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Phytochromes are key regulators of abiotic stress responses in tomato
Abstract
Phytochromes are the best characterized and most frequently studied plant photoreceptors. A plethora of studies have revealed important roles for phytochromes in plant development, and more recently, evidence indicates that these photoreceptors also modulate responses to a multitude of abiotic and biotic stresses. Thus, the present work aimed to investigate whether tomato phytochromes phyA, phyB1 and phyB2 are involved with responses to low water potential (polyethylene glycol 6000 at Ψw of −0.3 MPa), high salinity (100 mM NaCl), cadmium contamination (65 mM CdCl2), high temperature (42 °C for six hours during three days) and ultraviolet B radiation (UV-B − 280–320 nm for eight hours during three days) stresses. For this purpose, seedlings of tomato mutants impacted by phytochrome A (fri), phytochrome B1 (tri) and phytochrome B2 (phyB2) were subjected to abiotic stresses and evaluated for their growth, pigment and osmoprotectant accumulation and lipid peroxidation. Under the conditions of this study, the results did not shown large variations of phyA mutant when compared to the wild genotype. However, the tomato phytochromes B1 and B2 mainly act as negative regulators of growth, pigment maintenance and osmoprotectant accumulation during responses to the different abiotic stresses.
... Thus, it is not surprising that phys were previously described to regulate responses to diverse abiotic and biotic stresses (Carvalho, Campos, & Azevedo, 2011), such as salt stress (Indorf, Cordero, Neuhaus, & Rodríguez-Franco, 2007), drought stress (Kraepiel et al., 1994), low and high-temperature stress (Williams, Pellett, & Klein, 1972;Foreman et al., 2011) and high light (Wellmann, Schneider-Zeibert, & Beggs, 1984). Highlighting the phy type B family shows some similar responses among species and many research groups have targeted their efforts to understand phyB-modulated stress responses, because such responses could be altered in the same species, e.g., phyB1 and phyB2 gene duplication controlling different stress acclimation responses (Arico et al., 2019;Gavassi, Monteiro, Campos, Melo, & Carvalho, 2017;Kreslavski et al., 2015;Kwon et al., 2018;Yoo et al., 2017). Therefore, in this review, we summarised the phyB-modulated stress responses to elucidate future research for plant breeding. ...
... Temperature stress regulated by phyB is not limited to lower temperatures and also extends to heat stress. Gavassi et al. (2017) reported longer shoot length in phyB1 mutants compared to the WT after heat stress exposure. This mutant also presented lower MDA content (a product of lipid peroxidation), suggesting a presumptive phyB role in alleviating the deleterious effect of ROS. ...
... In fact, the evidence that UV-tolerance is negatively regulated by phyB has also been reported in tomato, but not on a molecular level. For example, phyB1 and phyB2 mutants were more tolerant to UV-B exposure and showed higher shoot and root dry weight and shoot and root length, as well as a decreased MDA content (Gavassi et al., 2017). However, these insights are preliminary and more studies are required to elucidate the crosstalk mechanisms between phyB and URV8, considering that phyB1 and phyB2 mutants also exhibited lower anthocyanin content and anthocyanin accumulation is a UV-tolerance characteristic, contradicting the positive role of phyB. ...
Photoreceptors are primarily known as key photomorphogenic modulators of various physiological events during plant development. Although there are different groups of photoreceptors, the phytochrome B (phyB) family mediates developmental responses in a wide range of plant species, from seed germination to flowering. In addition, these molecules also regulate abiotic stress acclimation responses, such as salinity, drought, low/high temperature, high light and heavy metals. The signalling pathways mediated by phyB could enhance plant resistance to environmental stresses, as phyB photoreceptors reduce leaf transpiration, increase the antioxidant system, enhance protective pigments and increase the expression of genes related to plant stress acclimation. Thus, the elucidation of positive or negative roles for phyB in these stress tolerance characteristics would provide essential knowledge for genetic engineering, improving plant growth and development in critical environments. In this review, we cover the main findings on how the phyB family works to modulate abiotic stress by discussing biochemical and molecular aspects of the underlying mechanisms operated by these photoreceptors.
... The system of phytochrome and cryptochrome photoreceptors is involved in the development of chloroplasts from etioplasts, the formation of chlorophyll, the functioning of stomata, and the activation of the adaptive mechanisms of the photosynthetic apparatus under unfavourable environmental conditions. For example, phytochromes and cryptochromes play an important role in the regulation of photosynthetic responses to elevated temperatures, drought, UV radiation and high-irradiation light (HIL) [3][4][5][6]. It is clear that environmental conditions can greatly affect plant productivity; therefore, research on photoreceptor regulation of photosynthetic stress responses has become the focus of many studies [3][4][5][6]. ...
... For example, phytochromes and cryptochromes play an important role in the regulation of photosynthetic responses to elevated temperatures, drought, UV radiation and high-irradiation light (HIL) [3][4][5][6]. It is clear that environmental conditions can greatly affect plant productivity; therefore, research on photoreceptor regulation of photosynthetic stress responses has become the focus of many studies [3][4][5][6]. ...
... As a consequence of the misregulation of these genes in A. thaliana, this mutant displayed a highly irradiancesensitive phenotype with significant photoinactivation of PSII, indicated by a reduced maximal fluorescence ratio. Impaired photoreceptors often lead not only to a deterioration of light and temperature signalling but also to a decrease in the stress resistance of the photosynthetic apparatus [4,5,14,17], in particular resistance to HIL stress [14]. On the other hand, in Solanum tuberosum, a superproducer of PHYB, and in A. thaliana, a superproducer of PHYA, an increase in the stress resistance of the photosynthetic apparatus to HIL was found [6,18]. ...
The effects of high-intensity light (HIL) on the activity of photosystem II (PSII) and photosynthesis in wild-type (WT) and single (phyB2, phyB1, phyA and cry1), double (phyB1B2, phyAB2 and phyAB1) and triple (phyAB1B2 and cry1phyAB1) mutants of Solanum lycopersicum were studied. In addition, changes in the activity of the antioxidant enzymes ascorbate peroxidase, glutathione reductase and guaiacol peroxidase as well as the photosynthetic pigment and anthocyanin contents in the leaves of phyB2 and cry1phAB1 mutants under HIL were examined. When plants were irradiated with HIL (2 h), the PSII resistance of the cry1phyAB1 mutant was the lowest, while the resistance of WT and single mutants excluding cry1 was the highest. The effect of HIL on PSII activity in all double mutants and the phyAB1B2 mutant was intermediate between the effects on the WT and the cry1phyAB1 mutant. The intensity of oxidative processes in the cry1phyAB1 mutant was higher than that in WT and phyB2, but in cry1phyAB1, the activity of antioxidant enzymes and the anthocyanin content were lower. The low resistance of the cry1phyAB1 mutant to HIL may be due to the low antioxidant activity of key enzymes and the reduced pigment content, which are consistent with the reduced expression of CHS and sAPX genes in the cry1phyAB1 mutant.
... Besides regulating photomorphogenesis, phytochromes also play an essential role in adapting to different sources of abiotic plant stress [2,[10][11][12][13][14][15]. The tomato phytochromes B1 and B2 mainly act as negative regulators of growth, pigment maintenance and osmoprotectant accumulation during responses to the different abiotic stresses. ...
... The tomato phytochromes B1 and B2 mainly act as negative regulators of growth, pigment maintenance and osmoprotectant accumulation during responses to the different abiotic stresses. However, phyA mutant showed similar growth variations under different abiotic stresses when compared to the wild genotype [10]. Indorf et al. [12] found that phyA, phyB and phyAphyB Arabidopsis thaliana mutants showed a reduced expression of salt tolerance genes, and the expression of these genes were also altered by exposure to different light conditions, suggesting that the phytochrome family contributes to salinity stress responses. ...
... Phytochromes are involved in plant tolerate to biotic and abiotic stressors [10,26,29,42]. Tomato contains five phytochrome genes, named PHYA, PHYB1, PHYB2, PHYE and PHYF [43]. ...
Background
Red (R) and far-red (FR) light distinctly influence phytochrome-mediated initial tomato growth and development, and more recent evidence indicates that these spectra also modulate responses to a multitude of abiotic and biotic stresses. This research investigated whether different R: FR values affect tomato growth response and salinity tolerance. Tomato seedlings were exposed to different R: FR conditions (7.4, 1.2 and 0.8) under salinity stress (100 mM NaCl), and evaluated for their growth, biochemical changes, active reactive oxygen species (ROS) and ROS scavenging enzymes, pigments, rate of photosynthesis, and chlorophyll fluorescence.
Results
The results showed that under conditions of salinity, tomato seedlings subjected to a lower R: FR value (0.8) significantly increased both their growth, proline content, chlorophyll content and net photosynthesis rate (Pn), while they decreased malondialdehyde (MDA) compared to the higher R: FR value (7.4). Under conditions of salinity, the lower R: FR value caused a decrease in both the superoxide anion (O2•−) and in hydrogen peroxide (H2O2) generation, an increase in the activities of superoxidase dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7) and catalase (CAT, EC 1.11.1.7). Tomato seedlings grown under the lower R: FR value and conditions of salinity showed a higher actual quantum yield of photosynthesis (ΦPSII), electron transport rate (ETR), and photochemical quenching (qP) than those exposed to a higher R: FR, indicating overall healthier growth. However, the salinity tolerance induced at the lower R: FR condition disappeared in the tomato phyB1 mutant.
Conlusion
These results suggest that growing tomato with a lower R: FR value could improve seedlings’ salinity tolerance, and phytochrome B1 play an very important role in this process. Therefore, different qualities of light can be used to efficiently develop abiotic stress tolerance in tomato cultivation.
... The phytochrome (Phy) system regulates a wide range of physiological processes from seed germination to flowering and fruiting [2,4,5]. The response of the plant metabolism to the action of various damaging factors, such as unfavorable temperatures, salinity, drought, UV radiation, is also under control of the phytochrome system [5][6][7][8][9][10][11][12][13][14]. It is assumed that the regulatory effects of phytochromes are primarily related to their effects on the activity of enzymes that regulate the metabolic processes, in particular the biosynthesis of low-molecular weight antioxidants and photosynthetic pigments, and the level of expression of phytochrome-regulated genes involved primarily in cellular signaling [11,12,15,16]. ...
... A detailed description of the relationship between anthocyanin accumulation and Pfr content is given in [64]. There are also data on the dependence of anthocyanin accumulation on the overall content of phytochromes [14]. ...
... Regarding the latter case, literature actually considers mainly the photoprotective action of RL as described by points 1) and 2), assuming that activating RL acts before UV irradiation [71]. Possible combined communication networks involving the overall irradiation, Pfr and the stressors are not yet analyzed in more detail [3,5,14]. ...
This review describes the phytochrome system in higher plants and cyanobacteria and its role in regulation of photosynthetic processes and stress protection of the photosynthetic apparatus. A relationship between the content of the different phytochromes, the changes in the ratios of the physiologically active forms of phytochromes to their total pool and the resulting influence on photosynthetic processes is reviewed. The role of the phytochromes in the regulation of the expression of genes encoding key photosynthetic proteins, antioxidant enzymes and other components involved in stress signaling is elucidated.
... Original Paper Plant, Soil and Environment, 69, 2023 (4): 152-160 https://doi.org/10.17221/415/2022-PSE an alternative route toward developing droughttolerant potatoes (Gavassi et al. 2017). Chlorophylls a and b content in potato leaves affected by DS and WS. ...
... Phytochromes are the best-characterised and most frequently studied plant photoreceptors, which modulate levels of pigments in leaves. Between them, the most important pigments are chlorophylls and carotenoids (Gavassi et al. 2017). ...
... Thus, we did not indicate an increase in resistance of the PA to short-term heating. In contrast to these data, the study of [11] showed that, with a longer exposure to stress (3 days), the degree of oxidative stress noticeably increased in tomato WT, but in PHYB1-(tri) and PHYB2-deficient (phyB2) mutants, stress was developed to a lesser extent. The authors suggested that mutation in PHYB genes triggered antioxidant responses to reduce the effects of ROS; however, the mechanism of this phenomenon is not known. ...
... The content of Chl a and b and carotenoids was determined in 96% ethanol extracts [39] by analyzing the absorption spectra of the samples on a Genesys 10 UV spectrophotometer (Thermo Fisher Scientific, Waltham, MA, USA) at λ max of 470, 649, and 665 nm. The content of UVAPs was determined using fully developed, healthy-looking upper leaves (8)(9)(10)(11)(12), which were kept for 24 h in acid methanol (methanol/water/HCl, 78:20:2) at +4 • C [40]. The optical density of the samples was determined in the UV range (maximum at 327 nm) using a spectrophotometer (Genesys 10 UV, Thermo Fisher Scientific, Waltham, MA, USA). ...
The effects of heating (40 °C, 1 and 2 h) in dark and light conditions on the photosynthetic activity (photosynthesis rate and photosystem II activity), content of photosynthetic pigments, activity of antioxidant enzymes, content of thiobarbituric acid reactive substances (TBARs), and expression of a number of key genes of antioxidant enzymes and photosynthetic proteins were studied. It was shown that, in darkness, heating reduced CO2 gas exchange, photosystem II activity, and the content of photosynthetic pigments to a greater extent in the phyB mutant than in the wild type (WT). The content of TBARs increased only in the phyB mutant, which is apparently associated with a sharp increase in the total peroxidase activity in WT and its decrease in the phyB mutant, which is consistent with a noticeable decrease in photosynthetic activity and the content of photosynthetic pigments in the mutant. No differences were indicated in all heated samples under light. It is assumed that the resistance of the photosynthetic apparatus to a short-term elevated temperature depends on the content of PHYB active form and is probably determined by the effect of phytochrome on the content of low-molecular weight antioxidants and the activity of antioxidant enzymes.
... Phytochromes, which are the major photoreceptors in higher plants, play pivotal roles in the regulation of sensing the ratio of red (R) to far-red (FR) light (R:FR) (Schwenk et al., 2021). In addition to modulating photomorphogenesis, phytochromes are involved in responses to abiotic stresses, such as salinity, drought, low/high temperature, high light, and heavy metals (Devireddy et al., 2020;Gaion et al., 2018;Gavassi et al., 2017;Junior et al., 2021). Moreover, high far-red light can improve the photosynthetic capacity of soybean leaves under shade conditions (Yang et al., 2018), and a low R: FR ratio in Arabidopsis can increase the CBF gene expression to improve the plant freezing tolerance (Franklin and Whitelam, 2007). ...
... Red (R) and far-red (FR) light play a critical role in regulating plant growth and development during a plant's life cycle. The ratio of R:FR in plant canopy is a major environmental factor in the regulation of plant morphology, growth, development, and stress tolerance via triggering the response of phytochrome (Cao et al., 2018;Devireddy et al., 2020;Gavassi et al., 2017). Regardless of salt stress, the leaf area, plant height, and biomass of tomato seedlings under low R:FR indicated that low R:FR had a positive function in promoting plan growth. ...
