Effect of methyl jasmonate and GA3 on canola (Brassica napus L.) growth, antioxidants activity, and nutrient concentration cultivated in salt-affected soils.

Salinity stress is a significant challenge in agricultural production. When soil contains high salts, it can adversely affect plant growth and productivity due to the high concentration of soluble salts in the soil water. To overcome this issue, foliar applications of methyl jasmonate (MJ) and gibberellic acid (GA3) can be productive amendments. Both can potentially improve the plant's growth attributes and flowering, which are imperative in improving growth and yield. However, limited literature is available on their combined use in canola to mitigate salinity stress. That's why the current study investigates the impact of different levels of MJ (at concentrations of 0.8, 1.6, and 3.2 mM MJ) and GA3 (0GA3 and 5 mg/L GA3) on canola cultivated in salt-affected soils. Applying all the treatments in four replicates. Results indicate that the application of 0.8 mM MJ with 5 mg/L GA3 significantly enhances shoot length (23.29%), shoot dry weight (24.77%), number of leaves per plant (24.93%), number of flowering branches (26.11%), chlorophyll a (31.44%), chlorophyll b (20.28%) and total chlorophyll (27.66%) and shoot total soluble carbohydrates (22.53%) over control. Treatment with 0.8 mM MJ and 5 mg/L GA3 resulted in a decrease in shoot proline (48.17%), MDA (81.41%), SOD (50.59%), POD (14.81%) while increase in N (10.38%), P (15.22%), and K (8.05%) compared to control in canola under salinity stress. In conclusion, 0.8 mM MJ + 5 mg/L GA3 can improve canola growth under salinity stress. More investigations are recommended at the field level to declare 0.8 mM MJ + 5 mg/L GA3 as the best amendment for alleviating salinity stress in different crops.

Gamma-aminobutyric acid (GABA) improves salinity stress tolerance in soybean seedlings by modulating their mineral nutrition, osmolyte contents, and ascorbate-glutathione cycle.

BACKGROUND: In plants, GABA plays a critical role in regulating salinity stress tolerance. However, the response of soybean seedlings (Glycine max L.) to exogenous gamma-aminobutyric acid (GABA) under saline stress conditions has not been fully elucidated. RESULTS: This study investigated the effects of exogenous GABA (2 mM) on plant biomass and the physiological mechanism through which soybean plants are affected by saline stress conditions (0, 40, and 80 mM of NaCl and Na2SO4 at a 1:1 molar ratio). We noticed that increased salinity stress negatively impacted the growth and metabolism of soybean seedlings, compared to control. The root-stem-leaf biomass (27- and 33%, 20- and 58%, and 25- and 59% under 40- and 80 mM stress, respectively]) and the concentration of chlorophyll a and chlorophyll b significantly decreased. Moreover, the carotenoid content increased significantly (by 35%) following treatment with 40 mM stress. The results exhibited significant increase in the concentration of hydrogen peroxide (H2O2), malondialdehyde (MDA), dehydroascorbic acid (DHA) oxidized glutathione (GSSG), Na+, and Cl- under 40- and 80 mM stress levels, respectively. However, the concentration of mineral nutrients, soluble proteins, and soluble sugars reduced significantly under both salinity stress levels. In contrast, the proline and glycine betaine concentrations increased compared with those in the control group. Moreover, the enzymatic activities of ascorbate peroxidase, monodehydroascorbate reductase, glutathione reductase, and glutathione peroxidase decreased significantly, while those of superoxide dismutase, catalase, peroxidase, and dehydroascorbate reductase increased following saline stress, indicating the overall sensitivity of the ascorbate-glutathione cycle (AsA-GSH). However, exogenous GABA decreased Na+, Cl-, H2O2, and MDA concentration but enhanced photosynthetic pigments, mineral nutrients (K+, K+/Na+ ratio, Zn2+, Fe2+, Mg2+, and Ca2+); osmolytes (proline, glycine betaine, soluble sugar, and soluble protein); enzymatic antioxidant activities; and AsA-GSH pools, thus reducing salinity-associated stress damage and resulting in improved growth and biomass. The positive impact of exogenously applied GABA on soybean plants could be attributed to its ability to improve their physiological stress response mechanisms and reduce harmful substances. CONCLUSION: Applying GABA to soybean plants could be an effective strategy for mitigating salinity stress. In the future, molecular studies may contribute to a better understanding of the mechanisms by which GABA regulates salt tolerance in soybeans.

