Endogenous hydrogen sulfide enhances salt tolerance by coupling the reestablishment of redox homeostasis and preventing salt-induced K⁺ loss in seedlings of Medicago sativa

Catalysts for sulfur: understanding the intricacies of enzymes orchestrating plant sulfur anabolism

MAIN CONCLUSION

This review highlights the sulfur transporters, key enzymes and their encoding genes involved in plant sulfur anabolism, focusing on their occurrence, chemistry, location, function, and regulation within sulfur assimilation pathways. Sulfur, a vital element for plant life, plays diverse roles in metabolism and stress response. This review provides a comprehensive overview of the sulfur assimilation pathway in plants, highlighting the intricate network of enzymes and their regulatory mechanisms. The primary focus is on the key enzymes involved: ATP sulfurylase (ATPS), APS reductase (APR), sulfite reductase (SiR), serine acetyltransferase (SAT), and O-acetylserine(thiol)lyase (OAS-TL). ATPS initiates the process by activating sulfate to form APS, which is then reduced to sulfite by APR. SiR further reduces sulfite to sulfide, a crucial step that requires significant energy. The cysteine synthase complex (CSC), formed by SAT and OAS-TL, facilitates the synthesis of cysteine, thereby integrating serine metabolism with sulfur assimilation. The alternative sulfation pathway, catalyzed by APS kinase and sulfotransferases, is explored for its role in synthesizing essential secondary metabolites. This review also delves into the regulatory mechanism of these enzymes such as environmental stresses, sulfate availability, phytohormones, as well as translational and post-translational regulations. Understanding the key transporters and enzymes in sulfur assimilation pathways and their corresponding regulation mechanisms can help researchers grasp the importance of sulfur anabolism for the life cycle of plants, clarify how these enzymes and their regulatory processes are integrated to balance plant life systems in response to changes in both external conditions and intrinsic signals.

The SlbHLH92 transcription factor enhances salt stress resilience by fine-tuning hydrogen sulfide biosynthesis in tomato

Ongoing soil salinization severely hampers plant growth and the sustainability of global crops production. Hydrogen sulfide (H2S), acting as a critical gaseous signaling molecule, plays a vital role in plant response to various environmental cues such as salt stress. Nonetheless, it is not well understood how the transcriptional network regulates H2S production in response to salt stress in tomato. Herein, we determine that the bHLH transcription factor SlbHLH92 functions as a transcriptional activator in tomato (Solanum lycopersicum L.), upregulating the expression of the L-CYSTEINE DESULFHYDRASE 1 (SlLCD1) gene involved in H2S biosynthesis, thereby enhancing the plants' tolerance to salt stress. When exposed to salt stress, overexpression of SlbHLH92 in tomato leads to enhanced salt tolerance compared to wild-type plants. In contrast, suppression of SlbHLH92 expression with RNAi silencing results in increased sensitivity to salt stress. Subsequent molecular and biochemical investigations confirm that the salt-induced SlbHLH92 upregulates the expression of SlLCD1, leading to an increase in H₂S levels, as well as other salt-responsive genes (SlCBL10 and SlVQ16), by directly binding to specific cis-elements in their promoter regions. Furthermore, the VQ-motif containing protein SlVQ16 physically interacts with SlbHLH92, thereby promoting an increase in its transcriptional activity. Taken together, our study reveals an emerging mechanism in which the SlbHLH92-SlVQ16-H2S signaling cascade contributes to enhancing salt tolerance in tomato, presenting potential genetic targets for breeding salt-tolerant tomato cultivars.

Enhancing stress resilience in soybeans (Glycine max): assessing the efficacy of priming and cross-priming for mitigating water deficit and waterlogging effects

Priming enables plants to respond more promptly, minimise damage, and survive subsequent stress events. Here, we aimed to assess the efficacy of priming and cross-priming in mitigating the stress caused by waterlogging and/or dehydration in soybeans (Glycine max ). Soybean plants were cultivated in a greenhouse in plastic pots in which soil moisture was maintained at pot capacity through irrigation. The first stress was applied in plants at the vegetative stage for 5days and involved either dehydration or waterlogging, depending on the treatment. Subsequently, the plants were irrigated or drained and maintained at pot capacity until the second stress. For the second stress, the conditions were repeated in plants at the reproductive stage. We then evaluated the levels of hydrogen peroxide (H2 O2 ), lipid peroxidation, total soluble sugars (TSS), amino acids, proline, and starch, and the activity of antioxidant, fermentative, and aminotransferase enzymes. Under waterlogging and dehydration, priming and cross-priming significantly increased the activity of antioxidant enzymes and the levels of TSS, amino acids, and proline while reducing H2 O2 concentration and lipid peroxidation. Under waterlogging, priming suppressed fermentative activity and increased carbohydrate content. This demonstrates that soybean plants activate their defence systems more promptly when subjected to priming.

Harmonizing hydrogen sulfide and nitric oxide: A duo defending plants against salinity stress

In the face of escalating salinity stress challenges in agricultural systems, this review article delves into the harmonious partnership between hydrogen sulfide (H2S) and nitric oxide (NO) as they collectively act as formidable defenders of plants. Once considered as harmful pollutants, H2S and NO have emerged as pivotal gaseous signal molecules that profoundly influence various facets of plant life. Their roles span from enhancing seed germination to promoting overall growth and development. Moreover, these molecules play a crucial role in bolstering stress tolerance mechanisms and maintaining essential plant homeostasis. This review navigates through the intricate signaling pathways associated with H2S and NO, elucidating their synergistic effects in combating salinity stress. We explore their potential to enhance crop productivity, thereby ensuring food security in saline-affected regions. In an era marked by pressing environmental challenges, the manipulation of H2S and NO presents promising avenues for sustainable agriculture, offering a beacon of hope for the future of global food production.

Mitigating salt toxicity and overcoming phosphate deficiency alone and in combination in pepper (Capsicum annuum L.) plants through supplementation of hydrogen sulfide

While it is widely recognized that hydrogen sulfide (H2S) promotes plant stress tolerance, the precise processes through which H2S modulates this process remains unclear. The processes by which H2S promotes phosphorus deficiency (PD) and salinity stress (SS) tolerance, simulated individually or together, were examined in this study. The adverse impacts on plant biomass, total chlorophyll and chlorophyll fluorescence were more pronounced with joint occurrence of PD and SS than with individual application. Malondialdehyde (MDA), hydrogen peroxide (H2O2), and electrolyte leakage (EL) levels in plant leaves were higher in plants exposed to joint stresses than in plants grown under an individual stress. When plants were exposed to a single stress as opposed to both stressors, sodium hydrosulfide (NaHS) treatment more efficiently decreased EL, MDA, and H2O2 concentrations. Superoxide dismutase, peroxidase, glutathione reductase and ascorbate peroxidase activities were increased by SS alone or in conjunction with PD, whereas catalase activity decreased significantly. The favorable impact of NaHS on all the evaluated attributes was reversed by supplementation with 0.2 mM hypotaurine (HT), a H2S scavenger. Overall, the unfavorable effects caused to NaHS-supplied plants by a single stress were less severe compared with those caused by the combined administration of both stressors.

Eugenol improves salt tolerance via enhancing antioxidant capacity and regulating ionic balance in tobacco seedlings

Salt stress inhibits plant growth by disturbing plant intrinsic physiology. The application of exogenous plant growth regulators to improve the plant tolerance against salt stress has become one of the promising approaches to promote plant growth in saline environment. Eugenol (4-allyl-2- methoxyphenol) is the main ingredient in clove oil and it is known for its strong antioxidant and anti-microbial activities. Eugenol also has the ability of inhibiting several plant pathogens, implying the potential use of eugenol as an environmental friendly agrichemical. However, little is known about the possible role of eugenol in the regulation of plant tolerance against abiotic stress. Therefore, here we investigated the effectiveness of phytochemical eugenol in promoting salt tolerance in tobacco seedlings through physiological, histochemical, and biochemical method. The seedling roots were exposed to NaCl solution in the presence or absence of eugenol. Salt stress inhibited seedling growth, but eugenol supplementation effectively attenuated its effects in a dose-dependent manner, with an optimal effect at 20 µM. ROS (reactive oxygen species) accumulation was found in seedlings upon salt stress which was further resulted in the amelioration of lipid peroxidation, loss of membrane integrity, and cell death in salt-treated seedlings. Addition of eugenol highly suppressed ROS accumulation and reduced lipid peroxidation generation. Both enzymatic and non-enzymatic antioxidative systems were activated by eugenol treatment. AsA/DHA and GSH/GSSG were also enhanced upon eugenol treatment, which helped maintain redox homeostasis upon salinity. Eugenol treatment resulted in an increase in the content of osmoprotectants (e.g. proline, soluble sugar and starch) in salt-treated seedlings. Na+ levels decreased significantly in seedlings upon eugenol exposure. This may result from the upregulation of the expression of two ionic transporter genes, SOS1 (salt-hypersensitive 1) and NHX1 (Na+/H+ anti-transporter 1). Hierarchical cluster combined correlation analysis uncovered that eugenol induced salt tolerance was mediated by redox homeostasis and maintaining ionic balance in tobacco seedlings. This work reveals that eugenol plays a crucial role in regulating plant resistant physiology. This may extend its biological function as a novel biostimulant and opens up new possibilities for improving crop productivity in the saline agricultural environment.

