Hydrogen Sulfide: A Gaseous Molecule in Postharvest Freshness

Advances in strawberry postharvest preservation and packaging: A comprehensive review

Strawberries spoil rapidly after harvest due to factors such as the ripening process, weight loss, and, most importantly, microbial contamination. Traditionally, several methods are used to preserve strawberries after harvest and extend their shelf life, including thermal, plasma, radiation, chemical, and biological treatments. Although these methods are effective, they are a concern from the perspective of safety and consumer acceptance of the treated food. To address these issues, more advanced environment-friendly technologies have been developed over the past decades, including modified and controlled atmosphere packaging, active biopolymer-based packaging, or edible coating formulations. This method can not only significantly extend the shelf life of fruit but also solve safety concerns. Some studies have shown that combining two or more of these technologies can significantly extend the shelf life of strawberries, which could significantly contribute to expanding the global supply chain for delicious fruit. Despite the large number of studies underway in this field of research, no systematic review has been published discussing these advances. This review aims to cover important information about postharvest physiology, decay factors, and preservation methods of strawberry fruits. It is a pioneering work that integrates, relates, and discusses all information on the postharvest fate and handling of strawberries in one place. Additionally, commercially used techniques were discussed to provide insight into current developments in strawberry preservation and suggest future research directions in this field of study. This review aims to enrich the knowledge of academic and industrial researchers, scientists, and students on trends and developments in postharvest preservation and packaging of strawberry fruits.

Foliar Application of Sulfur-Containing Compounds-Pros and Cons

Sulfate is taken up from the soil solution by the root system; and inside the plant, it is assimilated to hydrogen sulfide, which in turn is converted to cysteine. Sulfate is also taken up by the leaves, when foliage is sprayed with solutions containing sulfate fertilizers. Moreover, several other sulfur (S)-containing compounds are provided through foliar application, including the S metabolites hydrogen sulfide, glutathione, cysteine, methionine, S-methylmethionine, and lipoic acid. However, S compounds that are not metabolites, such as thiourea and lignosulfonates, along with dimethyl sulfoxide and S-containing adjuvants, are provided by foliar application-these are the S-containing agrochemicals. In this review, we elaborate on the fate of these compounds after spraying foliage and on the rationale and the efficiency of such foliar applications. The foliar application of S-compounds in various combinations is an emerging area of agricultural usefulness. In the agricultural practice, the S-containing compounds are not applied alone in spray solutions and the need for proper combinations is of prime importance.

Exploring the potential role of hydrogen sulfide and jasmonic acid in plants during heavy metal stress

In plants, hydrogen sulfide (H2S) is mainly considered as a gaseous transmitter or signaling molecule that has long been recognized as an essential component of numerous plant cellular and physiological processes. Several subcellular compartments in plants use both enzymatic and non-enzymatic mechanisms to generate H2S. Under normal and stress full conditions exogenous administration of H2S supports a variety of plant developmental processes, including growth and germination, senescence, defense, maturation and antioxidant machinery in plants. Due to their gaseous nature, they are efficiently disseminated to various areas of the cell to balance antioxidant pools and supply sulphur to the cells. Numerous studies have also been reported regarding H2S ability to reduce heavy metal toxicity when combined with other signaling molecules like nitric oxide (NO), abscisic acid (ABA), calcium ion (Ca2+), hydrogen peroxide (H2O2), salicylic acid (SA), ethylene (ETH), jasmonic acid (JA), proline (Pro), and melatonin. The current study focuses on multiple pathways for JA and H2S production as well as their signaling functions in plant cells under varied circumstances, more specifically under heavy metal, which also covers role of H2S and Jasmonic acid during heavy metal stress and interaction of hydrogen sulfide with Jasmonic acid.