Enhanced photochemical efficiency of PSII in Prosopis juliflora suggests contribution to invasion advantage over native C3 xero-halophytes under salt stress.

Chlorophyll a fluorescence parameters related to PSII photochemistry, photoprotection and photoinhibition were investigated in four C3 plant species growing in their natural habitat: Prosopis juliflora ; Abutilon indicum ; Salvadora persica ; and Phragmites karka . This study compared the light reaction responses of P. juliflora , an invasive species, with three native co-existing species, which adapt to varying water deficit and high salt stress. Chlorophyll a fluorescence quenching analyses revealed that P. juliflora had the highest photochemical quantum efficiency and yield, regulated by higher fraction of open reaction centres and reduced photoprotective energy dissipation without compromising the integrity of photosynthetic apparatus due to photoinhibition. Moreover, the elevated values of parameters obtained through polyphasic chlorophyll a fluorescence induction kinetics, which characterise the photochemistry of PSII and electron transport, highlighted the superior performance index of energy conservation in the transition from excitation to the reduction of intersystem electron carriers for P. juliflora compared to other species. Enhanced pigment contents and their stoichiometry in P. juliflora apparently contributed to upregulating fluxes and yields of energy absorbance, trapping and transport. This enhanced photochemistry, along with reduced non-photochemical processes, could explain the proclivity for invasion advantage in P. juliflora across diverse stress conditions.

Exogenous Hemin enhances the antioxidant defense system of rice by regulating the AsA-GSH cycle under NaCl stress.

Abiotic stress caused by soil salinization remains a major global challenge that threatens and severely impacts crop growth, causing yield reduction worldwide. In this study, we aim to investigate the damage of salt stress on the leaf physiology of two varieties of rice (Huanghuazhan, HHZ, and Xiangliangyou900, XLY900) and the regulatory mechanism of Hemin to maintain seedling growth under the imposed stress. Rice leaves were sprayed with 5.0 µmol·L-1 Hemin or 25.0 µmol·L-1 ZnPP (Zinc protoporphyrin IX) at the three leaf and one heart stage, followed by an imposed salt stress treatment regime (50.0 mmol·L-1 sodium chloride (NaCl)). The findings revealed that NaCl stress increased antioxidant enzymes activities and decreased the content of nonenzymatic antioxidants such as ascorbate (AsA) and glutathione (GSH). Furthermore, the content of osmoregulatory substances like soluble proteins and proline was raised. Moreover, salt stress increased reactive oxygen species (ROS) content in the leaves of the two varieties. However, spraying with Hemin increased the activities of antioxidants such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) and accelerated AsA-GSH cycling to remove excess ROS. In summary, Hemin reduced the effect of salt stress on the physiological characteristics of rice leaves due to improved antioxidant defense mechanisms that impeded lipid peroxidation. Thus, Hemin was demonstrated to lessen the damage caused by salt stress.

Application of prohexadione-calcium priming affects Brassica napus L. seedlings by regulating morph-physiological characteristics under salt stress.