The red light (R) to far-red light (FR) ratio (R:FR) regulates plant responses to salt stress, but the regulation mechanism is still unclear. In this study, tomato seedlings were grown under half-strength Hoagland solution with or without 150 mM NaCl at two different R:FR ratios (7.4 and 0.8). The photosynthetic capacity, antioxidant enzyme activities, and the phenotypes at chloroplast ultrastructure and whole plant levels were investigated. The results showed that low R:FR significantly alleviated the damage of tomato seedlings from salt stress. On day 4, 8, and 12 at low R:FR, the maximum photochemical quantum yields (Fv/Fm) of photosystem II (PSII) were increased by 4.53%, 3.89%, and 16.49%, respectively; the net photosynthetic rates (Pn) of leaves were increased by 16.21%, 90.81%, and 118.00%, respectively. Low R:FR enhanced the integrity and stability of the chloroplast structure of salinity-treated plants through maintaining the high activities of antioxidant enzymes and mitigated the degradation rate of photosynthetic pigments caused by reactive oxygen species (ROS) under salt stress. The photosynthesis, antioxidant enzyme-related gene expression, and transcriptome sequencing analysis of tomato seedlings under different treatments were also investigated. Low R:FR promoted the de novo synthesis of D1 protein via triggering psbA expression, and upregulated the transcripts of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) relative genes. Meanwhile, the transcriptome analysis confirmed the positive function of low R:FR on enhancing tomato salinity stress tolerance from the regulation of photosynthesis and ROS scavenging systems.
... Among the phytochromes, PHYA and PHYB play a key role, and their physicochemical properties are the most fully characterized [18,19]. PHYA and PHYB are involved in many responses of the PA during the development of oxidative stress caused by the effects of various environmental factors; an increase in the contents of PHYA and PHYB enhanced the resistance of the PA to oxidative stress, while a deficiency of these phytochromes decreased its resistance [14,[20][21][22][23][24][25]. Thus, the study of A. thaliana mutants deficient in PHYA and PHYB showed that these phytochromes are involved in plant responses to long-term [21] and short-term exposure to UV radiation [14,23] as well as the effects of HIL [25]. ...
... UV-B did not affect transpiration rate excluding WT (Table 1). Such effect can be Changes in PHYA, PHYB content and signalling play an important role in the gene expression of various proteins associated with photosynthesis and in the defense processes that develop in the PA under stress conditions such as high irradiance and UV-B [14,22]. Indeed, at any light exposure the level of the CAB1 gene in phyB mutant was lower than the level of the gene in phyA mutant and WT (Figs. 6 and 7). ...
The effects of high-intensity light (HIL, 4 and 24 h) and UV-B (1 h) on the net photosynthesis rate, activity of photosystem II (PSII), content of photosynthetic pigments, anthocyanin and UV-absorbing pigments as well as the expression of certain light-responsive genes (HY5,CAB1) chalcone synthase (CHS) and main antioxidants enzyme genes (APX1, GPX and GR) in the leaves of phyB and phyA mutant A. thaliana plants were studied. Both UV-B and 4 and 24 h HIL decreased the PSII maximum quantum yield (Fv/fm), PSII performance index (PIABS), photosynthesis and respiration rates in plants. Moreover, all stress treatments increased the dissipation of the absorbed energy (DI0/RC) as well as the flux of absorbed energy per RC (ABS/RC). The maximal changes in photosynthesis and chlorophyll fluorescence parameters were observed in the phyB mutant. The WT and the phyA mutant showed similar responses. In addition, the phyB mutant exhibited decreases in the expression of genes encoding enzyme CHS, the transcription factor HY5 and the antioxidant enzymes APX1 and GPX. One of the possible mechanisms protecting the photosynthetic apparatus from light excess or UV radiation is the elevated content of various pigments that can act as antioxidants or optical filters. We assume that the greater decrease in photosynthetic activity in the phyB mutant under HIL and UV-B conditions was due to the decreased content of carotenoids and UV-absorbing pigments in this mutant.
... Phytochromes have been shown to be involved in several photomorphogenic responses, for example, photocontrol of seed germination, plant architecture, biomass accumulation, stem elongation, leaf development, and flowering [35,37]. More recently, it has been well established that phytochromes play vital roles in number of different abiotic stresses such as water stress and are crucial part of signaling pathways in plants [5,38]. To establish the link between phytochromes and stress factors, numerous studies have employed phytochrome mutants to evaluate phytochrome-mediated responses in plants. ...
... The authors thus concluded that phyA and phyB serve antagonistic functions to cold response under FR. Further, FR activates phyA to induce ABA and JA signaling, which in turn triggers CBF pathway genes to positively regulate cold tolerance in tomato [38]. Another interesting report unveiled that the accumulation of anthocyanin in Arabidopsis is promoted by JA under FR and is dependent on phyA [41]. ...
Background: Phytochromes are plant photoreceptors that have long been associated with photomorphogenesis in
plants; however, more recently, their crucial role in the regulation of variety of abiotic stresses has been explored.
Chilling stress is one of the abiotic factors that severely affect growth, development, and productivity of crops. In
the present work, we have analyzed and compared physiological, biochemical, and molecular responses in two
contrasting phytochrome mutants of tomato, namely aurea (aur) and high pigment1 (hp1), along with wild-type
cultivar Micro-Tom (MT) under chilling stress. In tomato, aur is phytochrome-deficient mutant while hp1 is a
phytochrome-sensitive mutant. The genotype-specific physiological, biochemical, and molecular responses under
chilling stress in tomato mutants strongly validated phytochrome-mediated regulation of abiotic stress.
Results: Here, we demonstrate that phytochrome-sensitive mutant hp1 show improved performance compared to
phytochrome-deficient mutant aur and wild-type MT plants under chilling stress. Interestingly, we noticed
significant increase in several photosynthetic-related parameters in hp1 under chilling stress that include
photosynthetic rate, stomatal conductance, stomatal aperture, transpiration rate, chlorophyll a and carotenoids.
Whereas most parameters were negatively affected in aur and MT except a slight increase in carotenoids in MT
plants under chilling stress. Further, we found that PSII quantum efficiency (Fv/Fm), PSII operating efficiency (Fq′/Fm′),
and non-photochemical quenching (NPQ) were all positively regulated in hp1, which demonstrate enhanced
photosynthetic performance of hp1 under stress. On the other hand, Fv/Fm and Fq′/Fm′ were decreased significantly in
aur and wild-type plants. In addition, NPQ was not affected in MT but declined in aur mutant after chilling stress.
Noticeably, the transcript analysis show that PHY genes which were previously reported to act as molecular switches in
response to several abiotic stresses were mainly induced in hp1 and repressed in aur and MT in response to stress. Asexpected, we also found reduced levels of malondialdehyde (MDA), enhanced activities of antioxidant enzymes, and
higher accumulation of protecting osmolytes (soluble sugars, proline, glycine betaine) which further elaborate the
underlying tolerance mechanism of hp1 genotype under chilling stress.
Conclusion: Our findings clearly demonstrate that phytochrome-sensitive and phytochrome-deficient tomato mutants
respond differently under chilling stress thereby regulating physiological, biochemical, and molecular responses and
thus establish a strong link between phytochromes and their role in stress tolerance.
Keywords: Antioxidant enzymes, Chilling stress, Molecular response, Osmolytes, Phytochrome mutants aurea and high
pigment1, Tomato
... Plant photoreceptors are key mediators of environmental stress responses. Phytochromes have been the most characterized photoreceptors in terms of abiotic stress responses (Carvalho et al., 2011;D'Amico-Damião et al., 2015;Gavassi et al., 2017). However, the emerging role of crys is remarkable (D'Amico-Damião and , especially in the response to water deficit, one of the most critical abiotic stresses in plants (Lesk et al., 2016;González-Villagra et al., 2017;Sseremba et al., 2018). ...
... It is possible that other photoreceptors interact with cry1a during OS to modulate proline accumulation and that these molecules are activated by other wavelengths under WL. For example, strong candidates would be tomato phytochromes, as mutants defective in phya, phyb1 and phyb2 showed alterations in proline accumulation under water deficit (Gavassi et al., 2017). ...
The participation of plant cryptochromes in water deficit response mechanisms has been highlighted in several reports. However, the role of tomato (Solanum lycopersicum L.) cryptochrome 1a (cry1a) in the blue light fluence-dependent modulation of the water deficit response remains largely elusive. The tomato cry1a mutant and its wild-type counterpart were grown in water (no stress) or PEG6000 (osmotic stress) treatments under white light (60 μmol m⁻² s⁻¹) or from low to high blue light fluence (1, 5, 10, 15 and 25 μmol m⁻² s⁻¹). We first demonstrate that under nonstress conditions cry1a regulates seedling growth by mechanisms that involve pigmentation, lipid peroxidation and osmoprotectant accumulation in a blue light-dependent manner. In addition, we further highlighted under osmotic stress conditions that cry1a increased tomato growth by reduced malondialdehyde (MDA) and proline accumulation. Although blue light is an environmental signal that influences osmotic stress responses mediated by tomato cry1a, specific blue light fluence rates are required during these responses. Here, we show that CRY1a manipulation may be a potential biotechnological target to develop a drought-tolerant tomato variety. Nevertheless, the complete understanding of this phenomenon requires further investigation.
... Phytochromes have been shown to be involved in several photomorphogenic responses, for example, photocontrol of seed germination, plant architecture, biomass accumulation, stem elongation, leaf development, and flowering [35,37]. More recently, it has been well established that phytochromes play vital roles in number of different abiotic stresses such as water stress and are crucial part of signaling pathways in plants [5,38]. To establish the link between phytochromes and stress factors, numerous studies have employed phytochrome mutants to evaluate phytochrome-mediated responses in plants. ...
... The authors thus concluded that phyA and phyB serve antagonistic functions to cold response under FR. Further, FR activates phyA to induce ABA and JA signaling, which in turn triggers CBF pathway genes to positively regulate cold tolerance in tomato [38]. Another interesting report unveiled that the accumulation of anthocyanin in Arabidopsis is promoted by JA under FR and is dependent on phyA [41]. ...
Abstract
Background: Phytochromes are plant photoreceptors that have long been associated with photomorphogenesis in plants; however, more recently, their crucial role in the regulation of variety of abiotic stresses has been explored. Chilling stress is one of the abiotic factors that severely affect growth, development, and productivity of crops. In the present work, we have analyzed and compared physiological, biochemical, and molecular responses in two contrasting phytochrome mutants of tomato, namely aurea (aur) and high pigment1 (hp1), along with wild-type cultivar Micro-Tom (MT) under chilling stress. In tomato, aur is phytochrome-deficient mutant while hp1 is a phytochrome-sensitive mutant. The genotype-specific physiological, biochemical, and molecular responses under chilling stress in tomato mutants strongly validated phytochrome-mediated regulation of abiotic stress. Results: Here, we demonstrate that phytochrome-sensitive mutant hp1 show improved performance compared to phytochrome deficient mutant aur and wild-type MT plants under chilling stress. Interestingly, we noticed significant increase in several photosynthetic related parameters in hp1 under chilling stress that include photosynthetic rate, stomatal conductance, stomatal aperture, transpiration rate, chlorophyll a and carotenoids. Whereas most parameters were negatively affected in aur and MT except a slight increase in carotenoids in MT plants under chilling stress. Further, we found that PSII quantum efficiency (Fv/Fm), PSII operating efficiency (Fq′/Fm′), and non-photochemical quenching (NPQ) were all positively regulated in hp1, which demonstrate enhanced photosynthetic performance of hp1 under stress. On the other hand, Fv/Fm and Fq′/Fm′ were decreased significantly in aur and wild-type plants. In addition, NPQ was not affected in MT but declined in aur mutant after chilling stress. Noticeably, the transcript analysis show that PHY genes which were previously reported to act as molecular switches in response to several abiotic stresses were mainly induced in hp1 and repressed in aur and MT in response to stress. As expected, we also found reduced levels of malondialdehyde (MDA), enhanced activities of antioxidant enzymes, and higher accumulation of protecting osmolytes (soluble sugars, proline, glycine betaine) which further elaborate the underlying tolerance mechanism of hp1 genotype under chilling stress. Conclusion: Our findings clearly demonstrate that phytochrome-sensitive and phytochrome-deficient tomato mutants respond differently under chilling stress thereby regulating physiological, biochemical, and molecular responses and thus establish a strong link between phytochromes and their role in stress tolerance.
... Phytochromes have been shown to be involved in several photomorphogenic responses, for example, photocontrol of seed germination, plant architecture, biomass accumulation, stem elongation, leaf development, and flowering [35,37]. More recently, it has been well established that phytochromes play vital roles in number of different abiotic stresses such as water stress and are crucial part of signaling pathways in plants [5,38]. To establish the link between phytochromes and stress factors, numerous studies have employed phytochrome mutants to evaluate phytochrome-mediated responses in plants. ...
... The authors thus concluded that phyA and phyB serve antagonistic functions to cold response under FR. Further, FR activates phyA to induce ABA and JA signaling, which in turn triggers CBF pathway genes to positively regulate cold tolerance in tomato [38]. Another interesting report unveiled that the accumulation of anthocyanin in Arabidopsis is promoted by JA under FR and is dependent on phyA [41]. ...
Background
Phytochromes are plant photoreceptors that have long been associated with photomorphogenesis in plants; however, more recently, their crucial role in the regulation of variety of abiotic stresses has been explored. Chilling stress is one of the abiotic factors that severely affect growth, development, and productivity of crops. In the present work, we have analyzed and compared physiological, biochemical, and molecular responses in two contrasting phytochrome mutants of tomato, namely aurea ( aur ) and high pigment1 ( hp1 ), along with wild-type cultivar Micro-Tom (MT) under chilling stress. In tomato, aur is phytochrome-deficient mutant while hp1 is a phytochrome-sensitive mutant. The genotype-specific physiological, biochemical, and molecular responses under chilling stress in tomato mutants strongly validated phytochrome-mediated regulation of abiotic stress.
Results
Here, we demonstrate that phytochrome-sensitive mutant hp1 show improved performance compared to phytochrome-deficient mutant aur and wild-type MT plants under chilling stress. Interestingly, we noticed significant increase in several photosynthetic-related parameters in hp1 under chilling stress that include photosynthetic rate, stomatal conductance, stomatal aperture, transpiration rate, chlorophyll a and carotenoids. Whereas most parameters were negatively affected in aur and MT except a slight increase in carotenoids in MT plants under chilling stress. Further, we found that PSII quantum efficiency (Fv/Fm), PSII operating efficiency ( Fq ′/ Fm ′), and non-photochemical quenching (NPQ) were all positively regulated in hp1 , which demonstrate enhanced photosynthetic performance of hp1 under stress. On the other hand, Fv/Fm and Fq ′/ Fm ′ were decreased significantly in aur and wild-type plants. In addition, NPQ was not affected in MT but declined in aur mutant after chilling stress. Noticeably, the transcript analysis show that PHY genes which were previously reported to act as molecular switches in response to several abiotic stresses were mainly induced in hp1 and repressed in aur and MT in response to stress. As expected, we also found reduced levels of malondialdehyde (MDA), enhanced activities of antioxidant enzymes, and higher accumulation of protecting osmolytes (soluble sugars, proline, glycine betaine) which further elaborate the underlying tolerance mechanism of hp1 genotype under chilling stress.
Conclusion
Our findings clearly demonstrate that phytochrome-sensitive and phytochrome-deficient tomato mutants respond differently under chilling stress thereby regulating physiological, biochemical, and molecular responses and thus establish a strong link between phytochromes and their role in stress tolerance.
