sitosterol + campesterol in the organic fraction (11 compounds). The site mainly affected the linolenic acid levels, which were more abundant in Tarquinia than Viterbo in the hotter year, whereas ascorbate and myo-inositol were higher in Tarquinia in both years. The year × site interaction significantly affected the content of several amino acids, glucose, sucrose, and trigonelline. The bioinoculant effect was significant only for sucrose, while its interactions with the other factors showed little to no significance across all the measured metabolites.
... Some studies have demonstrated that AMF mycelial networks, which often extend through soil pores not explored by the plant roots, can help increase water absorption and transport water to the host plant (Liu et al., 2018;. Furthermore, research by Duc et al. (2018) and Augé et al. (2014) has shown that an increase in stomatal conductance leads to higher transpiration rates, pulling more water from AMF networks into the plant, which helps mitigate the impacts of drought on crop yields. Crops can adapt to or withstand drought stress through a mutualistic association with arbuscular mycorrhizal (AM) fungi (Oyewole et al., 2017). ...
... Among abiotic stresses, the most serious losses in horticultural and agricultural crops are caused by water shortage, especially long-term. Plants grown in field conditions are of-ten exposed to the simultaneous effects of several stresses, a typical example of which is the occurrence of drought and high temperature, common in many agricultural areas not only in Poland but also throughout the world (Duc et al. 2018). Crop losses caused by stress factors can reach up to 50-82% (Inculet et al. 2019). ...
... En contraste, nuestros resultados muestran que las plantas inoculadas con P. capsici presentaron una disminución en la actividad enzimática de CAT. Esta reducción en plantas tratadas con microorganismos ha sido documentada previamente (Duc et al., 2018), ya que CAT favorece la supervivencia del patógeno al inhibir el estrés oxidativo producido por el hospedero (Sharma et al., 2019). Aunque el equilibrio entre las actividades de SOD y CAT es crucial para mitigar los niveles tóxicos de las enzimas reactivas de oxígeno en la célula, una baja actividad de CAT podría indicar que la planta induce otros mecanismos compensatorios que involucran enzimas como ascorbato peroxidasa y glutation peroxidasa para reducir los niveles de SOD (Banerjee y Roychoudhury, 2019). ...
Background/Objective. The chilaca pepper (Capsicum annuum) is significantly impacted by the attack of the oomycete Phytophthora capsici, which causes chili wilt. Current methods for controlling this disease have been inefficient. Therefore, the search for more environmentally friendly alternatives is of great importance. In pursuit of this objective, we assessed the potential of arbuscular mycorrhizal fungi (AMF) and silver nanoparticles (AgNPs) to try to reduce or postpone chili pepper wilt. Materials and Methods. Growth parameters were measured in inoculated and non-inoculated chili pepper plants with AMF from a commercil consortium TM-73 (Biotecnología Microbiana) and the protective effects of AMF and AgNPs (NanoID®) against P. capsici as evaluated using a severity scale for wilt symptoms. Plant response to pathogen infection was assessed by measuring the activities of antioxidant enzymes: PER, SOD, CAT and H2O2. Results. The results indicated that AMF application improved the growth parameters of C. annuum, while the plant-pathogen interaction induced an antioxidant enzymatic response. AMF maintained wilt symptoms at or below 80%, preventing plant death. Meanwhile, AgNPs (50ppm) delayed plant mortality compared to the control treatment. Conclusion. The combined use of AMF and AgNPs offer options for future research in the disease management for chili peppers.
... In return, the AMF provides multiple benefits to hosts, including enhanced tolerance to biotic and abiotic stresses and mineral nutrition (Smith et al. 2011;Cheng et al. 2021). An enhanced drought tolerance results from the direct water supply by AMF extraradical hyphae (Auge et al. 2015;Chen et al. 2020) but also an improved nutrient status by AMF (Duc et al. 2018), hormonal regulation of stomata (Smith et al. 2011) and AMF increased the antioxidant levels in AMF colonized plants (Singh 2015). Growth and productivity of water-stressed plants of bean were enhanced by AMF species Rhizophagus irregularis inoculation (El-Tohamy et al. 1999). ...
Arbuscular mycorrhizal fungi (AMF) can improve water-deficit tolerance in tomatoes, although very few studies have examined the AMF contribution to the metabolism of proline under water-deficit stress. In our study, we investigated the effects of AMF inoculation on plant growth and drought tolerance in tomatoes (Solanum lycopersicum) under well-watered and drought conditions. AMF inoculations were applied in treatments with or without AMF, and with Rhizophagus intraradices, Funneliformis mosseae, or both. Our results evident that AMF colonization significantly increased the plant growth of tomatoes despite soil water conditions and significant with dually inoculated plants and R. intraradices was more effective than F. mosseae. During AMF inoculation and water stress conditions, photosynthesis increased significantly, while proline levels showed no significant change under these conditions. AMF could enhance the growth of the crop, drought tolerance through changes in morphological, physiological, and biochemical qualities of tomato crops. It summarized that AMF enhances the higher SLA, LAR, RGR, and photosynthetic yield under both watered and drought conditions. AMF enhanced the nutritional status, combined with leaf relative water content (RWC), which assists the plant’s translocation of minerals and alleviates the impact of drought on tomato growth.
... Further, the AMF colonization influenced the source-sink relationship of heat-stressed wheat plants which might have accounted for the altered physiology of the host plants to survive well under thermal stress [121]. Association of AM fungi Septoglomus constrictum and S. deserticola with tomato roots positively influenced the tolerance capacity of tomato to high-temperature stress [124]. In addition to that, maize plants infested with a consortium of AMF (Glomus sp., F. mosseae, and R. irregularis) also exhibited an alleviation in the negative impact of heat stress [119]. ...
The contemporary changes in global climate scenarios due to fast-evolving environmental extremities have adversely affected crop plants, resulting in drastic losses in the worldwide agricultural sector. To cope with environmental stressors like drought and heat, plants have evolved their sophisticated machinery to alleviate such perturbations. A strategy in this stress alleviation mechanism involves plant-associated microbes as ubiquitous organisms endowed with the capacity to enhance plant resilience. The use of microbial inoculants for conferring stress tolerance has gained much attention in recent decades to develop stress-resilient crops. This review highlights the specific microbes enriched upon exposure to drought and heat stress in crop plants, their application as bioinoculants to mitigate the stress regimes, the advantages of using microbe-based approaches, and discusses the mechanisms behind it. Furthermore, it also focuses on the challenges and prospects associated with the field applicability of various microbial inoculants and provide future direction for developing microbial formulations to achieve climate-smart agriculture.
... Under heat stress, mycorrhizal plants often exhibit enhanced activities of various antioxidant enzymes [69]. AMF Septoglomus deserticola and S. constrictum ameliorated heat stress-associated oxidative damage in tomato (Solanaceae lycopersicum) by reducing the levels of lipid peroxidation and H 2 O 2 , while elevating the antioxidant enzyme activities in root and leaves [70]. This dynamic symbiosis plays a critical role in successful plant performance, that AMF help to ameliorate plant responses to abiotic and biotic stressors [71]. ...
Arbuscular Mycorrhizal Fungi are used for soil fertility enhancements and stimulating plant growth in which they association with other organisms like terrestrial plants. Mycorrhizas create an association between fungi and the roots of plants. Therefore, the review was made to point out important fungal species involved in fungal plant interaction and their major roles in agriculture as well as ecosystem. 80% of plants form associations with mycorrhizal fungi. The fungal are used to use their different organs like chain, arbuscular, vesicle, supportive cells and spore to interact with the other plant/ plat's organ. The mycorrhizal fungi can be categorized into two principal classifications based on their anatomical interactions with the roots of host plants. Arbuscular Mycorrhizal and Ectomycorrhizal fungi utilize two distinct strategies for nutrient acquisition. The main categories of vesicular arbuscular mycorrhizal associations are linear or coiling and of ectomycorrhizal associations are epidermal or cortical. The rhizospheric and endophytic microbes promote plant growth as inoculated with crop. AM fungi as an obligate symbiont share a distinct feature called arbuscules as a site of nutrient exchanges between host and fungi. Arbuscules developed between cell wall and plasma membrane of root cortical cells and differentiated from plant plasma membrane by periarbuscular membrane. Arbuscular mycorrhizal fungi (AMF) play an indispensable role in augmenting plant nutrient acquisition, enhancing plant resilience and tolerance to various environmental stresses, improving soil fertility and structure, and providing numerous beneficial effects. AMF engage in interactions with other soil microorganisms, such as plant growth-promoting rhizobacteria, resulting in a synergistic effect that promotes plant growth and offers protection against pathogens associated with Rhizobia. Both AMF and Rhizobia utilize the same signaling pathways, which facilitate their association with host plants and enable nitrogen fixation within the soil ecosystem. A positive relationship has been established between AMF colonization and the diversity of soil microbial communities. Nitrogen-fixing rhizobia, mycorrhizal fungi, and root nodule symbioses typically exhibit synergistic interactions concerning infection rates and their effects on mineral nutrition and plant growth, thereby significantly enhancing the status of soil fertility, particularly with respect to soil quality characteristics.
... Enzymes such as catalases (CAT), peroxidases (POD), glutathione reductases (GR) and superoxide dismutases (SOD) are extensively used in the process detoxification of the reactive oxygen species (ROS) (Ahanger and Agarwal, 2017). Moreover, tomato(es) plants with which Scolecobasidium constrictum was inoculated with exhibited enhanced biomass output, stomatal conductance, leaf water relations and Fv/Fm in comparison with the un-inoculated plants when drought and salinity were applied simultaneously (Duc et al., 2018). Therefore, according to several studies (Abdel Latef, 2011;Abdel Latef and Chaoxing, 2011b;Abdel Latef and Chaoxing, 2014), AMF are essential for enhancing plant development and yield outputs under stress. ...
... Alongside AsA and GSH, Pro a compatible solute recognized as an important membrane stabilizer and powerful scavenger of ROS (Spormann et al., 2023), was accumulated to a greater extent in MR plants exposed to drought and heat compared to NMR plants. Although there are no reports on the performance of plants associated with P. involutus (or any other ECM species) exposed to heat and drought combined stress, these results are in accordance with Duc et al. (2018), where mycorrhization stimulated Pro production of tomato plants exposed to the combination of heat and drought stress, albeit it was attributed to arbuscular mycorrhizal fungi. ...
... AMF improves plant health under different plant stress tolerance conditions, as listed in Table 8.2. A study on tomato plants under heat and drought stress inoculated with Scolecobasidium constrictum showed higher growth than uninoculated ones [94]. The rate of photosynthesis, stomatal conductance, and leaf water content were higher in inoculated plants. ...
Global agriculture is threatened by growing world food demands and its supply under finite resources with degraded soil fertility and climatic variabilities. The yield of majority of crops is limited due to soil heterogeneity in nutrient availability. Arbuscular mycorrhizal fungi (AMF) are symbionts of majority of terrestrial land plants, including major agricultural crops. The hyphae network of AMF provides soil stability and helps mutually to plants in water and nutrient uptake. In this chapter, we discussed the role of AMF in Zn and Fe uptake in plants, and the significance of Zn and Fe in plant growth and stress tolerance. Further, we highlighted different mechanisms used by AMF in improving the uptake of Zn and Fe in various crop species.
