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

Relative effects of melatonin and hydrogen sulfide treatments in mitigating salt damage in wheat

Soil salinity poses a significant threat to agricultural productivity, impacting the growth and yield of wheat (Triticum aestivum L.) plants. This study investigates the potential of melatonin (MT; 100 µM) and hydrogen sulfide (H2S; 200 µM sodium hydrosulfide, NaHS) to confer the tolerance of wheat plants to 100 mM NaCl. Salinity stress induced the outburst of reactive oxygen species (ROS) resulting in damage to the chloroplast structure, growth, photosynthesis, and yield. Application of either MT or NaHS augmented the activity of antioxidant enzymes, superoxide dismutase, ascorbate peroxidase, glutathione reductase, and reduced glutathione (GSH) levels, upregulated the expression of Na+ transport genes (SOS1, SOS2, SOS3, NHX1), resulting in mitigation of salinity stress. Thus, improved stomatal behavior, gas-exchange parameters, and maintenance of chloroplast structure resulted in enhanced activity of the Calvin cycle enzymes and overall enhancement of growth, photosynthetic, and yield performance of plants under salinity stress. The use of DL-propargylglycine (PAG, an inhibitor of hydrogen sulfide biosynthesis) and p-chlorophenyl alanine (p-CPA, an inhibitor of melatonin biosynthesis) to plants under salt stress showed the comparative necessity of MT and H2S in mitigation of salinity stress. In the presence of PAG, more pronounced detrimental effects were observed than in the presence of p-CPA, emphasizing that MT was involved in mitigating salinity through various potential pathways, one of which was through H2S.

Metabolomics and transcriptomics combined with physiology reveal key metabolic pathway responses in tobacco roots exposed to NaHS

Hydrogen sulfide (H2S) has emerged as a novel endogenous gas signaling molecule, joining the ranks of nitric oxide (NO) and carbon monoxide (CO). Recent research has highlighted its involvement in various physiological processes, such as promoting root organogenesis, regulating stomatal movement and photosynthesis, and enhancing plant growth, development, and stress resistance. Tobacco, a significant cash crop crucial for farmers' economic income, relies heavily on root development to affect leaf growth, disease resistance, chemical composition, and yield. Despite its importance, there remains a scarcity of studies investigating the role of H2S in promoting tobacco growth. This study exposed tobacco seedlings to different concentrations of NaHS (an exogenous H2S donor) - 0, 200, 400, 600, and 800 mg/L. Results indicated a positive correlation between NaHS concentration and root length, wet weight, root activity, and antioxidant enzymatic activities (CAT, SOD, and POD) in tobacco roots. Transcriptomic and metabolomic analyses revealed that treatment with 600 mg/L NaHS significantly effected 162 key genes, 44 key enzymes, and two metabolic pathways (brassinosteroid synthesis and aspartate biosynthesis) in tobacco seedlings. The addition of exogenous NaHS not only promoted tobacco root development but also potentially reduced pesticide usage, contributing to a more sustainable ecological environment. Overall, this study sheds light on the primary metabolic pathways involved in tobacco root response to NaHS, offering new genetic insights for future investigations into plant root development.

Unraveling the potential of hydrogen sulfide as a signaling molecule for plant development and environmental stress responses: A state-of-the-art review

Over the past decade, a plethora of research has illuminated the multifaceted roles of hydrogen sulfide (H2S) in plant physiology. This gaseous molecule, endowed with signaling properties, plays a pivotal role in mitigating metal-induced oxidative stress and strengthening the plant's ability to withstand harsh environmental conditions. It fulfils several functions in regulating plant development while ameliorating the adverse impacts of environmental stressors. The intricate connections among nitric oxide (NO), hydrogen peroxide (H2O2), and hydrogen sulfide in plant signaling, along with their involvement in direct chemical processes, are contributory in facilitating post-translational modifications (PTMs) of proteins that target cysteine residues. Therefore, the present review offers a comprehensive overview of sulfur metabolic pathways regulated by hydrogen sulfide, alongside the advancements in understanding its biological activities in plant growth and development. Specifically, it centres on the physiological roles of H2S in responding to environmental stressors to explore the crucial significance of different exogenously administered hydrogen sulfide donors in mitigating the toxicity associated with heavy metals (HMs). These donors are of utmost importance in facilitating the plant development, stabilization of physiological and biochemical processes, and augmentation of anti-oxidative metabolic pathways. Furthermore, the review delves into the interaction between different growth regulators and endogenous hydrogen sulfide and their contributions to mitigating metal-induced phytotoxicity.

