Interplay between nitric oxide and sulfur assimilation in salt tolerance in plants

Comparative transcriptome responses of leaf and root tissues to salt stress in wheat strains with different salinity tolerances

Background: Salinity stress is a major adverse environmental factor that can limit crop yield and restrict normal land use. The selection of salt-tolerant strains and elucidation of the underlying mechanisms by plant breeding scientists are urgently needed to increase agricultural production in arid and semi-arid regions. Results: In this study, we selected the salt-tolerant wheat (Triticum aestivum) strain ST9644 as a model to study differences in expression patterns between salt-tolerant and salt-sensitive strains. High-throughput RNA sequencing resulted in more than 359.10 Gb of clean data from 54 samples, with an average of 6.65 Gb per sample. Compared to the IWGSC reference annotation, we identified 50,096 new genes, 32,923 of which have functional annotations. Comparisons of abundances between salt-tolerant and salt-sensitive strains revealed 3,755, 5,504, and 4,344 genes that were differentially expressed at 0, 6, and 24 h, respectively, in root tissue under salt stress. KEGG pathway analysis of these genes showed that they were enriched for phenylpropanoid biosynthesis (ko00940), cysteine and methionine metabolism (ko00270), and glutathione metabolism (ko00480). We also applied weighted gene co-expression network analysis (WGCNA) analysis to determine the time course of root tissue response to salt stress and found that the acute response lasts >6 h and ends before 12 h. We also identified key alternative splicing factors showing different splicing patterns in salt-sensitive and salt-tolerant strains; however, only few of them were differentially expressed in the two groups. Conclusion: Our results offer a better understanding of wheat salt tolerance and improve wheat breeding.

Nitric Oxide- and Sulfur-Mediated Reversal of Cadmium-Inhibited Photosynthetic Performance Involves Hydrogen Sulfide and Regulation of Nitrogen, Sulfur, and Antioxidant Metabolism in Mustard

This study aimed to test the role of hydrogen sulfide (H2S) in the responses regarding the nitric oxide- (NO) and sulfur (S)-mediated improvement in photosynthesis and growth under cadmium (Cd) stress in mustard (Brassica juncea L. cv. Giriraj), and integrate the mechanisms of S, nitrogen (N), and antioxidant metabolism. The plants grown with Cd (200 mg Cd kg−1 soil) exhibited reduced assimilation of S and N and diminished photosynthetic performance, which was associated with higher Cd accumulation-induced excess reactive oxygen species (ROS) production. The application of 100 μM of sodium nitroprusside (SNP, a NO donor) together with a more prominent concentration of S resulted in increased photosynthetic S- and N-use efficiency, production of non-protein thiols and phytochelatins, efficiency of enzymatic (superoxide dismutase, ascorbate peroxidase, and glutathione reductase), non-enzymatic antioxidants (ascorbate and glutathione) limiting Cd accumulation and, thus, reduced oxidative stress (superoxide radical, hydrogen peroxide, and thiobarbituric acid reactive species content). The benefit of NO together with S was manifested through a modulation in H2S production. The use of 100 μM of hypotaurine (HT; H2S scavenger) or 100 μM of cPTIO (2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) in plants treated with NO plus S reversed the action of NO plus S, with a higher reduction in photosynthesis and growth with the use of HT, suggesting that H2S plays a significant role in the NO- and S-mediated alleviation of Cd stress. The interplay of NO and ES with H2S may be used in augmenting the photosynthesis and growth of Cd-grown mustard plants.