... Reactive oxygen species (ROS) detoxification is performed by enzymes that typically include superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and glutathione reductase (GR) [3]. Furthermore, the combined application of drought and salinity on tomato plants inoculated with Scolecobasidium constrictum showed improved biomass production, leaf water ratio, stomatal conductance and Fv/Fm compared to uninoculated plants [31]. Therefore, AMFs are crucial to improving plant growth and yield under stressed conditions [1]. ...
Mycorrhiza is the keystone among microorganisms that form a critical linkage between the plant root and soil. This symbiotic association is characterized by bi-directional movement of nutrients where carbon flows to the fungus and inorganic nutrients move to the plants. Arbuscular mycorrhizal fungi (AMF) are soil fungi that form a symbiosis with the roots of plant. A variety of host benefits have been attributed to mycorrhiza, most commonly increasing uptake of immobile soil nutrients, particularly phosphorus and nitrogen. Understanding the impact of agronomic practices on these fungal communities would help ensure that symbiosis can be harnessed and can contribute to the success of sustainable agriculture. The co-evolution of mycorrhizae with plants represents an important evolutionary adaptation to the terrestrial environment. As a bio-inoculum, arbuscular mycorrhizal fungi (AMF) play a useful role in sustainable agriculture by symbiotically attaching to many crops and fungi, which provide the plant with nutrients such as P, Zn, Cu, etc., protection from water stress, toxic effects of heavy metals, and the infection of home soil diseases with increased plant growth. In addition, this association favors the formation of stable soil aggregates that improve soil structure stability, especially in granular soils, and reduces soil erosion. The production of the mycorrhizal fungal inoculum is complex and expensive due to its absolutely biotrophic nature. AMF spores in the soil can be collected by wet sieving and decanting, and a pure culture of mycorrhizal fungi can be prepared by the soil method or the single-spore method. The spores are then characterized according to their shape, size, color, and hyphal attachment and classified according to their morphology. Each type of mycorrhizal fungus has specific cell wall characteristics that can be used for identification. In this chapter, recent research advancement on the influence of AMF in promoting the morphological and physiological aspects of agricultural crops is reviewed. Successful AMF colonization could be the most organic way to significantly aid agricultural crop productivity and discuss briefly the exploitation of arbuscular mycorrhiza in sustainable agriculture.
... Arbuscular mycorrhizal fungi (AMF) are a type of endophytic fungi that are beneficial to plant growth and have significant roles in promoting plant growth, improving fruit quality, enhancing nutrient acquisition, and enhancing stress tolerance in citrus plants (Yang et al. 2021;Liu et al. 2022;Li et al. 2023;Wang et al. 2023). Duc et al. (2018) reported that mycorrhizal symbiosis could mitigate oxidative stress by enhancing antioxidant enzyme activity in tomato plants subjected to drought and heat stress, along with up-regulated expression of lipoxygenase D gene (LOXD). Pasbani et al. (2020) found that AMF dramatically raised CAT activity and accumulated more proline and free phenols in eggplant (Solanum melongena) in response to low-temperature stress. ...
Key message
CitCAT1 and CitCAT2 were cloned and highly expressed in mature leaves. High temperatures up-regulated CitCAT1 expression, while low temperatures and Diversispora versiformis up-regulated CitCAT2 expression, maintaining a low oxidative damage.
Abstract
Catalase (CAT), a tetrameric heme-containing enzyme, removes hydrogen peroxide (H2O2) to maintain low oxidative damage in plants exposed to environmental stress. This study aimed to clone CAT genes from Citrus sinensis cv. “Oita 4” and analyze their expression patterns in response to environmental stress, exogenous abscisic acid (ABA), and arbuscular mycorrhizal fungal inoculation. Two CAT genes, CitCAT1 (NCBI accession: PP067858) and CitCAT2 (NCBI accession: PP061394) were cloned, and the open reading frames of their proteins were 1479 bp and 1539 bp, respectively, each encoding 492 and 512 amino acids predicted to be localized in the peroxisome, with CitCAT1 being a stable hydrophilic protein and CitCAT2 being an unstable hydrophilic protein. The similarity of their amino acid sequences reached 83.24%, and the two genes were distantly related. Both genes were expressed in stems, leaves, flowers, and fruits, accompanied by the highest expression in mature leaves. In addition, CitCAT1 expression was mainly up-regulated by high temperatures (37 °C), exogenous ABA, and PEG stress within a short period of time, whereas CitCAT2 expression was up-regulated by exogenous ABA and low-temperature (4 °C) stress. Low temperatures (0 °C) for 12 h just up-regulated CitCAT2 expression in Diversispora versiformis-inoculated plants, and D. versiformis inoculation up-regulated CitCAT2 expression, along with lower hydrogen peroxide and malondialdehyde levels in mycorrhizal plants at low temperatures. It is concluded that CitCAT2 has an important role in resistance to low temperatures as well as mycorrhizal enhancement of host resistance to low temperatures.
... Within these regions, soils have low organic matter contents, neutral to alkaline pH, high salinity, carbonate accumulation, reduced biological activity and low humidity (De Deyn et al. 2008;Laity 2009). Furthermore, hot arid environments are characterized by high temperatures, intense ultraviolet radiation, infrequent and to biotic and abiotic stresses, including salinity, heavy metal exposure, heat stress and drought (Apple 2010; Duc et al. 2018), as well as pathogen tolerance (Jaiti et al. 2007). Thanks to these features, AMF is a crucial symbiont in desert soils with low nutrient and water availability, while enabling the plants to establish and survive (Al-Whaibi 2009; Albaqami et al. 2018). ...
Hot deserts impose extreme conditions on plants growing in arid soils. Deserts are expanding due to climate change, thereby increasing the vulnerability of ecosystems and the need to preserve them. Arbuscular mycorrhizal fungi (AMF) improve plant fitness by enhancing plant water/nutrient uptake and stress tolerance. However, few studies have focused on AMF diversity and community composition in deserts, and the soil and land use parameters affecting them. This study aimed to comprehensively describe AMF ecological features in a 5,000 m ² arid hyperalkaline region in AlUla, Saudi Arabia. We used a multimethod approach to analyse over 1,000 soil and 300 plant root samples of various species encompassing agricultural, old agricultural, urban and natural ecosystems. Our method involved metabarcoding using 18S and ITS2 markers, histological techniques for direct AMF colonization observation and soil spore extraction and observation. Our findings revealed a predominance of AMF taxa assigned to Glomeraceae, regardless of the local conditions, and an almost complete absence of Gigasporales taxa. Land use had little effect on the AMF richness, diversity and community composition, while soil texture, pH and substantial unexplained stochastic variance drove their structuring in AlUla soils. Mycorrhization was frequently observed in the studied plant species, even in usually non-mycorrhizal plant taxa. Date palms and Citrus trees, representing two major crops in the region, displayed however a very low mycorrhizal frequency and intensity. AlUla soils had a very low concentration of spores, which were mostly small. This study generated new insight on AMF and specific behavioral features of these fungi in arid environments.
Vegetables are an irreplaceable part of human diet as they bestow human body with vitamins, proteins, vital micro- and macronutrients, etc. They are constantly encountered with various phytopathogens like bacteria, fungi, viruses, nematodes and herbivores and environmental stressors like temperature, drought and salinity that have an adverse impact on their quality and yield. To escalate the growth and production and to counteract various stressors, chemical fertilizers and pesticides are indiscriminately used by vegetable growers. Their extensive use causes various threats to the environment, humans and other living organisms. Considering the harmful effects of these synthetic pesticides and chemical fertilizers, it has become necessary to cut down their use and shift to biological crop improvement methods for the enhancing the quality and quantity of vegetable crops. Microorganisms like arbuscular mycorrhizal fungi, plant growth promoting bacteria and various entomopathogenic nematodes act against different types of stresses and provide environment friendly and sustainable alternative for raising the productivity and improving the quality of vegetables. Thus, this book chapter highlights the role of various microorganisms against biotic and abiotic stresses faced by vegetables and different mechanisms employed by them in quantity and quality improvement in vegetable crops.
The increasing global demand for food caused by a growing world population has resulted in environmental problems, such as the destruction of ecologically significant biomes and pollution of ecosystems. At the same time, the intensification of crop production in modern agriculture has led to the extensive use of synthetic fertilizers to achieve higher yields. Although chemical fertilizers provide essential nutrients and accelerate crop growth, they also pose significant health and environmental risks, including pollution of groundwater and other bodies of water such as rivers and lakes. Soils that have been destabilized by indiscriminate clearing of vegetation undergo a desertification process that has profound effects on microbial ecological succession, impacting biogeochemical cycling and thus the foundation of the ecosystem. Tropical countries have positive aspects that can be utilized to their advantage, such as warmer climates, leading to increased primary productivity and, as a result, greater biodiversity. As an eco-friendly, cost-effective, and easy-to-apply alternative, biofertilizers have emerged as a solution to this issue. Biofertilizers consist of a diverse group of microorganisms that is able to promote plant growth and enhance soil health, even under challenging abiotic stress conditions. They can include plant growth-promoting rhizobacteria, arbuscular mycorrhizal fungi, and other beneficial microbial consortia. Bioremediators, on the other hand, are microorganisms that can reduce soil and water pollution or otherwise improve impacted environments. So, the use of microbial biotechnology relies on understanding the relationships among microorganisms and their environments, and, inversely, how abiotic factors influence microbial activity. The recent introduction of genetically modified microorganisms into the gamut of biofertilizers and bioremediators requires further studies to assess potential adverse effects in various ecosystems. This article reviews and discusses these two soil correcting/improving processes with the aim of stimulating their use in developing tropical countries.
Climate change is a major threat to global food security. Rising temperatures, changes in precipitation patterns, and more extreme weather events are all having a negative impact on crop yields. In addition, climate change is also affecting the soil microbiome, which is a complex community of microorganisms that play a vital role in plant health. The soil microbiome is responsible for a variety of important functions, including nutrient cycling, plant growth promotion, and disease suppression. Climate change is disrupting these functions, which is leading to decreased crop yields and increased susceptibility to pests and diseases. Vegetable crops are particularly vulnerable to the effects of climate change. This is because they are often grown in marginal environments, such as arid and semi-arid regions, where the soil microbiome is already under stress. In addition, vegetable crops are often harvested multiple times per year, which can further deplete the soil microbiome. There are several strategies to mitigate the negative effects of climate change on the soil microbiome and vegetable crop production. These includes using cover crops to protect the soil from erosion and improve nutrient cycling, planting vegetable crops that are adapted to the local climate, using sustainable agricultural practices, such as no-till farming and managing pests and diseases using integrated pest management (IPM). By taking these measures to protect and enhance the soil microbiome, we can help to improve the resilience of vegetable crops to climate change. This will help to ensure that vegetable crops can continue to provide a reliable source of food in the face of climate change.