Overexpression of Abscisic Acid Biosynthesis Gene OsNCED3 Enhances Survival Rate and Tolerance to Alkaline Stress in Rice Seedlings

Alkaline stress with high pH levels could significantly influence plant growth and survival. The enzyme 9-cis-epoxycarotenoid dioxygenase (NCED) serves as a critical bottleneck in the biosynthesis of abscisic acid (ABA), making it essential for regulating stress tolerance. Here, we show that OsNCED3-overexpressing rice lines have increased ABA content by up to 50.90% and improved transcription levels of numerous genes involved in stress responses that significantly enhance seedling survival rates. Overexpression of OsNCED3 increased the dry weight contents of the total chlorophyll, proline, soluble sugar, starch, and the activities of antioxidant enzymes of rice seedlings, while reducing the contents of O2·-, H2O2, and malondialdehyde under hydroponic alkaline stress conditions simulated by 10, 15, and 20 mmol L-1 of Na2CO3. Additionally, the OsNCED3-overexpressing rice lines exhibited a notable increase in the expression of OsNCED3; ABA response-related genes OsSalT and OsWsi18; ion homeostasis-related genes OsAKT1, OsHKT1;5, OsSOS1, and OsNHX5; and ROS scavenging-related genes OsCu/Zn-SOD, OsFe-SOD, OsPOX1, OsCATA, OsCATB, and OsAPX1 in rice seedling leaves. The results of these findings suggest that overexpression of OsNCED3 upregulates endogenous ABA levels and the expression of stress response genes, which represents an innovative molecular approach for enhancing the alkaline tolerance of rice seedlings.

Genome-wide identification, characterization and expression of C2H2 zinc finger gene family in Opisthopappus species under salt stress

BACKGROUND

The C2H2 zinc finger protein family plays important roles in plants. However, precisely how C2H2s function in Opisthopappus (Opisthopappus taihangensis and Opisthopappus longilobus) remains unclear.

RESULTS

In this study, a total of 69 OpC2H2 zinc finger protein genes were identified and clustered into five Groups. Seven tandem and ten fragment repeats were found in OpC2H2s, which underwent robust purifying selection. Of the identified motifs, motif 1 was present in all OpC2H2s and conserved at important binding sites. Most OpC2H2s possessed few introns and exons that could rapidly activate and react when faced with stress. The OpC2H2 promoter sequences mainly contained diverse regulatory elements, such as ARE, ABRE, and LTR. Under salt stress, two up-regulated OpC2H2s (OpC2H2-1 and OpC2H2-14) genes and one down-regulated OpC2H2 gene (OpC2H2-7) might serve as key transcription factors through the ABA and JA signaling pathways to regulate the growth and development of Opisthopappus species.

CONCLUSION

The above results not only help to understand the function of C2H2 gene family but also drive progress in genetic improvement for the salt tolerance of Opisthopappus species.

Effect of hydrogen sulfide (H2S) on the growth and development of tobacco seedlings in absence of stress

BACKGROUND

Hydrogen sulfide (H2S) is a novel signaling molecule involved in the growth and development of plants and their response to stress. However, the involvement of H2S in promoting the growth and development of tobacco plants is still unclear.