Salinity stress imposes severe constraints on plant growth and development. Here, we explored the impacts of prohexadione-calcium (Pro-Ca) on rapeseed growth under salt stress. We designed a randomized block design pot experiment using two rapeseed varieties, 'Huayouza 158R' and 'Huayouza 62'. We conducted six treatments, S0: non-primed + 0 mM NaCl, Pro-Ca+S0: Pro-Ca primed + 0 mM NaCl, S100: non-primed + 100 mM NaCl, Pro-Ca+S100: Pro-Ca primed + 100 mM NaCl, S150: non-primed + 150 mM NaCl, Pro-Ca+S150: Pro-Ca primed + 150 mM NaCl. The morphophysiological characteristics, and osmoregulatory and antioxidant activities were compared for primed and non-primed varieties. Our data analysis showed that salt stress induced morph-physiological traits and significantly reduced the antioxidant enzyme activities in both rapeseed varieties. The Pro-Ca primed treatment significantly improved seedlings, root, and shoot morphological traits and accumulated more dry matter biomass under salt stress. Compared to Huayouza 158R, Huayouza 62 performed better with the Pro-Ca primed treatment. The Pro-Ca primed treatment significantly enhanced chlorophyll content, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and actual photochemical quantum efficiency (ФPSII). Furthermore, the Pro-Ca primed treatment also improved ascorbic acid (ASA) content, superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) activity, and stimulated the accumulation of soluble proteins. These findings strongly suggested that the Pro-Ca primed treatment may effectively counteract the negative impacts of salinity stress by regulating the morph-physiological and antioxidant traits.

Mitigating salt stress by conditioning seeds with ultraviolet light (UV-C) in white oats (Avena sativa L.).

Seed conditioning with ultraviolet light (UV-C) might (1) improve crop yield and quality, (2) reduce the use of agrochemicals during cultivation, and (3) increase plant survival in high salinity environments. The aim of this study was to examine the effects of UV-C conditioning of white oat seeds at two doses (0.85 and 3.42 kJ m-2) under salinity stress (100 mM NaCl). Seeds were sown on germination paper and kept in a germination chamber at 20°C. Germination and seedling growth parameters were evaluated after 5 and 10 days. Data demonstrated that excess salt reduced germination and initial growth of white oat seedlings. In all the variables analyzed, exposure of seeds to UV-C under salt stress exerted a positive effect compared to non-irradiated control. The attenuating influence of UV-C in germination was greater at 0.85 than at 3.42 kJ m-2. Thus, data indicate that conditioning white oat seeds in UV-C light produced greater tolerance to salt stress. These findings suggest that UV-C conditioning of white oat seeds may be considered as a simple and economical strategy to alleviate salt-induced stress.

Unraveling the interplay between environmental microplastics and salinity stress on Mytilus galloprovincialis larval development: A holistic exploration.

The rise of plastic production has triggered a surge in plastic waste, overwhelming marine ecosystems with microplastics. The effects of climate change, notably changing salinity, have shaped the dynamics of coastal lagoons. Thus, understanding the combined impact of these phenomena on marine organisms becomes increasingly crucial. To address these knowledge gaps, we investigated for the first time the interactive effects of environmental microplastics (EMPs) and increased salinity on the early development of Mytilus galloprovincialis larvae. Morphological assessments using the larval embryotoxicity test revealed larval anomalies and developmental arrests induced by EMPs and increased salinity. Transcriptomic analyses targeting 12 genes involved in oxidative stress, apoptosis, DNA repair, shell formation, and stress proteins were conducted on D-larvae uncovered the potential effects of EMPs on shell biomineralization, highlighting the role of Histidine Rich Glycoproteine (HRG) and tubulin as crucial adaptive mechanisms in Mytilus sp. in response to environmental shifts. Furthermore, we explored oxidative stress and neurotoxicity using biochemical assays. Our findings revealed a potential interaction between EMPs and increased salinity, impacting multiple physiological processes in mussel larvae. Our data contribute to understanding the cumulative effects of emerging anthropogenic pollutants and environmental stressors, emphasizing the need for a holistic approach to assessing their impact on marine ecosystems.

Capsicum SIZ1 contributes to ABA-induced SUMOylation in pepper.