A more sustainable and agriculturally productive system is becoming increasingly necessary to maintain soil fertility and reduce the loss of biodiversity. Microbial bio-stimulants are cutting-edge technologies that can guarantee a high nutritional value in agricultural yield while overcoming the negative effects of environmental changes. This chapter presents an overview of fungal plant bio-stimulants and of their use in agriculture. Arbuscular Mycorrhizal Fungi (AMF) and Trichoderma are the two most important fungi that act as bio-stimulants in agriculture. Because of the ability of AMFs to function as bio-fertilizers, bio-protectors, or bio-degraders, these connections may affect plant productivity. Mycorrhizal fungi affect the diversity and quality of rhizosphere microflora, which changes the microbial activity in the rhizosphere as a whole. The benefits of synergistic interactions between AMF and other rhizosphere microorganisms, including rhizobia, non-symbiotic diazotrophs, phytohormone producers, and phosphate solubilizers, are widely acknowledged. The function of AMF in protecting plants from phytopathogenic bacteria and fungi is important. Despite these advantages, interactions between AMF and rhizosphere microflora in agriculture, horticulture, and forestry remain underutilized, partly because of the limitations imposed by their obligate biotrophic conditions and the absence of suitable technology for large-scale production. Nevertheless, further research is necessary, because the use of AMF-rhizosphere microflora combinations appears to be a potential method for promoting plant development against diseases and other environmental challenges.
The Role of Microbes and Microbiomes in Ecosystem Restoration provides an in-depth exploration of how microbes and microbiomes can drive sustainable environmental recovery. It covers key topics from microbial roles in pollution remediation, biofertilizer production, and waste management to advanced microbial techniques for ecosystem resilience. Key chapters discuss microbial-assisted bioremediation, agriculture support through biofertilizers, waste treatment systems, and the restoration of polluted soils. With a special focus on the latest advances, including microbial genomics and metagenomics, the book highlights practical applications for mitigating climate impacts and promoting a greener future. Key Features: - Explains microbial and microbiome roles in restoring ecosystems. - Covers practical applications for agriculture, waste management, and pollution control. - Introduces advanced microbial techniques in environmental management. - Provides insights into sustainable practices for reducing greenhouse gases and improving soil health.
As global temperatures rise and drought conditions become increasingly frequent, the need to develop sustainable agricultural practices has become paramount. Enhancing crop resilience to water scarcity is essential to secure food supplies for a growing global population. This study examined the effects of Arbuscular Mycorrhizal Fungi (AMF) and Trichoderma harzianum on the physiological responses and growth of common bean (Phaseolus vulgaris) under 100% and 50% irrigation regimes. Under a 50% irrigation regime, AMF and Trichoderma harzianum inoculation led to substantial increases in plant height (34.5%) and root length (16.79%), compared to the control. Additionally, significant enhancements were observed in chlorophyll a (175%), chlorophyll b (194%), and total chlorophyll (180%) content in plants subjected to T. harzianum inoculation under water deficit. The application of AMF resulted in an 18% increase in total carotenoid content, showing its efficacy in sustaining photosynthetic pigments. Furthermore, the study revealed that both treatments significantly reduced malondialdehyde (MDA) accumulation, with reductions of 46.3% compared to the control under drought conditions. Catalase (CAT), increased by 201% with T. harzianum application under full irrigation and by 217% with AMF under reduced irrigation, highlighting the role of these biostimulants in mitigating oxidative stress. Principal component analysis (PCA) further confirmed that these treatments effectively maintained cellular integrity and enhanced stress tolerance. These findings underscore the potential of AMF and T. harzianum as vital tools in enhancing crop resilience against drought, with significant implications for sustainable agriculture in arid and semi-arid regions.
The increasing severity of global climate change has led to more frequent extreme high‐temperature events, significantly damaging rice yield and quality, thus posing a threat to global food security. Research indicates that plant‐microbe interactions can enhance plant growth and overall health under adverse conditions. Therefore, this review aims to explore strategies to improve rice heat tolerance through thermophilic microorganism mediation. This paper systematically summarises the effects of heat stress on both the aboveground and underground parts of rice during its growth stages, identifies the molecular mechanisms by which rice responds to heat stress, and explores the potential roles of microorganisms. Additionally, we review existing studies on microorganisms that alleviate plant heat stress and their mechanisms of action. Through case studies, we explore how microorganisms enhance rice survival in high‐temperature environments by regulating its growth and development, along with their potential applications in sustainable agriculture. In the future, environmentally friendly and efficient microbial inoculants and biofertilizers are expected to be developed based on microbe‐mediated plant heat tolerance mechanisms, which will help mitigate the heat stress challenges crops face under global climate change.
Amid escalating challenges from global climate change and increasing environmental degradation, agricultural systems worldwide face a multitude of abiotic stresses, including drought, salinity, elevated temperatures, heavy metal pollution, and flooding. These factors critically impair crop productivity and yield. Simultaneously, biotic pressures such as pathogen invasions intensify the vulnerability of agricultural outputs. At the heart of mitigating these challenges, Arbuscular Mycorrhizal Fungi (AM fungi) form a crucial symbiotic relationship with most terrestrial plants, significantly enhancing their stress resilience. AM fungi improve nutrient uptake, particularly that of nitrogen and phosphorus, through their extensive mycelial networks. Additionally, they enhance soil structure, increase water use efficiency, and strengthen antioxidant defense mechanisms, particularly in environments stressed by drought, salinity, extreme temperatures, heavy metal contamination, and flooding. Beyond mitigating abiotic stress, AM fungi bolster plant defenses against pathogens and pests by competing for colonization sites and enhancing plant immune responses. They also facilitate plant adaptation to extreme environmental conditions by altering root morphology, modulating gene expression, and promoting the accumulation of osmotic adjustment compounds. This review discusses the role of AM fungi in enhancing plant growth and performance under environmental stress.
Priming modulates plant stress responses before the stress appears, increasing the ability of the primed plant to endure adverse conditions and thrive. In this context, we investigated the effect of biological (i.e., arbuscular mycorrhizal fungi, AMF) agents and natural compounds (i.e., salicylic acid applied alone or combined with chitosan) against water deficit and salinity on a commercial tomato genotype (cv. Moneymaker). Effects of seed treatments on AMF colonization were evaluated, demonstrating the possibility of using them in combination. Responses to water and salt stresses were analysed on primed plants alone or in combination with the AMF inoculum in soil. Trials were conducted on potted plants by subjecting them to water deficit or salt stress. The effectiveness of chemical seed treatments, both alone and in combination with post-germination AM fungal inoculation, was investigated using a multidisciplinary approach that included eco-physiology, biochemistry, transcriptomics, and untargeted metabolomics. Results showed that chemical seed treatment and AM symbiosis modified the tomato response to water deficit and salinity triggering a remodelling of both transcriptome and metabolome, which ultimately elicited the plant antioxidant and osmoprotective machinery. The plant physiological adaptation to both stress conditions improved, confirming the success of the adopted approaches in enhancing stress tolerance.
The major need of the hour is to increase crop productivity while utilizing limited land resources without over-exploiting natural resources. The frequent use of pesticides as well as fertilizers affects crop productivity as well as human health. To accomplish the goal of enhancing crop productivity and yield, instead of applying chemical fertilizers, biostimulants can be used. It will limit the dependence of farmers on fertilizers, eventually reducing the use of fertilizers on cultivated area, which is more cost-effective and environment friendly. Biostimulants are of plant origin and in addition may belong to microorganisms. Biostimulants are substances which when applied in limited quantity show improvement in crop yield, growth, and productivity simultaneously. Nanomaterials (NMs) and nanoparticles (NPs) are metals, semi-metals, and non-metals or nanomaterials of carbon, etc., which act as biostimulants/nanobiostimulants when applied in small quantity. It leads to enhancement and modification of nutraceutical quality, metabolism, and composition of food crop, simultaneously, strengthening the plant to sustain under stress conditions. Biotic stress and abiotic stress both lead to the production of secondary metabolites in plants.
These secondary metabolites are alkaloids, terpenoids, phenols, flavonoids, etc. The positive impact of the application of nanobiostimulants was identified on plants, in in vitro and in vivo conditions. Secondary metabolites are important, as they act as plant’s defense system against herbivores and pathogens and act as attractant by providing colors to plants and many other factors in plants. Nanobiostimulants influence secondary metabolites concentration by regulating plants gene expression, signaling pathways, and also modulating reactive nitrogen/oxygen species.
Under drought conditions, arbuscular mycorrhizal (AM) fungi may improve plant performance by facilitating the movement of water through extensive hyphal networks. When these networks interconnect neighboring plants in common mycorrhizal networks (CMNs), CMNs are likely to partition water among many individuals. The consequences of CMN-mediated water movement for plant interactions, however, are largely unknown. We set out to examine CMN-mediated interactions among Andropogon gerardii seedlings in a target-plant pot experiment, with watering (watered or long-term drought) and CMN status (intact or severed) as treatments. Intact CMNs improved the survival of seedlings under drought stress and mediated positive, facilitative plant interactions in both watering treatments. Watering increased mycorrhizal colonization rates and improved P uptake, particularly for large individuals. When drought stressed, improved access to water most likely benefited neighboring plants interacting across CMNs. CMNs appear to have provided the most limiting resource within each treatment, whether water, P, or both, thereby improving survival and growth. Neighbors near large, photosynthate-fixing target plants likely benefited from their establishment of extensive hyphal networks that could access water and dissolved P within soil micropores. In plant communities, CMNs may be vital during drought, which is expected to increase in frequency, intensity, and length with climate change.
This study investigates farmers' perceptions and adoption rates of AM fungi, identifying obstacles and proposing strategies for widespread implementation. It explores the long-term sustainability and resilience of agricultural systems enhanced by AM fungi, considering their adaptability to evolving climate conditions. Sustainable agriculture is an imperative global goal, given the increasing pressures on food production, environmental conservation and resource preservation. In this context, Arbuscular Mycorrhiza (AM) fungi, often overlooked beneath the soil's surface, emerge as a hidden key to achieving sustainability in agriculture. These symbiotic fungi form mutualistic relationships with the roots of most land plants, offering a multitude of benefits that encompass enhanced nutrient uptake, improved soil structure and heightened resistance to abiotic and biotic stressors. It aims to assess their diversity, quantify their impact on crop growth and evaluate their contributions to nutrient cycling and soil health.
Biotic and abiotic stresses pose significant challenges to crop
yield, food quality, and global food security, impacting various
physiological, biochemical, and molecular aspects of plants. Traditional
agricultural practices reliant on inorganic fertilizers and pesticides
exacerbate soil degradation and environmental pollution. Hence, there is
a pressing need to develop safer and sustainable agricultural
approaches.The utilization of plant growth-promoting microbes (PGPM)
and mycorrhizal fungi presents promising avenues for enhancing plant
growth under stress conditions while offering economically viable and
ecologically sound alternatives. PGPM contribute to plant growth by
modulating plant hormones, enhancing nutrient uptake, producing
siderophores, and bolstering the antioxidant system. Moreover, they
facilitate acquired systemic resistance (ASR) and induced systemic
resistance (ISR), effectively combating biotic stressors. Arbuscular
mycorrhizal (AM) fungi play a crucial role in stress mitigation by
improving nutrient and water uptake during adverse conditions, thereby
enhancing stress tolerance. This symbiotic plant-microbe interaction holds
immense potential for sustainable agriculture and industrial applications,
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as it relies on biological processes and replaces conventional agricultural
methods. Microbes, acting as ecological engineers, can address
environmental stressors, offering feasible solutions to global food
production challenges while minimizing adverse impacts on
environmental quality. Harnessing microbial technologies presents a
promising avenue for future agricultural practices, enabling the provision
of food to the growing global population while utilizing available
resources efficiently.This chapter aims to explore the diverse array of
abiotic and biotic stress-tolerant beneficial microorganisms and elucidate
their mechanisms of action in bolstering sustainable agricultural
production.