RESULTS

In this study, we explored the effect of pre-soaking or irrigating the roots of tobacco plants with 0.0, 2.0, 4.0, 6.0, and 8.0 mM of sodium hydrosulfide (NaHS) on endogenous H2S production, antioxidant enzymatic and cysteine desulfhydrase activities, seed germination, agronomic traits, photosynthetic pigments contents, and root vigor. The results revealed that exogenous NaHS treatment could significantly promote endogenous H2S production by inducing gene expression of D/L-CD and the activities of D/L-CD enzymes. Additionally, a significant increase in the agronomic traits and the contents of photosynthetic pigments, and no significant difference in carotenoid content among tobacco plants treated with 0.0 to 8.0 mM of NaHS was observed. Additionally, a significant increase in the germination speed, dry weight, and vigor of tobacco seeds, whereas no significant effect on the percentage of seed germination was observed on NaHS treatment. Furthermore, NaHS treatment could significantly increase the activity of superoxide dismutase (SOD) and peroxidase (POD) enzymes, which reduces damage due to oxidative stress by maintaining reactive oxygen species homeostasis.

CONCLUSIONS

These results would aid in enhancing our understanding of the involvement of H2S, a novel signaling molecule to promote the growth and development of tobacco plants.

Exogenous riboflavin (vitamin B2) application enhances salinity tolerance through the activation of its biosynthesis in rice seedlings under salinity stress

Salinity stress triggers the accumulation of reactive oxygen species (ROS), leading to impaired plant growth. Riboflavin (RIB; vitamin B2) is synthesized by plants, fungi, and microorganisms and is a precursor of the coenzymes, flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), which are important for cellular metabolism. In this study, we aimed to elucidate the mechanistic basis of the RIB-mediated alleviation of salinity stress in rice. We observed higher biomass accumulation and lower concentrations of malondialdehyde (MDA) and hydrogen peroxide (H2O2) in RIB-pretreated seedlings under salinity stress. In vitro assays showed that H2O2 was scavenged as the RIB concentration increased, implying that RIB may function as a non-enzymatic antioxidant in ROS detoxification. RIB-pretreated seedlings accumulated more Na+ in the roots than in the leaf blades because of the contributions of OsHKT2;1, OsNHX1, and OsHKT1;4 in the roots and leaf sheaths, respectively. Liquid chromatography-mass spectrometry (LC-MS/MS) analysis revealed increased RIB concentration in roots and shoots and upregulation of key genes (OsRIBA1, OsGCHI, OsLS, and OsRS) involved in RIB biosynthesis in the roots of RIB-pretreated seedlings. Taken together, our findings suggest that RIB pretreatment ameliorates salinity stress in rice by improving (1) oxidative stress tolerance, as increased RIB concentration may function as a non-enzymatic antioxidant, and (2) ionic stress tolerance, as RIB pretreatment limits Na+ accumulation in the leaf blades and maintains a favorable Na+/K+ balance.

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.

The role of NaHS pretreatment in improving salt stress resistance in foxtail millet seedlings: physiological and molecular mechanisms

Salt stress is a prevailing abiotic stress in nature, with soil salinization becoming a pressing issue worldwide. High soil salinity severely hampers plant growth and leads to reduced crop yields. Hydrogen sulfide (H2S), a gas signal molecule, is known to be synthesized in plants exposed to abiotic stress, contributing to enhanced plant stress resistance. To investigate the impact of sodium hydrosulfide hydrate (NaHS, a H2S donor) on millet's response to salt stress, millet seedlings were subjected to pretreatment with 200 μM NaHS, followed by 100 mM NaCl stress under soil culture conditions. The growth, osmotic adjustment substances, antioxidant characteristics, membrane damage, and expression levels of related genes in millet seedlings were detected and analyzed. The results showed that NaHS pretreatment alleviated the inhibition of salt stress on the growth of foxtail millet seedlings, increased the proline content and antioxidant enzyme activities, as well as the expression levels of SiASR4, SiRPLK35 and SiHAK23 genes under salt stress. These findings demonstrated that NaHS pretreatment can enhance salt tolerance in foxtail millet seedlings by regulating the content of osmotic adjustment substances and antioxidant enzyme activity, reducing electrolyte permeability, and activating the expression of salt-resistant genes.