Biochar amendment combined with partial root-zone drying irrigation alleviates salinity stress and improves root morphology and water use efficiency in cotton plant

An adsorption experiment and a pot experiment were executed in order to explore the mechanisms by which biochar amendment in combination with reduced irrigation affects sodium and potassium uptake, root morphology, water use efficiency, and salinity tolerance of cotton plants. In the adsorption experiment, ten NaCl concentration gradients (0, 50, 100, 150, 200, 250, 300, 350, 400, and 500 mM) were set for testing isotherm adsorption of Na+ by biochar. It was found that the isotherms of Na+ adsorption by wheat straw biochar (WSP) and softwood biochar (SWP) were in accordance with the Langmuir isotherm model, and the Na+ adsorption ability of WSP (55.20 mg g-1) was superior to that of SWP (47.38 mg g-1). The pot experiment consisted three factors, viz., three biochar amendments (no biochar, WSP, and SWP), three irrigation strategies (deficit irrigation, partial root-zone drying irrigation - PRD, full irrigation), and two NaCl concentrations gradients (0 mM and 200 mM). The findings indicated that salinity stress lowered K+ concentration, root length, root surface area, and root volume (RV), but increased Na+ concentration, root average diameter, and root tissue density. However, biochar amendment decreased Na+ concentration, increased K+ concentration, and improved root morphology. In particular, the combination of WSP and PRD increased K+/Na+ ratio, RV, root weight density, root surface area density, water use efficiency, and partial factor productivity under salt stress, which can be a promising strategy to cope with drought and salinity stress in cotton production.

Identification, characterization, and application of a d-cysteine desulfhydrase from rice seed (Oryza sativa L.)

Cysteine desulfhydrases decompose cysteine to produce pyruvate, ammonium, and hydrogen sulfide. Using d-cysteine (D-cys) as a substrate, an enzyme with this activity was purified from rice seeds and identified at the native protein level. MALDI-TOF-MS analysis of its tryptic peptides revealed a 426 amino acid protein encoded by the OsDCD1 gene (Os02g0773300). Recombinant OsDCD1 (rOsDCD1) was expressed in Escherichia coli cells and purified as a single protein by column chromatography. Gel filtration column chromatography indicated that the native enzyme was a homodimer. The enzyme exhibited maximum catalytic activity at approximately pH 7.5 and 40 °C and was stable at pH 5.5-7.5 and < 37 °C. Kinetics analysis indicated Km and Vmax values for D-cys of 136 μM and 45.5 μmol/min/mg protein, respectively. In contrast, l-cysteine (L-cys) acted as an inhibitor with mixed non-competitive inhibition. Based on the substrate specificity of rOsDCD1, the amount of D-cys in rice flour was quantified. Even in the presence of up to 1 mM L-cys, the quantification of low concentrations of D-cys was unaffected. We demonstrate for the first time that the amount of D-cys in rice flour varies in the range of 0.76-0.93 μmol/g depending on the variety.

Hydrogen sulfide priming enhanced salinity tolerance in sunflower by modulating ion hemostasis, cellular redox balance, and gene expression

BACKGROUND

The salinity threat represents an environmental challenge that drastically affects plant growth and yield. Besides salinity stress, the escalating world population will greatly influence the world's food security in the future. Therefore, searching for effective strategies to improve crop salinity resilience and sustain agricultural productivity under high salinity is a must. Seed priming is a reliable, simple, low-risk, and low-cost technique. Therefore, this work aimed to evaluate the impact of seed priming with 0.5 mM NaHS, as a donor of H2S, in mitigating salinity effects on sunflower seedlings. Primed and nonprime seeds were established in nonsaline soil irrigated with tape water for 14 d, and then exposed to 150 mM NaCl for 7 d.

RESULTS

Salinity stress significantly reduced the seedling growth, biomass accumulation, K+, Ca2+, and salinity tolerance index while elevating Na+ uptake and translocation. Salinity-induced adverse effects were significantly alleviated by H2S priming. Upregulation in gene expression (HaSOS2, HaGST) under NaCl stress was further enhanced by H2S priming. Also, H2S reduced lipid peroxidation, electrolyte leakage, and H2O2 content, but elevated the antioxidant defense system. NaCl-induced levels of ascorbate, glutathione, and α tocopherol, as well as the activities of AsA-GSH cycle enzymes: ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase, and glutathione S-transferase, were further enhanced by H2S priming. Increased level of H2S and total thiol by NaCl was also further stimulated by H2S priming.

CONCLUSION

H2S priming has proved to be an efficient strategy to improve sunflower seedlings' salinity tolerance by retaining ion homeostasis, detoxifying oxidative damage, modulating gene expression involved in ion homeostasis and ROS scavenging, and boosting endogenous H2S. These findings suggested that H2S acts as a regulatory molecule activating the functional processes responsible for sunflower adaptive mechanisms and could be adopted as a crucial crop management strategy to combat saline conditions. However, it would be of great interest to conduct further studies in the natural saline field to broaden our understanding of crop adaptive mechanisms and to support our claims.

Exogenous hydrogen sulfide improves salt stress tolerance of Reaumuria soongorica seedlings by regulating active oxygen metabolism

Hydrogen sulfide (H2S), as an endogenous gas signaling molecule, plays an important role in plant growth regulation and resistance to abiotic stress. This study aims to investigate the mechanism of exogenous H2S on the growth and development of Reaumuria soongorica seedlings under salt stress and to determine the optimal concentration for foliar application. To investigate the regulatory effects of exogenous H2S (donor sodium hydrosulfide, NaHS) at concentrations ranging from 0 to 1 mM on reactive oxygen species (ROS), antioxidant system, and osmoregulation in R. soongorica seedlings under 300 mM NaCl stress. The growth of R. soongorica seedlings was inhibited by salt stress, which resulted in a decrease in the leaf relative water content (LRWC), specific leaf area (SLA), and soluble sugar content in leaves, elevated activity levels of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT); and accumulated superoxide anion (O2-), proline, malondialdehyde (MDA), and soluble protein content in leaves; and increased L-cysteine desulfhydrase (LCD) activity and endogenous H2S content. This indicated that a high level of ROS was produced in the leaves of R. soongorica seedlings and seriously affected the growth and development of R. soongorica seedlings. The exogenous application of different concentrations of NaHS reduced the content of O 2-, proline and MDA, increased the activity of antioxidant enzymes and the content of osmoregulators (soluble sugars and soluble proteins), while the LCD enzyme activity and the content of endogenous H2S were further increased with the continuous application of exogenous H2S. The inhibitory effects of salt stress on the growth rate of plant height and ground diameter, the LRWC, biomass, and SLA were effectively alleviated. A comprehensive analysis showed that the LRWC, POD, and proline could be used as the main indicators to evaluate the alleviating effect of exogenous H2S on R. soongorica seedlings under salt stress. The optimal concentration of exogenous H2S for R. soongorica seedlings under salt stress was 0.025 mM. This study provides an important theoretical foundation for understanding the salt tolerance mechanism of R. soongorica and for cultivating high-quality germplasm resources.

Foliar Spraying of NaHS Alleviates Cucumber Salt Stress by Maintaining N+/K+ Balance and Activating Salt Tolerance Signaling Pathways

Hydrogen sulfide (H₂S) is involved in the regulation of plant salt stress as a potential signaling molecule. This work investigated the effect of H₂S on cucumber growth, photosynthesis, antioxidation, ion balance, and other salt tolerance pathways. The plant height, stem diameter, leaf area and photosynthesis of cucumber seedlings were significantly inhibited by 50 mmol·L^-1 NaCl. Moreover, NaCl treatment induced superoxide anion (O₂^·-) and Na⁺ accumulation and affected the absorption of other mineral ions. On the contrary, exogenous spraying of 200 μmol·L^-1 sodium hydrosulfide (NaHS) maintained the growth of cucumber seedlings, increased photosynthesis, enhanced the ascorbate-glutathione cycle (AsA-GSH), and promoted the absorption of mineral ions under salt stress. Meanwhile, NaHS upregulated SOS1, SOS2, SOS3, NHX1, and AKT1 genes to maintain Na⁺/K⁺ balance and increased the relative expression of MAPK3, MAPK4, MAPK6, and MAPK9 genes to enhance salt tolerance. These positive effects of H₂S could be reversed by 150 mmol·L^-1 propargylglycine (PAG, a specific inhibitor of H₂S biosynthesis). These results indicated that H₂S could mitigate salt damage in cucumber, mainly by improving photosynthesis, enhancing the AsA-GSH cycle, reducing the Na⁺/K⁺ ratio, and inducing the SOS pathway and MAPK pathway.