... Phytochromes are key regulators of plant responses under stress conditions (Kreslavski et al. 2009(Kreslavski et al. , 2018Gavassi et al. 2017), and their regulation depends on the RL/FRL ratio. We observed worse adaptation of lettuce plants grown in the experiment with the added FRL compared to the control without the addition of FRL (Fig. 4). ...
... In drought-tolerant plants, early flowering and rapid transpiration are indicators of evasive behaviour [70]. Phytochromes and PIFs play a crucial role in stress responses in plants at the physiological level, including changes to the stomatal aperture, growth regulation, ROS levels, alterations in osmoprotectants, and sensitivity to ABA [62], [71]], [72]. PIFs and PHYs may regulate stress-induced gene expression at the molecular level [61]. ...
Massive crop failures worldwide are caused by abiotic stress. In plants, adverse environmental conditions cause extensive damage to the overall physiology and agronomic yield at various levels. Phytochromes are photosensory phosphoproteins that absorb red (R)/far red (FR) light and play critical roles in different physiological and biochemical responses to light. Considering the role of phytochrome in essential plant developmental processes, genetically manipulating its expression offers a promising approach to crop improvement. Through modulated phytochrome-mediated signalling pathways, plants can become more resistant to environmental stresses by increasing photosynthetic efficiency, antioxidant activity, and expression of genes associated with stress resistance. Plant growth and development in adverse environments can be improved by understanding the roles of phytochromes in stress tolerance characteristics. A comprehensive overview of recent findings regarding the role of phytochromes in modulating abiotic stress by discussing biochemical and molecular aspects of these mechanisms of photoreceptors is offered in this review.
... Some researchers have shown that red laser radiation treatments on seeds can improve their tolerance to salinity, this mechanism is based on the fact that a part of the phytochrome family improves tolerance to salt stress in seeds and plants. (Gavassi et al. 2017;Yang et al. 2018;Cao et al. 2018). ...
This work discusses the laser irradiation effects on tomato seeds (Solanum lycopersicum L), regarding the initial plant development, salinity stress tolerance and harvest yield. The aim of this study was to find an optimal pre-sowing laser irradiation treatment to enhance tomato crop.A diode laser with wavelength of 660 nm and power 100 mW was used, 16 treatments were tested by 4 power densities (0.2, 0.4, 2 and 4 mW cm-2) applied during 4 exposure times (15, 30, 60, 120 s) and a control group without treatment. The study was divided into three stages,firstly it was selected an optimal laser treatment (04 mW cm-2, 30 s), in the second stage the optimal laser treatment was evaluated under salinity stress, and finally in the third stage the optimal laser treatment was evaluated on harvest yield. The optimal laser treatment, on the initial plant development enhanced germination by 10%, radicle growth by 19%, and hypocotyl growth by 13%, in comparison to the control. On seedlings under salinity stress, optimal laser treatment promote germination up to 20%, radicle growth up to 23%, and hypocotyl growth up to 12%.According to this study, saline stress inhibits PSII activity in tomato seedlings,whereas optimal laser treatment increased PSII activity around 71%. About greenhouse crop, optimal laser treatment improved mass produced by 26%. The present study shows a path for application ofpre-sowing red laser radiation treatments in tomato seeds to improve development, saline stress tolerance and final production of tomato crop.
... It is known that changes in the phytochrome system and its signaling components lead to rapid regulation of the expression of genes encoding photosynthetic proteins and antioxidant enzymes, which affect photosynthetic activity and the antioxidant status, changing the content of low-molecular weight antioxidants and antioxidant enzyme activity [7,8]. In addition, phytochrome-induced effects depend on the light quality in which plants grow [27]. ...
The effect of red (RL, 660 nm) and blue (BL, 450 nm) light on phy mutant tomato plants was studied. The rates of photosynthesis (Pn) and transpiration, the efficiency of the primary photochemical processes of photosynthesis, the contents of flavonoids and phenolic compounds, the low-molecular-weight antioxidant capacity (Trolox equivalent antioxidant capacity (TEAC)) of leaf extracts, and the expression of light-dependent genes were evaluated. Under RL, BL, and white fluorescent light (WFL), the Pn values decreased in the order: WT > phyb2 > phyaphyb2 > phyaphyb1phyb2, except for the Pn in phyb2 on BL. Phyb2 also had a larger number of stomata under BL and, as a result, it reached maximum transpiration. The noticeable accumulation of flavonoids and phenolic compounds was observed only in the phyb2 and phyaphyb2 mutants upon irradiation with BL, which agrees with the increased TEAC in the leaf extracts. We suggest that the increased antioxidant activity under PHYB2 deficiency and the maintenance of high photosynthesis under BL are based on an increase in the expression of the early signaling transcription factors genes BBX, HY5. The largest decrease in the content of flavonoids and TEAC was manifested with a deficiency in PHYB1, which is probably the key to maintaining the antioxidant status in BL plants.
... The tomato homolog ARF10 is involved in the fruit development and ripening through the chlorophyll accumulation, seed dormancy and germination through the regulation of ABSCISIC ACID INSENSITIVE 3 (ABI3) in the ABA signaling pathway [53]. PFBS is important for the chromophore activation in phytochromes and the downstream regulation of multiple aspects of plant development [11,54,55]. Then, the barley zinc binding CCCH transcription factors are also known to play important regulatory roles in both biotic and abiotic stress responses and in the developmental processes [12]. ...
The heavy metal associated isoprenylated plant proteins (HIPPs) are characterized by at least one heavy metal associated (HMA) domain and a C-terminal isoprenylation motif. Hordeum vulgare farnesylated protein 1 (HvFP1), a barley HIPP, is upregulated during drought stress, in response to abscisic acid (ABA) and during leaf senescence. To investigate the role of HvFP1, two independent gain-of-function lines were generated. In a physiological level, the overexpression of HvFP1 results in the delay of normal leaf senescence, but not in the delay of rapid, drought-induced leaf senescence. In addition, the overexpression of HvFP1 suppresses the induction of the ABA-related genes during drought and senescence, e.g., HvNCED, HvS40, HvDhn1. Even though HvFP1 is induced during drought, senescence and the ABA treatment, its overexpression suppresses the ABA regulated genes. This indicates that HvFP1 is acting in a negative feedback loop connected to the ABA signaling. The genome-wide transcriptomic analysis via RNA sequencing revealed that the gain-of-function of HvFP1 positively alters the expression of the genes related to leaf development, photomorphogenesis, photosynthesis and chlorophyll biosynthesis. Interestingly, many of those genes encode proteins with zinc binding domains, implying that HvFP1 may act as zinc supplier via its HMA domain. The results show that HvFP1 is involved in a crosstalk between stress responses and growth control pathways.
... Light plays a very important role in regulating plant growth and development; quantity and quality of light greatly affect plant growth. Thus, light is a highly important environmental signal that allows plants to thrive in their environment (Gavassi et al. 2017). The use of artificial light sources emitting photons over a continuous spectrum range, such as highpressure sodium (HPS) lamps and incandescent and metal halide lights, was common in growth rooms and greenhouses to supplement natural light (Economou and Read 1987;Krizek et al. 1998). ...
In this research, the combined effect of red and blue LED lights on tomato plants and fruit was investigated. Selected tomato plants were illuminated with a combination of red light (RL) and blue light (BL) at a ratio of (1:1) with a combined pho-tosynthetic photon flux density (PPFD) of 138 ± 5 µmol m −2 s −1. This illumination was installed above the plants and was terminated at different stages of plant growth, namely, at 50% flowering (FLW) and when fruit were mature green (MG). The plants were allowed to receive natural light during the day and were exposed to the light treatments 3 h after sunset and 3 h before sunrise. Control plants received only natural light. Growth, yield, and quality parameters were assessed. Both light treatments, whether terminated at FLW or MG, significantly enhanced plant height, number of leaves, and branching, with light treatment until the MG stage having a lesser, but nonetheless significant, effect. Plants that were treated with additional light until fruit were MG had a significantly increased total fruit mass compared with other treatments. Surprisingly , plants treated until FLW showed a significant increase in number of fruit per plant. Both treatments did not have a significant effect on colour parameters, while light treatments, particularly treatment until MG, were able to significantly enhance chlorophyll degradation in fruit. In addition, both light treatments resulted in a significant increase in fruit lycopene, the most important carotenoid in red tomato, while also potentially increasing the concentration of β-carotene, as well as total soluble solids (TSS), phenolics, and vitamin C. Treating tomato plants with a combination of LED light sources only until FLW was sufficient to enhance growth, yield, and antioxidant phytonutrients in tomatoes with no additional increase with further light treatment.
... AtHY5 has a DNA-binding domain but lacks any transcription activator domains; thus, it must cooperate with other transcription factors having such domains for the regulation of target genes [22][23][24][25]. HY5 maintains the appropriate PSII activity by controlling the balance between the oxidants and antioxidants [26][27][28], which protects the photosynthetic apparatus against oxidative stress under unfavourable environmental conditions [29][30][31]. HY5 mediates FRL induction of TANDEM ZINC-FINGER/PLUS3 (TZP) expression by directly binding to a G-box motif in the TZP promoter. Furthermore, TZP physically interacts with COP1, which inhibits COP1 interaction with HY5, ensuring its feedback regulation [32]. ...
Both light intensity and spectrum (280–800 nm) affect photosynthesis and, consequently, the formation of reactive oxygen species (ROS) during photosynthetic electron transport. ROS, together with antioxidants, determine the redox environment in tissues and cells, which in turn has a major role in the adjustment of metabolism to changes in environmental conditions. This process is very important since there are great spatial (latitude, altitude) and temporal (daily, seasonal) changes in light conditions which are accompanied by fluctuations in temperature, water supply, and biotic stresses. The blue and red spectral regimens are decisive in the regulation of metabolism because of the absorption maximums of chlorophylls and the sensitivity of photoreceptors. Based on recent publications, photoreceptor-controlled transcription factors such as ELONGATED HYPOCOTYL5 (HY5) and changes in the cellular redox environment may have a major role in the coordinated fine-tuning of metabolic processes during changes in light conditions. This review gives an overview of the current knowledge of the light-associated redox control of basic metabolic pathways (carbon, nitrogen, amino acid, sulphur, lipid, and nucleic acid metabolism), secondary metabolism (terpenoids, flavonoids, and alkaloids), and related molecular mechanisms. Light condition-related reprogramming of metabolism is the basis for proper growth and development of plants; therefore, its better understanding can contribute to more efficient crop production in the future.
... However, the molecular mechanisms underlying these responses are still poorly understood. In tomato, SlphyB1 and SlphyB2 mutants show increased growth during drought and salt stress, suggesting that SlphyB1 and SlphyB2 act as negative regulators of drought and salt tolerance (Gavassi et al., 2017). In agreement, tomato plants subjected to low R:FR ratio showed improved salt tolerance, mediated by SlphyB1 (Cao et al., 2018b). ...
Light is a key determinant for plant growth, development, and ultimately yield. Phytochromes, the red/far-red photoreceptors, play an important role in plant architecture, stress tolerance, and productivity. In the model plant Arabidopsis thaliana, it has been shown that PHYTOCHROME-INTERACTING FACTORS (PIFs; bHLH transcription factors) act as central hubs in the integration of external stimuli to regulate plant development. Recent studies have unveiled the importance of PIFs in crops. They are involved in the modulation of plant architecture and productivity through the regulation of cell division and elongation in response to different environmental cues. These studies show that different PIFs have overlapping but also distinct functions in the regulation of plant growth. Therefore, understanding the molecular mechanisms by which PIFs regulate plant development is crucial to improve crop productivity under both optimal and adverse environmental conditions. In this review, we discuss the current knowledge of PIFs acting as integrators of light and other signals in different crops, with particular focus on the role of PIFs in responding to different environmental conditions and how this can be used to improve crop productivity.
... Many studies have illustrated the role of PHYB in abiotic stresses such as those relating to light, heat, cold, drought, and salinity, while only a few have described the role of PHYA under these conditions. An ideal tool for studying the participation of PHYs in biotic and abiotic stress responses is to increase the availability of phy mutants in different plant species [38]. Therefore, this study aimed to identify the response of tomato PHYs A and B to HS during different growth stages using the phyA mutant and the phyB1B2 double mutant. ...
Heat stress (HS) is a prevalent negative factor affecting plant growth and development, as it is predominant worldwide and threatens agriculture on a large scale. PHYTOCHROMES (PHYs) are photoreceptors that control plant growth and development, and the stress signaling response partially interferes with their activity. PHYA, B1, and B2 are the most well-known PHY types in tomatoes. Our study aimed to identify the role of tomato ‘Money Maker’ phyA and phyB1B2 mutants in stable and fluctuating high temperatures at different growth stages. In the seed germination and vegetative growth stages, the phy mutants were HS tolerant, while during the flowering stage the phy mutants revealed two opposing roles depending on the HS exposure period. The response of the phy mutants to HS during the fruiting stage showed similarity to WT. The most obvious stage that demonstrated phy mutants’ tolerance was the vegetative growth stage, in which a high degree of membrane stability and enhanced water preservation were achieved by the regulation of stomatal closure. In addition, both mutants upregulated the expression of heat-responsive genes related to heat tolerance. In addition to lower malondialdehyde accumulation, the phyA mutant enhanced proline levels. These results clarified the response of tomato phyA and phyB1B2 mutants to HS.
... The light receptor group performs blue light deduction. They act immoderately in promoting elongation of the primary root, the opening of stomata in Arabidopsis, and induction of flowering circadian clock [32]. A similar result was observed in the case of root elongation in our study. ...
Among the various naturally occurring abiotic factors regulating plant development, different types of light play an important role in them. Photosynthesis, photoperiodism, and photo morphogenesis. In this trial the effects of different colors of light on (seed) germination, phytochrome conversion, length of seedling, biomass production in wheat varieties Shalkot and Tandojam. The rate of germination data indicates white 96%, Red 100%, far-red 95%, Blue 95%, and dark 64%, in Shalkot. In Tandojam rate of germination 94% White, 93% red, 82% far red, 92% blue, and 50% dark, were observed. Root and shoot length were higher in Shalkot under white light. Difference between dry and fresh weight in Shalkot under white, red, far-red, blue, dark, 1.66g, 0.94g, 0.98g, 0.97g, 0.6g, respectively. In Tandojam difference between dry and fresh weight observed under white, red, far-red, blue, dark, 1.48g, 0.92g, 0.70g, 0.97g, 0.4g respectively. By using bioinformatics tools identified some light-harvesting genes in wheat (Triticum aestivum) by using model plant Arabidopsis thaliana. The identified light-harvesting genes include cl02879, cl25816, cl33336, cl31857, cl28913.
... The study of acting mechanisms of individual phytochrome proteins revealed their participation in responses to different adverse conditions, with unique as well as redundant functions (53) ( Table 3). PhyB1 has been shown to be a negative regulator of salinity response as the tri mutant plants displayed better growth, higher proline and carotenoid contents, and a lower malondialdehyde level in comparison with the wild-type plants under the same treatment conditions (53). In addition, PhyB1 has been found to play an essential role in influencing plant tolerance to salinity in response to varied red to far-red light ratios (15) ( Table 3). ...