Abiotic and biotic stresses are the major factors limiting plant growth. Arabidopsis E3 SUMO ligase SIZ1 plays an essential role in plant stress tolerance. Herein, we identified a SIZ/PAIS-type protein in pepper (Capsicum annuum), namely CaSIZ1, which shares 60 % sequence identity with AtSIZ1. The stems and flowers of pepper had a relatively higher expression of CaSIZ1 than the fruits, leaves, and roots. ABA and NaCl treatments induced CaSIZ1. CaSIZ1 protein was localized in the nucleus and partially rescued the dwarf and ABA-sensitive phenotypes of Atsiz1-2, suggesting the functional replacement of CaSIZ1 with AtSIZ1. We found that CaSIZ1 interacted with CaABI5, and ABA promoted the accumulation of SUMO conjugates in pepper. CaSIZ1 knockdown did not only reduce ABA-induced SUMOylation, but also attenuated the salt tolerance of pepper. Overall, the results of this study suggest that CaSIZ1 has a significant role in ABA-induced SUMOylation and stress response.

Alternative oxidase (AOX) 1a and 1d limit proline-induced oxidative stress and aid salinity recovery in Arabidopsis.

Proline (Pro) catabolism and reactive oxygen species production have been linked in mammals and Caenorhabditis elegans, while increases in leaf respiration rate follow Pro exposure in plants. Here, we investigated how alternative oxidases (AOXs) of the mitochondrial electron transport chain accommodate the large, atypical flux resulting from Pro catabolism and limit oxidative stress during Pro breakdown in mature Arabidopsis (Arabidopsis thaliana) leaves. Following Pro treatment, AOX1a and AOX1d accumulate at transcript and protein levels, with AOX1d approaching the level of the typically dominant AOX1a isoform. We therefore sought to determine the function of both AOX isoforms under Pro respiring conditions. Oxygen consumption rate measurements in aox1a and aox1d leaves suggested these AOXs can functionally compensate for each other to establish enhanced AOX catalytic capacity in response to Pro. Generation of aox1a.aox1d lines showed complete loss of AOX proteins and activity upon Pro treatment, yet full respiratory induction in response to Pro remained possible via the cytochrome pathway. However, aox1a.aox1d leaves displayed symptoms of elevated oxidative stress and suffered increased oxidative damage during Pro metabolism compared to the wild-type (WT) or the single mutants. During recovery from salt stress, when relatively high rates of Pro catabolism occur naturally, photosynthetic rates in aox1a.aox1d recovered slower than in the WT or the single aox lines, showing that both AOX1a and AOX1d are beneficial for cellular metabolism during Pro drawdown following osmotic stress. This work provides physiological evidence of a beneficial role for AOX1a but also the less studied AOX1d isoform in allowing safe catabolism of alternative respiratory substrates like Pro.

Triacontanol modulates salt stress tolerance in cucumber by altering the physiological and biochemical status of plant cells.

Cucumber is an important vegetable but highly sensitive to salt stress. The present study was designed to investigate the comparative performance of cucumber genotypes under salt stress (50 mmol L-1) and stress alleviation through an optimized level of triacontanol @ 0.8 mg L-1. Four cucumber genotypes were subjected to foliar application of triacontanol under stress. Different physiological, biochemical, water relations and ionic traits were observed to determine the role of triacontanol in salt stress alleviation. Triacontanol ameliorated the lethal impact of salt stress in all genotypes, but Green long and Marketmore were more responsive than Summer green and 20252 in almost all the attributes that define the genetic potential of genotypes. Triacontanol performs as a good scavenger of ROS by accelerating the activity of antioxidant enzymes (SOD, POD, CAT) and compatible solutes (proline, glycinebetaine, phenolic contents), which lead to improved gas exchange attributes and water relations and in that way enhance the calcium and potassium contents or decline the sodium and chloride contents in cucumber leaves. Furthermore, triacontanol feeding also shows the answer to yield traits of cucumber. It was concluded from the results that the salinity tolerance efficacy of triacontanol is valid in enhancing the productivity of cucumber plants under salt stress. Triacontanol was more pronounced in green long and marketer green than in summer green and 20252. Hence, the findings of this study pave the way towards the usage of triacontanol @ 0.8 mg L-1, and green long and marketer genotypes may be recommended for saline soil.