Seedling nanopriming with selenium-chitosan nanoparticles mitigates the adverse effects of salt stress by inducing multiple defence pathways in bitter melon plants

Advances in the nanotechnology fields provided crucial applications in plant sciences, contributing to the plant performance and health under stress and stress-free conditions. Amid the applications, selenium (Se), chitosan and their conjugated forms as nanoparticles (Se-CS NPs) have been revealed to have potential of alleviating the harmful effects of the stress on several crops and subsequently enhancing the growth and productivity. The present study was addressed to assay the potential effects of Se-CS NPs in reversing or buffering the harmful effects of salt stress on growth, photosynthesis, nutrient concentration, antioxidant system and defence transcript levels in bitter melon )Momordica charantia(. In addition, some secondary metabolite-related genes were explicitly examined. In this regard, the transcriptional levels of WRKY1, SOS1, PM H⁺-ATPase, SKOR, Mc5PTase7, SOAR1, MAP30, α-MMC, polypeptide-P and PAL were quantified. Our results demonstrated that Se-CS NPs increased growth parameters, photosynthesis parameters (SPAD, ^Fv/_Fm, Y(II)), antioxidant enzymatic activity (POD, SOD, CAT) and nutrient homeostasis (Na⁺/K⁺, Ca²⁺, and Cl^-) and induced the expression of genes in bitter melon plants under salt stress (p ≤ 0.05). Therefore, applying Se-CS NPs might be a simple and effective way of improving crop plants' overall health and yield under salt stress conditions.

Improving salt tolerance of bean (Phaseolus vulgaris L.) with hydrogen sulfide

The current study examined the H2S applications on growth, biochemical and physiological parameters of bean seedlings under saline conditions. The findings of the study indicated that salt stress decreased plant growth and development, photosynthetic activity, and mineral and hormone content [excluding abscisic acid (ABA)] in bean seedlings. Plant and root fresh mass and dry mass with H2S applications increased as compared to the control treatment at the same salinity level. Both salinity and H2S treatments significantly affected the net assimilation rate, stomatal conductance, transpiration rate, and intercellular CO2 content of bean seedlings. Significant increases occurred in H2O2, malondialdehyde (MDA), proline, sucrose content, enzyme activity, and ABA content with salt stress. However, H2S applications inhibited the effects of salinity on plant growth, photosynthetic activity, and mineral content in beans. H2S applications reduced H2O2, MDA, proline, sucrose content, enzyme activity, and ABA content in beans. As a result, exogenous H2S applications could mitigate the negative impacts of salinity in beans.

Nitric oxide and hydrogen sulfide work together to improve tolerance to salinity stress in wheat plants by upraising the AsA-GSH cycle

The participation of nitric oxide (NO) in wheat plant tolerance to salinity stress (SS) brought about by hydrogen sulphide (H₂S) via modifying the ascorbate-glutathione (AsA-GSH) cycle was studied. The SS-plants received either 0.2 mM sodium hydrosulfide (NaHS; H₂S donor), or NaHS plus 0.1 mM sodium nitroprusside (SNP; a NO donor) through the nutrient solution. Salinity stress decreased plant growth, leaf water status, leaf K⁺, and glyoxalase II (gly II), while it elevated proline content, leaf Na⁺ content, oxidative stress, methylglyoxal (MG), glyoxalase I (gly I), the superoxide dismutase, catalase and peroxidase activities, contents of endogenous NO and H₂S. The NaHS supplementation elevated plant development, decreased leaf Na⁺ content and oxidative stress, and altered leaf water status, leaf K⁺ and involved enzymes in AsA-GSH, H₂S and NO levels. The SNP supplementation boosted the positive impact of NaHS on these traits in the SS-plants. Moreover, 0.1 mM cPTIO, scavenger of NO, countered the beneficial effect of NaHS by lowering NO levels. SNP and NaHS + cPTIO together restored the beneficial effects of NaHS by increasing NO content, implying that NO may have been a major factor in SS tolerance in wheat plants induced by H₂S via activating enzymes connected to the AsA-GSH cycle.

H2S Enhanced the Tolerance of Malus hupehensis to Alkaline Salt Stress through the Expression of Genes Related to Sulfur-Containing Compounds and the Cell Wall in Roots

Malus is an economically important plant that is widely cultivated worldwide, but it often encounters saline-alkali stress. The composition of saline-alkali land is a variety of salt and alkali mixed with the formation of alkaline salt. Hydrogen sulfide (H₂S) has been reported to have positive effects on plant responses to abiotic stresses. Our previous study showed that H₂S pretreatment alleviated the damage caused by alkaline salt stress to Malus hupehensis Rehd. var. pingyiensis Jiang (Pingyi Tiancha, PYTC) roots by regulating Na⁺/K⁺ homeostasis and oxidative stress. In this study, transcriptome analysis was used to investigate the overall mechanism through which H₂S alleviates alkaline salt stress in PYTC roots. Simultaneously, differentially expressed genes (DEGs) were explored. Transcriptional profiling of the Control-H₂S, Control-AS, Control-H₂S + AS, and AS-H₂S + AS comparison groups identified 1618, 18,652, 16,575, and 4314 DEGs, respectively. Further analysis revealed that H₂S could alleviate alkaline salt stress by increasing the energy maintenance capacity and cell wall integrity of M. hupehensis roots and by enhancing the capacity for reactive oxygen species (ROS) metabolism because more upregulated genes involved in ROS metabolism and sulfur-containing compounds were identified in M. hupehensis roots after H₂S pretreatment. qRT-PCR analysis of H₂S-induced and alkaline salt-response genes showed that these genes were consistent with the RNA-seq analysis results, which indicated that H₂S alleviation of alkaline salt stress involves the genes of the cell wall and sulfur-containing compounds in PYTC roots.

H2 S improves salt-stress recovery via organic acid turn-over in apple seedlings

Signalling roles of hydrogen sulphide (H₂ S) in stress biology are widely reported but not sufficiently established to urge its use in agronomic practice. Our lack of quantitative understanding of the metabolic rewiring in H₂ S signalling makes it difficult to elucidate its functions in stress tolerance on the biochemical level. Here, Malus hupehensis Rehd. var. pingyiensis seedlings were first treated with salt stress for 2 weeks and then treated with four different concentrations of NaHS. Through vigorous investigations, including phenotypic analysis, ¹³ C transient labelling and targeted metabolic and transcriptomic analysis, for the first time in the seedlings of a woody fruit crop, we found out that H₂ S recycles fixed carbons through glycolysis and tricarboxylic acid cycle to inhibit the futile accumulation of carbohydrates, to maintain an efficient CO₂ assimilation, to keep a balanced starch metabolism, to produce sufficient H₂ O₂ , to maintain malate/γ-aminobutyric acid homeostasis via an H₂ O₂ -induced anion channel (aluminium-activated malate transporter) and eventually to improve salt-stress recovery. Our results systematically demonstrate the vital roles of central carbon metabolism in H₂ S signalling and clarify the mode of action of H₂ S in apple seedlings. We conclude that H₂ S signalling interacts with central carbon metabolism in a bottom-up manner to recover plant growth after salt stress.

Exogenous hydrogen sulfide mediates Na+ and K+ fluxes of salt gland in salt-secreting mangrove plant Avicennia marina

Hydrogen sulfide (H2S), is a crucial biological player in plants. Here, we primarily explored the interaction between sodium hydrosulfide (NaHS, a H2S donor) and the fluxes of Na+ and K+ from the salt glands of mangrove species Avicennia marina (Forsk.) Vierh. with non-invasive micro-test technology (NMT) and quantitative real-time PCR (qRT-PCR) approaches under salinity treatments. The results showed that under 400-mM NaCl treatment, the addition of 200-μM NaHS markedly increased the quantity of salt crystals in the adaxial epidermis of A. marina leaves, accompanied by an increase in the K+/Na+ ratio. Meanwhile, the endogenous content of H2S was dramatically elevated in this process. The NMT result revealed that the Na+ efflux was increased from salt glands, whereas K+ efflux was decreased with NaHS application. On the contrary, the effects of NaHS were reversed by H2S scavenger hypotaurine (HT), and DL-propargylglycine (PAG), an inhibitor of cystathionine-γ-lyase (CES, a H2S synthase). Moreover, enzymic assay revealed that NaHS increased the activities of plasma membrane and tonoplast H+-ATPase. qRT-PCR analysis revealed that NaHS significantly increased the genes transcript levels of tonoplast Na+/H+ antiporter (NHX1), plasma membrane Na+/H+ antiporter (SOS1), plasma membrane H+-ATPase (AHA1) and tonoplast H+-ATPase subunit c (VHA-c1), while suppressed above-mentioned gene expressions by the application of HT and PAG. Overall, H2S promotes Na+ secretion from the salt glands of A. marina by up-regulating the plasma membrane and tonoplast Na+/H+ antiporter and H+-ATPase.