Nitric Oxide and Salicylic Acid Regulate Glutathione and Ethylene Production to Enhance Heat Stress Acclimation in Wheat Involving Sulfur Assimilation

Phytohormones have a role in stress adaptation. The major mechanism underlying the role of exogenously-sourced nitric oxide (NO; as sodium nitroprusside, SNP: 50.0 µM) and salicylic acid (SA; 0.5 mM) in the presence of 2.0 mM SO₄^-2 was assessed in heat stress (HS; 40 °C for 6 h daily for 15 days) tolerance in wheat (Triticum aestivum L. cv. HD-3226). The cultivar HD-3226 possessed high photosynthetic sulfur use efficiency (p-SUE) among the six cultivars screened. Plants grown under HS exhibited an increased content of reactive oxygen species (ROS; including superoxide radical and hydrogen peroxide) and extent of lipid peroxidation with a consequent reduction in photosynthesis and growth. However, both NO and SA were found to be protective against HS via enhanced S assimilation. Their application reduced oxidative stress and increased the activity of antioxidant enzymes. NO or SA supplementation along with S under HS recovered the losses and improved photosynthesis and growth. The use of SA inhibitor (2-aminoindane-2-phosphonic acid; AIP) and NO scavenger (cPTIO) confirmed that the mitigating effects of SA and NO involved induction in S assimilation.

Protective mechanisms of sulfur against arsenic phytotoxicity in Brassica napus by regulating thiol biosynthesis, sulfur-assimilation, photosynthesis, and antioxidant response

The contamination of agricultural soils with Arsenic (As) is a significant environmental stress that restricts plant growth, metabolism, and productivity worldwide. The present study examined the role of elemental sulfur (S⁰) in protecting Brassica napus plants from Arsenic (As) toxicity. Arsenic (100, and 200 mg As kg^-1 soil) in soil caused detrimental effects on five Brassica napus cultivars (Neelam, Teri-Uttam Jawahar, Him Sarson, GSC-101, and NUDB 26-11). The As toxicity inhibited the growth and photosynthesis indices in all cultivars with more deterioration effects in NUDB 26-11. Plant absorption and uptake of As caused the generation of oxidative injury by accumulating the reactive oxygen species (ROS), which simultaneously decreased the plant defence capability and ultimately the photosynthesis. Application of sulfur (S⁰, 100 or 200 mg S kg^-1 soil) alleviated the negative impacts and toxicity of As on the photosynthesis and growth matrices of plants, especially under high S level. S⁰ also boosted the antioxidant potential of plants and toned-down lipid peroxidation and ROS aggravation such as superoxide anion (O₂^•-) and H₂O₂, hydrogen peroxide, in As affected plants. In general, S⁰ at 200 mg kg^-1 soil more perceptibly increased the functionality of antioxidant enzymes, and non-enzymatic antioxidants, metal chelators and non-protein thiols. Further amendment of soil with S⁰ at fifteen days before seed sowing affected by As-induced toxic effects (added to soil at the time of sowing) considerably intensified the endogenous hydrogen sulfide (H₂S) content and its regenerating enzymes D-cysteine desulfhydrase (DCD) and L-cysteine desulfhydrase (LCD) that further strengthened the defense capability of plants to withstand As-stress. Our results suggest the role of H₂S in the S-induced defense operation of the B. napus plants in restraining As toxicity. The current study shows that S⁰ as a source of S might be used to promote the growth of B. napus plants in polluted agricultural soils.

Hydrogen sulfide manages hexavalent chromium toxicity in wheat and rice seedlings: The role of sulfur assimilation and ascorbate-glutathione cycle

The role of hydrogen sulfide (H₂S) is well known in the regulation of abiotic stress such as toxic heavy metal. However, mechanism(s) lying behind this amelioration are still poorly known. Consequently, the present study was focused on the regulation/mitigation of hexavalent chromium (Cr(VI) toxicity by the application of H₂S in wheat and rice seedlings. Cr(VI) induced accumulation of reactive oxygen species and caused protein oxidation which negatively affect the plant growth in both the cereal crops. We noticed that Cr(VI) toxicity reduced length of wheat and rice seedlings by 21% and 19%, respectively. These reductions in length of both the cereal crops were positively related with the down-regulation in the ascorbate-glutathione cycle, and were recovered by the application NaHS (a donor of H₂S). Though exposure of Cr(VI) slightly stimulated sulfur assimilation but addition of H₂S further caused enhancement in sulfur assimilation, suggesting its role in the H₂S-mediated Cr(VI) stress tolerance in studied cereal crops. Overall, the results revealed that H₂S renders Cr(VI) stress tolerance in wheat and rice seedlings by stimulating sulfur assimilation and ascorbate-glutathione which collectively reduce protein oxidation and thus, improved growth was observed.