Comparative transcriptomic and metabolic profiling provides insight into the mechanism by which the autophagy inhibitor 3-MA enhances salt stress sensitivity in wheat seedlings.

BACKGROUND: Salt stress hinders plant growth and production around the world. Autophagy induced by salt stress helps plants improve their adaptability to salt stress. However, the underlying mechanism behind this adaptability remains unclear. To obtain deeper insight into this phenomenon, combined metabolomics and transcriptomics analyses were used to explore the coexpression of differentially expressed-metabolite (DEM) and gene (DEG) between control and salt-stressed wheat roots and leaves in the presence or absence of the added autophagy inhibitor 3-methyladenine (3-MA). RESULTS: The results indicated that 3-MA addition inhibited autophagy, increased ROS accumulation, damaged photosynthesis apparatus and impaired the tolerance of wheat seedlings to NaCl stress. A total of 14,759 DEGs and 554 DEMs in roots and leaves of wheat seedlings were induced by salt stress. DEGs were predominantly enriched in cellular amino acid catabolic process, response to external biotic stimulus, regulation of the response to salt stress, reactive oxygen species (ROS) biosynthetic process, regulation of response to osmotic stress, ect. The DEMs were mostly associated with amino acid metabolism, carbohydrate metabolism, phenylalanine metabolism, carbapenem biosynthesis, and pantothenate and CoA biosynthesis. Further analysis identified some critical genes (gene involved in the oxidative stress response, gene encoding transcription factor (TF) and gene involved in the synthesis of metabolite such as alanine, asparagine, aspartate, glutamate, glutamine, 4-aminobutyric acid, abscisic acid, jasmonic acid, ect.) that potentially participated in a complex regulatory network in the wheat response to NaCl stress. The expression of the upregulated DEGs and DEMs were higher, and the expression of the down-regulated DEGs and DEMs was lower in 3-MA-treated plants under NaCl treatment. CONCLUSION: 3-MA enhanced the salt stress sensitivity of wheat seedlings by inhibiting the activity of the roots and leaves, inhibiting autophagy in the roots and leaves, increasing the content of both H2O2 and O2•-, damaged photosynthesis apparatus and changing the transcriptome and metabolome of salt-stressed wheat seedlings.

An ABA Functional Analogue B2 Enhanced Salt Tolerance by Inducing the Root Elongation and Reducing Peroxidation Damage in Maize Seedlings.

Salt stress negatively affects maize growth and yield. Application of plant growth regulator is an effective way to improve crop salt tolerance, therefore reducing yield loss by salt stress. Here, we used a novel plant growth regulator B2, which is a functional analogue of ABA. With the aim to determine whether B2 alleviates salt stress on maize, we studied its function under hydroponic conditions. When the second leaf was fully developed, it was pretreated with 100 µM ABA, 0.01 µM B2, 0.1 µM B2, and 1 µM B2, independently. After 5 days treatment, NaCl was added into the nutrient solution for salt stress. Our results showed that B2 could enhance salt tolerance in maize, especially when the concentration was 1.0 µMol·L-1. Exogenous application of B2 significantly enhanced root growth, and the root/shoot ratio increased by 7.6% after 6 days treatment under salt stress. Compared with control, the ABA level also decreased by 31% after 6 days, which might have resulted in the root development. What is more, B2 maintained higher photosynthetic capacity in maize leaves under salt stress conditions and increased the activity of antioxidant enzymes and decreased the generation rate of reactive oxygen species by 16.48%. On the other hand, B2 can enhance its water absorption ability by increasing the expression of aquaporin genes ZmPIP1-1 and ZmPIP1-5. In conclusion, the novel plant growth regulator B2 can effectively improve the salt tolerance in maize.