Expression profile, transcriptional and post-transcriptional regulation of genes involved in hydrogen sulphide metabolism connecting the balance between development and stress adaptation in plants: a data-mining bioinformatics approach

Recent research focused on novel aspects of sulphur and sulphur-containing molecules in fundamental plant processes has highlighted the importance of these compounds. Currently, the focus has shifted to the efficacy of hydrogen sulphide (H₂ S) as signalling compounds that regulate different development and stress mitigation in plants. Accordingly, we used an in silico approach to study the differential expression patterns of H₂ S metabolic genes at different growth/development stages and their tissue-specific expression patterns under a range of abiotic stresses. Moreover, to understand the multilevel regulation of genes involved in H₂ S metabolism, we performed computation-based promoter analysis, alternative splice variant analysis, prediction of putative miRNA targets and co-expression network analysis. Gene expression analysis suggests that H₂ S biosynthesis is highly influenced by developmental and stress stimuli. The functional annotation of promoter structures reveales a wide range of plant hormone and stress responsive cis-regulatory elements (CREs) that regulate H₂ S metabolism. Co-expression analysis suggested that genes involved in H₂ S metabolism are also associated with different metabolic processes. In this data-mining study, the primary focus was to understand the genetic architecture governing pathways of H₂ S metabolism in different cell compartments under various developmental and stress signalling cascades. The present study will help to understand the genetic architecture of H₂ S metabolism via cysteine metabolism and the functional roles of these genes in development and stress tolerance mechanisms.

Hydrogen sulphide alleviates cadmium stress in Trigonella foenum-graecum by modulating antioxidant enzymes and polyamine content

Cadmium (Cd) toxicity reduces growth and yield of crops grown in metal-polluted sites. Research was conducted to estimate the potential of hydrogen sulphide (H₂ S) to mitigate toxicity caused by Cd in fenugreek seedlings (Trigonella foenum-graecum L.). Different concentrations of CdCl₂ (Cd1-1 mM, Cd2-1.5 mM, Cd3-2mM) and H₂ S (HS1-100 µM, HS2-150 µM, HS3-200 µM) were assessed. Seeds of fenugreek were primed with sodium hydrosulphide (NaHS), as H₂ S donor. Seedlings growing in Cd-spiked media treated with H₂ S were harvested after 2 weeks. Cd stress affected growth of fenugreek seedlings. Cd toxicity decreased leaf relative water content (LRWC), intercellular CO₂ concentration, net photosynthesis, stomatal conductance and transpiration. However, application of H₂ S significantly improved seedling morphological attributes by increasing the activity of antioxidant enzymes, i.e. APX, CAT and SOD, in Cd-contaminated soil. H₂ S treatment also regulated phenolic and flavonoid content. H₂ S-induced biosynthesis of spermidine (Spd) and putrescine (Put) could account for the enhancement of growth and physiological performance of fenugreek seedlings under Cd stress. H₂ S treatment also reduced H₂ O₂ production (38%) and electrolyte leakage (EL, 51%) in seedlings grown in different concentrations of Cd. It is recommended to evaluate the efficacy of H₂ S in alleviating Cd toxicity in other crop plants.

Hydrogen sulphide signalling in plant response to abiotic stress

Throughout their whole life cycle, higher plants are often exposed to diverse environmental stresses, such as drought, salinity, heavy metals and extreme temperatures. In response to such stress, plant cells initiate signalling transduction, resulting in downstream responses, such as specific gene transcription and protein expression. Accumulating evidence has revealed that hydrogen sulphide (H₂ S) serves as a signalling molecule in plant acclimation to stressful conditions. More important, H₂ S interacts with other signalling molecules and phytohormones, contributing to transcriptional regulation and post-translational modification. Overall, the H₂ S-mediated signalling pathway and its interaction with other signals remains elusive. Here, we describe the role of the H₂ S signalling network in regulating physiological and molecular processes under various abiotic stresses.

Mitigation of salinity stress in cucumber seedlings by exogenous hydrogen sulfide

This research hypothesized that tolerance of cucumber seedlings to salinity stress could be increased by hydrogen sulfide (H₂S) treatments. In pot experiments, the cucumber seedlings were exposed to three levels of salt stress (0, 50 and 100 mM NaCl), and NaHS as H₂S donor was foliar applied to the cucumber seedlings at five different doses (0, 25, 50, 75 and 100 µM). The effects of the treatments on cucumber seedlings were tested with plant growth properties as well as physiological and biochemical analyses. As the salinity level increased, plant growth properties and chlorophyll reading value (SPAD) decreased. However, H₂S treatments significantly mitigated the impact of salinity. Salt stress elevated the membrane permeability (MP) and decreased the leaf relative water content (LRWC). H₂S applied leaves had lower MP and higher LRWC than non-H₂S applied leaves. On the other hand, photosynthetic properties (net photosynthetic rate, stomatal conductance, transpiration rate and intercellular CO₂ concentration) of the seedlings under salt stress conditions were decreased but this decrease was considerably relieved by H₂S treatment. The K/Na and Ca/Na ratios under salt stress conditions were higher in H₂S-applied plants than in non-applied plants. Furthermore, antioxidant enzyme activity [(catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD)] and hydrogen peroxide (H₂O₂), malondialdehyde (MDA), proline, and sucrose concentration in the leaves increased with salinity stress whereas they were reduced with H₂S treatments under salt stress. Mitigation of salt stress damage in cucumber using H₂S treatment can be expounded via modulation of enzyme activity, nutrient content, reactive oxygen species (ROS) formation, and osmolytes accumulation.

The Defensive Role of Endogenous H2S in Brassica rapa against Mercury-Selenium Combined Stress

Plants are always exposed to the environment, polluted by multiple trace elements. Hydrogen sulfide (H₂S), an endogenous gaseous transmitter in plant cells, can help plant combat single elements with excess concentration. Until now, little has been known about the regulatory role of H₂S in response to combined stress of multiple elements. Here we found that combined exposure of mercury (Hg) and selenium (Se) triggered endogenous H₂S signal in the roots of Brasscia rapa. However, neither Hg nor Se alone worked on it. In roots upon Hg + Se exposure, the defensive role of endogenous H₂S was associated to the decrease in reactive oxygen species (ROS) level, followed by alleviating cell death and recovering root growth. Such findings extend our knowledge of plant H₂S in response to multiple stress conditions.

Hydrogen sulfide-mediated mitigation and its integrated signaling crosstalk during salinity stress

Environmental stresses negatively affect plant development and significantly influence global agricultural productivity. The growth suppression due to soil salinity involves osmotic stress, which is accompanied by ion toxicity, nutritional imbalance, and oxidative stress. The amelioration of salinity stress is one of the fundamental goals to be achieved to ensure food security and better meet the issues related to global hunger. The application of exogenous chemicals is the imperative and efficient choice to alleviate stress in the agricultural field. Among them, hydrogen sulfide (H₂ S, a gasotransmitter) is known for its efficient role in stress mitigation, including salinity stress, along with other biological features related to growth and development in plants. H₂ S plays a role in improving photosynthesis and ROS homeostasis, and interacts with other signaling components in a cascade fashion. The current review gives a comprehensive view of the participation of H₂ S in salinity stress alleviation in plants. Further, its crosstalk with other stress ameliorating signaling component or supplement (e.g., NO, H₂ O₂ , melatonin) is also covered and discussed. Finally, we discuss the possible prospects to meet with success in agricultural fields.

Interplay between gasotransmitters and potassium is a K+ey factor during plant response to abiotic stress

Carbon monoxide (CO), nitric oxide (NO) and hydrogen sulfide (H₂S) are gasotransmitters known for their roles in plant response to (a)biotic stresses. The crosstalk between these gasotransmitters and potassium ions (K⁺) has received considerable attention in recent years, particularly due to the dual role of K⁺ as an essential mineral nutrient and a promoter of plant tolerance to abiotic stress. This review brings together what it is known about the interplay among NO, CO, H₂S and K⁺ in plants with focus on the response to high salinity. Some findings obtained for plants under water deficit and metal stress are also presented and discussed since both abiotic stresses share similarities with salt stress. The molecular targets of the gasotransmitters NO, CO and H₂S in root and guard cells that drive plant tolerance to salt stress are highlighted as well.

Hydrogen Sulfide Enhances Plant Tolerance to Waterlogging Stress

Hydrogen sulfide (H₂S) is considered the third gas signal molecule in recent years. A large number of studies have shown that H₂S not only played an important role in animals but also participated in the regulation of plant growth and development and responses to various environmental stresses. Waterlogging, as a kind of abiotic stress, poses a serious threat to land-based waterlogging-sensitive plants, and which H₂S plays an indispensable role in response to. In this review, we summarized that H₂S improves resistance to waterlogging stress by affecting lateral root development, photosynthetic efficiency, and cell fates. Here, we reviewed the roles of H₂S in plant resistance to waterlogging stress, focusing on the mechanism of its promotion to gained hypoxia tolerance. Finally, we raised relevant issues that needed to be addressed.