Plant Nutrition: An Effective Way to Alleviate Abiotic Stress in Agricultural Crops

By the year 2050, the world's population is predicted to have grown to around 9-10 billion people. The food demand in many countries continues to increase with population growth. Various abiotic stresses such as temperature, soil salinity and moisture all have an impact on plant growth and development at all levels of plant growth, including the overall plant, tissue cell, and even sub-cellular level. These abiotic stresses directly harm plants by causing protein denaturation and aggregation as well as increased fluidity of membrane lipids. In addition to direct effects, indirect damage also includes protein synthesis inhibition, protein breakdown, and membranous loss in chloroplasts and mitochondria. Abiotic stress during the reproductive stage results in flower drop, pollen sterility, pollen tube deformation, ovule abortion, and reduced yield. Plant nutrition is one of the most effective ways of reducing abiotic stress in agricultural crops. In this paper, we have discussed the effectiveness of different nutrients for alleviating abiotic stress. The roles of primary nutrients (nitrogen, phosphorous and potassium), secondary nutrients (calcium, magnesium and sulphur), micronutrients (zinc, boron, iron and copper), and beneficial nutrients (cobalt, selenium and silicon) in alleviating abiotic stress in crop plants are discussed.

Ethylene and hydrogen sulphide are essential for mitigating hexavalent chromium stress in two pulse crops

Chromium toxicity to crops is a major scientific problem of the present time. Thus, scientific attempts have been made for reducing chromium toxicity to crop plants. In this study, we examined the potential of ethylene (ET, 25 µM) and hydrogen sulphide (H₂ S, 10 µM) to alleviate hexavalent chromium [Cr(VI), 50 µM] stress in two pulse crops, black bean and mung bean, by assessing physiological and biochemical attributes. Cr(VI) reduced shoot and root length in black bean and mung bean in comparison to the control. Plants had increased accumulation of oxidative stress markers, i.e. superoxide radicals (SOR), hydrogen peroxide (H₂ O₂ ) and lipid peroxidation (as malondialdehyde, MDA). The addition of AVG (an inhibitor of ET biosynthesis) and PAG (an inhibitor of H₂ S biosynthesis) to Cr(VI)-treated plants further increased Cr(VI) toxicity, suggesting their endogenous levels are important for tolerating Cr(VI) toxicity. However, supplementation with either ET or H₂ S alleviated Cr(VI) toxicity. Interestingly, ET did not rescue negative effects of PAG under Cr(VI) stress but NaHS rescued negative effect of AVG. Overall, results indicate that, although both ET and H₂ S alleviate Cr(VI) stress, endogenous H₂ S is better. Furthermore, H₂ S appears to be a downstream signal for ET in alleviating Cr(VI) stress in these two pulse crops.

The Role of Nitric Oxide in Plant Responses to Salt Stress

The gas nitric oxide (NO) plays an important role in several biological processes in plants, including growth, development, and biotic/abiotic stress responses. Salinity has received increasing attention from scientists as an abiotic stressor that can seriously harm plant growth and crop yields. Under saline conditions, plants produce NO, which can alleviate salt-induced damage. Here, we summarize NO synthesis during salt stress and describe how NO is involved in alleviating salt stress effects through different strategies, including interactions with various other signaling molecules and plant hormones. Finally, future directions for research on the role of NO in plant salt tolerance are discussed. This summary will serve as a reference for researchers studying NO in plants.