The two-component system (TCS), which is one of the most evolutionarily conserved signaling pathway systems, has been known to regulate multiple biological activities and environmental responses in plants. Significant progress has been made in characterizing the biological functions of the TCS components, including signal receptor histidine kinase (HK) proteins, signal transducer histidine-containing phosphotransfer proteins, and effector response regulator proteins. In this review, our scope is focused on the diverse structure, subcellular localization, and interactions of the HK proteins, as well as their signaling functions during development and environmental responses across different plant species. Based on data collected from scientific studies, knowledge about acting mechanisms and regulatory roles of HK proteins is presented. This comprehensive summary ofthe HK-related network provides a panorama of sophisticated modulating activities of HK members and gaps in understanding these activities, as well as the basis for developing biotechnological strategies to enhance the quality of crop plants.
... Contrarily, the spinach leaves grown under the gray netting received less radiation, making the leaves slightly less green than the other treatments. According to Gavassi et al. (2017), chlorophyll content can be affected by the manipulation of light through the different-colored shade nettings used to grow vegetables. Low levels of radiation bring a reduction in chlorophyll content that causes plants to have a whitish color (Dussi, 2007;Fischer and Pérez, 2012). ...
Consumers are demanding foods with high sensory and nutritional quality including a higher content of compounds that help maintain good health. Given this scenario, new technologies are emerging to produce fresh salads that have the characteristics currently in demand. Shade nettings or photoselective filters on fruit and vegetable crops are a technology that provides protection, modifies the light spectrum resulting in a higher accumulation of antioxidant compounds, making them more desirable to consumers. The objective of this study was to compare the effect of shade netting on the fresh quality parameters of baby leaf spinach grown in a hydroponic system at harvest and after a period of 10 days at 4 • C. By using different shade netting colors, the average photosynthetic photon flux density (PPFD) that reaches the plants was modified during the growing period of baby leaf spinach (red: 118.35 μmol m − 2 s − 1 ; blue:117.96 μmol m − 2 s − 1 ; gray: 63.18 μmol m − 2 s − 1 and control without shade nettings: 278.12 μmol m − 2 s − 1). At harvest, baby leaf spinach grown under the red shade netting reached the highest yield. However, with the blue filter, leaves showed a value of 9.3 % dry weight, significantly higher than the values from red and gray filters with values of 7.3 and 6.3 %, respectively. The phenolic compound contents reached significantly higher values of 485.5 mg gallic acid equivalent (GAE) per 100 g − 1 FW for the baby leaf spinach grown under the red filter compared to the blue, gray and control filters with values of 472.5; 387.6 and 316.5 mg GAE per 100 g − 1 FW, respectively. The antioxidant capacity was significantly higher under the red filter. The sensory quality parameters indicated that spinach grown under color filters did not show off-flavors and maintained its turgidity and appearance at harvest. In the postharvest period, baby leaf spinach grown under red filter maintained the highest total phenol content and antioxidant activity after 10 days at 4 • C with similar appearance and turgidity as the control.
... Thus, this sensor triggers the light-dependent signal transduction cascade to regulate the expression of numerous genes that result in specific physiological responses (Viczián et al., 2017). Furthermore, various reports have shown that the plant signaling pathways involved in the responses to abiotic and biotic stresses, including insect herbivory, salinity, drought, hot or cold temperatures, and UV-B radiation, are modulated by phytochromes (Donohue et al., 2008;D'Amico-Damião et al., 2015;Gavassi et al., 2017). However, these responses remain unclear due to the complex light signaling pathways that are operated by other photoreceptors along the light spectrum Fiorucci and Fankhauser, 2017;Demarsy et al., 2018). ...
Leaves of the spiny winter annual Silybum marianum express white patches (variegation)
that can cover significant surface areas, the outcome of air spaces formed between
the epidermis and the green chlorenchyma. We asked: (1) what characterizes the
white patches in S. marianum and what differs them from green patches? (2) Do
white patches differ from green patches in photosynthetic efficiency under lower
temperatures? We predicted that the air spaces in white patches have physiological
benefits, elevating photosynthetic rates under low temperatures. To test our hypotheses
we used both a variegated wild type and entirely green mutants. We grew the plants
under moderate temperatures (20�C/10�C d/n) and compared them to plants grown
under lower temperatures (15�C/5�C d/n). The developed plants were exposed to
different temperatures for 1 h and their photosynthetic activity was measured. In
addition, we compared in green vs. white patches, the reflectance spectra, patch
structure, chlorophyll and dehydrin content, stomatal structure, plant growth, and leaf
temperature. White patches were not significantly different from green patches in their
biochemistry and photosynthesis. However, under lower temperatures, variegated wildtype leaves were significantly warmer than all-green mutants – possible explanations
for that are discussed These findings support our hypothesis, that white variegation
of S. marianum leaves has a physiological role, elevating leaf temperature during cold
winter days
... PhyA is mainly involved in far-red light sensing (Sineshchekov 2010). In some species, PhyA, PhyB1 and PhyB2 were implicated in plant responses to low water potential, high salinity, cadmium contamination, high temperature and ultraviolet B radiation (Gavassi et al. 2017). Also, higher levels of PhyB in transgenic potato plants increased resistance of photosynthetic apparatus to high irradiance (Thiele et al. 1999) and UV-B (Kreslavski et al. 2015). ...
Our recent studies showed that A. thaliana L. phyAphyB double mutants (DM) grown under red light (RL) and white light (WL) had higher photosystem II (PSII) vulnerability to UV-B than wild type (WT). The present work was aimed at revealing the mechanistic basis for this difference by analyzing the content of UV-absorbing pigments (UAPs) and chloroplast ultrastructure in leaves of DM and WT grown under different light conditions, of different photoperiods (12, 16 and 24 h) and light quality (WL vs RL). The content of UAPs in leaves of WT plants grown under RL showed a strong dependence of photoperiod and decreased in a sequence 24 h > 16 h > 12 h. In all treatments, contents of UAPs were higher in WT compared to mutant plants. While 1 h of UV treatment had only a small impact on chloroplast ultrastructure, it substantially inhibited PSII activity (maximum and effective PSII quantum yields). In all treatments, the UV-induced decreases of PSII activities were compared with each other. At any photoperiod, decreases in PSII activity were smaller in WT compared to that in mutant plants. Higher UAPs contents led to lesser PSII inhibition, while low UAPs contents resulted in strong decline in PSII activity. The results demonstrate that content of UAPs significantly contributes to PSII resistance to short-time UV-B exposures, and decreased content of UAPs in phytochrome double mutant can explain the reduced PSII resistance of these plants to UV-B radiation.
... It has been shown in crops that phytochromes are important for agricultural traits (Gupta et al. 2014;Kharshiing and Sinha 2015). The use of genetic tools involving phytochromes, such as mutant and transgenic plants, allows high planting densities, early flowering and increased biomass accumulation (Ballare and Pierik 2017;Mawphlang and Kharshiing 2017;Yang et al. 2016) as well as tolerance to biotic and abiotic disturbances (Carvalho et al. 2011;Gavassi et al. 2017), drawing attention to the importance of the manipulation of these photoreceptors for plant breeding. ...
Cryptochromes are photoreceptors that coordinate multiple processes during the plant life cycle through UV-A/blue light. In the present study, we used tomato cry1a mutant to understand how LeCRY1a influences the vegetative and reproductive development during different stages of growth. When compared to the wild type of tomato, the cry1a mutant showed greater plant height, number of leaves and leaf area during the life cycle. However, leaf pigment biosynthesis in cry1a was impaired compared with wild-type plants. Moreover, cry1a influenced the partitioning of photoassimilates between the shoot and root, mainly by positively influencing the initial root growth. Although the wild-type plants exhibited lower shoot and root biomass accumulation at the final stage of plant growth than did the mutant, the wild type exhibited higher yield, as evidenced by its greater number of ripe fruits per plant. The results reveal a complex role of cry1a throughout shoot and root growth and fruit development in tomato, causing this photoreceptor to stand out as target molecules for plant breeding programs.
... Thus, this sensor triggers the light-dependent signal transduction cascade to regulate the expression of numerous genes that result in specific physiological responses (Viczián et al., 2017). Furthermore, various reports have shown that the plant signaling pathways involved in the responses to abiotic and biotic stresses, including insect herbivory, salinity, drought, hot or cold temperatures, and UV-B radiation, are modulated by phytochromes (Donohue et al., 2008;Ballaré, 2009;Carvalho et al., 2011;D'Amico-Damião et al., 2015;Gavassi et al., 2017). However, these responses remain unclear due to the complex light signaling pathways that are operated by other photoreceptors along the light spectrum (Kami et al., 2010;Fiorucci and Fankhauser, 2017;Demarsy et al., 2018). ...
It is well known that light is a crucial environmental factor that has a fundamental role in plant growth and development from seed germination to fruiting. For this process, plants contain versatile and multifaceted photoreceptor systems to sense variations in the light spectrum and to acclimate to a range of ambient conditions. Five main groups of photoreceptors have been found in higher plants, cryptochromes, phototropins, UVR8, zeitlupes, and phytochromes, but the last one red/far red wavelengths photoreceptor is the most characterized. Among the many responses modulated by phytochromes, these molecules play an important role in biotic and abiotic stress responses, which is one of the most active research topics in plant biology, especially their effect on agronomic traits. However, regarding the light spectrum, it is not surprising to consider that other photoreceptors are also part of the stress response modulated by light. In fact, it has become increasingly evident that cryptochromes, which mainly absorb in the blue light region, also act as key regulators of a range of plant stress responses, such as drought, salinity, heat, and high radiation. However, this information is rarely evidenced in photomorphogenetic studies. Therefore, the scope of the present review is to compile and discuss the evidence on the abiotic stress responses in plants that are modulated by cryptochromes.
Water availability is a limiting factor to plant development and productivity. Many drought‐induced physiological processes that affect patterns of growth, biomass allocation, and ultimately, yield, are also regulated by the red/far‐red photoreceptor phytochromes (PHYs). However, as the mechanisms and responses to drought stress vary among plant developmental phases, it is reasonable to conjecture that PHY‐dependent morphophysiological responses to drought may be different according to the plant growth stage. In this study, we submitted tomato phyB1 mutant plants to water deficit in two distinct growth stages, during vegetative and flower‐bearing reproductive phases, comparing the morphophysiological development, fruit yield and quality to wild‐type (WT). In general, phyB1 plants overcome growth limitations imposed by water availability limitations during vegetative phase, being taller and leafier than WT. Restrictions to growth are less acute for both genotypes when water deficit occurs during reproductive phase compared to vegetative phase. phyB1 yield is lower when water is limited during reproductive phase, but its fruits accumulate more soluble solids, associated with better quality. These results highlight that drought‐induced modulations in tomato growth and yield are dependent upon PHYB1 regulation and the developmental phase when water deficit is applied.
Environmental factors, such as light of different spectral compositions and temperature, can change the level of activated photoreceptors which, in turn, can affect the biosynthesis of secondary metabolites in the cells of green fruit. By briefly irradiating the harvested fruit of Capsicum annuum L. hot peppers with red light (RL, maximum 660 nm) and far-red light (FRL, maximum 730 nm) and by keeping them at a low temperature, we attempted to determine whether the state of phytochromes in fruit affects the biosynthesis of secondary metabolites. Using HPLC, we analysed the qualitative composition and quantitative content of the main carotenoids and alkaloids and the chlorophylls and ascorbate, in pepper fruit exposed to the above factors. We measured the parameters characterising the primary photochemical processes of photosynthesis and the transcript levels of genes encoding capsaicin biosynthesis enzymes. The total carotenoids content in the fruit increased most noticeably after 24 h of RL irradiation (more than 3.5 times compared to the initial value), and the most significant change in the composition of carotenoids occurred when the fruit was irradiated with FRL for 72 h. The capsaicin alkaloid content increased markedly after 72 h of FRL irradiation (more than 8 times compared to the initial value). It was suggested that decrease in the activity of phytochromes due to a low temperature or FRL may result in an increase in the expression of the PAL and CAM genes.
Drought is one of the most critical stresses, which causes an enormous reduction in crop yield. Plants develop various strategies like drought escape, drought avoidance, and drought tolerance to cope with the reduced availability of water during drought. Plants adopt several morphological and biochemical modifications to fine-tune their water-use efficiency to alleviate drought stress. ABA accumulation and signaling plays a crucial role in the response of plants towards drought. Here, we discuss how drought-induced ABA regulates the modifications in stomatal dynamics, root system architecture, and the timing of senescence to counter drought stress. These physiological responses are also regulated by light, indicating the possibility of convergence of light- and drought-induced ABA signaling pathways. In this review, we provide an overview of investigations reporting light-ABA signaling cross talk in Arabidopsis as well as other crop species. We have also tried to describe the potential role of different light components and their respective photoreceptors and downstream factors like HY5, PIFs, BBXs, and COP1 in modulating drought stress responses. Finally, we highlight the possibilities of enhancing the plant drought resilience by fine-tuning light environment or its signaling components in the future.
Light-induced changes in miRNAs, morphogenesis, and photosynthetic processes in phytochrome-deficient mutant plants grown under different light qualities were studied. miRNA activity in many processes is regulated by phytochromes and phytochrome-interacting factors (PIFs). The reduced content of photoreceptors in phytochrome mutants affects the PIF-microRNA interaction. In plants grown under red light (RL) and white light (WL), the phenotype of phyb mutant was distorted; however, under blue light (BL) conditions, the phyb phenotype was normalized. The photosynthetic rates of both the mutants and wild type were higher under BL than under RL and WL. The expression of most studied miRNAs increased in phyaphyb mutants under BL conditions, which is probably one of the reasons for the normalization of the phenotype, the increase in PSII activity, and the photosynthetic rate. MicroRNAs under BL can partially improve photosynthesis and phenotype of the mutants, which indicates the conjugation of the functioning of phytochromes in miRNA formation.
Spectral quality, intensity and period of light modify many regulatory and stress signaling pathways in plants. Both nitrate and sulfate assimilations must be synchronized with photosynthesis, which ensures energy and reductants for these pathways. However, photosynthesis is also a source of reactive oxygen species, whose levels are controlled by glutathione and other antioxidants. In this study, we investigated the effect of supplemental far-red (735 nm) and blue (450 nm) lights on the diurnal expression of the genes related to photoreceptors, the circadian clock, nitrate reduction, glutathione metabolism and various antioxidants in barley. The maximum expression of the investigated four photoreceptor and three clock-associated genes during the light period was followed by the peaking of the transcripts of the three redox-responsive transcription factors during the dark phase, while most of the nitrate and sulfate reduction, glutathione metabolism and antioxidant-enzyme-related genes exhibited high expression during light exposure in plants grown in light/dark cycles for two days. These oscillations changed or disappeared in constant white light during the subsequent two days. Supplemental far-red light induced the activation of most of the studied genes, while supplemental blue light did not affect or inhibited them during light/dark cycles. However, in constant light, several genes exhibited greater expression in blue light than in white and far-red lights. Based on a correlation analysis of the gene expression data, we propose a major role of far-red light in the coordinated transcriptional adjustment of nitrate reduction, glutathione metabolism and antioxidant enzymes to changes of the light spectrum.