Global climate change has significantly reduced the yield of many crops due to various abiotic stressors. These stressors include water-related issues such as drought and flooding, thermal changes like extremely low and high temperatures, salinity, and adverse soil pH conditions including alkalinity and acidity. Biostimulants have emerged as promising and effective tools for mitigating the damage caused by these abiotic stressors in plants, ultimately enhancing both the quantity and quality of crops. Biostimulants are naturally derived substances that include humic acid, protein hydrolysates, nitrogenous compounds, seaweed extracts, beneficial bacteria, and molds. Even at low concentrations, biostimulants play a critical role in activating important plant enzymes, inducing antioxidant defenses, improving water relations and photosynthetic activity, stimulating hormone-like activities (particularly auxins, gibberellins, and cytokinins), and modulating root system development. This review discusses the physiological effects of microbial biostimulants on the quality and productivity of fruit crops, as well as their experimental applications.
The most familiar and common mutualistic association existing in the majority of crop plants is the arbuscular mycorrhizal (AM) symbiosis that aids in crop growth and development. In the plant-AM fungal interaction, the fungi acquire carbon from their host plant and in exchange, the fungi increase the supply of important nutrients in particular phosphorous via expanding the roots into the nutrient absorbing sites. Also, the AM fungi enhance crops performance and existence under different abiotic and biotic stresses through different mechanisms. As a natural crop-root colonizer, AM fungi impart essential micro-and macronutrients thereby promoting crop growth and productivity in nutrient-stressed soils. The AM-fungal mediated crop growth promotion involves several pathways and a sequence of multifarious communications between the crop and the fungus. Owing to its crop growth-promoting activity, several AM fungal species are developed into potential bioinoculants for the ecofriendly management of anthropogenic ecosystems like agriculture. In this chapter, we comprehend the existing knowledge on the role of AM fungi in the establishment and survival of crops under normal and stressful environments that hampers crop growth and development like drought, salinity, heavy metals and infestation by pathogens. In addition, the role of AM fungi in crop growth promotion through nutrient uptake and other pathways, application of AM fungi in improving the water relations and nutritional quality in crop species under unfavourable conditions are also discussed. The exploitation of AM fungal symbiosis in agricultural habitats can lead to the creation of self-sustaining ecosystems for future.
Plants are aerobic, sessile, and autotrophic organisms that face a wide variety of climatic adversities and pathogen attacks. They have evolved to deal with such challenges, that is, the case of the antioxidant defense to avoid oxidative stress (OS) caused by the overproduction of reactive oxygen and nitrogen species (ROS/RONS). ROS/RONS can be by-products of many physiological functions and biochemical pathways, but particularly from the fundamental electronic transfer processes: photosynthesis and respiration. Photosynthesis is crucial for plant nutrition, trophic webs and maintenance of O2/CO2 balance in biosphere. Respiration is a source of energy for organisms. Both processes generate ROS and its overproduction can lead OS, modifying essential biomolecules and altering fundamental biochemical pathways and plant development. Antioxidant defense prevents such harmful accumulation of ROS. Plants interact with microbiota, a well-structured microbial community conferring adaptive and defense tools in both abiotic and biotic stressing conditions. We present the beneficial influence of the plant microbiome promotes the adaptability, resistance, and defense of plants using our results obtained in plants confronted drought. Microbiota can be used in agriculture in different ways, including adaptation to soil of micro-propagated plants, bioproducts for plant growth and pest control and processing and preservation of agriculture products.
Field experiment was carried out at the experimental station of Szent István University, Gödöllő, Hungary to explore the impact of arbuscular mycorrhizal fungi only alone or together with Trichoderma and plant growth-promoting bacteria on defense enzymes and yield of three pepper varieties. The seven inoculation treatments consisting of arbuscular mycorrhizal fungi (AM), Trichoderma (Tri), plant growth promoting bacteria (Pse) and their combinations (AM+Tri; AM+Tri+Pse; AM+Pse) together with three pepper hybrids and non-inoculation (control) plants were arranged in a randomized complete block design. Defense enzyme activities polyphenol oxidase (PPO), peroxidase (POD), superoxide dismutase (SOD), catalase (CAT) of various treated plants were measured just before flowering, representing the most sensitive stage of plants. The results showed that AM+Tri+Pse treatment enhanced the yield most among microbial inoculations. Highest yield was recorded in the triple treatment in Karpex cultivar, however, Karpia and Kaptur variety obtained more improved yield by microbial inoculations. Defense enzymes activities generally were most induced in the combination of three inoculants in cultivars whereas different responses in induction of defense enzymes were found in other microbial treatments, depending on specific interactions between microbe and pepper genotype. These results suggested that the triple application brought more benefits to the host plant.
The arbuscular mycorrhizal (AM) symbiosis has been shown to improve maize tolerance to different drought stress scenarios by regulating a wide range of host plants aquaporins. The objective of this study was to highlight the differences in aquaporin regulation by comparing the effects of the AM symbiosis on root aquaporin gene expression and plant physiology in two maize cultivars with contrasting drought sensitivity. This information would help to identify key aquaporin genes involved in the enhanced drought tolerance by the AM symbiosis. Results showed that when plants were subjected to drought stress the AM symbiosis induced a higher improvement of physiological parameters in drought-sensitive plants than in drought-tolerant plants. These include efficiency of photosystem II, membrane stability, accumulation of soluble sugars and plant biomass production. Thus, drought-sensitive plants obtained higher physiological benefit from the AM symbiosis. In addition, the genes ZmPIP1;1, ZmPIP1;3, ZmPIP1;4, ZmPIP1;6, ZmPIP2;2, ZmPIP2;4, ZmTIP1;1, and ZmTIP2;3 were down-regulated by the AM symbiosis in the drought-sensitive cultivar and only ZmTIP4;1 was up-regulated. In contrast, in the drought-tolerant cultivar only three of the studied aquaporin genes (ZmPIP1;6, ZmPIP2;2, and ZmTIP4;1) were regulated by the AM symbiosis, resulting induced. Results in the drought-sensitive cultivar are in line with the hypothesis that down-regulation of aquaporins under water deprivation could be a way to minimize water loss, and the AM symbiosis could be helping the plant in this regulation. Indeed, during drought stress episodes, water conservation is critical for plant survival and productivity, and is achieved by an efficient uptake and stringently regulated water loss, in which aquaporins participate. Moreover, the broader and contrasting regulation of these aquaporins by the AM symbiosis in the drought-sensitive than the drought-tolerant cultivar suggests a role of these aquaporins in water homeostasis or in the transport of other solutes of physiological importance in both cultivars under drought stress conditions, which may be important for the AM-induced tolerance to drought stress.
Temperature is one of the most important environmental factors that determine the growth and productivity of plants across the globe. Many physiological and biochemical processes and functions are affected by low and high temperature stresses. Arbuscular mycorrhizal (AM) symbiosis has been shown to improve tolerance to temperature stress in plants. This chapter addresses the effect of AM symbiosis on plant growth and biomass production, water relations (water potential, stomatal conductance, and aquaporins), photosynthesis (photosynthetic rate, chlorophyll, and chlorophyll fluorescence), plasma membrane permeability (malondialdehyde and ATPase), reactive oxygen species (ROS) and antioxidants, osmotic adjustment, carbohydrate metabolism, nutrient acquisition, and secondary metabolism under low or high temperature stress. The possible mechanisms of AM symbiosis improving temperature stress tolerance of the host plants via enhancing water and nutrient uptake, improving photosynthetic capacity and efficiency, protecting plant against oxidative damage, and increasing accumulation of osmolytes are discussed. This chapter also provides some future perspectives for better understanding the mechanisms of AM plant tolerance against temperature stress.
Background
Abiotic stresses due to environmental factors could adversely affect the growth and development of crops. Among the abiotic stresses, drought and heat stress are two critical threats to crop growth and sustainable agriculture worldwide. Considering global climate change, incidence of combined drought and heat stress is likely to increase. The aim of this study was to shed light on plant growth performance and leaf physiology of three tomatoes cultivars (‘Arvento’, ‘LA1994’ and ‘LA2093’) under control, drought, heat and combined stress.
Results
Shoot fresh and dry weight, leaf area and relative water content of all cultivars significantly decreased under drought and combined stress as compared to control. The net photosynthesis and starch content were significantly lower under drought and combined stress than control in the three cultivars. Stomata and pore length of the three cultivars significantly decreased under drought and combined stress as compared to control. The tomato ‘Arvento’ was more affected by heat stress than ‘LA1994’ and ‘LA2093’ due to significant decreases in shoot dry weight, chlorophyll a and carotenoid content, starch content and NPQ (non-photochemical quenching) only in ‘Arvento’ under heat treatment. By comparison, the two heat-tolerant tomatoes were more affected by drought stress compared to ‘Arvento’ as shown by small stomatal and pore area, decreased sucrose content, ΦPSII (quantum yield of photosystem II), ETR (electron transport rate) and qL (fraction of open PSII centers) in ‘LA1994’ and ‘LA2093’. The three cultivars showed similar response when subjected to the combination of drought and heat stress as shown by most physiological parameters, even though only ‘LA1994’ and ‘LA2093’ showed decreased Fv/Fm (maximum potential quantum efficiency of photosystem II), ΦPSII, ETR and qL under combined stress.
Conclusions
The cultivars differing in heat sensitivity did not show difference in the combined stress sensitivity, indicating that selection for tomatoes with combined stress tolerance might not be correlated with the single stress tolerance. In this study, drought stress had a predominant effect on tomato over heat stress, which explained why simultaneous application of heat and drought revealed similar physiological responses to the drought stress. These results will uncover the difference and linkage between the physiological response of tomatoes to drought, heat and combined stress and be important for the selection and breeding of tolerant tomato cultivars under single and combine stress.
The function of aquaporin (AQP) protein in transporting water is crucial for plants to survive in drought stress. With 47 homologues in tomato (Solanum lycopersicum) were reported, but the individual and integrated functions of aquaporins involved in drought response remains unclear. Here, three plasma membrane intrinsic protein genes, SlPIP2;1, SlPIP2;7 and SlPIP2;5, were identified as candidate aquaporins genes because of highly expressed in tomato roots. Assay on expression in Xenopus oocytes demonstrated that SlPIP2s protein displayed water channel activity and facilitated water transport into the cells. With real-time PCR and in situ hybridization analysis, SlPIP2s were considered to be involved in response to drought treatment. To test its function, transgenic Arabidopsis and tomato lines overexpressing SlPIP2;1, SlPIP2;7 or SlPIP2;5 were generated. Compared with wild type, the over-expression of SlPIP2;1, SlPIP2;7 or SlPIP2;5 transgenic Arabidopsis and tomato plants all showed significantly higher hydraulic conductivity levels and survival rates under both normal and drought conditions. Taken together, this study concludes that aquaporins (SlPIP2;1, SlPIP2;7 and SlPIP2;5) contribute substantially to root water uptake in tomato plants through improving plant water content and maintaining osmotic balance.