Exogenous melatonin-mediated regulation of K+ /Na+ transport, H+ -ATPase activity and enzymatic antioxidative defence operate through endogenous hydrogen sulphide signalling in NaCl-stressed tomato seedling roots

Melatonin (Mel) and hydrogen sulphide (H₂ S) have emerged as potential regulators of plant metabolism during abiotic stress. Presence of excess NaCl in the soil is one of the main causes of reduced crop productivity worldwide. The present investigation examines the role of exogenous Mel and endogenous H₂ S in tomato seedlings grown under NaCl stress. Effect of 30 µm Mel on endogenous synthesis of H₂ S was examined in roots of NaCl-stressed (200 mm) tomato seedlings. Also, the impact of treatments on the oxidative stress markers, transport of K⁺ and Na⁺ , and activity of H⁺ -ATPase and antioxidant enzymes was assessed. Results show that NaCl-stressed seedlings supplemented with 30 µm Mel had increased levels of endogenous H₂ S through enhanced L-cysteine desulfhydrase activity. Mel in association with H₂ S overcame the deleterious effect of NaCl and induced retention of K⁺ that maintained a higher K⁺ /Na⁺ ratio. Use of plasma membrane inhibitors and an H₂ S scavenger revealed that Mel-induced regulation of K⁺ /Na⁺ homeostasis in NaCl-stressed seedling roots operates through endogenous H₂ S signalling. Synergistic effects of Mel and H₂ S also reduced the generation of ROS and oxidative destruction through the enhanced activity of antioxidant enzymes. Thus, it is suggested that the protective function of Mel against NaCl stress operates through an endogenous H₂ S-dependent pathway, wherein H⁺ -ATPase-energized secondary active transport regulates K⁺ /Na⁺ homeostasis.

Hydrogen Sulfide: A Robust Combatant against Abiotic Stresses in Plants

Hydrogen sulfide (H2S) is predominantly considered as a gaseous transmitter or signaling molecule in plants. It has been known as a crucial player during various plant cellular and physiological processes and has been gaining unprecedented attention from researchers since decades. They regulate growth and plethora of plant developmental processes such as germination, senescence, defense, and maturation in plants. Owing to its gaseous state, they are effectively diffused towards different parts of the cell to counterbalance the antioxidant pools as well as providing sulfur to cells. H2S participates actively during abiotic stresses and enhances plant tolerance towards adverse conditions by regulation of the antioxidative defense system, oxidative stress signaling, metal transport, Na+/K+ homeostasis, etc. They also maintain H2S-Cys-cycle during abiotic stressed conditions followed by post-translational modifications of cysteine residues. Besides their role during abiotic stresses, crosstalk of H2S with other biomolecules such as NO and phytohormones (abscisic acid, salicylic acid, melatonin, ethylene, etc.) have also been explored in plant signaling. These processes also mediate protein post-translational modifications of cysteine residues. We have mainly highlighted all these biological functions along with proposing novel relevant issues that are required to be addressed further in the near future. Moreover, we have also proposed the possible mechanisms of H2S actions in mediating redox-dependent mechanisms in plant physiology.

Strigolactones regulate arsenate uptake, vacuolar-sequestration and antioxidant defense responses to resist arsenic toxicity in rice roots

We explored genetic evidence for strigolactones' role in rice tolerance to arsenate-stress. Comparative analyses of roots of wild-type (WT) and strigolactone-deficient mutants d10 and d17 in response to sodium arsenate (Na₂AsO₄) revealed differential growth inhibition [WT (11.28%) vs. d10 (19.76%) and d17 (18.03%)], biomass reduction [(WT (33.65%) vs. d10 (74.86%) and d17 (60.65%)] and membrane damage (WT < d10 and d17) at 250 μM Na₂AsO₄. Microscopic and biochemical analyses showed that roots of WT accumulated lower levels of arsenic and oxidative stress indicators like reactive oxygen species and malondialdehyde than those of strigolactone-deficient mutants. qRT-PCR data indicated lower expression levels of genes (OsPT1, OsPT2, OsPT4 and OsPT8) encoding phosphate-transporters in WT roots than mutant roots, explaining the decreased arsenate and phosphate uptake by WT roots. Increased levels of glutathione and OsPCS1 and OsABCC1 transcripts indicated an efficient vacuolar-sequestration of arsenic in WT roots. Furthermore, higher activities (transcript levels) of SOD (OsCuZnSOD1 and OsCuZnSOD2), APX (OsAPX1 and OsAPX2) and CAT (OsCATA) corresponded to lower oxidative damage in WT roots compared with strigolactone-mutant roots. Collectively, these results highlight that strigolactones are involved in arsenic-stress mitigation by regulating arsenate-uptake, glutathione-biosynthesis, vacuolar-sequestration of arsenic and antioxidant defense responses in rice roots.

Hydrogen Sulfide Alleviates Alkaline Salt Stress by Regulating the Expression of MicroRNAs in Malus hupehensis Rehd. Roots

Malus hupehensis Rehd. var. pingyiensis Jiang (Pingyi Tiancha, PYTC) is an excellent apple rootstock and ornamental tree, but its tolerance to salt stress is weak. Our previous study showed that hydrogen sulfide (H₂S) could alleviate damage in M. hupehensis roots under alkaline salt stress. However, the molecular mechanism of H₂S mitigation alkaline salt remains to be elucidated. MicroRNAs (miRNAs) play important regulatory roles in plant response to salt stress. Whether miRNAs are involved in the mitigation of alkaline salt stress mediated by H₂S remains unclear. In the present study, through the expression analysis of miRNAs and target gene response to H₂S and alkaline salt stress in M. hupehensis roots, 115 known miRNAs (belonging to 37 miRNA families) and 15 predicted novel miRNAs were identified. In addition, we identified and analyzed 175 miRNA target genes. We certified the expression levels of 15 miRNAs and nine corresponding target genes by real-time quantitative PCR (qRT-PCR). Interestingly, H₂S pretreatment could specifically induce the downregulation of mhp-miR408a expression, and upregulated mhp-miR477a and mhp-miR827. Moreover, root architecture was improved by regulating the expression of mhp-miR159c and mhp-miR169 and their target genes. These results suggest that the miRNA-mediated regulatory network participates in the process of H₂S-mitigated alkaline salt stress in M. hupehensis roots. This study provides a further understanding of miRNA regulation in the H₂S mitigation of alkaline salt stress in M. hupehensis roots.

Hydrogen sulfide implications on easing NaCl induced toxicity in eggplant and tomato seedlings

In the present study, the role of hydrogen sulfide (H₂S) in alleviating NaCl (20 mM) induced toxicity on growth, photosynthetic pigments and photochemistry of PS II, and impact on oxidative stress and antioxidant systems of eggplant and tomato was studied. To confirm the role of H₂S (donor sodium hydrogen sulphide (NaHS; 40 μM)) under stress, H₂S scavenger; hypotaurine (HT; 200 μM) and inhibitor, propargylglycine (PAG; 100 μM) in combination with NaHS was added to the growth medium of NaCl stressed seedlings. The NaCl reduced the overall growth of the seedlings as the Na⁺ uptake was increased which led to removal of K⁺, thereby Na⁺/K⁺ homeostasis was disturbed. This condition caused severe impact on photosynthetic pigments and PS II photochemistry, thus significant decline in the values of fluorescence kinetics parameters such as F_v/F_m, F_V/F₀, φE₀, ѱ_0, PI_ABS except F₀/F_V and enhancement in energy flux parameters such as ABS/RC, TR₀/RC, ET₀/RC and DI₀/RC was obtained. Exogenous H₂S not only abolished the toxic symptoms in test seedlings but also completely alleviated the decline in growth in case of tomato seedlings. Reactive oxygen species accumulation was significantly declined in both the seedlings as evident by in vitro and in vivo analysis with the supplementation of NaHS, indicating appreciable recovery in membrane damage caused by NaCl toxicity. Antioxidative enzymes: SOD, POD, CAT and GST activities were further stimulated in response to H₂S (NaHS) supplementation to the stressed seedlings, thus maintaining the redox homeostasis of cell and bringing the seedlings back to the healthy state. Moreover, the role of endogenous and exogenous H₂S was also justified using the scavenger of H₂S (HT; 200 μM) and inhibitor of enzymes of H₂S (PAG; 100 μM). Thus, present study emphasizes the role of NaHS as H₂S donor in alleviating NaCl stress in crops particularly vegetables tomato and eggplant, and may be considered as a part of important strategies to cope up with NaCl toxicity which is prevailing in natural field condition.