Hydrogen sulfide and sulfaceutic or sulfanutraceutic agents: Classification, differences and relevance in preclinical and clinical studies

Hydrogen sulfide (H2S) has been extensively studied as a signal molecule in the body for the past 30 years. Researchers have conducted studies using both natural and synthetic sources of H2S, known as H2S donors, which have different characteristics in terms of how they release H2S. These donors can be inorganic salts or have various organic structures. In recent years, certain types of sulfur compounds found naturally in foods have been characterized as H2S donors and explored for their potential health benefits. These compounds are referred to as "sulfanutraceuticals," a term that combines "nutrition" and "pharmaceutical". It is used to describe products derived from food sources that offer additional health advantages. By introducing the terms "sulfaceuticals" and "sulfanutraceuticals," we categorize sulfur-containing substances based on their origin and their use in both preclinical and clinical research, as well as in dietary supplements.

Hydrogen sulfide alleviates osmotic stress-induced root growth inhibition by promoting auxin homeostasis

Hydrogen sulfide (H₂ S) promotes plant tolerance against various environmental cues, and d-cysteine desulfhydrase (DCD) is an enzymatic source of H₂ S to enhance abiotic stress resistance. However, the role of DCD-mediated H₂ S production in root growth under abiotic stress remains to be further elucidated. Here, we report that DCD-mediated H₂ S production alleviates osmotic stress-mediated root growth inhibition by promoting auxin homeostasis. Osmotic stress up-regulated DCD gene transcript and DCD protein levels and thus H₂ S production in roots. When subjected to osmotic stress, a dcd mutant showed more severe root growth inhibition, whereas the transgenic lines DCDox overexpressing DCD exhibited less sensitivity to osmotic stress in terms of longer root compared to the wild-type. Moreover, osmotic stress inhibited root growth through repressing auxin signaling, whereas H₂ S treatment significantly alleviated osmotic stress-mediated inhibition of auxin. Under osmotic stress, auxin accumulation was increased in DCDox but decreased in dcd mutant. H₂ S promoted auxin biosynthesis gene expression and auxin efflux carrier PIN-FORMED 1 (PIN1) protein level under osmotic stress. Taken together, our results reveal that mannitol-induced DCD and H₂ S in roots promote auxin homeostasis, contributing to alleviating the inhibition of root growth under osmotic stress.

Effects of Hydrogen Sulfide on Sugar, Organic Acid, Carotenoid, and Polyphenol Level in Tomato Fruit

Hydrogen sulfide (H₂S) is known to have a positive effect on the postharvest storage of vegetables and fruits, but limited results are available on its influence in fruit flavor quality. Here, we presented the effect of H₂S on the flavor quality of tomato fruit during postharvest. H₂S decreased the content of fructose, glucose, carotene and lycopene but increased that of soluble protein, organic acid, malic acid and citric acid. These differences were directly associated with the expression of their metabolism-related genes. Moreover, H₂S treatment raised the contents of total phenolics, total flavonoids and most phenolic compounds, and up-regulated the expression level of their metabolism-related genes (PAL5, 4CL, CHS1, CHS2, F3H and FLS). However, the effects of the H₂S scavenger hypotaurine on the above flavor quality parameters were opposite to that of H₂S, thus confirming the role of H₂S in tomato flavor quality. Thus, these results provide insight into the significant roles of H₂S in tomato fruit quality regulation and implicate the potential application of H₂S in reducing the flavor loss of tomato fruit during postharvest.

Biological Functions of Hydrogen Sulfide in Plants

Hydrogen sulfide (H₂S), which is a gasotransmitter, can be biosynthesized and participates in various physiological and biochemical processes in plants. H₂S also positively affects plants' adaptation to abiotic stresses. Here, we summarize the specific ways in which H₂S is endogenously synthesized and metabolized in plants, along with the agents and methods used for H₂S research, and outline the progress of research on the regulation of H₂S on plant metabolism and morphogenesis, abiotic stress tolerance, and the series of different post-translational modifications (PTMs) in which H₂S is involved, to provide a reference for future research on the mechanism of H₂S action.