Characterization of a Novel Polysaccharide Derived from Rhizospheric Paecilomyces vaniformisi and Its Mechanism for Enhancing Salinity Resistance in Rice Seedlings

Soil salinity is an important limiting factor in agricultural production. Rhizospheric fungi can potentially enhance crop salinity tolerance, but the precise role of signaling substances is still to be systematically elucidated. A rhizospheric fungus identified as Paecilomyces vaniformisi was found to enhance the salinity tolerance of rice seedlings. In this study, a novel polysaccharide (PPL2b) was isolated from P. vaniformisi and identified as consisting of Manp, Glcp, GalpA, and Galp. In a further study, PPL2b showed significant activity in alleviating salinity stress-induced growth inhibition in rice seedlings. The results indicated that under salinity stress, PPL2b enhances seed germination, plant growth (height and biomass), and biochemical parameters (soluble sugar and protein contents). Additionally, PPL2b regulates genes such as SOS1 and SKOR to decrease K+ efflux and increase Na+ efflux. PPL2b increased the expression and activity of genes related to antioxidant enzymes and nonenzyme substances in salinity-induced oxidative stress. Further study indicated that PPL2b plays a crucial role in regulating osmotic substances, such as proline and betaine, in maintaining the osmotic balance. It also modulates plant hormones to promote rice seedling growth and enhance their tolerance to soil salinity. The variables interacted and were divided into two groups (PC1 77.39% and PC2 18.77%) based on their relative values. Therefore, these findings indicate that PPL2b from P. vaniformisi can alleviate the inhibitory effects of salinity stress on root development, osmotic adjustment, ion balance, oxidative stress balance, and growth of rice seedlings. Furthermore, it suggests that polysaccharides produced by rhizospheric fungi could be utilized to enhance crop tolerance to salinity.

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.

Spatiotemporal, physiological and transcriptomic dynamics of wild jujube seedlings under saline conditions

Soil salinity is a major constraint limiting jujube production in China. Wild jujube (Ziziphus jujuba var. spinosa (Bunge) Hu ex H. F. Chow) is widely used as the rootstock of jujube (Z. jujuba) to overcome the saline conditions. To understand the adaptive mechanism in wild jujube under saline conditions, we combined spatiotemporal and physiological assessments with transcriptomic analysis on wild jujube seedlings undergoing various salt treatments. These salt treatments showed dose and duration effects on biomass, photosynthesis, (K+) and (Na+) accumulation. Salt treatments induced higher levels of salicylic acid in roots and leaves, whereas foliar abscisic acid was also elevated after 8 days. The number of differential expression genes increased with higher doses and also longer exposure of NaCl treatments, with concomitant changes in the enriched Gene Ontology terms that were indicative of altered physiological activities. Gene co-expression network analysis identified the core gene sets associated with salt-induced changes in leaves, stems and roots, respectively. The nitrogen transporters, potassium transporters and a few transcription factors belonging to WRKY/MYB/bHLH families were clustered as the hub genes responding to salt treatments, which were related to elevated nitrogen and K+/Na+. Ectopic overexpression of two WRKY transcription factor genes (ZjWRKY6 and ZjWRKY65) conferred stronger salt-tolerance in Arabidopsis thaliana transformants by enhancing the activities of antioxidant enzymes, decreasing malondialdehyde accumulation and maintaining K+/Na+ homeostasis. This study provided evidence about the spatiotemporal, physiological and transcriptomic dynamics of wild jujube during salt stress and identified potential genes for further research to improve salt tolerance in jujube.

Genome-wide identification of bHLH transcription factors and their response to salt stress in Cyclocarya paliurus