Aims
To evaluate the role of the AM symbiosis on nutrient allocation in Triticum aestivum L. cv. 1110 at different growth stages before and after heat-stress at anthesis.
Methods
Measurements of plant biomass and grain yield at anthesis, grain-filling and maturity; determination of macro- and micronutrient concentrations in aboveground biomass; evaluation of AM fungal structures in roots and assessment of light-use efficiency of plants.
Results
AM increased grain number in wheat under heat-stress, and altered nutrient allocation and tiller nutrient composition. Heat increased number of arbuscules in wheat root, whereas number of vesicles and total colonization were unaffected. Heat increased photosystem II yield and the electron transfer rate, whereas non-photochemical quenching decreased during the first 2 days of heat-stress.
Conclusions
Nutrient allocation and –composition in wheat grown under heat-stress were altered by AM symbiosis, which lowered the K/Ca ratio, whereas it was increased by heat-stress. The increased carbon availability in spikes at this developmental stage, related to the C sink strength of the AM symbiosis and its influence on source-sink relationships in the host-plant, resulted in increased number of grains in heat-stressed AM plants.
Arbuscular mycorrhizal (AM) fungi, which form symbioses with the roots of the most important crop species, are usually considered bio-fertilizers, whose exploitation could represent a promising avenue for the development in the future of a more sustainable next-generation agriculture. The best understood function in symbiosis is an improvement in plant mineral nutrient acquisition, as exchange for C compounds derived from the photosynthetic process: this can enhance host growth and tolerance to environmental stresses, e.g., water stress (WS). However, physiological and molecular mechanisms occurring in AM-colonized plants and directly involved in the mitigation of water stress effects need to be further investigated. The main goal of this work is to verify the potential impact of the AM symbiosis on the plant response to WS. To this aim, the effect of two AM fungi (Funneliformis mosseae and Rhizophagus intraradices) on tomato under WS condition was studied. A combined approach, involving eco-physiological, morphometric, biochemical and molecular analyses, has been used to highlight the mechanisms involved in plant response to water stress during AM symbiosis. Gene expression analyses focused on a set of target genes putatively involved in the plant response to drought and, in parallel, we considered the expression changes induced by the imposed stress on a group of fungal genes playing a key role in water-transport process. Taken together, results show that AM symbiosis positively affects the tolerance to water stress in tomato with a different plant response depending on the AM fungi species involved.
In field conditions, plants are often simultaneously exposed to multiple biotic and abiotic stresses resulting in substantial yield loss. Plants have evolved various physiological and molecular adaptations to protect themselves under stress combinations. Emerging evidences suggest that plant responses to a combination of stresses are unique from individual stress responses. In addition, plants exhibit shared responses which are common to individual stresses and stress combination. In this review, we provide an update on the current understanding of both unique and shared responses. Specific focus of this review is on heat–drought stress as a major abiotic stress combination and, drought–pathogen and heat–pathogen as examples of abiotic–biotic stress combinations. We also comprehend the current understanding of molecular mechanisms of cross talk in relation to shared and unique molecular responses for plant survival under stress combinations. Thus, the knowledge of shared responses of plants from individual stress studies and stress combinations can be utilized to develop varieties with broad spectrum stress tolerance.
Arbuscular mycorrhizal (AM) symbiosis alleviates drought stress in plants. However the intimate mechanisms involved, as well as its effect on the production of signalling molecules associated to the host plant-AM fungus interaction remains largely unknown. In the present work, the effects of drought on lettuce and tomato plant performance and hormone levels were investigated in non-AM and AM plants. Three different water regimes were applied and their effects analysed over time. AM plants showed an improved growth rate and efficiency of photosystem II than non-AM plants under drought from very early stages of plant colonization. The levels of the phytohormone abscisic acid, as well as the expression of the corresponding marker genes, were influenced by drought stress in non-AM and AM plants. The levels of strigolactones and the expression of corresponding marker genes were affected by both AM symbiosis and drought. The results suggest that AM symbiosis alleviates drought stress by altering the hormonal profiles and affecting plant physiology in the host plant. In addition, a correlation between AM root colonization, strigolactone levels and drought severity is shown, suggesting that under these unfavourable conditions plants might increase strigolactone production in order to promote symbiosis establishment to cope with the stress.
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This study evaluates antioxidant responses and jasmonate regulation in Digitaria eriantha cv. Sudafricana plants inoculated (AM) and non-inoculated (non-AM) with Rhizophagus irregularis and subjected to drought, cold, or salinity. Stomatal conductance, photosynthetic efficiency, biomass production, hydrogen peroxide accumulation, lipid peroxidation, antioxidants enzymes activities, and jasmonate levels were determined. Stomatal conductance and photosynthetic efficiency decreased in AM and non-AM plants under all stress conditions. However, AM plants subjected to drought, salinity, or non-stress conditions showed significantly higher stomatal conductance values. AM plants subjected to drought or non-stress conditions increased their shoot/root biomass ratios, whereas salinity and cold caused a decrease in these ratios. Hydrogen peroxide accumulation, which was high in non-AM plant roots under all treatments, increased significantly in non-AM plant shoots under cold stress and in AM plants under non-stress and drought conditions. Lipid peroxidation increased in the roots of all plants under drought conditions. In shoots, although lipid peroxidation decreased in AM plants under non-stress and cold conditions, it increased under drought and salinity. AM plants consistently showed high catalase (CAT) and ascorbate peroxidase (APX) activity under all treatments. By contrast, the glutathione reductase (GR) and superoxide dismutase (SOD) activity of AM roots was lower than that of non-AM plants and increased in shoots. The endogenous levels of cis-12-oxophytodienoc acid (OPDA), jasmonic acid (JA), and 12-OH-JA showed a significant increase in AM plants as compared to non-AM plants. 11-OH-JA content only increased in AM plants subjected to drought. Results show that D. eriantha is sensitive to drought, salinity, and cold stresses and that inoculation with AM fungi regulates its physiology and performance under such conditions, with antioxidants and jasmonates being involved in this process.
The plant hormone abscisic acid (ABA) regulates many key processes involved in plant development and adaptation to biotic and abiotic stresses. Under stress conditions, plants synthesize ABA in various organs and initiate defense mechanisms, such as the regulation of stomatal aperture and expression of defense-related genes conferring resistance to environmental stresses. The regulation of stomatal opening and closure is important to pathogen defense and control of transpirational water loss. Recent studies using a combination of approaches, including genetics, physiology, and molecular biology, have contributed considerably to our understanding of ABA signal transduction. A number of proteins associated with ABA signaling and responses—especially ABA receptors—have been identified. ABA signal transduction initiates signal perception by ABA receptors and transfer via downstream proteins, including protein kinases and phosphatases. In the present review, we focus on the function of ABA in stomatal defense against biotic and abiotic stresses, through analysis of each ABA signal component and the relationships of these components in the complex network of interactions. In particular, two ABA signal pathway models in response to biotic and abiotic stress were proposed, from stress signaling to stomatal closure, involving the pyrabactin resistance (PYR)/PYR-like (PYL) or regulatory component of ABA receptor (RCAR) family proteins, 2C-type protein phosphatases, and SnRK2-type protein kinases.
The production of H2O2 is critical for brassinosteroid (BR)- and abscisic acid (ABA)-induced stress tolerance in plants. In this study, the relationship between BR and ABA in the induction of H2O2 production and their roles in response to heat and paraquat (PQ) oxidative stresses were studied in tomato. Both BR and ABA induced increases in RBOH1 gene expression, NADPH oxidase activity, apoplastic H2O2 accumulation, and heat and PQ stress tolerance in wild-type plants. BR could only induced transient increases in these responses in the ABA biosynthetic mutant notabilis (not), whereas ABA induced strong and prolonged increases in these responses in the BR biosynthetic mutant d
^im compared with wild-type plants. ABA levels were reduced in the BR biosynthetic mutant but could be elevated by exogenous BR. Silencing of RBOH1 compromised BR-induced apoplastic H2O2 production, ABA accumulation, and PQ stress responses; however, ABA-induced PQ stress responses were largely unchanged in the RBOH1-silenced plants. BR induces stress tolerance involving a positive feedback mechanism in which BR induces a rapid and transient H2O2 production by NADPH oxidase. The process in turn triggers increased ABA biosynthesis, leading to further increases in H2O2 production and prolonged stress tolerance. ABA induces H2O2 production in both the apoplastic and chloroplastic compartments.
Background
Abiotic stresses which include drought and heat are amongst the main limiting factors for plant growth and crop productivity. In the field, these stress types are rarely presented individually and plants are often subjected to a combination of stress types. Sorghum bicolor is a cereal crop which is grown in arid and semi-arid regions and is particularly well adapted to the hot and dry conditions in which it originates and is now grown as a crop. In order to better understand the mechanisms underlying combined stress tolerance in this important crop, we have used microarrays to investigate the transcriptional response of Sorghum subjected to heat and drought stresses imposed both individually and in combination.
Results
Microarrays consisting of 28585 gene probes identified gene expression changes equating to ~4% and 18% of genes on the chip following drought and heat stresses respectively. In response to combined stress ~20% of probes were differentially expressed. Whilst many of these transcript changes were in common with those changed in response to heat or drought alone, the levels of 2043 specific transcripts (representing 7% of all gene probes) were found to only be changed following the combined stress treatment. Ontological analysis of these ‘unique’ transcripts identified a potential role for specific transcription factors including MYB78 and ATAF1, chaperones including unique heat shock proteins (HSPs) and metabolic pathways including polyamine biosynthesis in the Sorghum combined stress response.
Conclusions
These results show evidence for both cross-talk and specificity in the Sorghum response to combined heat and drought stress. It is clear that some aspects of the combined stress response are unique compared to those of individual stresses. A functional characterization of the genes and pathways identified here could lead to new targets for the enhancement of plant stress tolerance, which will be particularly important in the face of climate change and the increasing prevalence of these abiotic stress types.
Electronic supplementary material
The online version of this article (doi:10.1186/1471-2164-15-456) contains supplementary material, which is available to authorized users.
Environmental stress conditions such as drought, heat, salinity, cold, or pathogen infection can have a devastating impact on plant growth and yield under field conditions. Nevertheless, the effects of these stresses on plants are typically being studied under controlled growth conditions in the laboratory. The field environment is very different from the controlled conditions used in laboratory studies, and often involves the simultaneous exposure of plants to more than one abiotic and/or biotic stress condition, such as a combination of drought and heat, drought and cold, salinity and heat, or any of the major abiotic stresses combined with pathogen infection. Recent studies have revealed that the response of plants to combinations of two or more stress conditions is unique and cannot be directly extrapolated from the response of plants to each of the different stresses applied individually. Moreover, the simultaneous occurrence of different stresses results in a high degree of complexity in plant responses, as the responses to the combined stresses are largely controlled by different, and sometimes opposing, signaling pathways that may interact and inhibit each other. In this review, we will provide an update on recent studies focusing on the response of plants to a combination of different stresses. In particular, we will address how different stress responses are integrated and how they impact plant growth and physiological traits.