The Arabidopsis thaliana L. photoreceptor genes homologues in tomato (Solanum lycopersicum L.) genome were analysed using bioinformatic tools. The expression pattern of these genes under cold stress was also evaluated. Transcriptome analysis of the tomato sequence revealed that the photoreceptor gene family is involved in abiotic stress tolerance. They participate in various pathways and controlling multiple metabolic processes. They are structurally related to PAS, LIGHT-OXYGEN-VOLTAGE-SENSING (LOV), DNA photolyase, 5,10-methenyl tetrahydrofolate (MTHF), flavin-binding kelch F-box, GAF, PHY, Seven-bladed β-propeller and C27 domains. They also interact with flavin adenine dinucleotide (FAD), (5S)-5-methyl-2-(methylsulfanyl)-5-phenyl-3-(phenylamino)-3,5-dihydro-4H-imidazol-4-one (FNM) and Phytochromobilin (PϕB) ligands. These interactions help to create a cascade of protein phosphorylation involving in cell defence transcription or stress-regulated genes. They localisation of these gene families on tomato chromosomes appeared to be uneven. Phylogenetic tree of tomato and Arabidopsis photoreceptor gene family were classified into eight subgroups, indicating gene expression diversity. Morphological and physiological assessment revealed no dead plant after 4h of cold treatment. All the plants were found to be alive, but there were some variations in the data across different parameters. Cold stress significantly reduced the rate of photosynthesis from 10.06 to 3.16μmolm-2 s-1, transpiration from 4.6 to 1.3mmolm-2 s-1, and stomatal conductance from 94.6 to 25.6mmolm-2 s-1. The cold stressed plants also had reduced height, root/shoot length, and fresh/dry biomass weight than the control plants. Relative expression analysis under cold stress revealed that after 4h, light stimulates the transcript level of Cry2 from 1.9 to 5.7 and PhyB from 0.98 to 6.9 compared to other photoreceptor genes.
The impacts of high-intensity light (HIL) (4 h) and UV-B radiation (1 h) on the photosynthetic activity, content of photosynthetic and UV-absorbing pigments (UAPs), activity of antioxidant enzymes (ascorbate peroxidase (APX) and guaiacol-dependent peroxidase (GPX)), content of thiobarbituric acid reactive substances (TBARs), expression of some light-regulated genes in 25-day-old wild type (WT) and the cryptochrome 1 (Cry1) hy4 mutant of A. thaliana Col-0 plants grown under blue light (BL) were studied. HIL and UV-B treatments led to decreases in the photosynthetic rate (Pn), photochemical activity of PSII (FV/FM) and PSII performance index (PIABS) of WT and mutant plants grown under high-intensity BL (HBL) and moderate intensity BL (MBL). However, in HBL plants, the decrease in the photosynthetic activity in hy4 plants was significantly greater than that in WT plants. In addition, hy4 HBL plants demonstrated lowered UAP and carotenoid contents as well as lower activity of APX and GPX enzymes. The difference in the decline in the photosynthetic activity of WT and hy4 plants grown at MBL in response to HIL was nonsignificant, while that in response to UV-B was small. We assume that the deficiency in cryptochrome 1 under HIL irradiation disrupts the interaction between HY5 and HFR1 transcription factors and photoreceptors, which affects the transcription of light-induced genes, such as CAB1, PSY and PAL1 linked to carotenoid and flavonoid biosynthesis. It was concluded that PA stress resistance in WT and hy4 plants depends on the light intensity and reduced stress resistance of hy4, and HBL is likely linked to low UAP and carotenoid contents as well as lowered APX and GPX enzyme activities in hy4 mutants.
The participation of plant cryptochromes in water deficit response mechanisms has been highlighted in several reports. However, nothing is known about the role of tomato (Solanum lycopersicum L.) cryptochrome 1a (cry1a) in the blue light fluence-dependent modulation of the water deficit response. The tomato cry1a mutant and its wild-type counterpart were grown in water (no stress) or PEG6000 (osmotic stress) treatments under white light (60 μmol m-2 s-1) or blue light (1, 5, 10, 15 and 25 μmol m-2 s-1). We first demonstrated under nonstress conditions that CRY1a regulates seedling growth by control mechanisms that involve pigmentation, lipid peroxidation and osmoprotectant accumulation in a blue light-dependent manner. In addition, we further highlighted under osmotic stress conditions that cry1a increased tomato growth by reduced malondialdehyde (MDA) and proline accumulation. Although blue light is an environmental signal that influences osmotic stress responses mediated by tomato cry1a, specific blue light fluence rates are required during these responses. Here, we show that CRY1a manipulation may be a potential tool to develop more water-deficit-tolerant tomato crops, as the cry1a mutant was more sensitive to osmotic stress. Nevertheless, the full understanding of how this phenomenon occurs is still very complex and requires further investigation.
It is well known that phytochromes mediate a wide range of photomorphogenic processes in plants. In addition, many studies have demonstrated the involvement of phytochromes as part of abiotic stress signaling responses. However, little is known about cadmium (Cd) stress regulation by phytochromes. Thus, in this study, we used the phyA (far red-insensitive; fri), phyB1 (temporary redinsensitive; tri) and phyB2 (phyB2) tomato (Solanum lycopersicum L.) mutants to investigate the roles of these three phytochromes on Cd stress responses. The plants were grown over a 21-d period in the presence of Cd. We evaluated plant growth, Cd and chlorophyll content and anatomical changes in the leaves. The results indicated that all genotypes were affected by Cd and showed reduced growth of the shoots and roots, as well as reduced chlorophyll content. The accumulation of Cd was similar for all genotypes, and a higher Cd content was found in roots. Anatomical analysis of the vascular bundles revealed that fri and tri seem to be more disrupted by Cd. Overall, these results indicate that phytochromes do not determine Cd stress tolerance in tomato plants.
Key words
abiotic stress; heavy metal; mutants; plant anatomy; Solanum lycopersicum. L
There is a very effective cross-talk between signals triggered by reactive oxygen species and the hormonal response in plants, inducing the expression of genes or activating proteins/enzymes likely to be involved in stress tolerance. Although abiotic stress responses and the role of the antioxidant system have been well explored in the literature, the understanding of the interrelationship between hormones and their effects on antioxidant system is not clear or well investigated. We attempted to scan the field of hormonal modulation of oxidative stress in plants. We feel that this topic is one of the most promising and emerging field in abiotic stress research because multiple responses can be controlled by hormones. We are presenting an overview of the more recent literature on what has been done regarding the interaction between auxin (AUX), gibberellins (GA), cytokinins (CK), abscisic acid (ABA), ethylene (ET) and oxidative molecules and antioxidant compounds. Even knowing that several stress-responsive genes respond to hormones, some of which have already been documented showing that AUX, GA, CK, ABA and ET are part of stress signaling, a lot more is needed in order to have a clearer view of how and which hormones regulate abiotic stress responses.
The far red light insensitive (fri) mutant of tomato, which is phytochrome A (phyA) deficient, displays some characteristics that have recently indicated important functions of this photoreceptor in water relations. With respect to the relationship between nutrition and water relations, we investigated the growth and nutritional status of fri supplied with Hoagland's complete solution and solutions with the individual omission of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S). For this purpose, 20-day-old tomato plants of the WT (cv. Moneymaker) and fri mutant were transplanted into pots (one plant per pot) that contained Hoagland and Arnon (1950) solution diluted to 50 per cent in the first week and to 100 per cent from the second week of cultivation until the end of the experiment (50 DAT). Seven treatments were performed: a complete nutrient solution (KH2PO4, KNO3, Ca(NO3)2.5H2O, MgSO4.7H2O, KCl, CaCl2, H3BO3, MnCl2.4H2O, ZnCl2, CuCl2, H2MoO4H2O and Fe EDTA) and the individual omission N (KNO3, Ca(NO3)2.5H2O); P (KH2PO4); K (KH2PO4, KNO3); Ca (CaCl2); Mg and S (MgSO4.7H2O) from a balanced nutrient solution. The experiment was arranged in a completely randomized factorial design with two genotypes and seven types of nutrient solutions with three replications. Upon harvest, the following measurements were performed: the height of the plants, measured from the base of the stem of each plant to the insertion of the first fully expanded leaf; the stem diameter; the total number of leaves per plant; an indirect chlorophyll measurement, which we called the green color index, and the leaf area. Statistical analysis was performed using analysis of variance (ANOVA) followed by Tukey's test. First, based on growth analyses, fri showed an enhanced dry weight of the shoot, root and whole plant in complete solution compared with the wild type (WT). In addition, the phyA mutant had a multifaceted response compared with that of the WT when the nutrients were omitted. For the fri mutant, the height and green color index were reduced without N and K; the leaf area without P, K and S; the dry weight of the root and shoot without N, P, K and S, and the root, shoot and total plant dry weight without P, K and S. On the other hand, the green color index of the fri mutant was enhanced without Ca and Mg. Together, these results show that in addition to revealing an altered response to nutrition in the fri mutant, phyA can play a role in light signaling in the nutrition and nutritional stress of tomato.
Due to their nature as sessile organisms, plants must accurately sense their surroundings and then translate this information into efficient acclimation responses in order to maximize development. Light and temperature are two major stimuli that provide immediate cues regarding energy availability, daylength, proximity of other species and seasonal changes. Both cues are sensed by complex systems and the integration of these signals is of very high value to properly respond to environmental changes without being disguised by random changes. For instance, a cold day has a different significance if it occurs during the illuminated phase of the day or during the night, or when days are shortening during the fall instead of a long-day in spring. Here we summarize recent advances in the nature of signaling components that operate as connectors of light and temperature signaling, with emphasis on the emerging hubs. Despite the nature of the thermosensors is still in its infancy compared to an important body of knowledge about plant sensory photoreceptors, the interaction of both types of signaling will not only bring clues of how plants integrate environmental information, but also will help in leading research in the nature of the thermosensors themselves. This article is protected by copyright. All rights reserved.
Plants coordinate their responses to various biotic and abiotic stresses in order to optimize their developmental and acclimatory
programmes. The ultimate response to an excessive amount of stress is local induction of cell death mechanisms. The death
of certain cells can help to maintain tissue homeostasis and enable nutrient remobilization, thus increasing the survival
chances of the whole organism in unfavourable environmental conditions. UV radiation is one of the environmental factors that
negatively affects the photosynthetic process and triggers cell death. The aim of this work was to evaluate a possible role
of the red/far-red light photoreceptors phytochrome A (phyA) and phytochrome B (phyB) and their interrelations during acclimatory
responses to UV stress. We showed that UV-C treatment caused a disturbance in photosystem II and a deregulation of photosynthetic
pigment content and antioxidant enzymes activities, followed by increased cell mortality rate in phyB and phyAB null mutants. We also propose a regulatory role of phyA and phyB in CO2 assimilation, non-photochemical quenching, reactive oxygen species accumulation and salicylic acid content. Taken together,
our results suggest a novel role of phytochromes as putative regulators of cell death and acclimatory responses to UV.
The activity of catalase (CAT), guaiacol peroxidase (GPOX), ascorbate peroxidase (APX), glutathione reductase (GR), and the isoenzymes of superoxide dismutase (SOD) were determined in the organs of tomato (Lycopersicon esculentum) cultivar Micro-Tom after 104 days of development. The total activities of CAT, GPOX, and GR were higher in the stem than in others tissues, whereas the stem exhibited the lowest APX activity. Activity staining analysis following gel electrophoresis revealed the existence of four SOD isoenzymes in leaves, three in fruits, but only two in the roots and stems. This characterization is essential for an investigation into the effect of abiotic and biotic stresses on the oxidative stress responses by this plant model system.
Carotenoids are photosynthetic pigments essential for the protection against excess light. During deetiolation, their production is regulated by a dynamic repression-activation module formed by PIF1 and HY5. These transcription factors directly and oppositely control the expression of the gene encoding phytoene synthase (PSY), the first and main rate-determining enzyme of the carotenoid pathway. Antagonistic modules also regulate the responses of deetiolated plants to vegetation proximity and shade, i.e. to the perception of far-red enriched light filtered through or reflected from neighboring plants. These responses, aimed to adapt to eventual shading from plant competitors, include a reduced accumulation of carotenoids. Here we show that PIF1 and related photolabile PIFs (but not photostable PIF7) promote the shade-triggered decrease in carotenoid accumulation. While HY5 does not appear to be required for this process, other known PIF antagonists were found to modulate the expression of the Arabidopsis thaliana PSY gene and the biosynthesis of carotenoids early after exposure to shade. In particular, PAR1, a transcriptional co-factor that prevents binding of true transcription factors to their target promoters, was found to interact with PIF1 and hence directly induce PSY expression. By contrast, a change in the levels of the transcriptional co-factor HFR1, which also binds to PIF1 and other PIFs to regulate shade-related elongation responses, did not impact PSY expression or carotenoid accumulation. Our data suggest that fine regulation of carotenoid biosynthesis in response to shade relies on specific modules of antagonistic transcriptional factors and co-factors.
Copyright © 2015, Plant Physiology.
The influence of phytochrome B overproduction in 50- to 60-day-old transgenic potato plants (Solanum tuberosum L., lines Dara 5 and Dara 12 with moderate and intense expression of PHYB, respectively) on the resistance of photosynthetic apparatus to UV-B irradiation was investigated. In plants unexposed to UV-B, there was no significant difference in photosynthetic rates (P
n) and fluorescence parameters (F
v/F
m, qN, qP) between the nontransformed (NT) line and Dara-5 and Dara-12 lines, whereas the content of photosynthetic pigments per 1 cm2 leaf area was higher in the transgenic plants. Irradiation with UV-B resulted in the decrease in photosynthetic rate in NT plants by 35–45%, whereas in Dara-12 line this rate was lowered by only 20–25%. Exposure to UV-B reduced the amplitudes of both fast and slow components of delayed fluorescence (DF), which indicated the diminished efficiency of photosystem II (PSII). The decrease in the maximum amplitude of the slow DF component was markedly lower in Dara-12 (19%) than in NT line (33%). The maximal photochemical quantum yield of PSII (F
v/F
m ratio) in plants exposed to UV-B was also suppressed stronger in NT line than in Dara-12. The line Dara-5 had intermediate position among other lines in terms of UV-B resistance of photosynthesis and PSII activity, but it was closer to NT than to Dara-12. Thus, the potato plants actively expressing the gene of Arabidopsis phytochrome B apoprotein (PHYB) demonstrated a higher resistance of photosynthetic apparatus to UV-B radiation compared to nontransformed plants. The elevated UV-B tolerance is most likely related to the increased leaf content of chlorophyll, carotenoids, and flavonoids.
Phytochrome-interacting factor 3 (PIF3) activates light-responsive transcriptional network genes in coordination with the circadian clock and plant hormones to modulate plant growth and development. However, little is known of the roles PIF3 plays in the responses to abiotic stresses. In this study, the cloning and functional characterization of the ZmPIF3 gene encoding a maize PIF3 protein is reported. Subcellular localization revealed the presence of ZmPIF3 in the cell nucleus. Expression patterns revealed that ZmPIF3 is expressed strongly in leaves. This expression responds to polyethylene glycol, NaCl stress, and abscisic acid application, but not to cold stress. ZmPIF3 under the control of the ubiquitin promoter was introduced into rice. No difference in growth and development between ZmPIF3 transgenic and wild-type plants was observed under normal growth conditions. However, ZmPIF3 transgenic plants were more tolerant to dehydration and salt stresses. ZmPIF3 transgenic plants had increased relative water content, chlorophyll content, and chlorophyll fluorescence, as well as significantly enhanced cell membrane stability under stress conditions. The over-expression of ZmPIF3 increased the expression of stress-responsive genes, such as Rab16D, DREB2A, OSE2, PP2C, Rab21, BZ8 and P5CS, as detected by real-time PCR analysis. Taken together, these results improve our understanding of the role ZmPIF3 plays in abiotic stresses signaling pathways; our findings also indicate that ZmPIF3 regulates the plant response to drought and salt stresses.