Hydrogen sulfide priming can enhance the tolerance of artichoke seedlings to individual and combined saline-alkaline and aniline stresses

Regulatory roles of hydrogen sulfide (H₂S) under saline-alkaline and/or aniline stress have not been studied yet. In this study, we investigated the insights into saline-alkaline and/or aniline stresses-induced toxicity in artichoke plants and its alleviation by H₂S priming. Individual saline-alkaline or aniline stress and their combination reduced plant growth and photosynthetic pigments. Principal component analysis (PCA) revealed that these detrimental impacts were caused by the higher oxidative damage and disruption of osmolyte homeostasis. Interestingly, only aniline stress (25 mg L^-1) caused neither oxidative nor osmotic stress thus almost slight growth retarding effects had ensued. On the other hand, the presence of aniline in saline-alkaline conditions exacerbated stress-induced deleterious effects on plants, as evidenced by PCA and heatmap. However, H₂S priming markedly eased the stress-induced deleteriousness as evident by enhanced chlorophyll, soluble proteins, soluble carbohydrates and up-regulated water relation in H₂S-primmed plants compared with only stressed plants resulting in improved plant phenotypic features. Furthermore, H₂S priming enhanced endogenous H₂S content, phenylalanine ammonia-lyase, non-enzymatic antioxidants (ascorbic acid, flavonoids, glutathione, α-tocopherol, and anthocyanins) and enzymatic antioxidants (superoxide dismutase, catalase, and ascorbate peroxidase), whereas reduced oxidative stress markers (superoxide, hydrogen peroxide, hydroxyl radical, malondialdehyde, and methylglyoxal) compared with only stressed plants, indicating a protective function of H₂S against oxidative damage. The PCA also clarified that H₂S-mediated saline-alkaline and/or aniline stress tolerance strongly connected with the improved antioxidant system. Overall, our finding proposed that H₂S priming could be an effective technique to mitigate saline-alkaline and/or aniline stress in artichoke, and perhaps in other crop plants.

Hydrogen sulfide, a signaling molecule in plant stress responses

Gaseous molecules, such as hydrogen sulfide (H₂ S) and nitric oxide (NO), are crucial players in cellular and (patho)physiological processes in biological systems. The biological functions of these gaseous molecules, which were first discovered and identified as gasotransmitters in animals, have received unprecedented attention from plant scientists in recent decades. Researchers have arrived at the consensus that H₂ S is synthesized endogenously and serves as a signaling molecule throughout the plant life cycle. However, the mechanisms of H₂ S action in redox biology is still largely unexplored. This review highlights what we currently know about the characteristics and biosynthesis of H₂ S in plants. Additionally, we summarize the role of H₂ S in plant resistance to abiotic stress. Moreover, we propose and discuss possible redox-dependent mechanisms by which H₂ S regulates plant physiology.

Hydrogen sulfide: Roles in plant abiotic stress response and crosstalk with other signals

Hydrogen sulfide (H₂S) has been recently recognized as an endogenous gas transmitter alongside nitric oxide and carbon monoxide. Exposure of plants to H₂S, for example through applicating H₂S donors, reveals that H₂S play important roles in plant response to abiotic stresses such as heavy metals, salinity, drought and extreme temperatures. Sodium hydrosulfide is the most widely used donor in plants due to its direct and instantaneous release of H₂S, followed by GYY4137. H₂S can enhance plant tolerance to salt and heavy metal stresses through regulating Na⁺/K⁺ homeostasis and the uptake and transport of metal ions. H₂S also promotes the H₂S-Cys cycle balance under abiotic stress and enhances its roles in regulation of the antioxidant system, alternative respiratory pathway, and heavy metal chelators synthesis. H₂S coordinates with gaseous signal molecules, reactive oxygen species and nitric oxide to respond to stress directly through influencing their generation or competing for the regulation of the downstream signaling. Moreover, H₂S interacts with phytohormones including abscisic acid, ethylene, salicylic acid and melatonin as well as polyamines to regulate plant response to abiotic stresses. In this review, the application of H₂S donors and their functional mechanism are summarized. We propose promising new research directions, which can lead to new insights on the role of this gastrasmitter during plant growth and development.

Hydrogen sulfide (H2S) signaling in plant development and stress responses

ABSTRACT

Hydrogen sulfide (H₂S) was initially recognized as a toxic gas and its biological functions in mammalian cells have been gradually discovered during the past decades. In the latest decade, numerous studies have revealed that H₂S has versatile functions in plants as well. In this review, we summarize H₂S-mediated sulfur metabolic pathways, as well as the progress in the recognition of its biological functions in plant growth and development, particularly its physiological functions in biotic and abiotic stress responses. Besides direct chemical reactions, nitric oxide (NO) and hydrogen peroxide (H₂O₂) have complex relationships with H₂S in plant signaling, both of which mediate protein post-translational modification (PTM) to attack the cysteine residues. We also discuss recent progress in the research on the three types of PTMs and their biological functions in plants. Finally, we propose the relevant issues that need to be addressed in the future research.

GRAPHIC ABSTRACT

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s42994-021-00035-4.

Mechanistic Insight of Allantoin in Protecting Tomato Plants Against Ultraviolet C Stress

Allantoin ((AT) a purine metabolite)-mediated ultraviolet C (UVC) stress mitigation has not been studied to date. Here, we reported the physicochemical mechanisms of UVC-induced stress in tomato (Solanum lycopersicum L.) plants, including an AT-directed mitigation strategy. UVC stress reduced plant growth and photosynthetic pigments. Heatmap and principal component analysis (PCA) revealed that these toxic impacts were triggered by the greater oxidative damage and disruption of osmolyte homeostasis. However, pre-treatment of AT noticeably ameliorated the stress-induced toxicity as evident by enhanced chlorophyll, soluble protein, and soluble carbohydrate contents in AT-pretreated UVC-stressed plants relative to only stressed plants leading to the improvement of the plant growth and biomass. Moreover, AT pre-treatment enhanced endogenous AT and allantoate content, phenylalanine ammonia-lyase, non-enzymatic antioxidants, and the enzymatic antioxidants leading to reduced oxidative stress markers compared with only stressed plants, indicating the protective effect of AT against oxidative damage. Moreover, PCA displayed that the protective roles of AT strongly associate with the improved antioxidants. On the other hand, post-treatment of AT showed less efficacy in UVC stress mitigation relative to pre-treatment of AT. Overall, this finding illustrated that AT pre-treatment could be an effective way to counteract the UVC stress in tomato, and perhaps in other crop plants.

A nuclear-localized cysteine desulfhydrase plays a role in fruit ripening in tomato

Hydrogen sulfide (H₂S) is a gaseous signaling molecule that plays multiple roles in plant development. However, whether endogenous H₂S plays a role in fruit ripening in tomato is still unknown. In this study, we show that the H₂S-producing enzyme L-cysteine desulfhydrase SlLCD1 localizes to the nucleus. By constructing mutated forms of SlLCD1, we show that the amino acid residue K24 of SlLCD1 is the key amino acid that determines nuclear localization. Silencing of SlLCD1 by TRV-SlLCD1 accelerated fruit ripening and reduced H₂S production compared with the control. A SlLCD1 gene-edited mutant obtained through CRISPR/Cas9 modification displayed a slightly dwarfed phenotype and accelerated fruit ripening. This mutant also showed increased cysteine content and produced less H₂S, suggesting a role of SlLCD1 in H₂S generation. Chlorophyll degradation and carotenoid accumulation were enhanced in the SlLCD1 mutant. Other ripening-related genes that play roles in chlorophyll degradation, carotenoid biosynthesis, cell wall degradation, ethylene biosynthesis, and the ethylene signaling pathway were enhanced at the transcriptional level in the lcd1 mutant. Total RNA was sequenced from unripe tomato fruit treated with exogenous H₂S, and transcriptome analysis showed that ripening-related gene expression was suppressed. Based on the results for a SlLCD1 gene-edited mutant and exogenous H₂S application, we propose that the nuclear-localized cysteine desulfhydrase SlLCD1 is required for endogenous H₂S generation and participates in the regulation of tomato fruit ripening.

H2S pretreatment mitigates the alkaline salt stress on Malus hupehensis roots by regulating Na+/K+ homeostasis and oxidative stress

Hydrogen sulfide (H₂S) plays an important role in the plant salt stress response. The main component of salt stress is neutral salt (NaCl); NaHCO₃ and Na₂CO₃ play a key role in soil alkaline due to the influence of pH. Malus hupehensis Rehd. var. pingyiensis Jiang (Pingyi Tiancha, PYTC) is a salt-sensitive apple rootstock. Seedlings of PYTC pretreated with NaHS (an H₂S donor) were exposed to an alkaline salt solution, and then the plant growth, root architecture, oxidative damage, Na⁺/K⁺ homeostasis and gene expression of MhSOS1 and MhSKOR were investigated. The results showed that NaHS pretreatment increased the endogenous H₂S content in seedlings, significantly alleviated the alkaline salt stress-induced growth inhibition and oxidative damage by inducing antioxidant enzymes activities, and sustained the root activity and root architecture of PYTC in the alkaline salt solution. NaHS pretreatment significantly decreased the root Na⁺ content and increased K⁺ content to maintain the homeostasis of Na⁺/K⁺, and effect the expression of MhSOS1 and MhSKOR at the transcription level in the presence of the alkaline salt. Our study reveals that application of H₂S could mitigate the toxic effect of alkaline salt stress on Malus hupehensis seedlings, thus providing a foundation for improved plant tolerance to alkaline salt stress.