Contents
Summary
32
I.
Introduction
32
II.
Effects of stress combination on growth, yield and physiological traits in plants and crops
34
III.
The complexity of stress response signaling during stress combination
38
IV.
Conclusions
39
Acknowledgements
41
References
41
The relationship between modulation by arbuscular mycorrhizae (AM) of aquaporin expression in the host plant and changes in root hydraulic conductance, plant water status, and performance under stressful conditions is not well known. This investigation aimed to elucidate how the AM symbiosis modulates the expression of the whole set of aquaporin genes in maize plants under different growing and drought stress conditions, as well as to characterize some of these aquaporins in order to shed further light on the molecules that may be involved in the mycorrhizal responses to drought. The AM symbiosis regulated a wide number of aquaporins in the host plant, comprising members of the different aquaporin subfamilies. The regulation of these genes depends on the watering conditions and the severity of the drought stress imposed. Some of these aquaporins can transport water and also other molecules which are of physiological importance for plant performance. AM plants grew and developed better than non-AM plants under the different conditions assayed. Thus, for the first time, this study relates the well-known better performance of AM plants under drought stress to not only the water movement in their tissues but also the mobilization of N compounds, glycerol, signaling molecules, or metalloids with a role in abiotic stress tolerance. Future studies should elucidate the specific function of each aquaporin isoform regulated by the AM symbiosis in order to shed further light on how the symbiosis alters the plant fitness under stressful conditions.
Male reproduction in flowering plants is highly sensitive to high temperature (HT). To investigate molecular mechanisms of the response of cotton anthers to HT, a relatively complete comparative transcriptome analysis was performed during anther development of Gossypium hirsutum '84021' and 'H05' under normal temperature and HT conditions. Totally, 4599 differentially expressed genes (DEGs) were screened; the DEGs were mainly related to epigenetic modifications, carbohydrate metabolism, and plant hormone signaling. Detailed studies showed that deficiency in S-ADENOSYL-L-HOMOCYSTEINE HYDROLASE1 (SAHH1) and the inhibition of methyltransferases contributed to genome-wide hypomethylation in 'H05', and the increased expression of histone constitution genes contributed to DNA stability in '84021'. Furthermore, HT induced expression of CASEIN KINASE I (GhCKI) in 'H05', coupled with the suppression of starch synthase activity, decreases in the glucose level during anther development, and increases in the indole-3-acetic acid (IAA) level in late-stage anthers. The same changes also were observed in Arabidopsis GhCKI overexpression lines. These results suggest that GhCKI, sugar, and auxin may be key regulators of the anther response to HT stress. Moreover, PHYTOCHROME-INTERACTING FACTOR GENES (PIFs), which are involved in linking sugar and auxin and are regulated by sugar, might positively regulate IAA biosynthesis in the cotton anther response to HT. Additionally, exogenous IAA application revealed that high background IAA may be a disadvantage for late-stage cotton anthers during HT stress. Overall, the linking of HT, sugar, PIFs, and IAA, together with our previously reported data on GhCKI, may provide dynamic coordination of plant anther responses to HT stress.
Arbuscular mycorrhizal fungi (AMF) have mutualistic relationships with more than 80% of terrestrial plant species. This symbiotic relationship is ancient and would have had important roles in establishment of plants on land. Despite their abundance and wide range of relationship with plant species, AMF have shown low species diversity. However, molecular studies have suggested that diversity of these fungi may be much higher, and genetic variation of AMF is very high within a species and even within a single spore. Despite low diversity and lack of host specificity, various functions have been associated with plant growth responses to arbuscular mycorrhizal fungal colonization. In addition, different community composition of AMF affects plants differently, and plays a potential role in ecosystem variability and productivity. AMF have high functional diversity because different combinations of host plants and AMF have different effects on the various aspects of symbiosis. Consequently, recent studies have focused on the different functions of AMF according to their genetic resource and their roles in ecosystem functioning. This review summarizes taxonomic, genetic, and functional diversities of AMF and their roles in natural ecosystems.
Background
Jasmonates are important regulators in plant responses to biotic and abiotic stresses as well as in development. Synthesized from lipid-constituents, the initially formed jasmonic acid is converted to different metabolites including the conjugate with isoleucine. Important new components of jasmonate signalling including its receptor were identified, providing deeper insight into the role of jasmonate signalling pathways in stress responses and development.ScopeThe present review is an update of the review on jasmonates published in this journal in 2007. New data of the last five years are described with emphasis on metabolites of jasmonates, on jasmonate perception and signalling, on cross-talk to other plant hormones and on jasmonate signalling in response to herbivores and pathogens, in symbiotic interactions, in flower development, in root growth and in light perception.Conclusions
The last few years have seen breakthroughs in the identification of JASMONATE ZIM DOMAIN (JAZ) proteins and their interactors such as transcription factors and co-repressors, and the crystallization of the jasmonate receptor as well as of the enzyme conjugating jasmonate to amino acids. Now, the complex nature of networks of jasmonate signalling in stress responses and development including hormone cross-talk can be addressed.
The influence of the arbuscular mycorrhizal (AM) fungus, Glomus fasciculatum, on the growth, heat stress responses and the antioxidative activity in cyclamen (Cyclamen persicum Mill.) plants was studied. Cyclamen plants (inoculated or not with the AM fungus) were placed in a commercial potting media at 17-20 °C for 12 weeks in a greenhouse and subsequently subjected to two temperature conditions in a growth chamber. Initially, plants were grown at 20 °C for 4 weeks as a no heat stress (HS-) condition, followed by 30 °C for another 4 weeks as a heat stress (HS+) condition. Different morphological and physiological growth parameters were compared between G. fasciculatum-inoculated and noninoculated plants. The mycorrhizal symbiosis markedly enhanced biomass production and HS + responses in plants compared to that in the controls. A severe rate of leaf browning (80-100 %) was observed in control plants, whereas the mycorrhizal plants showed a minimum rate of leaf browning under HS + conditions. The mycorrhizal plants showed an increase activity of antioxidative enzymes such as superoxide dismutase and ascorbate peroxidase, as well as an increase in ascorbic acid and polyphenol contents. The 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity also showed a greater response in mycorrhizal plants than in the control plants under each temperature condition. The results indicate that in cyclamen plants, AM fungal colonisation alleviated heat stress damage through an increased antioxidative activity and that the mycorrhizal symbiosis strongly enhanced temperature stress tolerance which promoted plant growth and increased the host biomass under heat stress.
Festuca arundinacea is one of the most drought-tolerant species within the Lolium–Festuca complex and was used as a model for research aimed at identifying the chloroplast components involved in the proteomic response for drought stress in forage grasses. Individual F. arundinacea genotypes with contrasting levels of drought tolerance, the high-drought-tolerant (HDT) and the low-drought-tolerant (LDT) genotypes, were selected for comparative physiological and proteomic work. Measurements of water uptake, chlorophyll fluorescence, relative water content, electrolyte leakage, and gas exchange during drought and rewatering periods were followed by investigations on accumulation levels of chloroplast proteins before drought conditions, on d 3 and 11 of drought treatment, and after 10 d of subsequent watering, using two-dimensional gel electrophoresis. The proteins that were accumulated differentially between the selected plants were then identified by mass spectrometry. The LDT genotype revealed lower levels of water uptake and relative water content as drought progressed, and this was accompanied by lower levels of transpiration and net photosynthesis, and a higher level of electrolyte leakage observed in this genotype. Eighty-two protein accumulation profiles were compared between the HDT and LDT genotypes and ten proteins were shown to be differentially accumulated between them. The functions of the selected proteins in plant cells and their probable influence on the process of recovery after drought treatment in F. arundinacea are discussed.
Methyl jasmonate (MeJA), a plant-signalling molecule, is involved in an array of plant development and the defence responses. This study was conducted to explore the role of exogenous MeJA application in alleviating the adversities of drought stress in soybean (Glycine max L. Merrill.). Soybean plants were grown under normal conditions until blooming and were then subjected to drought by withholding irrigation followed by foliar application of (50 μm) MeJA. Drought stress substantially suppressed the yield and yield-related traits, whereas it accelerated the membrane lipid peroxidation. Nonetheless, substantial increase in activities of enzymatic antioxidants (superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)), proline, relative water contents (RWC) with simultaneous decrease in membrane lipid peroxidation was observed in MeJA-treated plants under drought. These beneficial effects led to improvement in biological and grain yield, and harvest index under drought. Interestingly, MeJA application was also useful under well-watered conditions. These results suggest the involvement of MeJA in improving the drought tolerance of soybean by modulating the membrane lipid peroxidation and antioxidant activities.
It emerged recently that there is an inter-relationship between drought and ultraviolet-B (UV-B) radiation in plant responses, in that both stresses provoke an oxidative burst. The purpose of this investigation was to compare the effects and interaction of drought and UV-B in wheat and pea. The absence of changes in relative leaf water content (RWC) after UV-B treatments indicate that changes in water content were not involved. RWC was the main factor resulting in reduced growth in response to drought. Increases in anthocyanin and phenols were detected after exposure to UV-B. The increases do not appear to be of sufficient magnitude to act as a UV-B screen. UV-B application caused greater membrane damage than drought stress, as assessed by lipid peroxidation as well as osmolyte leakage. An increase in the specific activities of antioxidant enzymes was measured after UV-B alone as well as after application to droughted plants. Proline increased primarily in drought-stressed pea or wheat. Proline may be the drought-induced factor which has a protective role in response to UV-B. The physiological and biochemical parameters measured indicate the UV-B light has stronger stress effectors than drought on the growth of seedlings of both species. The two environmental stresses acted synergistically to induce protective mechanisms in that pre-application of either stress reduced the damage caused by subsequent application of the other stress.
The purpose of this study was to investigate the effects of arbuscular mycorrhizal (AM) symbiosis on gas exchange, chlorophyll
fluorescence, pigment concentration and water status of maize plants in pot culture under high temperature stress. Zea mays L. genotype Zhengdan 958 were cultivated in soil at 26/22°C for 6weeks, and later subjected to 25, 35 and 40°C for 1week.
The plants inoculated with the AM fungus Glomus etunicatum were compared with the non-inoculated plants. The results showed that high temperature stress decreased the biomass of the
maize plants. AM symbiosis markedly enhanced the net photosynthetic rate, stomatal conductance and transpiration rate in the
maize leaves. Compared with the non-mycorrhizal plants, mycorrhizal plants had lower intercellular CO2 concentration under 40°C stress. The maximal fluorescence, maximum quantum efficiency of PSII photochemistry and potential
photochemical efficiency of mycorrhizal plants were significantly higher than corresponding non-mycorrhizal plants under high
temperature stress. AM-inoculated plants had higher concentrations of chlorophyll a, chlorophyll b and carotenoid than non-inoculated
plants. Furthermore, AM colonization increased water use efficiency, water holding capacity and relative water content. In
conclusion, maize roots inoculated with AM fungus may protect the plants against high temperature stress by improving photosynthesis
and water status.