Coordinated Role of Nitric Oxide, Ethylene, Nitrogen, and Sulfur in Plant Salt Stress Tolerance

Salt stress significantly contributes to major losses in agricultural productivity worldwide. The sustainable approach for salinity-accrued toxicity has been explored. The use of plant growth regulators/phytohormones, mineral nutrients and other signaling molecules is one of the major approaches for reversing salt-induced toxicity in plants. Application of the signaling molecules such as nitric oxide (NO) and ethylene (ETH) and major mineral nutrient such as nitrogen (N) and sulfur (S) play significant roles in combatting the major consequences of salt stress impacts in plants. However, the literature available on gaseous signaling molecules (NO/ETH) or/and mineral nutrients (N/S) stands alone, and major insights into the role of NO or/and ETH along with N and S in plant-tolerance to salt remained unclear. Thus, this review aimed to (a) briefly overview salt stress and highlight salt-induced toxicity, (b) appraise the literature reporting potential mechanisms underlying the role of gaseous signaling molecules and mineral nutrient in salt stress tolerance, and (c) discuss NO and ETH along with N and S in relation to salt stress tolerance. In addition, significant issues that have still to be investigated in this context have been mentioned.

The Resistance of Oilseed Rape Microspore-Derived Embryos to Osmotic Stress Is Associated With the Accumulation of Energy Metabolism Proteins, Redox Homeostasis, Higher Abscisic Acid, and Cytokinin Contents

The present study aims to investigate the response of rapeseed microspore-derived embryos (MDE) to osmotic stress at the proteome level. The PEG-induced osmotic stress was studied in the cotyledonary stage of MDE of two genotypes: Cadeli (D) and Viking (V), previously reported to exhibit contrasting leaf proteome responses under drought. Two-dimensional difference gel electrophoresis (2D-DIGE) revealed 156 representative protein spots that have been selected for MALDI-TOF/TOF analysis. Sixty-three proteins have been successfully identified and divided into eight functional groups. Data are available via ProteomeXchange with identifier PXD024552. Eight selected protein accumulation trends were compared with real-time quantitative PCR (RT-qPCR). Biomass accumulation in treated D was significantly higher (3-fold) than in V, which indicates D is resistant to osmotic stress. Cultivar D displayed resistance strategy by the accumulation of proteins in energy metabolism, redox homeostasis, protein destination, and signaling functional groups, high ABA, and active cytokinins (CKs) contents. In contrast, the V protein profile displayed high requirements of energy and nutrients with a significant number of stress-related proteins and cell structure changes accompanied by quick downregulation of active CKs, as well as salicylic and jasmonic acids. Genes that were suitable for gene-targeting showed significantly higher expression in treated samples and were identified as phospholipase D alpha, peroxiredoxin antioxidant, and lactoylglutathione lyase. The MDE proteome profile has been compared with the leaf proteome evaluated in our previous study. Different mechanisms to cope with osmotic stress were revealed between the genotypes studied. This proteomic study is the first step to validate MDE as a suitable model for follow-up research on the characterization of new crossings and can be used for preselection of resistant genotypes.

Nitric Oxide Regulates Plant Growth, Physiology, Antioxidant Defense, and Ion Homeostasis to Confer Salt Tolerance in the Mangrove Species, Kandelia obovata