Genome- and Transcriptome-Wide Identification of C3Hs in Common Bean (Phaseolus vulgaris L.) and Structural and Expression-Based Analyses of Their Functions During the Sprout Stage Under Salt-Stress Conditions

CCCH (C3H) zinc-finger proteins are involved in plant biotic and abiotic stress responses, growth and development, and disease resistance. However, studies on C3H genes in Phaseolus vulgaris L. (common bean) are limited. Here, 29 protein-encoding C3H genes, located on 11 different chromosomes, were identified in P. vulgaris. A phylogenetic analysis categorized the PvC3Hs into seven subfamilies on the basis of distinct features, such as exon–intron structure, cis-regulatory elements, and MEME motifs. A collinearity analysis revealed connections among the PvC3Hs in the same and different species. The PvC3H genes showed tissue-specific expression patterns during the sprout stage, as assessed by real-time quantitative PCR (RT-qPCR). Using RNA-sequencing and RT-qPCR data, PvC3Hs were identified as being enriched through Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses in binding, channel activity, and the spliceosome pathway. These results provide useful information and a rich resource that can be exploited to functionally characterize and understand PvC3Hs. These PvC3Hs, especially those enriched in binding, channel activity, and the spliceosome pathway will further facilitate the molecular breeding of common bean and provide insights into the correlations between PvC3Hs and salt-stress responses during the sprout stage.

Silicon is dependent on hydrogen sulphide to improve boron toxicity tolerance in pepper plants by regulating the AsA-GSH cycle and glyoxalase system

The role of endogenous hydrogen sulphide (H₂S) in silicon-induced improvement in boron toxicity (BT) tolerance in pepper plants was studied. Two-week old seedlings were subjected to control (0.05 mM B) or 2.0 mM BT in a nutrient solution. These two treatments were combined with 2.0 mM Si. BT caused considerable reduction in biomass, chlorophyll a &b, photosystem II maximum quantum efficiency (Fv/Fm), glutathione and ascorbate in the pepper seedlings. However, it enhanced malondialdehyde (MDA) and hydrogen peroxide, electrolyte leakage, proline, H₂S, and activities of catalase, superoxide dismutase, peroxidase, and L-DES. Silicon stimulated growth, proline content and activities of various antioxidant biomolecules and enzymes, leaf Ca²⁺, K⁺ and N, endogenous H₂S and L-DES activity, but reduced H₂O₂ and MDA contents, membrane leakage and leaf B. Silicon-induced B tolerance was further enhanced by 0.2 mM NaHS, a H₂S donor. A scavenger of H₂S, hypotaurine (0.1 mM HT), was supplied together with Si and Si + NaHS to assess the involvement of H₂S in Si-induced BT tolerance of pepper plants. Hypotaurine inverted the positive role of Si on the antioxidant defence system by reducing endogenous H₂S, but NaHS supply along with Si + HT reversed the negative effects of HT, showing that H₂S participated in Si-induced BT tolerance of pepper plants.

Appraisal of H2S metabolism in Arabidopsis thaliana: In silico analysis at the subcellular level

Hydrogen sulfide (H₂S) has become a new signal molecule in higher plants which seems to be involved in almost all physiological processes from seed germination, root and plant growth until flowering and fruit ripening. Moreover, H₂S also participates in the mechanism of response against adverse environmental stresses. However, its basic biochemistry in plant cells can be considered in a nascent stage. Using the available information of the model plant Arabidopsis thaliana, the goal of the present study is to provide a broad overview of H₂S metabolism and to display an in silico analysis of the 26 enzymatic components involved in the metabolism of H₂S and their subcellular compartmentation (cytosol, chloroplast and mitochondrion) thus providing a wide picture of the cross-talk inside the organelles and amongst them and, consequently, to get a better understanding of the cellular and tissue implications of H₂S. This information will be also relevant for other crop species, especially those whose whole genome is not yet available.

Hydrogen sulfide promotes rice drought tolerance via reestablishing redox homeostasis and activation of ABA biosynthesis and signaling

Hydrogen sulfide (H₂S) has been explored as the third biologically gasotransmitter regulating plant adaptation response, however, its possible mechanisms on drought tolerance are not completely clear yet. Here, we discovered that during dehydration treatment, the activities of L-cysteine desulfhydrase (LCD), the important synthetic enzymes of H₂S in rice, was enhanced in rice seedling leaves, further leading to continuous increasing of endogenous H₂S production. Pretreatment with NaHS, a well-known H₂S donor, significantly improved rice performance under drought stress. The beneficial roles of NaHS were confirmed by the alleviation of lipid peroxidation, and the activation of antioxidant defence system. Importantly, besides repressing its degradation pathway, NaHS pretreatment promoted ABA de-novo synthesis as well. This resulted in an increase of ABA accumulation and the expression of downstream ABA-responsive genes in rice seedling upon drought stress. Together, the present study illustrated that H₂S improve drought tolerance via reestablishing redox homeostasis and triggering ABA signaling.

Current approaches for detection of hydrogen sulfide and persulfidation in biological systems

The past decades have witnessed hydrogen sulfide (H₂S) serving as gaseous signaling molecule participating in diverse cellular and physiological processes in biological systems. Recently, a considerable number of studies highlight the signaling role of this redox-regulating molecule occurs via persulfidation, which is a post-translation modification of protein cysteine residues by covalent addition of thiol group form persulfide. However, our current understanding on detection of H₂S and persulfidation in biological systems still lags behind. This review aims to summarize current approaches for measuring H₂S and persulfidated levels in biological systems. Meanwhile, potential interference may exist in plant research has been proposed and discussed.

Crosstalk among hydrogen sulfide (H2S), nitric oxide (NO) and carbon monoxide (CO) in root-system development and its rhizosphere interactions: A gaseous interactome

Root development in higher plants is achieved by a precise intercellular communication which determines cell fate in the primary embryonic meristem where the gasotransmitters H₂S, NO and CO participate dynamically. Furthermore, the rhizosphere interaction of these molecules with microbial and soil metabolism also affects root development. NO regulates root growth and architecture in association with several other biomolecules like auxin indole-3-acetic acid (IAA), ethylene, jasmonic acid (JA), strigolactones, alkamides and melatonin. The CO-mediated signal transduction pathway in roots is closely linked to the NO-mediated signal cascades. Interestingly, H₂S acts also as an upstream component in IAA and NO-mediated crosstalk during root development. Heme oxygenase (HO) 1 generates CO and functions as a downstream component in H₂S-mediated adventitious rooting and H₂S-CO crosstalk. Likewise, reactive oxygen species (ROS), H₂S and NO crosstalk are important components in the regulation of root architecture. Deciphering these interactions will be a potential biotechnological tool which could provide benefits in crop management in soils, especially under adverse environmental conditions. This review aims to provide a comprehensive update of the complex networks of these gasotransmitters during the development of roots.

The coordination of guard-cell autonomous ABA synthesis and DES1 function in situ regulates plant water deficit responses

Introduction

Drought stress triggers the synthesis and accumulation of the phytohormone abscisic acid (ABA), which regulates stomatal aperture and hence reducing plant water loss. Hydrogen sulfide (H₂S), which is produced by the enzyme L-cysteine desulfhydrase 1 (DES1) that catalyzes the desulfuration of L-cysteine in Arabidopsis, also plays a critical role in the regulation of drought-induced stomatal closure. However, little is known about the regulation of DES1 or the crosstalk between H₂S and ABA signaling in response to dehydration.

Objectives

To demonstrate the potential crosstalk between DES1-dependent H₂S and ABA signaling in response to dehydration and its regulation mechanism.

Methods

Firstly, by introducing guard cell-specific MYB60 promoter, to produce complementary lines of DES1 or ABA3 into guard cell of des1 or aba3 mutant. And the related genes expression and water loss under ABA, NaHS, or dehydration treatment in these mutant or transgenics lines were determinate.

Results

We found that dehydration-induced expression of DES1 is abolished in the abscisic acid deficient 3 (aba3) mutants that are deficient in ABA synthesis. Both the complementation of ABA3 expression in guard cells of the aba3 mutants and ABA treatment rescue the dehydration-induced expression of DES1, as well as the wilting phenotype observed in these mutants. Moreover, the drought-induced expression of ABA synthesis genes was suppressed in des1 mutants. While the addition of ABA or the expression of either ABA3 or DES1 in the guard cells of the aba3/des1 double mutant did not alter the wilting phenotype of these mutants, the wild type phenotype was fully restored by the expression of both ABA3 and DES1, or by the application of NaHS.

Conclusion

These results demonstrate that the coordinated synthesis of ABA and DES1 expression is required for drought-induced stomatal closure in Arabidopsis.