KeywordsArbuscular mycorrhiza–Chlorophyll fluorescence–Gas exchange–High temperature stress–Water status
The influence of the arbuscular mycorrhizal (AM) fungus, Glomus mosseae, on characteristics of growth, photosynthetic pigments, osmotic adjustment, membrane lipid peroxidation and activity of antioxidant
enzymes in leaves of tomato (Lycopersicon esculentum cv Zhongzha105) plants was studied in pot culture under low temperature stress. The tomato plants were placed in a sand and
soil mixture at 25°C for 6weeks, and then subjected to 8°C for 1week. AM symbiosis decreased malondialdehyde (MDA) content
in leaves. The contents of photosynthetic pigments, sugars and soluble protein in leaves were higher, but leaf proline content
was lower in mycorrhizal than non-mycorrhizal plants. AM colonization increased the activities of superoxide dismutase (SOD),
catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) in leaves. The results indicate that the AM fungus is capable
of alleviating the damage caused by low temperature stress on tomato plants by reducing membrane lipid peroxidation and increasing
the photosynthetic pigments, accumulation of osmotic adjustment compounds, and antioxidant enzyme activity. Consequently,
arbuscular mycorrhiza formation highly enhanced the cold tolerance of tomato plant, which increased host biomass and promoted
plant growth.
KeywordsAntioxidant enzymes–Arbuscular mycorrhizal fungi–Chlorophyll–Low temperature stress–Membrane lipid peroxidation–Osmotic adjustment–Tomato
The movement of water through mycorrhizal fungal tissues and between the fungus and roots is little understood. It has been demonstrated that arbuscular mycorrhizal (AM) symbiosis regulates root hydraulic properties, including root hydraulic conductivity. However, it is not clear whether this effect is due to a regulation of root aquaporins (cell-to-cell pathway) or to enhanced apoplastic water flow. Here we measured the relative contributions of the apoplastic versus the cell-to-cell pathway for water movement in roots of AM and non-AM plants.
We used a combination of two experiments using the apoplastic tracer dye light green SF yellowish and sodium azide as an inhibitor of aquaporin activity. Plant water and physiological status, root hydraulic conductivity and apoplastic water flow were measured.
Roots of AM plants enhanced significantly relative apoplastic water flow as compared with non-AM plants and this increase was evident under both well-watered and drought stress conditions. The presence of the AM fungus in the roots of the host plants was able to modulate the switching between apoplastic and cell-to-cell water transport pathways.
The ability of AM plants to switch between water transport pathways could allow a higher flexibility in the response of these plants to water shortage according to the demand from the shoot.
Jasmonic acid (JA) and arbuscular mycorrhizal (AM) symbioses are known to protect plants against abiotic and biotic stresses, but are also involved in the regulation of root hydraulic conductance (L). The objective of this experiment was to elucidate the role of JA in the water relations and hormonal regulation of AM plants under drought by using tomato plants defective in the synthesis of JA (def-1). Our results showed that JA is involved in the uptake and transport of water through its effect on both physiological parameters (stomatal conductance and L), and molecular parameters, mainly by controlling the expression and abundance of aquaporins. Concretely, we observed that def-1 plants increased the expression of seven plant aquaporins genes under well-watered conditions in the absence of AM fungus, which partly explain the increment of L by this mutation under well-watered conditions. Otherwise, the effects of the AM symbiosis on plants were modified by the def-1 mutation, being disturbed the expression of some aquaporins and plant hormone concentration. On the other hand, MeSA content was raised in non-mycorrhizal def-1 plants suggesting that MeSA and JA can act together in the regulation of L. In complementary experiment, it was found that exogenous MeSA increased L, confirming our hypothesis. Likewise, we confirmed that JA, ABA and SA are hormones involved in plant mechanisms to cope with stressful situations, being its concentration controlled by the AM symbiosis. In conclusion, under well-watered conditions, def-1 mutation mimics the effects of AM symbiosis, but under drought conditions def-1 mutation changed the effects of the AM symbiosis on plants.
At a world scale, tomato is an important horticultural crop, but its productivity is highly reduced by drought stress. Combining the application of beneficial microbial inoculants with breeding and grafting techniques may be key to cope with reduced tomato yield under drought. This study aimed to investigate the growth responses and physiological mechanisms involved in the performance under drought stress of four tomato recombinant inbred lines (RIL) after inoculation with the arbuscular mycorrhizal (AM) fungus Rhizophagus irregularis and the plant growth promoting rhizobacteria (PGPR) Variovorax paradoxus 5C-2. Results showed a variation in the efficiency of the different tomato RILs under drought stress and a differential effect of the microbial inoculants, depending on the RIL involved. The inoculants affected plant parameters such as net photosynthetic capacity, oxidative damage to lipids, osmolyte accumulation, root hydraulic conductivity or aquaporin abundance and phosphorylation status. RIL66 was the one obtaining maximum benefit from the microbial inoculants under drought stress conditions, due likely to improved CO2-fixation capacity and root hydraulic conductivity. We propose that RIL66 could be selected as a good plant material to be used as rootstock to improve tomato growth and productivity under water limiting conditions. Since RIL66 is highly responsive to microbial inoculants, this grafting strategy should be combined with inoculation of R. irregularis and V. paradoxus in order to improve plant yield under conditions of drought stress.
Cyclamen (Cyclamen persicum) is one of the most popular ornamental pot-plants that is intolerant to heat stress and susceptible to diseases. In this study, influence of arbuscular mycorrhizal fungi (AMF); Glomus mosseae (Gm), Gl. Fasciculatum (Gf) ) symbiosis on tolerance to anthracnose caused by Colletotrichum gloeosporioides (Cg) under heat stress condition and the changes in antioxidative ability were investigated using three cyclamen cultivars (‘Eve’, ‘IPMSP9’ and ‘MIC3’). During the production period, temperature of greenhouse and pot soil was recorded and the highest temperature was around 40C. Higher biomass under heat stress was observed for Gm added to the media in ‘IPMSP9’ and ‘MIC3’. Disease incidence and severity of symptoms in non-AMF plots were the highest in ‘IPMSP9’ and lowest in ‘MIC3’. In AMF plots, disease incidence and severity of symptoms were lower than non-AMF plots among all the cultivars, regardless of the AMF species. As for antioxidative ability, superoxide dismutase (SOD) activity and diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity in shoots and roots showed higher levels in some of the AMF plots after Cg inoculation. Thus, the findings indicate that AMF association has the ability to promote the growth of cyclamen under heat stress condition and could suppress anthracnose in cyclamen production with Gm being most for this purpose. In this case, antioxidative abilities increased under heat stress and pathogen-stressed conditions, so that the tolerance would be associated with such factors.
The formation of an arbuscular mycorrhizal (AM) symbiosis is initiated by the bidirectional exchange of diffusible molecules. While strigolactone hormones, secreted from plant roots, stimulate hyphal branching and fungal metabolism, fungal short-chain chitin oligomers as well as sulfated and nonsulfated lipochitooligosaccharides (s/nsMyc-LCOs) elicit pre-symbiosis responses in the host. Fungal LCO signals are structurally related to rhizobial Nod-factor LCOs. Genome-wide expression studies demonstrated that defined sets of genes were induced by Nod-, sMyc- and nsMyc-LCOs, indicating LCO-specific perception in the pre-symbiosis phase. During hyphopodium formation and the subsequent root colonization, cross-talk between plant roots and AM fungi also involves phytohormones. Notably, gibberellins control arbuscule formation via DELLA proteins, which themselves serve as positive regulators of arbuscule formation. The establishment of arbuscules is accompanied by a substantial transcriptional and post-transcriptional reprogramming of host roots, ultimately defining the unique protein composition of arbuscule-containing cells. Based on cellular expression profiles, key checkpoints of AM development as well as candidate genes encoding transcriptional regulators and regulatory microRNAs were identified. Detailed functional analyses of promoters specified short motifs sufficient for cell-autonomous gene regulation in cells harboring arbuscules, and suggested simultaneous, multi-level regulation of the mycorrhizal phosphate uptake pathway by integrating AM symbiosis and phosphate starvation response signaling.
Stomata regulate rates of carbon assimilation and water loss. Arbuscular mycorrhizal (AM) symbioses often modify stomatal behavior and therefore play pivotal roles in plant productivity. The size of the AM effect on stomatal conductance to water vapor (g s ) has varied widely, has not always been apparent, and is unpredictable. We conducted a meta-analysis of 460 studies to determine the size of the AM effect under ample watering and drought and to examine how experimental conditions have influenced the AM effect. Across all host and symbiont combinations under all soil moisture conditions, AM plants have shown 24 % higher g s than nonmycorrhizal (NM) controls. The promotion of g s has been over twice as great during moderate drought than under amply watered conditions. The AM influence on g s has been even more pronounced under severe drought, with over four times the promotion observed with ample water. Members of the Claroideoglomeraceae, Glomeraceae, and other AM families stimulated g s by about the same average amount. Colonization by native AM fungi has produced the largest promotion. Among single-AM symbionts, Glomus deserticola, Claroideoglomus etunicatum, and Funneliformis mosseae have had the largest average effects on g s across studies. Dicotyledonous hosts, especially legumes, have been slightly more responsive to AM symbiosis than monocotyledonous hosts, and C3 plants have shown over twice the AM-induced promotion of C4 plants. The extent of root colonization is important, with heavily colonized plants showing ×10 the g s promotion of lightly colonized plants. AM promotion of g s has been larger in growth chambers and in the field than in greenhouse studies, almost ×3 as large when plants were grown under high light than low light, and ×2.5 as large in purely mineral soils than in soils having an organic component. When AM plants have been compared with NM controls given NM pot culture, they have shown only half the promotion of g s as NM plants not given anything at inoculation to control for associated soil organisms. The AM effect has been much greater when AM plants were larger or had more phosphorus than NM controls. These findings should assist in further investigations of predictions and mechanisms of the AM influence on host g s .
The role of jasmonic acid in the induction of stomatal closure is well known. However, its role in regulating root hydraulic conductivity (L) has not yet been explored. The objectives of the present research were to evaluate how JA regulates L and how calcium and abscisic acid (ABA) could be involved in such regulation. We found that exogenous methyl jasmonate (MeJA) increased L of Phaseolus vulgaris, Solanum lycopersicum and Arabidopsis thaliana roots. Tomato plants defective in JA biosynthesis had lower values of L than wt plants, and that L was restored by addition of MeJA. The increase of L by MeJA was accompanied by an increase of the phosphorylation state of the aquaporin PIP2. We observed that MeJA addition increased the concentration of cytosolic calcium and that calcium channel blockers inhibited the rise of L caused by MeJA. Treatment with fluoridone, an inhibitor of ABA biosynthesis, partially inhibited the increase of L caused by MeJA, and tomato plants defective in ABA biosynthesis increased their L after application of MeJA. It is concluded that JA enhances L and that this enhancement is linked to calcium and ABA dependent and independent signalling pathways.