As a highly valued and multiple function tree species, the leaves of Cyclocarya paliurus are enriched in diverse bioactive substances with healthy function. To meet the requirement for its leaf production and medical use, the land with salt stress would be a potential resource for developing C. paliurus plantations due to the limitation of land resources in China. The basic helix-loop-helix (bHLH) transcription factor protein family, the second largest protein family in plants, has been found to play essential roles in the response to multiple abiotic stresses, especially salt stress. However, the bHLH gene family in C.paliurus has not been investigated. In this study, 159 CpbHLH genes were successfully identified from the whole-genome sequence data, and were classified into 26 subfamilies. Meanwhile, the 159 members were also analyzed from the aspects of protein sequences alignment, evolution, motif prediction, promoter cis-acting elements analysis and DNA binding ability. Based on transcriptome profiling under a hydroponic experiment with four salt concentrations (0%, 0.15%, 0.3%, and 0.45% NaCl), 9 significantly up- or down-regulated genes were screened, while 3 genes associated with salt response were selected in term of the GO annotation results. Totally 12 candidate genes were selected in response to salt stress. Moreover, based on expression analysis of the 12 candidate genes sampled from a pot experiment with three salt concentrations (0%, 0.2% and 0.4% NaCl), CpbHLH36/68/146 were further verified to be involved in the regulation of salt tolerance genes, which is also confirmed by protein interaction network analysis. This study was the first analysis of the transcription factor family at the genome-wide level of C. paliurus, and our findings would not only provide insight into the function of the CpbHLH gene family members involved in salt stress but also drive progress in genetic improvement for the salt tolerance of C. paliurus.

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.

The Alleviation of Metal Stress Nuisance for Plants—A Review of Promising Solutions in the Face of Environmental Challenges

Environmental changes are inevitable with time, but their intensification and diversification, occurring in the last several decades due to the combination of both natural and human-made causes, are really a matter of great apprehension. As a consequence, plants are exposed to a variety of abiotic stressors that contribute to their morpho-physiological, biochemical, and molecular alterations, which affects plant growth and development as well as the quality and productivity of crops. Thus, novel strategies are still being developed to meet the challenges of the modern world related to climate changes and natural ecosystem degradation. Innovative methods that have recently received special attention include eco-friendly, easily available, inexpensive, and, very often, plant-based methods. However, such approaches require better cognition and understanding of plant adaptations and acclimation mechanisms in response to adverse conditions. In this succinct review, we have highlighted defense mechanisms against external stimuli (mainly exposure to elevated levels of metal elements) which can be activated through permanent microevolutionary changes in metal-tolerant species or through exogenously applied priming agents that may ensure plant acclimation and thereby elevated stress resistance.

Trehalose alleviates salt tolerance by improving photosynthetic performance and maintaining mineral ion homeostasis in tomato plants

Trehalose (Tre), which was an osmoprotective or stabilizing molecule, played a protective role against different abiotic stresses in plants and showed remarkable perspectives in salt stress. In this study, the potential role of Tre in improving the resistance to salt stress in tomato plants was investigated. Tomato plants (Micro Tom) were treated with Hoagland nutrient solution (CK), 10 mM Tre (T), 150 mM sodium chloride (NaCl, S), and 10 mM Tre+150 mM NaCl (S+T) for 5 days. Our results showed that foliar application of Tre alleviated the inhibition of tomato plant growth under salt stress. In addition, salt stress decreased the values of net photosynthetic rate (Pn, 85.99%), stomata conductance (gs, 57.3%), and transpiration rate (Tr, 47.97%), but increased that of intercellular carbon dioxide concentration (Ci, 26.25%). However, exogenous application of Tre significantly increased photosynthetic efficiency, increased the activity of Calvin cycle enzymes [ribulose diphosphate carboxylase/oxygenase (Rubisco), fructose-1,6-bisphosphate aldolase (FBA), fructose-1, 6-bisphosphatase (FBPase), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and transketolase (TK)], up-regulated the expression of genes encoding enzymes, induced stomatal opening, and alleviated salt-induced damage to the chloroplast membrane and structure. In the saline environment, photosynthetic electron transport was restricted, resulting the J-I-P phase to decrease. At the same time, the absorption, capture, and transport energies per excited cross-section and per active reaction center decreased, and the dissipation energy increased. Conversely, Tre reversed these values and enhanced the photosystem response to salt stress by protecting the photosynthetic electron transport system. In addition, foliage application with Tre significantly increased the potassium to sodium transport selectivity ratio (S _K-Na ) by 16.08%, and increased the levels of other ions to varying degrees. Principal component analysis (PCA) analysis showed that exogenous Tre could change the distribution of elements in different organs and affect the expressions of SlSOS1, SlNHX, SlHKT1.1, SlVHA, and SlHA-A at the transcriptional level under salt stress, thereby maintaining ion homeostasis. This study demonstrated that Tre was involved in the process of mitigating salt stress toxicity in tomato plants and provided specific insights into the effectiveness of Tre in mediating salt tolerance.