Facultative halophyte Kandelia obovata plants were exposed to mild (1.5% NaCl) and severe (3% NaCl) salt stress with or without sodium nitroprusside (SNP; 100 µM; a NO donor), hemoglobin (Hb, 100 µM; a NO scavenger), or Nω-nitro-L-arginine methyl ester (L-NAME, 100 µM; a NO synthase inhibitor). The plants were significantly affected by severe salt stress. They showed decreases in seedling growth, stomatal conductance, intercellular CO2 concentration, SPAD value, photosynthetic rate, transpiration rate, water use efficiency, and disrupted antioxidant defense systems, overproduction of reactive oxygen species, and visible oxidative damage. Salt stress also induced ion toxicity and disrupted nutrient homeostasis, as indicated by elevated leaf and root Na+ contents, decreased K+ contents, lower K+/Na+ ratios, and decreased Ca contents while increasing osmolyte (proline) levels. Treatment of salt-stressed plants with SNP increased endogenous NO levels, reduced ion toxicity, and improved nutrient homeostasis while further increasing Pro levels to maintain osmotic balance. SNP treatment also improved gas exchange parameters and enhanced antioxidant enzymes' activities (catalase, ascorbate peroxidase, monodehydroascorbate reductase, and dehydroascorbate reductase). Treatment with Hb and l-NAME reversed these beneficial SNP effects and exacerbated salt damage, confirming that SNP promoted stress recovery and improved plant growth under salt stress.

GABA reverses salt-inhibited photosynthetic and growth responses through its influence on NO-mediated nitrogen-sulfur assimilation and antioxidant system in wheat

Gamma-aminobutyric acid (GABA) is a newly recognized signaling molecule participating in physiological processes, growth, and development of plants under optimal and stressful environments. In the present reported research, we investigated the role of GABA in imparting salt stress tolerance in wheat (Triticum aestivum L.). Exposure of wheat plants to 100 mM NaCl resulted in increased oxidative stress, glucose content, nitric oxide (NO) production together with reduced growth and photosynthetic traits of plants. Contrarily, GABA application improved nitrogen (N) metabolism, sulfur (S) assimilation, ion homeostasis, growth and photosynthesis under salt stress. Additionally, GABA mitigated oxidative stress induced by salt stress with the increased ascorbate-glutathione cycle and proline metabolism. The study with NO inhibitor, c-PTIO [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxy-3-oxide] in GABA experiment suggested that the impact of GABA on improvement of growth and photosynthesis under salt stress was mediated by NO and influenced N and S assimilation and antioxidant systems. The results suggested that the GABA has a significant potential in reversing the salt stress response in wheat plants, and GABA-mediated signals are manifested through NO.

Understanding salt tolerance mechanism using transcriptome profiling and de novo assembly of wild tomato Solanum chilense

Soil salinity affects the plant growth and productivity detrimentally, but Solanum chilense, a wild relative of cultivated tomato (Solanum lycopersicum L.), is known to have exceptional salt tolerance. It has precise adaptations against direct exposure to salt stress conditions. Hence, a better understanding of the mechanism to salinity stress tolerance by S. chilense can be accomplished by comprehensive gene expression studies. In this study 1-month-old seedlings of S. chilense and S. lycopersicum were subjected to salinity stress through application of sodium chloride (NaCl) solution. Through RNA-sequencing here we have studied the differences in the gene expression patterns. A total of 386 million clean reads were obtained through RNAseq analysis using the Illumina HiSeq 2000 platform. Clean reads were further assembled de novo into a transcriptome dataset comprising of 514,747 unigenes with N50 length of 578 bp and were further aligned to the public databases. Genebank non-redundant (Nr), Viridiplantae, Gene Ontology (GO), KOG, and KEGG databases classification suggested enrichment of these unigenes in 30 GO categories, 26 KOG, and 127 pathways, respectively. Out of 265,158 genes that were differentially expressed in response to salt treatment, 134,566 and 130,592 genes were significantly up and down-regulated, respectively. Upon placing all the differentially expressed genes (DEG) in known signaling pathways, it was evident that most of the DEGs involved in cytokinin, ethylene, auxin, abscisic acid, gibberellin, and Ca²⁺ mediated signaling pathways were up-regulated. Furthermore, GO enrichment analysis was performed using REVIGO and up-regulation of multiple genes involved in various biological processes in chilense under salinity were identified. Through pathway analysis of DEGs, “Wnt signaling pathway” was identified as a novel pathway for the response to the salinity stress. Moreover, key genes for salinity tolerance, such as genes encoding proline and arginine metabolism, ROS scavenging system, transporters, osmotic regulation, defense and stress response, homeostasis and transcription factors were not only salt-induced but also showed higher expression in S. chilense as compared to S. lycopersicum. Thus indicating that these genes may have an important role in salinity tolerance in S. chilense. Overall, the results of this study improve our understanding on possible molecular mechanisms underlying salt tolerance in plants in general and tomato in particular.