Expression of the tomato gene encoding 13-lipoxygenase,TomloxD, is stimulated by wounding, pathogen infection, jasmonate, and systemin, but its role during growth and development of tomato (Lycopersicon Spp.) remains unclear. To assess the physiological role of TomloxD, we produced transgenic tomato plants with greatly increased TomloxD content using sense constructs under the control of the CaMV 35S promoter. Overexpression of TomloxD in transgenic tomatoes led to a marked increase in the levels of lipoxygenase activity and content of endogenous jasmonic acid (JA), which suggested that TomloxD can use α-linolenic acid as a substrate to produce (13S)-hydroperoxyoctadecatrienoic acid (13-HPOT); the 13-HPOT produced appears to be metabolized further to synthesize JA. Real-time RT-PCR revealed that the expression levels of defense genes LeHSP90, LePR1, LePR6 and LeZAT in the transformants were higher than those in non-transformed plants. Assay for resistance to pathogenic fungus and high temperature stresses suggested that transgenic plants harboring TomloxD were more tolerant to Cladosporium fulvum and high temperature stress than non-transformed tomato plants. The data presented here indicate clearly that TomloxD is involved in endogenous JA synthesis and tolerance to biotic and abiotic stress. The tomloxD gene has potential applications in engineering cropping plants that are resistant to biotic and/or abiotic stress factors.
Maize (Zea mays L.) was grown in fertilized calcareous soil in pots which were separated by 30 μm nylon nets into three compartments, the central one for root growth and the two outer ones for hyphal growth. The size of each compartment was 40 × 25 × 3 cm. The treatments comprised of sterilized soil, either inoculated with rhizosphere microorganisms (other than VA mycorrhizal fungi), with rhizosphere microorganisms together with a VA mycorrhizal fungus [Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe] or remained non-inoculated (sterile control). As inoculum for rhizosphere microorganisms the roots with adhering rhizosphere soil of non-mycorrhizal maize plants was used.
Compared to the non-inoculated (sterile) control, inoculation with rhizosphere microorganisms did not affect shoot dry weight and morphology, but increased total root length (17 %) and root length per unit root dry weight (35%). The additional inoculation with VA mycorrhizal fungi had no influence on the shoot dry weight but increased area and dry weight of the leaf blades by about 30% and the ratio leaf blade:leaf sheath + stem (w/w) by 41 %. The most profound effect of VA mycorrhizal fungi inoculation was on root growth and morphology. Compared to the non-inoculated control, root dry weight was decreased by 16%, root length by 31 % and root hair density and length by 41 and 43 %, respectively.
In mycorrhizal plants the transpiration rates per plant were about 30 % higher than in the other treatments and this is attributed to the larger leaf area. Water uptake rate per unit root length and per unit time was about twice as high in mycorrhizal plants. For several reasons a substantial hyphal water transport seems unlikely. The results stress the necessity of detailed studies on root morphology for interpretation of effects of mycorrhizal fungi on mineral nutrient uptake and water relations in plants.
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The ability of several species of vesicular–arbuscular (VA) mycorrhizal fungi to form hyphae in soil was compared in two glasshouse experiments. We measured the length of hyphae in soil and related this to the length of infected root. Species of VA mycorrhizal fungi differed in the length of external hyphae produced per cm of infected root. Glomus fasciculatum (Thaxter sensu Gerd.) Gerd. and Trappe produced less external hyphae per cm infected root than did Gigaspora calospora (Nicol. and Gerd.) Gerd. at all harvest times and when inoculum was either placed in a band below the seed or mixed throughout the soil. Glomus tenue (Greenall) Hall and Acaulospora laevis Gerd. and Trappe both produced similar lengths of external hyphae per cm infected root to that formed by G. calospora .
Differences among isolates of VA mycorrhizal fungi in the distribution of hyphae in soil may be as important as differences in the length of external hyphae when selecting fungi that are effective at increasing nutrient uptake.
Cotton, Gossypium hirsutum L., was grown in the greenhouse in sand-nutrient culture at five phosphorus (P) concentrations, and root systems were examined after 10 and 20 days. Extension rates of primary laterals and numbers of secondary laterals increased with increasing P. Cotton was grown for 6 weeks in environment cabinets in soils of three P concentrations with and without mycorrhizas. Increased P and mycorrhizas both stimulated plant growth (f. wt shoot d. wt), but however specific root length (cm root g' root f. wt) of mycorrhizal plants was reduced.
The two most commonly used methods to analyze data from real-time, quantitative PCR experiments are absolute quantification and relative quantification. Absolute quantification determines the input copy number, usually by relating the PCR signal to a standard curve. Relative quantification relates the PCR signal of the target transcript in a treatment group to that of another sample such as an untreated control. The 2(-DeltaDeltaCr) method is a convenient way to analyze the relative changes in gene expression from real-time quantitative PCR experiments. The purpose of this report is to present the derivation, assumptions, and applications of the 2(-DeltaDeltaCr) method. In addition, we present the derivation and applications of two variations of the 2(-DeltaDeltaCr) method that may be useful in the analysis of real-time, quantitative PCR data. (C) 2001 Elsevier science.
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Assessment of infection is an essential part of many studies involving VA mycorrhiza. A summary is given of the range of techniques that have been used. We calculated the standard error of four methods of assessment based on observations of stained root samples either randomly arranged in a petri dish or mounted on microscope slides. The methods are based on presence or absence of infection at root/grid intersect points, on a visual estimate of percentage cortex occupied by fungus or on estimates of length, or presence or absence of infection in root pieces mounted on slides. The number of replicate observations required for a given standard error % infection can be read from the curves provided. The advantages of the different methods of assessment are discussed and reasons given why they all probably overestimate the true values.
The paper is addressed to soil scientists who use Time-Domain Reflectometry (TDR) technology to measure soil moisture. The practical aspects of the measurement calibration are discussed, and an empirical approach to establishing the existence of a universal calibration function is presented.
Samples of 11 mineral soil horizons and seven organic soil horizons with different chemical and physical properties (including magnetic properties) were selected with the aim of determining their dielectric constant-volumetric water content relationship as calibration functions for TDR soil moisture measurements. These samples were supplemented by other, soil-like, capillary-porous reference materials (montmorillonite, glass beads, washed sand and a sand from a C horizon).
The study showed that a unique calibration function for mineral soils and another distinct calibration function for organic soils can be established.
• Species of arbuscular mycorrhizal fungi (AMF) differ markedly in their improvement of plant nutrition and health. However, it is not yet possible to relate the diversity of an AMF community to its functional properties due to the lack of information on the functional diversity at each taxonomic level. This study investigates the inter- and intraspecific functional diversity of four Glomus species in relation to a phylogenetic analysis of large ribosomal subunit (LSU) sequences.• Growth and P nutrition of cucumber (Cucumis sativus) associated with 24 different isolates of AMF were measured in a two-compartment system with a 33P-labelled root-free soil compartment.• Intraspecific differences were found in plant growth response and the extension of the fungal mycelium into the root-free soil patch whereas length-specific P uptake of the hyphae remained rather constant within each AMF species. Hence, the length-specific P uptake differed according to species, whereas lower phylogenetic levels were required to match functional characteristics such as fungal growth pattern and plant growth promotion.• The large intraspecific diversity observed for mycelium growth and improvement of P uptake means that AMF communities of low species diversity may still contain considerable functional heterogeneity.
Summary • The widespread occurrence of anastomoses and nuclear migration in intact extraradical arbuscular mycorrhizal (AM) networks is reported here. • Visualization and quantification of intact extramatrical hyphae spreading from colonized roots into the surrounding environment was obtained by using a two-dimensional experimental model system. • After 7 d the length of extraradical mycelium in the AM symbiont Glomus mosseae ranged from 5169 mm in Thymus vulgaris to 7096 mm in Prunus cerasifera and 7471 mm in Allium porrum, corresponding to 10, 16 and 40 mm mm−1 root length, respectively. In mycelium spreading from colonized roots of P. cerasifera and T. vulgaris, contacts leading to hyphal fusion were 64% and 78%, with 0.46 and 0.51 anastomoses mm−1 of hypha, respectively. Histochemical localization of succinate dehydrogenase activity in hyphal bridges demonstrated protoplasmic continuity, while the detection of nuclei in the hyphal bridges confirmed the viability of anastomosed hyphae. • The ability of AM extraradical mycelium to form anastomosis and to exchange nuclei suggests that, beyond the nutritional flow, an information flow might also be active in the network.
Imaging of chlorophyll a fluorescence from leaves has enabled the spatial resolution of the fluorescence parameter, F/Fm-;. Although this parameter provides a reliable estimate of photosynthetic efficiency under most conditions, the extent to which this efficiency is defined by (i) competition with other energy-dissipating processes operating at photosystem II and (ii) by processes on the reducing side of photosystem II, such as carbon assimilation, requires the use of additional parameters. Of particular value are qP, which quantifies the photochemical capacity of photosystem II, and Fv-;/Fm-;, which quantifies the extent to which photochemistry at photosystem II is limited by competition with thermal decay processes. Imaging of both qP and Fv-;/Fm-; requires measurement of Fo-; (the minimum fluorescence yield in the light-adapted state), which cannot be imaged with existing systems. In this paper, a method is described which estimates Fo-; through a simple equation involving the minimum fluorescence yield in the dark-adapted state (Fo), the maximum fluorescence yield in the dark-adapted state (Fm), and the maximum fluorescence yield in the light-adapted state (Fm-;). This method is tested here, through comparison of measured and calculated values of Fo-;. An example of the application of this method to analysis of photosynthetic performance in leaves, from images of chlorophyll a fluorescence, is also presented.
Vesicular-arbuscular mycorrhizal fungi can affect the water balance of both amply watered and droughted host plants. This
review summarizes these effects and possible causal mechanisms. Also discussed are host drought resistance and the influence
of soil drying on the fungi.
Plant microRNAs have a vital role in various abiotic stress responses by regulating gene expression. Heat stress is one of the most severe abiotic stresses, and affects plant growth and development, even leading to death. To identify heat-responsive miRNAs at the genome-wide level in Populus, Solexa sequencing was employed to sequence two libraries from Populus tomentosa, treated and untreated by heat stress. Sequence analysis identified 134 conserved miRNAs belonging to 30 miRNA families, and 16 novel miRNAs belonging to 14 families. Among these miRNAs, 52 miRNAs from 15 families were responsive to heat stress and most of them were down-regulated. qRT-PCR analysis confirmed that the conserved and novel miRNAs were expressed in P. tomentosa, and revealed similar expression trends to the Solexa sequencing results obtained under heat stress. One hundred and nine targets of the novel miRNAs were predicted. This study opens up a new avenue for understanding the regulatory mechanisms of miRNAs involvement in the heat stress response of trees.
We report the effect of heat, drought and combined stress on the expression of a group of genes that are up-regulated under these conditions in durum wheat (Triticum turgidum subsp. durum) plants. Modulation of gene expression was studied by cDNA-AFLP performed on RNAs extracted from flag leaves. By this approach, we identified several novel durum wheat genes whose expression is modulated under different stress conditions. We focused on a group of hitherto undescribed up-regulated genes in durum wheat, among these, 7 are up-regulated by heat, 8 by drought stress, 15 by combined heat and drought stress, 4 are up-regulated by both heat and combined stress, and 3 by both drought and combined stress. The functional characterization of these genes will provide new data that could help the developing of strategies aimed at improving durum wheat tolerance to field stress.
Most assays for superoxide dismutase depend upon competition between the enzyme and some indicating scavenger for O2−. We have investigated the effects of experimental variables on assays based upon the use of either ferricytochrome c or nitro blue tetrazolium. Our results should help investigators to avoid the numerous potential pitfalls which necessarily surround these assay methods.