Hydrogen sulfide: an emerging component against abiotic stress in plants

As a result of climate change, abiotic stresses are the most common cause of crop losses worldwide. Abiotic stresses significantly impair plants' physiological, biochemical, molecular and cellular mechanisms, limiting crop productivity under adverse climate conditions. However, plants can implement essential mechanisms against abiotic stressors to maintain their growth and persistence under such stressful environments. In nature, plants have developed several adaptations and defence mechanisms to mitigate abiotic stress. Moreover, recent research has revealed that signalling molecules like hydrogen sulfide (H₂ S) play a crucial role in mitigating the adverse effects of environmental stresses in plants by implementing several physiological and biochemical mechanisms. Mainly, H₂ S helps to implement antioxidant defence systems, and interacts with other molecules like nitric oxide (NO), reactive oxygen species (ROS), phytohormones, etc. These molecules are well-known as the key players that moderate the adverse effects of abiotic stresses. Currently, little progress has been made in understanding the molecular basis of the protective role of H₂ S; however, it is imperative to understand the molecular basis using the state-of-the-art CRISPR-Cas gene-editing tool. Subsequently, genetic engineering could provide a promising approach to unravelling the molecular basis of stress tolerance mediated by exogenous/endogenous H₂ S. Here, we review recent advances in understanding the beneficial roles of H₂ S in conferring multiple abiotic stress tolerance in plants. Further, we also discuss the interaction and crosstalk between H₂ S and other signal molecules; as well as highlighting some genetic engineering-based current and future directions.

Alkaline Stress Induces Different Physiological, Hormonal and Gene Expression Responses in Diploid and Autotetraploid Rice

Saline−alkaline stress is a critical abiotic stress that negatively affects plants’ growth and development. Considerably higher enhancements in plant tolerance to saline−alkaline stress have often been observed in polyploid plants compared to their diploid relatives, the underlying mechanism of which remains elusive. In this study, we explored the variations in morphological and physiological characteristics, phytohormones, and genome-wide gene expression between an autotetraploid rice and its diploid relative in response to alkaline stress. It was observed that the polyploidization in the autotetraploid rice imparted a higher level of alkaline tolerance than in its diploid relative. An eclectic array of physiological parameters commonly used for abiotic stress, such as proline, soluble sugars, and malondialdehyde, together with the activities of some selected antioxidant enzymes, was analyzed at five time points in the first 24 h following the alkaline stress treatment between the diploid and autotetraploid rice. Phytohormones, such as abscisic acid and indole-3-acetic acid were also comparatively evaluated between the two types of rice with different ploidy levels under alkaline stress. Transcriptomic analysis revealed that gene expression patterns were altered in accordance with the variations in the cellular levels of phytohormones between diploid and autotetraploid plants upon alkaline stress. In particular, the expression of genes related to peroxide and transcription factors was substantially upregulated in autotetraploid plants compared to diploid plants in response to the alkaline stress treatment. In essence, diploid and autotetraploid rice plants exhibited differential gene expression patterns in response to the alkaline stress, which may shed more light on the mechanism underpinning the ameliorated plant tolerance to alkaline stress following genome duplication.

Enhanced Salt Tolerance of Torreya grandis Genders Is Related to Nitric Oxide Level and Antioxidant Capacity