Involvement of L-Cysteine Desulfhydrase and Hydrogen Sulfide in Glutathione-Induced Tolerance to Salinity by Accelerating Ascorbate-Glutathione Cycle and Glyoxalase System in Capsicum

The aim of this study is to assess the role of l-cysteine desulfhydrase (l-DES) and endogenous hydrogen sulfide (H₂S) in glutathione (GSH)-induced tolerance to salinity stress (SS) in sweet pepper (Capsicum annuum L.). Two weeks after germination, before initiating SS, half of the pepper seedlings were retained for 12 h in a liquid solution containing H₂S scavenger, hypotaurine (HT), or the l-DES inhibitor dl-propargylglycine (PAG). The seedlings were then exposed for three weeks to control or SS (100 mmol L⁻¹ NaCl) and supplemented with or without GSH or GSH+NaHS (sodium hydrosulfide, H₂S donor). Salinity suppressed dry biomass, leaf water potential, chlorophyll contents, maximum quantum efficiency, ascorbate, and the activities of dehydroascorbate reductase, monodehydroascorbate reductase, and glyoxalase II in plants. Contrarily, it enhanced the accumulation of hydrogen peroxide, malondialdehyde, methylglyoxal, electrolyte leakage, proline, GSH, the activities of glutathione reductase, peroxidase, catalase, superoxide dismutase, ascorbate peroxidase, glyoxalase I, and l-DES, as well as endogenous H₂S content. Salinity enhanced leaf Na⁺ but reduced K⁺; however, the reverse was true with GSH application. Overall, the treatments, GSH and GSH+NaHS, effectively reversed the oxidative stress and upregulated salt tolerance in pepper plants by controlling the activities of the AsA-GSH and glyoxalase-system-related enzymes as well as the levels of osmolytes.

Chemico-Proteomics Reveal the Enhancement of Salt Tolerance in an Invasive Plant Species via H2S Signaling

H₂S is a small molecule known to have multiple signaling roles in animals. Recently, evidence shows that H₂S also has signaling functions in plants; however, the role of H₂S in invasive plants is unknown. Spartina alterniflora is a typical invasive species growing along the beaches of southern China. A physiological comparison proves that S. alterniflora is highly tolerant to salinity stress compared with the native species Cyperus malaccensis. To decipher the mechanism that enables S. alterniflora to withstand salinity stress, a chemico-proteomics analysis was performed to examine the salt stress response of the two species; an inhibitor experiment was additionally designed to investigate H₂S signaling on salinity tolerance in S. alterniflora. A total of 86 proteins belonging to nine categories were identified and differentially expressed in S. alterniflora exposed to salt stress. Moreover, the expression level of enzymes responsible for the H₂S biosynthesis was markedly upregulated, indicating the potential role of H₂S signaling in the plant's response to salt stress. The results suggested that salt triggered l-CD enzyme activity and induced the production of H₂S, therefore upregulating expression of the antioxidants ascorbate peroxidase, superoxide dismutase, and S-nitrosoglutathione reductase, which mitigates damage from reactive nitrogen species. Additionally, H₂S reduced the potassium efflux, thereby sustaining intracellular sodium/potassium ion homeostasis and enhancing S. alterniflora salt tolerance. These findings indicate that H₂S plays an important role in the adaptation of S. alterniflora to saline environments, which provides greater insight into the function of H₂S signaling in the adaptation of an invasive plant species.

A turn-on fluorescence probe for hydrogen sulfide in absolute aqueous solution

A turn-on hydrogen sulfide (H₂S) fluorescence probe, 4-{2-[4-(2,4-dinitrophenoxy)-phenyl]-vinyl}-1-methyl-pyridinium iodide (DPPVP), based on the thiolysis reaction of dinitrophenyl ethers (DNP) has been proposed. Pyridinium structure enhanced the water solubility of DPPVP, which could quickly respond to H₂S in absolute PBS solution and the fluorescence spectra of DPPVP at 520 nm were turned on by H₂S. The spectra results exhibited that DPPVP could sensitively detect H₂S with satisfied linear range (0-40 μM) and detection limit (13.4 nM). The high selectivity for H₂S against biothiols was attributed to the significant difference in the pKa and the molecular size. Moreover, DPPVP has been successfully used for detecting H₂S in vegetable.

Hydrogen Sulfide Alleviates Waterlogging-Induced Damage in Peach Seedlings via Enhancing Antioxidative System and Inhibiting Ethylene Synthesis

Peach (Prunus persica L. Batsch) is a shallow root fruit tree with poor waterlogging tolerance. Hydrogen sulfide (H2S) is a signal molecule which regulates the adaptation of plants to adverse environments. Nevertheless, the effects of exogenous applications of H2S in fruit tree species especially in peach trees under waterlogging stress have been scarcely researched. Thus, the goal of this research was to investigate the alleviating effect of exogenous H2S on peach seedlings under waterlogging stress. In the present study, we found that the effect of exogenous H2S depended on the concentration and 0.2 mM sodium hydrosulfide (NaHS) showed the best remission effect on peach seedlings under waterlogging stress. Waterlogging significantly reduced the stomatal opening, net photosynthetic rate, and Fv/Fm of peach seedlings. The results of histochemical staining and physiological and biochemical tests showed that waterlogging stress increased the number of cell deaths and amounts of reactive oxygen species (ROS) accumulated in leaves, increased the number of root cell deaths, significantly increased the electrolyte permeability, O2.- production rate, H2O2 content and ethylene synthesis rate of roots, and significantly reduced root activity. With prolonged stress, antioxidative enzyme activity increased initially and then decreased. Under waterlogging stress, application of 0.2 mM NaHS increased the number of stomatal openings, improved the chlorophyll content, and photosynthetic capacity of peach seedlings. Exogenous H2S enhanced antioxidative system and significantly alleviate cell death of roots and leaves of peach seedlings caused by waterlogging stress through reducing ROS accumulation in roots and leaves. H2S can improve the activity and proline content of roots, reduce oxidative damage, alleviated lipid peroxidation, and inhibit ethylene synthesis. The H2S scavenger hypotaurine partially eliminated the effect of exogenous H2S on alleviating waterlogging stress of peach seedlings. Collectively, our results provide an insight into the protective role of H2S in waterlogging-stressed peach seedlings and suggest H2S as a potential candidate in reducing waterlogging-induced damage in peach seedlings.

Insights into nitric oxide-mediated water balance, antioxidant defence and mineral homeostasis in rice (Oryza sativa L.) under chilling stress

Being a chilling-sensitive staple crop, rice (Oryza sativa L.) is vulnerable to climate change. The competence of rice to withstand chilling stress should, therefore, be enhanced through technological tools. The present study employed chemical intervention like application of sodium nitroprusside (SNP) as nitric oxide (NO) donor and elucidated the underlying morpho-physiological and biochemical mechanisms of NO-mediated chilling tolerance in rice plants. At germination stage, germination indicators were interrupted by chilling stress (5.0 ± 1.0 °C for 8 h day^-1), while pretreatment with 100 μM SNP markedly improved all the indicators. At seedling stage (14-day-old), chilling stress caused stunted growth with visible toxicity along with alteration of biochemical markers, for example, increase in oxidative stress markers (superoxide, hydrogen peroxide, and malondialdehyde) and osmolytes (total soluble sugar; proline and soluble protein content, SPC), and decrease in chlorophyll (Chl), relative water content (RWC), and antioxidants. However, NO application attenuated toxicity symptoms with improving growth attributes which might be related to enhance activities of antioxidants, mineral contents, Chl, RWC and SPC. Furthermore, principal component analysis indicated that water imbalance and increased oxidative damage were the main contributors to chilling injury, whereas NO-mediated mineral homeostasis and antioxidant defense were the critical determinants for chilling tolerance in rice. Collectively, our findings revealed that NO protects against chilling stress through valorizing cellular defense mechanisms, suggesting that exogenous application of NO could be a potential tool to evolve cold tolerance as well as climate resilience in rice.

Responses of nitric oxide and hydrogen sulfide in regulating oxidative defence system in wheat plants grown under cadmium stress

We conducted a study to evaluate the interactive effect of NO and H₂ S on the cadmium (Cd) tolerance of wheat. Cadmium stress considerably reduced total dry weight, chlorophyll a and b content and ratio of Fv/Fm by 36.7, 48.6, 26.7 and 19.5%, respectively, but significantly enhanced the levels of hydrogen peroxide (H₂ O₂ ) and malondialdehyde (MDA), endogenous H₂ S and NO, and the activities of antioxidant enzymes. Exogenously applied sodium nitroprusside (SNP) and sodium hydrosulfide (NaHS), donors of NO and H₂ S, respectively, enhanced total plant dry matter by 47.8 and 39.1%, chlorophyll a by 92.3 and 61.5%, chlorophyll b content by 29.1 and 27.2%, Fv/Fm ratio by 19.7 and 15.2%, respectively, and the activities of antioxidant enzymes, but lowered oxidative stress and proline content in Cd-stressed wheat plants. NaHS and SNP also considerably limited both the uptake and translocation of Cd, thereby improving the levels of some key mineral nutrients in the plants. Enhanced levels of NO and H₂ S induced by NaHS were reversed by hypotuarine application, but they were substantially reduced almost to 50% by cPTIO (a NO scavenger) application. Hypotuarine was not effective, but cPTIO was highly effective in reducing the levels of NO and H₂ S produced by SNP in the roots of Cd-stressed plants. The results showed that interactive effect of NO and H₂ S can considerably improve plant resistance against Cd toxicity by reducing oxidative stress and uptake of Cd in plants as well as by enhancing antioxidative defence system and uptake of some essential mineral nutrients.