A fully water-soluble Calix[4]arene probe for fluorometric and colorimetric detection of toxic hydrosulfide and cyanide ions: Practicability in living cells and food samples

Although hydrosulfide and cyanide anions play important roles in daily life that they are available in a lot of foods. However, their excess amounts contaminate water, land, and food and cause serious problems to human health. Herein, we introduce a water-soluble macrocyclic sensor based-on Calix[4]arene (MPI-Calix[4]) with dual response sites for fluorescence recognizing cyanide (CN^-) and hydrogen sulfide (HS^-) under longwave light. MPI-Calix[4] exhibits a high selectivity and sensitivity in the detection of CN^- and HS^-, where the limits of detection were as low as 0.115 and 8.12 μmol/L, respectively. The cell imaging studies shows that this probe can be easily used in the detection of CN^- and HS^- on living cells. Full understanding of these results paved a fruitful system to improve an applicable analytical process for food safety and quality.

Focus on Nitric Oxide Homeostasis: Direct and Indirect Enzymatic Regulation of Protein Denitrosation Reactions in Plants

Protein cysteines (Cys) undergo a multitude of different reactive oxygen species (ROS), reactive sulfur species (RSS), and/or reactive nitrogen species (RNS)-derived modifications. S-nitrosation (also referred to as nitrosylation), the addition of a nitric oxide (NO) group to reactive Cys thiols, can alter protein stability and activity and can result in changes of protein subcellular localization. Although it is clear that this nitrosative posttranslational modification (PTM) regulates multiple signal transduction pathways in plants, the enzymatic systems that catalyze the reverse S-denitrosation reaction are poorly understood. This review provides an overview of the biochemistry and regulation of nitro-oxidative modifications of protein Cys residues with a focus on NO production and S-nitrosation. In addition, the importance and recent advances in defining enzymatic systems proposed to be involved in regulating S-denitrosation are addressed, specifically cytosolic thioredoxins (TRX) and the newly identified aldo-keto reductases (AKR).

The secret of H2 S to keep plants young and fresh and its products

Recently, accumulating evidence has shown that hydrogen sulphide (H₂ S), a newly determined gasotransmitter, plays important roles in senescence, which is an essential biological process for plant fitness and an important agricultural trait that is critical for the yield and quality of farm produce. Here, in this review, we summarize the roles of H₂ S in senescence, both before and after the harvesting of agricultural products, and the underlying mechanism is also discussed. During the plant growth process, the function of H₂ S in the leaf senescence process has been studied extensively, and H₂ S plays roles during the whole process, including the initiation, reorganization and terminal stages. While during the postharvest stage, H₂ S can prevents farm products from deterioration resulting from over-ripening, pathogen attack and incorrect storage. The underlying H₂ S-related mechanisms during different stages of the senescence process are summarized and compared. The most prominent interaction occurs between H₂ S and reactive oxygen species, and the molecular mechanism is explored. Additionally, the conserved action mode of H₂ S in different life processes and different species is also discussed. In the future, multi-omics analyses over time will be needed to investigate the detailed mechanisms of H₂ S, and a safety attribute analysis of H₂ S is also required before it can be used in agricultural production.

H2S in Horticultural Plants: Endogenous Detection by an Electrochemical Sensor, Emission by a Gas Detector, and Its Correlation with L-Cysteine Desulfhydrase (LCD) Activity