A NAC transcription factor OsNAC3 positively regulates ABA response and salt tolerance in rice.

BACKGROUND: NAC (NAM, ATAF and CUC) transcription factors (TFs) play vital roles in plant development and abiotic stress tolerance. Salt stress is one of the most limiting factors for rice growth and production. However, the mechanism underlying salt tolerance in rice is still poorly understood. RESULTS: In this study, we functionally characterized a rice NAC TF OsNAC3 for its involvement in ABA response and salt tolerance. ABA and NaCl treatment induced OsNAC3 expression in roots. Immunostaining showed that OsNAC3 was localized in all root cells. OsNAC3 knockout decreased rice plants' sensitivity to ABA but increased salt stress sensitivity, while OsNAC3 overexpression showed an opposite effect. Loss of OsNAC3 also induced Na+ accumulation in the shoots. Furthermore, qRT-PCR and transcriptomic analysis were performed to identify the key OsNAC3 regulated genes related to ABA response and salt tolerance, such as OsHKT1;4, OsHKT1;5, OsLEA3-1, OsPM-1, OsPP2C68, and OsRAB-21. CONCLUSIONS: This study shows that rice OsNAC3 is an important regulatory factor in ABA signal response and salt tolerance.

Metabolomics and Physiological Insights into the Ability of Exogenously Applied Chlorogenic Acid and Hesperidin to Modulate Salt Stress in Lettuce Distinctively.

Recent studies in the agronomic field indicate that the exogenous application of polyphenols can provide tolerance against various stresses in plants. However, the molecular processes underlying stress mitigation remain unclear, and little is known about the impact of exogenously applied phenolics, especially in combination with salinity. In this work, the impacts of exogenously applied chlorogenic acid (CA), hesperidin (HES), and their combination (HES + CA) have been investigated in lettuce (Lactuca sativa L.) through untargeted metabolomics to evaluate mitigation effects against salinity. Growth parameters, physiological measurements, leaf relative water content, and osmotic potential as well as gas exchange parameters were also measured. As expected, salinity produced a significant decline in the physiological and biochemical parameters of lettuce. However, the treatments with exogenous phenolics, particularly HES and HES + CA, allowed lettuce to cope with salt stress condition. Interestingly, the treatments triggered a broad metabolic reprogramming that involved secondary metabolism and small molecules such as electron carriers, enzyme cofactors, and vitamins. Under salinity conditions, CA and HES + CA distinctively elicited secondary metabolism, nitrogen-containing compounds, osmoprotectants, and polyamines.

Altered Root Growth, Auxin Metabolism and Distribution in Arabidopsis thaliana Exposed to Salt and Osmotic Stress.

Salt and osmotic stress are the main abiotic stress factors affecting plant root growth and architecture. We investigated the effect of salt (100 mM NaCl) and osmotic (200 mM mannitol) stress on the auxin metabolome by UHPLC-MS/MS, auxin distribution by confocal microscopy, and transcript levels of selected genes by qRT-PCR in Arabidopsis thaliana ecotype Columbia-0 (Col-0) and DR5rev::GFP (DR5) line. During long-term stress (13 days), a stability of the auxin metabolome and a tendency to increase indole-3-acetic acid (IAA) were observed, especially during salt stress. Short-term stress (3 h) caused significant changes in the auxin metabolome, especially NaCl treatment resulted in a significant reduction of IAA. The data derived from auxin profiling were consistent with gene expressions showing the most striking changes in the transcripts of YUC, GH3, and UGT transcripts, suggesting disruption of auxin biosynthesis, but especially in the processes of amide and ester conjugation. These data were consistent with the auxin distribution observed in the DR5 line. Moreover, NaCl treatment caused a redistribution of auxin signals from the quiescent center and the inner layers of the root cap to the epidermal and cortical cells of the root elongation zone. The distribution of PIN proteins was also disrupted by salt stress; in particular, PIN2 was suppressed, even after 5 min of treatment. Based on our results, the DR5 line was more sensitive to the applied stresses than Col-0, although both lines showed similar trends in root morphology, as well as transcriptome and metabolome parameters under stress conditions.