Nitric oxide (NO), a bioactive molecule, is often involved in the regulation of physiological and biochemical processes in stressed plants. However, the effects of NO donors on dioecious plants remain unclear. Using a pot experiment, female and male Torreya grandis were used to study the role of sex and NO in salt stress tolerance. In the present study, female and male T. grandis seedlings pretreated with an NO donor (sodium nitroprusside, SNP) were exposed to salt stress, and then leaf relative water content (RWC), photosynthetic pigments, chlorophyll fluorescence parameters, NO and glutathione levels, oxidative damage, and antioxidant enzyme activities were investigated. Female T. grandis plants had better tolerance to salinity, as they were characterized by significantly higher RWC, pigment content, and photochemical activities of photosystem II (PSII) and fewer negative effects associated with higher nitrate reductase (NR) activity and NO content. Pretreatment with an NO donor further increased the endogenous NO content and NR activity of both female and male T. grandis plants compared with salt treatment. Moreover, pretreatment with an NO donor alleviated salt-induced oxidative damage of T. grandis, especially in male plants, as indicated by reduced lipid peroxidation, through an enhanced antioxidant system, including proline and glutathione accumulation, and increased antioxidant enzyme activities. However, the ameliorating effect of the NO donor was not effective in the presence of the NO scavenger (Nω-nitro-L-arginine methyl ester, L-name). In conclusion, enhanced salt tolerance in T. grandis plants is related to nitric oxide levels and the supply of NO donors is an interesting strategy for alleviating the negative effect of salt on T. grandis. Our data provide new evidence to contribute to the current understanding of NO-induced salt stress tolerance.

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.

Nitric Oxide Improves Salt Tolerance of Cyclocarya paliurus by Regulating Endogenous Glutathione Level and Antioxidant Capacity

Cyclocarya paliurus is commonly used to treat diabetes in China. However, the natural habitats of C. paliurus are typically affected by salt stress. Previous studies showed that nitric oxide (NO) level was related to salt tolerance of C. paliurus, and its synthesis was induced by exogenous hydrogen sulfide. However, the effects of different NO donors in alleviating the negative effect of salt stress are still unclear. In the present study, C. paliurus seedlings pretreated with three NO donors (S-nitroso-N-acetylpenicillamine, SNAP and S-nitrosoglutathione, GSNO and sodium nitroprusside, SNP) were exposed to salt stress, and then, the total biomass, chlorophyll fluorescence parameters, NO and glutathione levels, oxidative damage, and antioxidant enzyme activities were investigated. The results showed that pretreatment of NO donors maintained chlorophyll fluorescence and attenuated the loss of plant biomass under salt stress, and the best performance was observed in C. paliurus under SNP treatment. We also found that pretreatment of NO donors further increased the endogenous NO content and nitrate reductase (NR) activity compared with salt treatment. Moreover, pretreatment with NO donors, especially SNP, alleviated salt-induced oxidative damage, as indicated by lowered lipid peroxidation, through an enhanced antioxidant system including glutathione accumulation and increased antioxidant enzyme activities. The supply of NO donors is an interesting strategy for alleviating the negative effect of salt on C. paliurus. Our data provide new evidence contributing to the current understanding of NO-induced salt stress tolerance.

The Interplay between Hydrogen Sulfide and Phytohormone Signaling Pathways under Challenging Environments

Hydrogen sulfide (H₂S) serves as an important gaseous signaling molecule that is involved in intra- and intercellular signal transduction in plant–environment interactions. In plants, H₂S is formed in sulfate/cysteine reduction pathways. The activation of endogenous H₂S and its exogenous application has been found to be highly effective in ameliorating a wide variety of stress conditions in plants. The H₂S interferes with the cellular redox regulatory network and prevents the degradation of proteins from oxidative stress via post-translational modifications (PTMs). H₂S-mediated persulfidation allows the rapid response of proteins in signaling networks to environmental stimuli. In addition, regulatory crosstalk of H₂S with other gaseous signals and plant growth regulators enable the activation of multiple signaling cascades that drive cellular adaptation. In this review, we summarize and discuss the current understanding of the molecular mechanisms of H₂S-induced cellular adjustments and the interactions between H₂S and various signaling pathways in plants, emphasizing the recent progress in our understanding of the effects of H₂S on the PTMs of proteins. We also discuss future directions that would advance our understanding of H₂S interactions to ultimately mitigate the impacts of environmental stresses in the plants.