H2S has acquired great attention in plant research because it has signaling functions under physiological and stress conditions. However, the direct detection of endogenous H2S and its potential emission is still a challenge in higher plants. In order to achieve a comparative analysis of the content of H2S among different plants with agronomical and nutritional interest including pepper fruits, broccoli, ginger, and different members of the genus Allium such as garlic, leek, Welsh and purple onion, the endogenous H2S and its emission was determined using an ion-selective microelectrode and a specific gas detector, respectively. The data show that endogenous H2S content range from pmol to μmol H2S · g-1 fresh weight whereas the H2S emission of fresh-cut vegetables was only detected in the different species of the genus Allium with a maximum of 9 ppm in garlic cloves. Additionally, the activity and isozymes of the L-cysteine desulfhydrase (LCD) were analyzed, which is one of the main enzymatic sources of H2S, where the different species of the genus Allium showed the highest activities. Using non-denaturing gel electrophoresis, the data indicated the presence of up to nine different LCD isozymes from one in ginger to four in onion, leek, and broccoli. In summary, the data indicate a correlation between higher LCD activity with the endogenous H2S content and its emission in the analyzed horticultural species. Furthermore, the high content of endogenous H2S in the Allium species supports the recognized benefits for human health, which are associated with its consumption.

Hydrogen sulfide inhibits the abscission of tomato pedicel through reconstruction of a basipetal auxin gradient

Abscission is an important developmental process and an essential agricultural trait. Auxin and ethylene are two phytohormones with important roles in the complex, but still elusive signaling network of abscission. Here, we found that hydrogen sulfide (H₂S), a newly identified gasotransmitter, inhibits the initiation of tomato pedicel abscission. The underlying mechanism was explored through transcriptome profile analysis in various pedicel tissues with or without H₂S treatment in the early abscission stage. The data suggested that H₂S strongly influences the global transcription of pedicel tissues, exerts differential expression regulation along the pedicel, and markedly influences both the auxin and ethylene signaling pathways. Computational analysis revealed that H₂S reconstructs a basipetal auxin gradient along the pedicel at 4 h after treatment; this finding was further substantiated by the GUS-staining results of DR5::GUS pedicels. The inhibitory effect of H₂S to the ethylene signaling pathway might be an indirect action. Moreover, the subtilisin-like proteinase family members involved in the release of peptide signal molecules are critical components of the abscission signaling network downstream of auxin and ethylene.

Sulfur in Seeds: An Overview

Sulfur is a growth-limiting and secondary macronutrient as well as an indispensable component for several cellular components of crop plants. Over the years various scientists have conducted several experiments on sulfur metabolism based on different aspects of plants. Sulfur metabolism in seeds has immense importance in terms of the different sulfur-containing seed storage proteins, the significance of transporters in seeds, the role of sulfur during the time of seed germination, etc. The present review article is based on an overview of sulfur metabolism in seeds, in respect to source to sink relationships, S transporters present in the seeds, S-regulated seed storage proteins and the importance of sulfur at the time of seed germination. Sulfur is an essential component and a decidable factor for seed yield and the quality of seeds in terms of oil content in oilseeds, storage of qualitative proteins in legumes and has a significant role in carbohydrate metabolism in cereals. In conclusion, a few future perspectives towards a more comprehensive knowledge on S metabolism/mechanism during seed development, storage and germination have also been stated.

Nitric oxide is involved in hydrogen sulfide-induced adventitious rooting in tomato (Solanum lycopersicum)

Nitric oxide (NO) and hydrogen sulfide (H2 S) are signalling molecules that regulate adventitious rooting in plants. However, little is known about the cross-talk between NO and H2 S during adventitious rooting. Tomato (Solanum lycopersicum L.) explants were used to investigate the roles of and relationships between NO and H2 S during rooting. Effects of the NO donor sodium nitroprusside (SNP) and the H2 S donor sodium hydrosulfide (NaHS) on adventitious rooting were dose-dependent, and the greatest biological responses were observed under 25μM SNP and 50μM NaHS. The positive effect of NaHS was reversed by the NO scavenger 2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), indicating that the H2 S-induced response was partially NO-dependent. Peroxidase (POD), polyphenol oxidase (PPO), and superoxide dismutase (SOD) activities significantly increased by SNP and NaHS treatment, and indoleacetic acid oxidase (IAAO) activity and the O2 - and H2 O2 content significantly decreased by SNP and NaHS treatment. SNP and NaHS treatment also increased the content of soluble sugar and protein and indole-3-acetic acid (IAA). cPTIO significantly mitigated the increases in POD, PPO and SOD activity and soluble sugar, protein and IAA content induced by NaHS. SNP and NaHS upregulated the expression of auxin-related genes (ARF4 and ARF16 ), cell cycle-related genes (CYCD3 , CYCA3 and CDKA1 ), and antioxidant-related genes (TPX2 , SOD and POD ); whereas cPTIO significantly inhibited the increase in the expression of these genes induced by NaHS. Overall, these results show that NO may be involved in H2 S-induced adventitious rooting by regulating the activity of rooting-related enzymes, the expression of related genes, and the content of various nutrients.