Nitric Oxide Pre-Treatment Advances Seed Germination and Alleviates Copper-Induced Photosynthetic Inhibition in Indian Mustard

This investigation tested the efficiency of nitric oxide (NO) in alleviation of Cu-induced adverse impacts on seed germination and photosynthesis in Indian mustard (Brassica juncea L.). Pre-treatment of B. juncea seeds with sodium nitroprusside (SNP; NO donor) significantly improved the seed germination rate and also alleviated Cu-accrued oxidative stress. However, in the absence of NO, Cu caused a higher reduction in seed germination rate. The presence of NO strengthened the antioxidant defense system (glutathione reductase, ascorbate peroxidase, and superoxide dismutase) and thereby sustained the lower lipid peroxidation, reduced H2O2 content, and thiobarbituric acid reactive substances in Cu-exposed seeds. NO pre-treated seeds also retained a higher amylase activity and exhibited an improved seed germination rate. This effect of NO under Cu stress was also seen in plants originated from the NO pre-treated seeds, where the role of NO pre-treatment was reflected in the improved photosynthetic potential of B. juncea. Overall, NO pre-treatment not only improved the germination rate in seeds but also carried its effects in the grown seedlings evidenced as improved photosynthesis and growth. Potential mechanisms involved in the action of NO pre-treatment included NO-mediated significant strengthening of the antioxidant defense system and decreases in Cu-caused oxidative stress parameters.

Mechanisms and Role of Nitric Oxide in Phytotoxicity-Mitigation of Copper

Phytotoxicity of metals significantly contributes to the major loss in agricultural productivity. Among all the metals, copper (Cu) is one of essential metals, where it exhibits toxicity only at its supra-optimal level. Elevated Cu levels affect plants developmental processes from initiation of seed germination to the senescence, photosynthetic functions, growth and productivity. The use of plant growth regulators/phytohormones and other signaling molecules is one of major approaches for reversing Cu-toxicity in plants. Nitric oxide (NO) is a versatile and bioactive gaseous signaling molecule, involved in major physiological and molecular processes in plants. NO modulates responses of plants grown under optimal conditions or to multiple stress factors including elevated Cu levels. The available literature in this context is centered mainly on the role of NO in combating Cu stress with partial discussion on underlying mechanisms. Considering the recent reports, this paper: (a) overviews Cu uptake and transport; (b) highlights the major aspects of Cu-toxicity on germination, photosynthesis, growth, phenotypic changes and nutrient-use-efficiency; (c) updates on NO as a major signaling molecule; and (d) critically appraises the Cu-significance and mechanisms underlying NO-mediated alleviation of Cu-phytotoxicity. The outcome of the discussion may provide important clues for future research on NO-mediated mitigation of Cu-phytotoxicity.

Synergetic Effects of Zinc, Boron, Silicon, and Zeolite Nanoparticles on Confer Tolerance in Potato Plants Subjected to Salinity