Modulation of salt-induced stress impact in Gladiolus grandiflorus L. by exogenous application of salicylic acid.

Salinity is challenging threats to the agricultural system and leading cause of crop loss. Salicylic acid (SA) is an important endogenous signal molecule, which by regulating growth and physiological processes improves the plant ability to tolerate salt stress. Considering the prime importance of Gladiolus grandiflorus (L.) in the world's cut-flower market, the research work was undertaken to elucidate salinity tolerance in G. grandiflorus by exogenous application of SA irrigated with saline water. Results revealed that increasing salinity (EC: 2, 4 and 6 dS m-1) considerably altered morpho-growth indices (corm morphology and plant biomass) in plants through increasing key antioxidants including proline content and enzymes activity (superoxide dismutase, catalase and peroxidase), while negatively affected the total phenolic along with activity of defense-related enzymes (phenylalanine ammonia lyase, and polyphenol oxidase activity). SA application (50-200 ppm) in non-saline control or saline conditions improved morpho-physiological traits in concentration-dependent manners. In saline conditions, SA minimized salt-stress by enhancing chlorophyll content, accumulating organic osmolytes (glycine betaine and proline content), total phenolic, and boosting activity of antioxidant and defense-related enzymes. Principle component analysis based on all 16 morphological and physiological variables generated useful information regarding the classification of salt tolerant treatment according to their response to SA. These results suggest SA (100 or 150 ppm) could be used as an effective, economic, easily available and safe phenolic agent against salinity stress in G. grandiflorus.

At the Edges of Photosynthetic Metabolic Plasticity-On the Rapidity and Extent of Changes Accompanying Salinity Stress-Induced CAM Photosynthesis Withdrawal.

The common ice plant (Mesembryanthemum crystallinum L.) is a facultative crassulacean acid metabolism (CAM) plant, and its ability to recover from stress-induced CAM has been confirmed. We analysed the photosynthetic metabolism of this plant during the 72-h response period following salinity stress removal from three perspectives. In plants under salinity stress (CAM) we found a decline of the quantum efficiencies of PSII (Y(II)) and PSI (Y(I)) by 17% and 15%, respectively, and an increase in nonphotochemical quenching (NPQ) by almost 25% in comparison to untreated control. However, 48 h after salinity stress removal, the PSII and PSI efficiencies, specifically Y(II) and Y(I), elevated nonphotochemical quenching (NPQ) and donor side limitation of PSI (YND), were restored to the level observed in control (C3 plants). Swelling of the thylakoid membranes, as well as changes in starch grain quantity and size, have been found to be components of the salinity stress response in CAM plants. Salinity stress induced an over 3-fold increase in average starch area and over 50% decline of average seed number in comparison to untreated control. However, in plants withdrawn from salinity stress, during the first 24 h of recovery, we observed chloroplast ultrastructures closely resembling those found in intact (control) ice plants. Rapid changes in photosystem functionality and chloroplast ultrastructure were accompanied by the induction of the expression (within 24 h) of structural genes related to the PSI and PSII reaction centres, including PSAA, PSAB, PSBA (D1), PSBD (D2) and cp43. Our findings describe one of the most flexible photosynthetic metabolic pathways among facultative CAM plants and reveal the extent of the plasticity of the photosynthetic metabolism and related structures in the common ice plant.

Rice OsWRKY50 Mediates ABA-Dependent Seed Germination and Seedling Growth, and ABA-Independent Salt Stress Tolerance.