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 treatment increases the antioxidant capacity of fresh Lingwu Long Jujube (Ziziphus jujuba cv. Mill) fruit during storage

Hydrogen sulfide (H₂S) has been identified as an important gaseous signal molecule in plants. Here, we investigated the effects of H₂S on postharvest senescence and antioxidant metabolism of Lingwu Long Jujube (Ziziphus jujuba cv. Mill) fruits (LLJF). Fumigation of Jujube fruits with H₂S released from 0.4 mm NaHS could significantly prolong the postharvest shelf life of jujube fruits, reduce the decay rate of fruit, the weight loss of fruit, and inhibit the fruit loss, hardness, color, soluble solids, and titratable acidity. Compared with the control group, exogenous H₂S fumigation significantly decreased the loss of chlorophyll, carotenoids, soluble protein, ascorbic acid, phenols, and flavonoids in jujube fruits during post-harvest storage. At the same time, H₂S could significantly delay the accumulation of malondialdehyde (MDA), hydrogen peroxide (H₂O₂) and superoxide anion (O₂^∙−) and promote catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase (POD) activity, and inhibit polyphenol oxidase (PPO) activity. To summarize, H₂S can effectively alleviate postharvest senescence and decay of jujube fruits by regulating the ROS accumulation and antioxidant enzymes, and prolong the storage period of postharvest.

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H₂S treatment could significantly prolong the postharvest shelf life of jujube fruits.

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H₂S could significantly delay the accumulation of MDA, H₂O₂ and O₂^∙− during storage of jujube fruits.

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H₂S treatment promote CAT, SOD, APX, POD activity, and inhibit PPO activity during storage of jujube fruits.

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Provides a new method for storage of post-harvest jujube fruits.

Nitric oxide and hydrogen sulfide: an indispensable combination for plant functioning

Nitric oxide (NO) and hydrogen sulfide (H₂S) are gasotransmitters, which are involved in almost all plant physiological and stress-related processes. With its antioxidant regulatory properties, NO on its own ameliorates plant stress, while H₂S, a foul-smelling gas, has differential effects. Recent studies have shown that these signaling molecules are involved in intertwined pathway networks. This is due to the contrasting effects of NO and H₂S depending on cell type, subcellular compartment, and redox status, as well as the flux and dosage of NO and H₂S in different plant species and cellular contexts. Here, we provide a comprehensive review of the complex networks of these molecules, with particular emphasis on root development, stomatal movement, and plant cell death.

Protein Persulfidation in Plants: Function and Mechanism

As an endogenous gaseous transmitter, the function of hydrogen sulfide (H2S) has been extensively studied in plants. Once synthesized, H2S may be involved in almost all life processes of plants. Among them, a key route for H2S bioactivity occurs via protein persulfidation, in which process oxidizes cysteine thiol (R-SH) groups into persulfide (R-SSH) groups. This process is thought to underpin a myriad of cellular processes in plants linked to growth, development, stress responses, and phytohormone signaling. Multiple lines of emerging evidence suggest that this redox-based reversible post-translational modification can not only serve as a protective mechanism for H2S in oxidative stress, but also control a variety of biochemical processes through the allosteric effect of proteins. Here, we collate emerging evidence showing that H2S-mediated persulfidation modification involves some important biochemical processes such as growth and development, oxidative stress, phytohormone and autophagy. Additionally, the interaction between persulfidation and S-nitrosylation is also discussed. In this work, we provide beneficial clues for further exploration of the molecular mechanism and function of protein persulfidation in plants in the future.