Phytochromes are red/far-red light photoreceptors that mediate a variety of photomorphogenic processes in plants, from germination to flowering. In addition, there is evidence that phytochromes are also part of the stress signalling response, especially in response to water deficit stress, which is the major abiotic factor limiting plant growth and crop productivity worldwide. In this study, we used the phyA (far red-insensitive; fri), phyB1 (temporary red-insensitive; tri) and phyB2 mutants of tomato (Solanum lycopersicum L.) to study the roles of these three phytochromes in drought stress responses. Compared to wild type (WT) plants grown under water-deficit stress conditions, the fri, tri, and phyB2 mutants did not exhibit altered dry weights, leaf areas, stomatal densities, or stomatal opening. The stomatal conductance of all three mutants was severely reduced under both fully-hydrated and water-deficit conditions. Although relative water contents did change after drought stress in each mutant, the most significant reduction in water potential during water stress was observed in the fri mutant. However, this mutant returned its water status to WT levels during rehydration. Although the phyB2 mutant lost more water from detached leaves during abscisic acid (ABA) treatment, phyB2 behaved like WT plants, indicating that this mutant was not insensitive to ABA. Overall, these results indicate that the phytochromes phyA, phyB1, and phyB2 modulate drought stress responses in tomato.
This paper discusses and interprets the facts related with the mainstays (chemistry, biosynthesis, compartmentalization, significance) commonly and potentially shared by these two enigmatic compounds, namely glutathione and proline in plants.
Bacteriophytochromes (BphPs) are light-sensing regulatory proteins encoded in photosynthetic and non-photosynthetic bacteria. This protein class incorporate bilin as their chromophore, with majority of them bearing a light- regulated His kinase or His kinase related module in the C-terminal. We studied the His kinase actives in the temperature range of 5°C to 40°C on two BphPs, Agp1 from Agrobacterium tumefaciens and Cph1 from cyanobacterium Synechocystis PCC 6803. As reported, the phosphorylation activities of the far red (FR) irradiated form of the holoprotein is stronger than that of the red (R) irradiated form in both phytochromes. We observed for the apoprotein and FR irradiated holoprotein of Agp1 an increase in the phosphorylation activities from 5°C to 25°C and a decrease from 25°C to 40°C. At 5°C the activities of the apoprotein were significantly lower than those of the FR irradiated holoprotein, which was opposite at 40°C. A similar temperature pattern was observed for Cph1, but the maximum of the apoprotein was at 20°C while the maximum of the FR irradiated holoprotein was at 10°C. At 40°C, prolonged R irradiation leads to an irreversible bleaching of Cph1, an effect which depends on the C-terminal His kinase module. A more prominent and reversible temperature effect on spectral properties of Agp1, mediated by the His kinase, has been reported before. His kinases in phytochromes could therefore share similar temperature characteristics. We also found that phytochrome B mutants of Arabidopsis have reduced hypocotyl growth at 37°C in darkness, suggesting that this phytochrome senses the temperature or mediates signal transduction of temperature effects.
Shrubs often form the understorey in Mediterranean oak woodlands. These shrubs are exposed to recurrent water deficits, but how they will respond to predicted future exacerbation of drought is not yet understood. The ecophysiology of the shrub Cistus salvifolius L. was studied over the summer of 2005, which was during a heat-wave superimposed on the most severe drought in the Iberian Peninsula in the last 140 years. Branch water potential fell drastically during the summer, accompanied by stomatal closure and downregulation of PSII, with a concomitant loss of chlorophyll in the leaves. A parallel increase in the ratio of light-dissipating to light-capturing pigments and the proportion of xanthophyll cycle pigments in the de-epoxidated state, along with alterations in the structure of the light harvesting complex, may have reduced the potential for damage to leaves. Substantial increases in leaf tocopherol content during high radiation may have reduced damage from free radicals. Following autumn rains, leaves of the same shrubs showed physiological recovery, indicating the resilience of this Mediterranean species, for which an extremely dry hydrological year with 45% less rainfall than average, did not prevent healthy leaf functioning in response to renewed soil moisture availability.
The salt-sensitive humid tropical biodiesel crop, Jatropha curcas, was subjected to a 28-day exposure to salinity (0, 50, 100, and 200 mM NaCl), and activities of antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX), the rate of lipid peroxidation, stomatal conductance, mineral contents, and chlorophyll (Chl) content were compared to corresponding characteristics of J. cinerea, a related wild species of saline-dry areas. Biomass production decreased under the influence of 50 mM NaCl in both species, and the reduction was larger in J. curcas than in J. cinerea at the higher NaCl concentrations. In both species, stomatal conductance and transpiration decreased, leaf temperature and Na+ concentration increased under salt treatment; salinity effect was stronger in J. curcas. Chl degradation was enhanced only in J. curcas. In both Jatropha species, SOD, CAT, and POX activities increased with salinity. J. curcas showed the higher antioxidant activity than J. cinerea. Lipid peroxidation was observed only in J. curcas at concentrations above 100 mM NaCl, partially due to a greater reduction in stomatal conductance and/or the poor ROS-scavenging system. Thus, J. cinerea had more favorable characteristics to adapt to saline environments, and young J. curcas plants could adapt to salt-affected land if soil salinity was moderate (about 50 mM NaCl in solution).
Tolerance of plants to abiotic stressors such as drought and salinity is triggered by complex multicomponent signaling pathways to restore cellular homeostasis and promote survival. Major plant transcription factor families such as bZIP, NAC, AP2/ERF, and MYB orchestrate regulatory networks underlying abiotic stress tolerance. Sucrose non-fermenting 1-related protein kinase 2 and mitogen-activated protein kinase pathways contribute to initiation of stress adaptive downstream responses and promote plant growth and development. As a convergent point of multiple abiotic cues, cellular effects of environmental stresses are not only imbalances of ionic and osmotic homeostasis but also impaired photosynthesis, cellular energy depletion, and redox imbalances. Recent evidence of regulatory systems that link sensing and signaling of environmental conditions and the intracellular redox status have shed light on interfaces of stress and energy signaling. ROS (reactive oxygen species) cause severe cellular damage by peroxidation and de-esterification of membrane-lipids, however, current models also define a pivotal signaling function of ROS in triggering tolerance against stress. Recent research advances suggest and support a regulatory role of ROS in the cross talks of stress triggered hormonal signaling such as the abscisic acid pathway and endogenously induced redox and metabolite signals. Here, we discuss and review the versatile molecular convergence in the abiotic stress responsive signaling networks in the context of ROS and lipid-derived signals and the specific role of stomatal signaling.
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
Abiotic stresses collectively are responsible for crop losses worldwide. Among these, drought and salinity are the most destructive. Different strategies have been proposed for management of these stresses. Being a complex trait, conventional breeding approaches have resulted in less success. Biotechnology has emerged as an additional and novel tool for deciphering the mechanism behind these stresses. The role of compatible solutes in abiotic stress tolerance has been studied extensively. Osmotic adjustment, at the physiological level, is an adaptive mechanism involved in drought or salinity tolerance, which permits the maintenance of turgor under conditions of water deficit, as it can counteract the effects of a rapid decline in leaf water potential. Increasing evidence from a series of in vivo and in vitro studies of the physiology, biochemistry, genetics, and molecular biology of plants suggest strongly that Glycine Betaine (GB) performs an important function in plants subjected to environmental stresses. It plays an adaptive role in mediating osmotic adjustment and protecting the sub-cellular structures in stressed plants, protection of the transcriptional and translational machineries and intervention as a molecular chaperone in the refolding of enzymes. Many important crops like rice do not accumulate glycinebetaine under stress conditions. Both the exogenous application of GB and the genetically engineered biosynthesis of GB in such crops is a promising strategy to increase stress tolerance. In this review we will discuss the importance of GB for abiotic stress tolerance in plants. Further, strategies like exogenic application and transgenic development of plants accumulating GB will be also be discussed. Work done on exogenic application and genetically engineered biosynthesis of GB will be listed and its advantages and limitations will be described.
Absorption of UV-B by DNA induces the formation of covalent bonds between adjacent pyrimidines. In maize and arabidopsis, plants deficient in chromatin remodeling show increased DNA damage compared to WT plants after a UV-B treatment. However, the role of enzymes that participate in DNA methylation in DNA repair after UV-B damage was not previously investigated. In this work, we analyzed how chromatin remodeling activities that have an effect on DNA methylation affects the repair of UV-B damaged DNA using plants deficient in the expression of DDM1 and ROS1. First, we analyzed their regulation by UV-B radiation in arabidopsis plants. Then, we demonstrated that ddm1 mutants accumulated more DNA damage after UV-B exposure compared to Col0 plants. Surprisingly, ros1 mutants show less CPDs and 6-4PPs than WT plants after the treatment under light conditions, while the repair under dark conditions is impaired. Transcripts for two photolyases are highly induced by UV-B in ros1 mutants, suggesting that the lower accumulation of photoproducts by UV-B is due to increased photorepair in these mutants. Finally, we demonstrate that oxidative DNA damage does not occur after UV-B exposure in arabidopsis plants; however, ros1 plants accumulate high levels of oxoproducts, while ddm1 mutants have less oxoproducts than Col0 plants, suggesting that both ROS1 and DDM1 have a role in the repair of oxidative DNA damage. Together, our data provide evidence that both DDM1 and ROS1, directly or indirectly, participate in UV-B induced- and oxidative DNA damage repair.
The effect of preillumination with low intensity (10μmol quanta m(-2)s(-1), 10min) light of different wavelengths in the spectral range of 550-730nm on photosynthesis and activity of PSII, the content of photosynthetic pigments and H2O2, as well as the peroxidase activity in the leaves of 26-d-old Arabidopsis thaliana wild-type (WT) plants in response to UV-A radiation was studied. UV-A decreased the activity of the PSII, the content of Chl a, Chl b and carotenoids, as well as increased the peroxidase activity and H2O2 level in the WT leaves. Preillumination of the leaves with red light (RL, λmax=664nm) reduced the inhibitory effect of UV radiation on photosynthesis and activity of the PSII, indicated by delayed light emission as well as the H2O2 level, but increased the peroxidase activity in the leaves compared to illumination by UV radiation only. Illumination with RL alone and the subsequent exposure of plants to darkness increased the peroxidase activity and the transcription activity of genes of the transcription factors APX1 and HYH. Preillumination of leaves with RL, then far red light (FRL, λmax=727nm) partially compensated the effect of the RL for all studied parameters, suggesting that the active form of phytochrome (PFR) is involved in these processes. Preillumination with the wavelengths of 550, 594 and 727nm only did not have a marked effect on photosynthesis. The hy2 mutant of Arabidopsis with reduced synthesis of the phytochrome B chromophore showed decreased resistance of PSII to UV-A compared with the WT of Arabidopsis. UV radiation reduced Chl a fluorescence much faster in the hy2 mutant compared to the WT. Preillumination of the hy2 mutant with RL did not affect the PSII activity and H2O2 level in UV-irradiated leaves. It is assumed that the formation of the increased resistance of the photosynthetic apparatus of Arabidopsis to UV-A radiation involves PFR and the antioxidant system of plants, partly by inducing transcriptional activity of some antioxidant and transcription factors genes.
Salinity is a major abiotic stress reducing the yield of a wide variety of crops all over the world. In order to investigate the antioxidant enzymes activity of four pumpkin genotypes (Iskenderun-4, AB-44, CU-7 and A-24) in response to salinity grown in hydroponic culture, 4 to 5 true leaf stages of pumpkin seedlings were subjected to 100 mM NaCl for 7 days. Salt stress induced changes in antioxidant enzymes, SOD, CAT, GR and APX, total chlorophyll content, lipid peroxidation and root and shoot fresh weight were measured. Salt treatment decreased root and shoots weight, chlorophyll content in salt sensitive genotypes more than salt tolerant genotypes. The four genotypes showed an increase in malondialdehyde (MDA) content under salt condition, but the increase in sensitive genotypes (CU-7 and A-24) were higher than that in salt tolerant genotypes (Iskenderun-4, AB-44). SOD, CAT, GR and APX activities increased salt stress. However these increases were higher in salt tolerant Iskenderun-4, AB- 44 than salt sensitive CU-7 and A-24. These results indicate that pumpkin genotypes respond to salt induced oxidative stress by enzymatic defense systems.
As sessile organisms, higher plants have evolved the capacity to sense and interpret diverse light signals to modulate their development. In Arabidopsis thaliana, low-intensity and long-wavelength UV-B light is perceived as an informational signal to mediate UV-B-induced photomorphogenesis. Here, we report that the multifunctional E3 ubiquitin ligase, CONSTITUTIVE PHOTOMORPHOGENESIS1 (COP1), a known key player in UV-B photomorphogenic responses, is also a UV-B-inducible gene. Two transcription factors, FAR-RED ELONGATED HYPOCOTYL3 (FHY3) and ELONGATED HYPOCOTYL5 (HY5), directly bind to distinct regulatory elements within the COP1 promoter, which are essential for the induction of the COP1 gene mediated by photomorphogenic UV-B signaling. Absence of FHY3 results in impaired UV-B-induced hypocotyl growth and reduced tolerance against damaging UV-B. Thus, FHY3 positively regulates UV-B-induced photomorphogenesis by directly activating COP1 transcription, while HY5 promotes COP1 expression via a positive feedback loop. Furthermore, FHY3 and HY5 physically interact with each other, and this interaction is diminished by UV-B. Together, our findings reveal that COP1 gene expression in response to photomorphogenic UV-B is controlled by a combinatorial regulation of FHY3 and HY5, and this UV-B-specific working mode of FHY3 and HY5 is distinct from that in far-red light and circadian conditions.
Publisher Summary This chapter presents detailed information on chlorophylls and carotenoids to give practical directions toward their quantitative isolation and determination in extracts from leaves, chloroplasts, thylakoid particles, and pigment proteins. The chapter focuses on the spectral characteristics and absorption coefficients of chlorophylls, pheophytins, and carotenoids, which are the basis for establishing equations to quantitatively determine them. Therefore, the specific absorption coefficients of the pigments are re-evaluated. This is achieved by using a two-beam spectrophotometer of the new generation, which allows programmed automatic recording and printing out of the proper wavelengths and absorbancy values. Several procedures have been developed for the separation of the photosynthetic pigments, including column (CC), paper (PC), and thin-layer chromatography (TLC) and high-pressure liquid chromatography (HPLC). All chloroplast carotenoids exhibit a typical absorption spectrum that is characterized by three absorption maxima (violaxanthin, neoxanthin) or two maxima with one shoulder (lutein and β-carotene) in the blue spectral region.