Plant WRKY transcription factors play crucial roles in plant growth and development, as well as plant responses to biotic and abiotic stresses. In this study, we identified and characterized a WRKY transcription factor in rice, OsWRKY50. OsWRKY50 functions as a transcriptional repressor in the nucleus. The transcription of OsWRKY50 was repressed under salt stress conditions, but activated after abscisic acid (ABA) treatment. OsWRKY50-overexpression (OsWRKY50-OX) plants displayed increased tolerance to salt stress compared to wild type and control plants. The expression of OsLEA3, OsRAB21, OsHKT1;5, and OsP5CS1 in OsWRKY50-OX were much higher than wild type and control plants under salt stress. Furthermore, OsWRKY50-OX displayed hyposensitivity to ABA-regulated seed germination and seedling establishment. The protoplast-based transient expression system and yeast hybrid assay demonstrated that OsWRKY50 directly binds to the promoter of OsNCED5, and thus further inhibits its transcription. Taken together, our results demonstrate that rice transcription repressor OsWRKY50 mediates ABA-dependent seed germination and seedling growth and enhances salt stress tolerance via an ABA-independent pathway.

The Arabidopsis HY2 Gene Acts as a Positive Regulator of NaCl Signaling during Seed Germination.

Phytochromobilin (PΦB) participates in the regulation of plant growth and development as an important synthetase of photoreceptor phytochromes (phy). In addition, Arabidopsis long hypocotyl 2 (HY2) appropriately works as a key PΦB synthetase. However, whether HY2 takes part in the plant stress response signal network remains unknown. Here, we described the function of HY2 in NaCl signaling. The hy2 mutant was NaCl-insensitive, whereas HY2-overexpressing lines showed NaCl-hypersensitive phenotypes during seed germination. The exogenous NaCl induced the transcription and the protein level of HY2, which positively mediated the expression of downstream stress-related genes of RD29A, RD29B, and DREB2A. Further quantitative proteomics showed the patterns of 7391 proteins under salt stress. HY2 was then found to specifically mediate 215 differentially regulated proteins (DRPs), which, according to GO enrichment analysis, were mainly involved in ion homeostasis, flavonoid biosynthetic and metabolic pathways, hormone response (SA, JA, ABA, ethylene), the reactive oxygen species (ROS) metabolic pathway, photosynthesis, and detoxification pathways to respond to salt stress. More importantly, ANNAT1-ANNAT2-ANNAT3-ANNAT4 and GSTU19-GSTF10-RPL5A-RPL5B-AT2G32060, two protein interaction networks specifically regulated by HY2, jointly participated in the salt stress response. These results direct the pathway of HY2 participating in salt stress, and provide new insights for the plant to resist salt stress.

EGY3 mediates chloroplastic ROS homeostasis and promotes retrograde signaling in response to salt stress in Arabidopsis.

The chloroplast is the main organelle for stress-induced production of reactive oxygen species (ROS). However, how chloroplastic ROS homeostasis is maintained under salt stress is largely unknown. We show that EGY3, a gene encoding a chloroplast-localized protein, is induced by salt and oxidative stresses. The loss of EGY3 function causes stress hypersensitivity while EGY3 overexpression increases the tolerance to both salt and chloroplastic oxidative stresses. EGY3 interacts with chloroplastic Cu/Zn-SOD2 (CSD2) and promotes CSD2 stability under stress conditions. In egy3-1 mutant plants, the stress-induced CSD2 degradation limits H2O2 production in chloroplasts and impairs H2O2-mediated retrograde signaling, as indicated by the decreased expression of retrograde-signal-responsive genes required for stress tolerance. Both exogenous application of H2O2 (or APX inhibitor) and CSD2 overexpression can rescue the salt-stress hypersensitivity of egy3-1 mutants. Our findings reveal that EGY3 enhances the tolerance to salt stress by promoting the CSD2 stability and H2O2-mediated chloroplastic retrograde signaling.