Gibberellic acid maintains postharvest quality of Agaricus bisporus mushroom by enhancing antioxidative system and hydrogen sulfide synthesis

The application of gibberellic acid (GA₃ ) treatment to the postharvest quality maintenance of white button mushroom (Agaricus bisporus) was investigated. The optimum concentration of exogenous GA₃ was 100 mg/L. At this concentration, the color change was inhibited, the firmness was maintained, and the weight loss and respiratory rates were reduced. The GA₃ group had significantly lower malonaldehyde (MDA) content and membrane permeability. Reactive oxygen species accumulation was reduced due to the regulation of polyphenol oxidase (PPO), peroxidase (POD), and superoxide dismutase (SOD) enzyme activities. Moreover, the production of endogenous gaseous signaling molecule hydrogen sulfide (H₂ S) was triggered by GA₃ treatment, which enhanced cystathionine γ-lyase (AbCSE) and cystathionine β-synthase (AbCBS) activities alongside the corresponding gene expressions. The preservation of button mushroom postharvest storage quality by GA₃ was most likely due to the regulation of reactive oxygen species metabolism and hydrogen sulfide biosynthesis. PRACTICAL APPLICATIONS: Mushroom is rich in nutrients and functional substances. However, due to the lack of cuticle, high respiration rate, and moisture content, mushroom's postharvest quality deteriorates rapidly. A safe and effective reagent that prevents the senescence and quality deterioration of harvested mushroom is urgently needed. The effects of plant hormone GA₃ on the postharvest quality of edible fungi remain unclear. The present study provided convincing evidence that 100 mg L^-1 of GA₃ effectively maintained postharvest button mushroom quality by regulating reactive oxygen species metabolism and hydrogen sulfide biosynthesis.

Mechanism of Growth Regulation of Yeast Involving Hydrogen Sulfide From S-Propargyl-Cysteine Catalyzed by Cystathionine-γ-Lyase

Pathogenic fungi are recognized as a progressive threat to humans, particularly those with the immunocompromised condition. The growth of fungi is controlled by several factors, one of which is signaling molecules, such as hydrogen sulfide (H₂S), which was traditionally regarded as a toxic gas without physiological function. However, recent studies have revealed that H₂S is produced enzymatically and endogenously in several species, where it serves as a gaseous signaling molecule performing a variety of critical biological functions. However, the influence of this endogenous H₂S on the biological activities occurring within the pathogenic fungi, such as transcriptomic and phenotypic alternations, has not been elucidated so far. Therefore, the present study was aimed to decipher this concern by utilizing S-propargyl-cysteine (SPRC) as a novel and stable donor of H₂S and Saccharomyces cerevisiae as a fungal model. The results revealed that the yeast could produce H₂S by catabolizing SPRC, which facilitated the growth of the yeast cells. This implies that the additional intracellularly generated H₂S is generated primarily from the enhanced sulfur-amino-acid-biosynthesis pathways and serves to increase the growth rate of the yeast, and presumably the growth of the other fungi as well. In addition, by deciphering the implicated pathways and analyzing the in vitro enzymatic activities, cystathionine-γ-lyase (CYS3) was identified as the enzyme responsible for catabolizing SPRC into H₂S in the yeast, which suggested that cystathionine-γ-lyase might play a significant role in the regulation of H₂S-related transcriptomic and phenotypic alterations occurring in yeast. These findings provide important information regarding the mechanism underlying the influence of the gaseous signaling molecules such as H₂S on fungal growth. In addition, the findings provide a better insight to the in vivo metabolism of H₂S-related drugs, which would be useful for the future development of anti-fungal drugs.