Salinity stress is a severe environmental stress that affects plant growth and productivity of potato, a strategic crop moderately sensitive to saline soils. Limited studies are available on the use of combined nano-micronutrients to ameliorate salinity stress in potato plants (Solanum tuberosum L.). Two open field experiments were conducted in salt-affected sandy soil to investigate plant growth, physiology, and yield of potato in response to soil salinity stress under single or combined application of Zn, B, Si, and Zeolite nanoparticles. It was hypothesized that soil application of nanoparticles enhanced plant growth and yield by alleviating the adverse impact of soil salinity. In general, all the nano-treatments applications significantly increased plant height, shoot dry weight, number of stems per plant, leaf relative water content, leaf photosynthetic rate, leaf stomatal conductance, chlorophyll content, and tuber yield, as compared to the untreated control. Furthermore, soil application of these treatments increased the concentration of nutrients (N, P, K, Ca, Zn, and B) in plant tissues, leaf proline, and leaf gibberellic acid hormone (GA3) in addition to contents of protein, carbohydrates, and antioxidant enzymes (polyphenol oxidase (PPO) and peroxidase (POD) in tubers. Compared to other treatments, the combined application of nanoparticles showed the highest plant growth, physiological parameters, endogenous elements (N, P, K, Ca, Zn, and B) and the lowest concentration of leaf abscisic acid (ABA) and transpiration rate. The present findings suggest that soil addition of the aforementioned nanoparticles can be a promising approach to improving crop productivity in salt-affected soils.

Effect of elicitors on the metabolites in the suspension cell culture of Salvia miltiorrhiza Bunge

The effect of elicitors on the metabolites in the suspension cells of Salvia miltiorrhiza Bunge was elucidated by comparing and analyzing the metabolites of induced and uninduced suspension cells. The primary metabolites were detected by GC-MS. Twelve types of secondary metabolites, namely, shikimic acid, tanshinol, protocatechuic acid, caffeic acid, p-coumaric acid, rosmarinic acid, salvianolic acid B, salvianolic acid A, dihydrotanshinone, cryptotanshinone, tanshinone I, and tanshinone II A were detected by HPLC. Results indicated a total of 90 primary metabolites in the cells. These metabolites consisted of 49 kinds of sugars and their derivatives, 15 organic acids, 9 amino acids and their derivatives, 9 hydrocarbons, and 8 other substances. OPLS-DA results indicated five differential primary metabolites, namely, gluconic acid, mannopyranose, glucose, inositol, and ketoisovalerate, between the callus and suspension cells. SA significantly induced glucose metabolism in the S. miltiorrhiza suspension cells, and the mean contents of glucose, fructose, and mannose were significantly lower in the induced cells than in the control. However, SA, as a plant inducer, could significantly promote the increase in 10 secondary metabolites, except protocatechuic acid and tanshinone I, in the suspension cells at different times or degrees. The effect of NaCl on the S. miltiorrhiza cell mainly depended on the downstream pathway of glucose metabolism. Fructose and glucose were the decomposition products of sucrose, and glucose was processed through monosaccharide metabolism. Induction by NaCl resulted in significantly lower levels of these primary metabolites in the induced cells than in the control group. However, NaCl could significantly promote 10 secondary metabolites, except tanshinol and protocatechuic acid, at different times or degrees. After elicitation by AgNO3, sucrose and proline were higher in the induced cells than in the control group. However, galactose and fructose were lower in the experimental cells than in the control. This phenomenon may have been caused by the induction of plant stress response by AgNO3. AgNO3 could significantly promote shikimic acid, caffeic acid, p-coumaric acid, rosmarinic acid, salvianolic acid B, salvianolic acid A, dihydrotanshinone, cryptotanshinone, tanshinone I, and tanshinone IIA. This study will provide a reference for future studies on the effects of primary metabolites on the secondary metabolites and the potential relation of these metabolites to plant stress response in S. miltiorrhiza.

Interaction of sulfur with phytohormones and signaling molecules in conferring abiotic stress tolerance to plants

Sulfur (S) is a macronutrient for the plant, which has an immense role in basic plant processes and regulation of several metabolic pathways. It has also a major role in providing protection against adverse conditions. Sulfur-containing amino acids and metabolites maintain plant cell mechanisms to improve stress tolerance. It interacts with several biomolecules such as phytohormones, polyamines, nitric oxide (NO), and even with other plant nutrients, which can produce some derivatives those are essential for abiotic stress tolerance. Different S derivatives stimulate signaling cascades, for the upregulation of different cellular messengers such as abscisic acid, Ca²⁺, and NO. Sulfur is also known to interact with some essential plant nutrients by influencing their uptake and transport, hence, confers nutrient homeostasis efficiencies. This review focuses on how S is interacted with several signaling molecules like NO, glutathiones, phytohormones, hydrogen sulfide, polyamines, etc. This is a concise summary aimed at guiding the researchers to study S-related plant processes in the light of abiotic stress tolerance.