This work examines the involvement of haem oxygenase-1 (HO-1) in salicylic acid (SA)-induced alleviation of oxidative stress as a result of cadmium (Cd) stress in alfalfa (Medicago sativa L.) seedling roots. CdCl(2) exposure caused severe growth inhibition and Cd accumulation, which were potentiated by pre-treatment with zinc protoporphyrin (ZnPPIX), a potent HO-1 inhibitor. Pre-treatment of plants with the HO-1 inducer haemin or SA, both of which could induce MsHO1 gene expression, significantly reduced the inhibition of growth and Cd accumulation. The alleviation effects were also evidenced by a decreased content of thiobarbituric acid-reactive substances (TBARS). The antioxidant behaviour was confirmed by histochemical staining for the detection of lipid peroxidation and the loss of plasma membrane integrity. Furthermore, haemin and SA pre-treatment modulated the activities of ascorbate peroxidase (APX), superoxide dismutase (SOD), and guaiacol peroxidase (POD), or their corresponding transcripts. Significant enhancement of the ratios of reduced/oxidized homoglutathione (hGSH), ascorbic acid (ASA)/dehydroascorbate (DHA), and NAD(P)H/NAD(P)(+), and expression of their metabolism genes was observed, consistent with a decreased reactive oxygen species (ROS) distribution in the root tips. These effects are specific for HO-1, since ZnPPIX blocked the above actions, and the aggravated effects triggered by SA plus ZnPPIX were differentially reversed when carbon monoxide (CO) or bilirubin (BR), two catalytic by-products of HO-1, was added. Together, the results suggest that HO-1 is involved in the SA-induced alleviation of Cd-triggered oxidative stress by re-establishing redox homeostasis.
Harnessing the toxic properties of reactive oxygen species (ROS) to fight off invading pathogens can be considered a major evolutionary success story. All aerobic organisms have evolved the ability to regulate the levels of these toxic intermediates, whereas some have evolved elaborate signalling pathways to dramatically increase the levels of ROS and use them as weapons in mounting a defence response, a process commonly referred to as the oxidative burst. The balance between steady state levels of ROS and the exponential increase in these levels during the oxidative burst has begun to shed light on complex signalling networks mediated by these molecules. Here, we discuss the different sources of ROS that are present in plant cells and review their role in the oxidative burst. We further describe two well-studied ROS generating systems, the NADPH oxidase and apoplastic peroxidase proteins, and their role as the primary producers of ROS during pathogen invasion. We then discuss what is known about the metabolic and proteomic fluxes that occur in plant cells during the oxidative burst and after pathogen recognition, and try to highlight underlying biochemical processes that may provide more insight on the complex regulation of ROS in plants.
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.
Good reviews have been published over the years regarding many aspects of plant response to light, such as important advances
in understanding the molecular mechanisms of light perception, signaling and control of gene expression by the photoreceptors.
Moreover, many efforts have been undertaken on the manipulation of these mechanisms to improve horticultural crop production.
In this paper we present an overview about the photoreceptors, the relationship between their absorptive and reflective properties
and their control of plant development as well perspectives focused on photomorphogenesis manipulation.
KeywordsPhotomorphogenesis–Plant pigments–Photoperception–Light manipulation
The periodide method for quaternary ammonium compounds (QAC) analysis was modified to permit rapid screening of numerous replicate
plant samples. This procedure provides a valuable tool for assessing salt tolerance. Aqueous plant extracts were used without
further purification. Total QAC were precipitated as the periodide complexes at low pH. In neutral media, only choline periodide
crystallized; other major QAC (e.g. glycinebetaine) were soluble at pH 6.8–7.0 QAC concentration was then determined spectrophotometrically.
The influence of oven-drying of plant material at 80°C was tested by comparing this technique to lyophilization. Since QAC
values were essentially identical from both drying techniques, oven-drying was used routinely because of its economy and practicality.
The optimum range of acid concentration for precipitation of total QAC was established.
Phytochrome B (phyB) can adjust morphological and physiological responses according to changes in the red : far-red (R:FR) ratio. phyB-driven acclimation of plants to open environments (high R:FR ratio) increases carbon gain at the expense of increased water loss. This behaviour alleviates stressful conditions generated by an excess of light, but increases the chances of desiccation. Here we evaluated how phyB modulates this drought-tolerance response by comparing wild-type Arabidopsis thaliana adult plants to the null phyB in response to water shortage. phyB wilted before the wild type, and this was due to phyB maintaining open stomata under a reduction in soil water availability. Although phyB presented enhanced ABA levels under well-watered conditions, this mutant was less sensitive than the wild type in diminishing stomatal conductance in response to exogenous ABA application. Reduced sensitivity to ABA in phyB correlated with a lower expression of ABCG22, which encodes a putative ABA influx transporter, and PYL5, which encodes a soluble ABA receptor. Furthermore, the expression of RAB18 and RD29A, both typical ABA-induced genes, was lower in phyB than the wild type after ABA treatment. We propose that phyB contributes to the acclimation of plants to open environments by enhancing ABA sensitivity when soil water becomes limiting.
Modulation of water relations, activities of antioxidant enzymes and ion accumulation was assessed in the plants of two wheat cultivars S-24 (salt tolerant) and MH-97 (moderately salt sensitive) subjected to saline conditions and glycinebetaine (GB) applied foliarly. Different levels of GB, i.e., 0 (unsprayed), 50 and 100 mM (in 0.10% Tween-20 solution) were applied to the wheat plants at the vegetative growth stage. Leaf water potential, leaf osmotic potential and turgor potential were decreased due to salt stress. Salt stress increased the Na+ and Cl− accumulation coupled with a decrease in K+ and Ca2+ in the leaves and roots of both cultivars thereby decreasing tissue K+/Na+ and Ca2+/Na+ ratios. Furthermore, salt stress decreased the activities of superoxide dismutase (SOD), whereas it increased the activities of catalase (CAT) and peroxidase (POD) in both wheat cultivars. However, accumulation of GB in the leaves of both wheat cultivars was consistently increased with an increase in concentration of exogenous GB application under both non-saline and saline conditions. Accumulation of Na+ was decreased with an increase in K+ accumulation upon a consistent increase in GB accumulation under salt stress conditions thereby resulting in better K+/Na+ and Ca2+/Na+ ratios in the leaves and roots. High accumulation of GB and K+ mainly contributed to osmotic adjustment, which is one of the factors known to be responsible for improving growth and yield under salt stress. The activities of all antioxidant enzymes, SOD, CAT and POD were enhanced by GB application in cv. MH-97 under saline conditions, whereas all these except SOD were reduced in cv. S-24. It is likely that both applied GB and intrinsic SOD scavenged ROS in the tolerant cultivar thereby resulting into low activities of CAT and POD enzymes under salt stress. In conclusion, the adverse effects of salt stress on wheat can be alleviated by the exogenous application of 100 mM GB by modulating activities of antioxidant enzymes and changes in water relations and ion homeostasis. Furthermore, effectiveness of GB application on regulation of activities of antioxidant enzymes was found to be cultivar-specific.
The behaviour of enzymes involved in nitrogen metabolism, as well as oxidative stress generation and heme oxygenase gene and protein expression and activity, were analysed in soybean (Glycine max L.) nodules exposed to 50, 100 and 200 mM NaCl concentrations. A significant increase in lipid peroxidation was found with 100 and 200 mM salt treatments. Moreover, superoxide dismutase, catalase and peroxidase activities were decreased under 100 and 200 mM salt. Nitrogenase activity and leghemeoglobin content were diminished and ammonium content increased only under 200 mM NaCl. At 100 mM NaCl, glutamine synthetase (GS) and NADH-glutamate dehydrogenase (GDH) activities were similar to controls, whereas a significant increase (64%) in NADH-glutamate synthase (GOGAT) activity was observed. GS activity did not change at 200 mM salt treatment, but GOGAT and GDH significantly decreased (40 and 50%, respectively). When gene and protein expression of GS and GOGAT were analysed, it was found that they were positively correlated with enzyme activities. In addition, heme oxygenase (HO) activity, protein synthesis and gene expression were significantly increased under 100 mM salt treatment. Our data demonstrated that the up-regulation of HO, as part of antioxidant defence system, could be protecting the soybean nodule nitrogen fixation and assimilation under saline stress conditions.
Previous pharmacological results confirmed that haem oxygenase-1 (HO-1) is involved in protection of cells against ultraviolet
(UV)-induced oxidative damage in soybean [Glycine max (L.) Merr.] seedlings, but there remains a lack of genetic evidence. In this study, the link between Arabidopsis thaliana HO-1 (HY1) and UV-C tolerance was investigated at the genetic and molecular levels. The maximum inducible expression of HY1 in wild-type Arabidopsis was observed following UV-C irradiation. UV-C sensitivity was not observed in ho2, ho3, and ho4 single and double mutants. However, the HY1 mutant exhibited UV-C hypersensitivity, consistent with the observed decreases in chlorophyll content, and carotenoid and
flavonoid metabolism, as well as the down-regulation of antioxidant defences, thereby resulting in severe oxidative damage.
The addition of the carbon monoxide donor carbon monoxide-releasing molecule-2 (CORM-2), in particular, and bilirubin (BR),
two catalytic by-products of HY1, partially rescued the UV-C hypersensitivity, and other responses appeared in the hy1 mutant. Transcription factors involved in the synthesis of flavonoid or UV responses were induced by UV-C, but reduced in
the hy1 mutant. Overall, the findings showed that mutation of HY1 triggered UV-C hypersensitivity, by impairing carotenoid and flavonoid
synthesis and antioxidant defences.
Stresses resulting from high transpiration demand induce adjustments in plants that lead to reductions of water loss. These adjustments, including changes in water absorption, transport and/or loss by transpiration, are crucial to normal plant development. Tomato wild type (WT) and phytochrome A mutant plants, fri1-1, were exposed to either low or high transpiration demand conditions and several morphological and physiological changes were measured during stressing conditions. Mutant plants rapidly wilted compared to WT plants after exposure to high evaporative demand. Root size and hydraulic conductivity did not show significant differences between genotypes, suggesting that water absorption and transport through this organ could not explain the observed phenotype. Moreover, stomata density was similar between genotypes, whereas transpiration and stomata conductance were both lower in mutant than in wild type plants. This was accompanied by a lower stem specific hydraulic conductivity in mutant plants than in wild type, which was associated to smaller xylem vessel number and transversal area in fri1-1 plants, producing a reduction in water supply to the leaves, rapidly reaching wilting under high evaporative demand. Phytochrome A signaling might facilitate the adjustment to environments differing widely in water evaporative demand in part through the modulation of xylem dimensions.
The tomato (Solanum lycopersicum L.) plant is both an economically important food crop and an ideal dicot model to investigate various physiological phenomena not possible in Arabidopsis thaliana. Due to the great diversity of tomato cultivars used by the research community, it is often difficult to reliably compare phenotypes. The lack of tomato developmental mutants in a single genetic background prevents the stacking of mutations to facilitate analysis of double and multiple mutants, often required for elucidating developmental pathways.
We took advantage of the small size and rapid life cycle of the tomato cultivar Micro-Tom (MT) to create near-isogenic lines (NILs) by introgressing a suite of hormonal and photomorphogenetic mutations (altered sensitivity or endogenous levels of auxin, ethylene, abscisic acid, gibberellin, brassinosteroid, and light response) into this genetic background. To demonstrate the usefulness of this collection, we compared developmental traits between the produced NILs. All expected mutant phenotypes were expressed in the NILs. We also created NILs harboring the wild type alleles for dwarf, self-pruning and uniform fruit, which are mutations characteristic of MT. This amplified both the applications of the mutant collection presented here and of MT as a genetic model system.
The community resource presented here is a useful toolkit for plant research, particularly for future studies in plant development, which will require the simultaneous observation of the effect of various hormones, signaling pathways and crosstalk.
The aim of this study was to investigate the effects of cadmium stress on growth and physiological traits in young date palms and to evaluate the role of exogenous proline in cadmium stress alleviation. Two-year-old date palm plants were subjected for five months to different cadmium stress levels (10 and 30mgCdCl2kg-1 soil) supplied or not with exogenous proline (20mM) through irrigation water. Cadmium stress caused a decline in growth, macronutrient contents (Ca2+, Mg2+, and K+), membrane stability index (MSI), starch content and guaiacol peroxidase (POD) activity. In contrast, an increase of H2O2, soluble sugar, ascorbate peroxidase (APX) activity as well as total polyphenols was observed. Interestingly, exogenous proline effectively mitigated the adverse effects of cadmium on young date palms. Indeed, Cd accumulation was decreased and antioxidant defense systems were significantly (p≤0.05) activated in date palm leaves and roots. Consequently, growth and mineral nutrition were enhanced when proline was added to Cd stressed plants.
Proline accumulation at the cost of growth inhibition is commonly observed in plants subjected to salt stress, because an increased amount of energy is stored as nitrogen. The hypothesis tested in this study was that exogenous proline addition will alleviate deleterious effects of high salinity on plant growth. Eurya emarginata plants were treated with 10 mM proline and 200 mM NaCl for 35 days. Growth-related parameters were determined in leaves, including fresh weight, tissue water content, concentrations of malondialdehyde (MDA), proline, Na+, and K+, and activities of superoxide dismutase, catalase, peroxidase, glutathione peroxidase (GPX), H + -ATPase, pyrroline-5-carboxylate synthetase (P5CS) and proline dehydrogenase (PDH). Exogenous proline increased fresh weight, endogenous proline and K+ concentrations, and reduced Na+ and MDA concentrations in under salt treatment. These effects were not observed in non-salt-treated soil. Increased K+ and decreased MDA concentrations were associated with increased H+-ATPase activity and increased activities of antioxidant enzymes except GPX, respectively. Although P5CS activity was sharply reduced and PDH activity remained unchanged, exogenous proline compensated for the decrease in endogenous synthetic proline, indicating more energy stored as nitrogen would be used for growth. Correlations between enzyme activities and MDA or ion concentrations were observed, indicating that changes at the enzyme level may underlie the patterns of salt stress, and accordingly affect accumulation of ions and peroxide. Thus, exogenous proline significantly affected the salinity tolerance of Eurya emarginata, through diverse protective effects on water relations, ionic and osmotic adjustment, and antioxidant defense. © 2015, Franciszek Górski Institute of Plant Physiology, Polish Academy of Sciences, Kraków.
Phytochrome mutants (phyA, phyB and phyAB) of Arabidopsis thaliana were grown under ambient and UV-excluded sunlight to understand their influence on growth and development by mutual exclusion. Phytochrome A and B played a complementary role in the regulation of germination. Suppression of hypocotyl length was predominantly under the control of phytochrome B; UV photoreceptors were active in suppression of hypocotyl growth only in phyB and phyAB mutants. Exclusion of UV promoted the number and the area of rosette leaves only in presence of phytochrome A and B. Phytochrome mutation reduced petiole length, whereas UV exclusion led to an increase. Requirement of long-day period for flowering was removed in the mutants. Under short-day conditions, flowering was predominantly under the control of phytochrome B, since phyB mutants flowered earlier than phyA mutants. Solar UV regulates the number of boltings and number of siliques per plant. Overall biomass of the plants is enhanced by the exclusion of UV only in the wild type. The interaction of phytochromes with UV photoreceptors is discussed in the paper.