Trehalose Alleviated Salt Stress in Tomato by Regulating ROS Metabolism, Photosynthesis, Osmolyte Synthesis, and Trehalose Metabolic Pathways

Trehalose plays a critical role in plant response to salinity but the involved regulatory mechanisms remain obscure. Here, this study explored the mechanism of exogenous trehalose-induced salt tolerance in tomato plants by the hydroponic test method. Our results indicated that 10 mM trehalose displayed remarkable plant biomass by improving growth physiology, which were supported by the results of chlorophyll fluorescence and rapid light-response curve. In the salinity environment, trehalose + NaCl treatment could greatly inhibit the decrease of malondialdehyde level, and it increases the contents of other osmotic substances, carbohydrates, K+, and K+/Na+ ratio. Meanwhile, trehalose still had similar effects after recovery from salt stress. Furthermore, trehalose pretreatment promoted trehalose metabolism; significantly increased the enzymatic activity of the trehalose metabolic pathway, including trehalose-6-phosphate synthase (TPS), trehalose-6-phosphate phosphatase (TPP), and trehalase (TRE); and upregulated the expression of SlTPS1, SlTPS5, SlTPS7, SlTPPJ, SlTPPH, and SlTRE under saline conditions. However, the transcriptional levels of SlTPS1, SlTPS5, and SlTPS7 genes and the activity of TPS enzyme were reversed after recovery. In addition, we found that hydrogen peroxide (H2O2) and superoxide anion (O2 -) were accumulated in tomato leaves because of salt stress, but these parameters were all recovered by foliar-applied trehalose, and its visualization degree was correspondingly reduced. Antioxidant enzyme activities (SOD, POD, and CAT) and related gene expression (SlCu/Zn-SOD, SlFe-SOD, SlMn-SOD, SlPOD, and SlCAT) in salt-stressed tomato leaves were also elevated by trehalose to counteract salt stress. Collectively, exogenous trehalose appeared to be the effective treatment in counteracting the negative effects of salt stress.

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.

Hydrogen sulfide alleviates salinity stress in Cyclocarya paliurus by maintaining chlorophyll fluorescence and regulating nitric oxide level and antioxidant capacity

Cyclocarya paliurus is commonly used to treat diabetes in China. However, the natural habitats of C. paliurus are typically affected by salt stress. Hydrogen sulfide (H₂S) is a growth regulator that is widely used to enhance plant stress tolerance, but the possible mechanism underlying H₂S-alleviated salt stress in C. paliurus remains unclear. C. paliurus seedlings pretreated with NaHS (an H₂S donor) were exposed to salt stress, and then, the leaf and total biomass, chlorophyll fluorescence parameters, nitric oxide (NO) content, oxidative damage, and proline and phenolic content were investigated to test the hypothesis that H₂S and NO were involved in the salt tolerance of C. paliurus. The results showed that H₂S pretreatment maintained chlorophyll fluorescence and attenuated the loss of plant biomass. We also found that H₂S pretreatment further increased the endogenous NO content and nitrate reductase activity compared with salt treatment. Moreover, H₂S pretreatment alleviated salt-induced oxidative damage, as indicated by lowered lipid peroxidation, through an enhanced antioxidant system including more proline and phenolic accumulation and increased antioxidant enzyme activities. However, C. paliurus leaves treated with the NO scavenger significantly diminished H₂S-mediated NO production and alleviation of membrane lipid peroxidation. Thus, we concluded that H₂S-induced NO was involved in C. paliurus salt tolerance.

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.

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.

Response Mechanisms of Plants Under Saline-Alkali Stress

As two coexisting abiotic stresses, salt stress and alkali stress have severely restricted the development of global agriculture. Clarifying the plant resistance mechanism and determining how to improve plant tolerance to salt stress and alkali stress have been popular research topics. At present, most related studies have focused mainly on salt stress, and salt-alkali mixed stress studies are relatively scarce. However, in nature, high concentrations of salt and high pH often occur simultaneously, and their synergistic effects can be more harmful to plant growth and development than the effects of either stress alone. Therefore, it is of great practical importance for the sustainable development of agriculture to study plant resistance mechanisms under saline-alkali mixed stress, screen new saline-alkali stress tolerance genes, and explore new plant salt-alkali tolerance strategies. Herein, we summarized how plants actively respond to saline-alkali stress through morphological adaptation, physiological adaptation and molecular regulation.

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.