RNAseq analysis reveals pathways and candidate genes associated with salinity tolerance in a spaceflight-induced wheat mutant

Salinity stress has become an increasing threat to food security worldwide and elucidation of the mechanism for salinity tolerance is of great significance. Induced mutation, especially spaceflight mutagenesis, is one important method for crop breeding. In this study, we show that a spaceflight-induced wheat mutant, named salinity tolerance 1 (st1), is a salinity-tolerant line. We report the characteristics of transcriptomic sequence variation induced by spaceflight, and show that mutations in genes associated with sodium ion transport may directly contribute to salinity tolerance in st1. Furthermore, GO and KEGG enrichment analysis of differentially expressed genes (DEGs) between salinity-treated st1 and wild type suggested that the homeostasis of oxidation-reduction process is important for salt tolerance in st1. Through KEGG pathway analysis, "Butanoate metabolism" was identified as a new pathway for salinity responses. Additionally, key genes for salinity tolerance, such as genes encoding arginine decarboxylase, polyamine oxidase, hormones-related, were not only salt-induced in st1 but also showed higher expression in salt-treated st1 compared with salt-treated WT, indicating that these genes may play important roles in salinity tolerance in st1. This study presents valuable genetic resources for studies on transcriptome variation caused by induced mutation and the identification of salt tolerance genes in crops.

RNAseq analysis reveals pathways and candidate genes associated with salinity tolerance in a spaceflight-induced wheat mutant

Salinity stress has become an increasing threat to food security worldwide and elucidation of the mechanism for salinity tolerance is of great significance. Induced mutation, especially spaceflight mutagenesis, is one important method for crop breeding. In this study, we show that a spaceflight-induced wheat mutant, named salinity tolerance 1 (st1), is a salinity-tolerant line. We report the characteristics of transcriptomic sequence variation induced by spaceflight, and show that mutations in genes associated with sodium ion transport may directly contribute to salinity tolerance in st1. Furthermore, GO and KEGG enrichment analysis of differentially expressed genes (DEGs) between salinity-treated st1 and wild type suggested that the homeostasis of oxidation-reduction process is important for salt tolerance in st1. Through KEGG pathway analysis, "Butanoate metabolism" was identified as a new pathway for salinity responses. Additionally, key genes for salinity tolerance, such as genes encoding arginine decarboxylase, polyamine oxidase, hormones-related, were not only salt-induced in st1 but also showed higher expression in salt-treated st1 compared with salt-treated WT, indicating that these genes may play important roles in salinity tolerance in st1. This study presents valuable genetic resources for studies on transcriptome variation caused by induced mutation and the identification of salt tolerance genes in crops.

Nitric oxide signaling and its crosstalk with other plant growth regulators in plant responses to abiotic stress

Nitric oxide (NO) is a free radical molecule involved in an array of functions under physiological and adverse environmental conditions. As other free radical molecules, NO biological action depends on its cellular concentration, acting as a signal molecule when produced at low concentration or resulting in cellular damage when produced at sufficiently high levels to trigger nitro-oxidative stress. Over the last decade, significant progress has been made in characterizing NO metabolism and action mechanism, revealing that diverse biosynthetic routes can generate this free radical in plants and its action mainly occurs through posttranslational modification (nitration and S-nitrosylation) of target proteins. Intricate crosstalk networks between NO and other signaling molecules have been described involving phytohormones, other second messengers, and key transcription factors. This review will focus on our current understanding of NO interplay with phytohormones and other plant growth regulators under abiotic stress conditions.