Cadmium (Cd) is an important metal due to its industrial use but also one of the most dangerous metals because of its accumulation in the environment. This can eventually lead to entrance into the food chain if the Cd is taken up by crop plants used for feeding animals and humans. Thus, a large number of reviews have discussed the many aspects of stress induced by Cd and other metals in a wide range of species. In relation to plants, useful reviews have been published over the years regarding molecular and biochemical aspects of Cd stress. In this minireview, we have concentrated on promising and emerging topics of Cd-stress research in plants, such as hormonal control of the antioxidant system and interaction between organisms and plants.
As a key enzyme of heme degradation, heme oxygenase (HO) is essential in phytochrome chromophore synthesis, cell protection and stomatal regulation in higher plants. The activity or transcript of HO has been detected in many plant species. Arabidopsis HO1 (HY1), the first map-based cloning gene, could catalyze the transition of heme to carbon monoxide (CO) in vivo. In this review, we first describe HO1 is evolutionarily conserved through comparative analysis of different plants HO1 proteins. Then, we highlight the role of HO1 involved in plants responses to various abiotic stresses such as salinity, drought, cadmium, mercury, ultraviolet radiation, reactive oxygen species, abscisic acid, and hematin. Based on the relationship analysis between nitric oxide, CO, and hydrogen peroxide, we proposed HO1 may be a central repeater for cross talk among them in plants.
S-like ribonucleases (S-like RNases) are homologous to S-ribonucleases (S-RNases), but are not involved in self-incompatibility. In dicotyledonous plants, S-like RNases play an important role in phosphate recycling during senescence and are induced by inorganic phosphate-starvation and in response to defense and mechanical wounding. However, little information about the functions of the S-like RNase in monocots has been reported. Here, we investigated the expression patterns and roles of an S-like RNase gene, OsRNS4, in abscisic acid (ABA)-mediated responses and phytochrome-mediated light responses as well as salinity tolerance in rice. The OsRNS4 gene was expressed at relatively high levels in leaves although its transcripts were detected in various organs. OsRNS4 expression was regulated by salt, PEG and ABA. The seedlings overexpressing OsRNS4 had longer coleoptiles and first leaves than wild-type seedlings under red light (R) and far-red light (FR), suggesting negative regulation of OsRNS4 in photomorphogenesis in rice seedlings. Moreover, ABA-induced growth inhibition of rice seedlings was significantly increased in the OsRNS4-overexpression (OsRNS4-OX) lines compared with that in WT, suggesting that OsRNS4 probably acts as a positive regulator in ABA responses in rice seedlings. In addition, our results demonstrate that OsRNS4-OX lines have enhanced tolerance to high salinity compared to WT. Our findings supply new evidence on the functions of monocot S-like RNase in regulating photosensitivity and abiotic stress responses.
In photosynthetic cells the plastidic ascorbate-glutathione pathway is considered the major sequence involved in the elimination of active oxygen species. Ascorbate peroxidase (APO; EC 1.11.1.11) is an essential constituent of this pathway. In the present paper control of the appearance of APO was studied in the cotyledons of mustard (Sinapis alba L.) seedlings with the following results: (i) Two isoforms of APO (APO I, APO II) could be separated by anion-exchange chromatography; APO I is a plastidic protein, while APO II is extraplastidic, very probably cytosolic. (ii) The appearance of APO is regulated by light via phytochrome. This control is observed with both isoforms. Moreover, a strong positive control over APO II appearance (very probably over APO II synthesis) is exerted by photooxidative treatment of the plastids. (iii) Additional synthesis of extraplastidic APO II is induced by a signal created by intraplastidic pigment-photosensitized oxidative stress. The response is obligatorily oxygen-dependent and abolished by quenchers of singlet oxygen such as α-tocopherol and p-benzoquinone. (iv) A short-term (4 h) photooxidative treatment suffices to saturate the signal. Signal transduction cannot be abolished or diminished by replacing the plants in non-photooxidizing conditions. Several observations indicate that control of APO synthesis by active oxygen is not an experimental artifact but a natural phenomenon.
Proline has been recognized as a multi-functional molecule, accumulating in high concentrations in response to a variety of abiotic stresses. It is able to protect cells from damage by acting as both an osmotic agent and a radical scavenger. Proline accumulated during a stress episode is degraded to provide a supply of energy to drive growth once the stress is relieved. Proline homeostasis is important for actively dividing cells as it helps to maintain sustainable growth under long-term stress. It also underpins the importance of the expansion of the proline sink during the transition from vegetative to reproductive growth and the initiation of seed development. Its role in the reproductive tissue is to stabilize seed set and productivity. Thus to cope with abiotic stress, it is important to develop strategies to increase the proline sink in the reproductive tissue. We give an holistic account of proline homeostasis, taking into account the regulation of proline synthesis, its catabolism and intra- and intercellular transport, all of which are vital components of growth and development in plants challenged by stress.
Ultraviolet-B (UV-B) is a relatively minor component of sunlight, but can induce stress-related physiological processes or UV-B-specific photomorphogenic responses in plants. In the last decade, significant progress has been made in understanding the UV-B photomorphogenic pathway, including identification of the key components in the pathway, molecular characterization of UV-B photoreceptor and perception mechanism, and elucidation of the signal transduction mechanisms from the photoactivated UV-B receptor to downstream gene expression. This review summarizes the key players identified to date in the UV-B photomorphogenic pathway and their roles in mediating UV-B signal transduction.
Phytochrome apoproteins in angiosperms are encoded by a small gene family. Tomato (Solatium lycopersicum L.) serves well as a dicotyledonous model system for elucidating the extent of this gene family, its expression patterns, and the roles of individual members of the family. Five phytochrome genes (PHYA, PHYB1, PHYB2, PHYE and PHYF have been characterized in tomato. Quantitative measurements of transcript abundances from each tomato PHY throughout the life cycle indicate that transcript levels generally range from 10 to 100 μmol mol−1 total mRNA, in the following order of decreasing abundance: PHYA, PHYB1, PHYE, PHYB2 and PHYF. PHYA transcripts were found to be most abundant in seedling roots, while PHYB2 and PHYF transcripts were expressed preferentially in fruit. PHYA mutants (fri) have been found to be the consequence of a single nucleotide substitution adjacent to the 3′ terminus of an intron. What are almost certainly PHYB1 mutants have also been described, although the molecular nature of these mutants remains to be revealed. Efforts to obtain PHYB2, PHYE and PHYF mutants are currently underway.
Proline, which increases proportionately faster than other amino acids in plants under water stress, has been suggested as an evaluating parameter for irrigation scheduling and for selecting drought-resistant varieties. The necessity to analyze numerous samples from multiple replications of field grown materials prompted the development of a simple, rapid colorimetric determination of proline. The method detected proline in the 0.1 to 36.0 moles/g range of fresh weight leaf material.
Ultrastructure of plant chloroplasts was studied by a single-molecule spectroscopy setup at a temperature of 77 K exploring spatial location of photosystems. Two chloroplast thylakoid membrane regions were visualized by fluorescence microscopy and detected at different wavelengths. The size of these regions and the spatial resolution of the microscope allowed us to measure their chlorophyll fluorescence emission spectra of these membrane domains. While the grana regions are characterized by a predominant presence of Photosystem II pigment–protein complexes emitting at 685 nm, Photosystem I complexes are localized in stroma regions and emit at 730 nm.
Heat stress due to increased temperature is an agricultural problem in many areas in the world. Transitory or constantly high temperatures cause an array of morpho-anatomical, physiological and biochemical changes in plants, which affect plant growth and development and may lead to a drastic reduction in economic yield. The adverse effects of heat stress can be mitigated by developing crop plants with improved thermotolerance using various genetic approaches. For this purpose, however, a thorough understanding of physiological responses of plants to high temperature, mechanisms of heat tolerance and possible strategies for improving crop thermotolerance is imperative. Heat stress affects plant growth throughout its ontogeny, though heat-threshold level varies considerably at different developmental stages. For instance, during seed germination, high temperature may slow down or totally inhibit germination, depending on plant species and the intensity of the stress. At later stages, high temperature may adversely affect photosynthesis, respiration, water relations and membrane stability, and also modulate levels of hormones and primary and secondary metabolites. Furthermore, throughout plant ontogeny, enhanced expression of a variety of heat shock proteins, other stress-related proteins, and production of reactive oxygen species (ROS) constitute major plant responses to heat stress. In order to cope with heat stress, plants implement various mechanisms, including maintenance of membrane stability, scavenging of ROS, production of antioxidants, accumulation and adjustment of compatible solutes, induction of mitogen-activated protein kinase (MAPK) and calcium-dependent protein kinase (CDPK) cascades, and, most importantly, chaperone signaling and transcriptional activation. All these mechanisms, which are regulated at the molecular level, enable plants to thrive under heat stress. Based on a complete understanding of such mechanisms, potential genetic strategies to improve plant heat-stress tolerance include traditional and contemporary molecular breeding protocols and transgenic approaches. While there are a few examples of plants with improved heat tolerance through the use of traditional breeding protocols, the success of genetic transformation approach has been thus far limited. The latter is due to limited knowledge and availability of genes with known effects on plant heat-stress tolerance, though these may not be insurmountable in future. In addition to genetic approaches, crop heat tolerance can be enhanced by preconditioning of plants under different environmental stresses or exogenous application of osmoprotectants such as glycinebetaine and proline. Acquiring thermotolerance is an active process by which considerable amounts of plant resources are diverted to structural and functional maintenance to escape damages caused by heat stress. Although biochemical and molecular aspects of thermotolerance in plants are relatively well understood, further studies focused on phenotypic flexibility and assimilate partitioning under heat stress and factors modulating crop heat tolerance are imperative. Such studies combined with genetic approaches to identify and map genes (or QTLs) conferring thermotolerance will not only facilitate marker-assisted breeding for heat tolerance but also pave the way for cloning and characterization of underlying genetic factors which could be useful for engineering plants with improved heat tolerance.
Hormones are likely to be important factors modulating the light-dependent anthocyanin accumulation. Here we analyzed anthocyanin contents in hypocotyls of near isogenic Micro-Tom (MT) tomato lines carrying hormone and phytochrome mutations, as single and double-mutant combinations. In order to recapitulate mutant phenotype, exogenous hormone applications were also performed. Anthocyanin accumulation was promoted by exogenous abscisic acid (ABA) and inhibited by gibberellin (GA), in accordance to the reduced anthocyanin contents measured in ABA-deficient (notabilis) and GA-constitutive response (procera) mutants. Exogenous cytokinin also enhanced anthocyanin levels in MT hypocotyls. Although auxin-insensitive diageotropica mutant exhibited higher anthocyanin contents, pharmacological approaches employing exogenous auxin and a transport inhibitor did not support a direct role of the hormone in anthocyanin accumulation. Analysis of mutants exhibiting increased ethylene production (epinastic) or reduced sensitivity (Never ripe), together with pharmacological data obtained from plants treated with the hormone, indicated a limited role for ethylene in anthocyanin contents. Phytochrome-deficiency (aurea) and hormone double-mutant combinations exhibited phenotypes suggesting additive or synergistic interactions, but not fully espistatic ones, in the control of anthocyanin levels in tomato hypocotyls. Our results indicate that phytochrome-mediated anthocyanin accumulation in tomato hypocotyls is modulated by distinct hormone classes via both shared and independent pathways.
In plants, the heat stress response (HSR) is highly conserved and involves multiple pathways, regulatory networks and cellular compartments. At least four putative sensors have recently been proposed to trigger the HSR. They include a plasma membrane channel that initiates an inward calcium flux, a histone sensor in the nucleus, and two unfolded protein sensors in the endoplasmic reticulum and the cytosol. Each of these putative sensors is thought to activate a similar set of HSR genes leading to enhanced thermotolerance, but the relationship between the different pathways and their hierarchical order is unclear. In this review, we explore the possible involvement of different thermosensors in the plant response to warming and heat stress.
We report that phytochrome B (phyB) mutants exhibit improved drought tolerance compared to wild type (WT) rice (Oryza sativa L. cv. Nipponbare). To understand the underlying mechanism by which phyB regulates drought tolerance, we analyzed root growth and water loss from the leaves of phyB mutants. The root system showed no significant difference between the phyB mutants and WT, suggesting that improved drought tolerance has little relation to root growth. However, phyB mutants exhibited reduced total leaf area per plant, which was probably due to a reduction in the total number of cells per leaf caused by enhanced expression of Orysa;KRP1 and Orysa;KRP4 (encoding inhibitors of cyclin-dependent kinase complex activity) in the phyB mutants. In addition, the developed leaves of phyB mutants displayed larger epidermal cells than WT leaves, resulting in reduced stomatal density. phyB deficiency promoted the expression of both putative ERECTA family genes and EXPANSIN family genes involved in cell expansion in leaves, thus causing greater epidermal cell expansion in the phyB mutants. Reduced stomatal density resulted in reduced transpiration per unit leaf area in the phyB mutants. Considering all these findings, we propose that phyB deficiency causes both reduced total leaf area and reduced transpiration per unit leaf area, which explains the reduced water loss and improved drought tolerance of phyB mutants.
Heme oxygenase-1 (HO-1) has been recently identified as an endogenous signaling system in animals. In this study, HO-1 upregulation and its role in acquired salt tolerance (salinity acclimation) were investigated in wheat plants. We discovered that pretreatment with a low concentration of NaCl (25 mmol/L) not only led to the induction of HO-1 protein and gene expression, as well as enhanced HO activity, but also to a salinity acclimatory response thereafter. The effect is specific for HO-1, since the potent HO-1 inhibitor zinc protoporphyrin IX blocks the above cytoprotective actions, and the cytotoxic responses conferred by 200 mmol/L NaCl are reversed partially when HO-1 inducer hemin is added. Heme oxygenase catalytic product, carbon monoxide (CO) aqueous solution pretreatment, mimicked the salinity acclimatory responses. Meanwhile, the CO-triggered re-establishment of reactive oxygen species (ROS) homeostasis was mainly guaranteed by the induction of total and isozymatic activities, or corresponding transcripts of superoxide dismutase, ascorbate peroxidase, and cytosolic peroxidase (POD), as well as the downregulation of NADPH oxidase expression and cell-wall POD activity. A requirement of hydrogen peroxide homeostasis for HO-1-mediated salinity acclimation was also discovered. Taken together, the above results suggest that the upregulation of HO-1 expression was responsible for the observed salinity acclimation through the regulation of ROS homeostasis.
The ability to withstand environmental temperature variation is essential for plant survival. Former studies in Arabidopsis revealed that light signalling pathways had a potentially unique role in shielding plant growth and development from seasonal and daily fluctuations in temperature. In this paper we describe the molecular circuitry through which the light receptors cry1 and phyB buffer the impact of warm ambient temperatures. We show that the light signalling component HFR1 acts to minimise the potentially devastating effects of elevated temperature on plant physiology. Light is known to stabilise levels of HFR1 protein by suppressing proteasome-mediated destruction of HFR1. We demonstrate that light-dependent accumulation and activity of HFR1 are highly temperature dependent. The increased potency of HFR1 at warmer temperatures provides an important restraint on PIF4 that drives elongation growth. We show that warm ambient temperatures promote the accumulation of phosphorylated PIF4. However, repression of PIF4 activity by phyB and cry1 (via HFR1) is critical for controlling growth and maintaining physiology as temperatures rise. Loss of this light-mediated restraint has severe consequences for adult plants which have greatly reduced biomass.