Hydrogen sulfide: An emerging signaling molecule regulating drought stress response in plants

Hydrogen sulfide (H₂ S) is a small, reactive signaling molecule that is produced within chloroplasts of plant cells as an intermediate in the assimilatory sulfate reduction pathway by the enzyme sulfite reductase. In addition, H₂ S is also produced in cytosol and mitochondria by desulfhydration of l-cysteine catalyzed by l-cysteine desulfhydrase (DES1) in the cytosol and from β-cyanoalanine in mitochondria, in a reaction catalyzed by β-cyano-Ala synthase C1 (CAS-C1). H₂ S exerts its numerous biological functions by post-translational modification involving oxidation of cysteine residues (RSH) to persulfides (RSSH). At lower concentrations (10-1000 μmol L^-1 ), H₂ S shows huge agricultural potential as it increases the germination rate, the size, fresh weight, and ultimately the crop yield. It is also involved in abiotic stress response against drought, salinity, high temperature, and heavy metals. H₂ S donor, for example, sodium hydrosulfide (NaHS), has been exogenously applied on plants by various researchers to provide drought stress tolerance. Exogenous application results in the accumulation of polyamines, sugars, glycine betaine, and enhancement of the antioxidant enzyme activities in response to drought-induced osmotic and oxidative stress, thus, providing stress adaptation to plants. At the biochemical level, administration of H₂ S donors reduces malondialdehyde content and lipoxygenase activity to maintain the cell integrity, causes abscisic acid-mediated stomatal closure to prevent water loss through transpiration, and accelerates the photosystem II repair cycle. Here, we review the crosstalk of H₂ S with secondary messengers and phytohormones towards the regulation of drought stress response and emphasize various approaches that can be addressed to strengthen research in this area.

Delaying Broccoli Floret Yellowing by Phytosulfokine α Application During Cold Storage

During postharvest life, broccoli suffers from floret yellowing confining its economic and nutritional value. The objective of the present study was to explore the mechanisms employed by phytosulfokine α (PSKα) at 150 nM for delaying floret yellowing in broccoli during storage at 4°C for 28 days. Our results showed that the higher endogenous accumulation of hydrogen sulfide (H₂S) resulting from the higher gene expression and activities of l-cysteine desulfhydrase (LCD) and d-cysteine desulfhydrase (DCD) in broccoli floret treated with 150 nM PSKα may serve as an endogenous signaling molecule for delaying senescence. Moreover, the suppressed ethylene biosynthesis in broccoli floret treated with 150 nM PSKα might be ascribed to lower gene expression and activities of ACC synthase (ACS) and ACC oxidase (ACO). Furthermore, lower gene expression and activities of Mg²⁺ dechelatase (MDC), pheophytinase (PPH), and pheophorbide a oxygenase (PaO) might be the reasons for the higher accumulation of chlorophyll in broccoli floret treated with 150 nM PSKα. Based on our findings, exogenous PSKα application could be employed as signaling bioactive hormone for retarding floret yellowing of broccoli during storage at 4°C for 28 days.

Nitric oxide and hydrogen sulfide modulate the NADPH-generating enzymatic system in higher plants

Nitric oxide (NO) and hydrogen sulfide (H2S) are two key molecules in plant cells that participate, directly or indirectly, as regulators of protein functions through derived post-translational modifications, mainly tyrosine nitration, S-nitrosation, and persulfidation. These post-translational modifications allow the participation of both NO and H2S signal molecules in a wide range of cellular processes either physiological or under stressful circumstances. NADPH participates in cellular redox status and it is a key cofactor necessary for cell growth and development. It is involved in significant biochemical routes such as fatty acid, carotenoid and proline biosynthesis, and the shikimate pathway, as well as in cellular detoxification processes including the ascorbate-glutathione cycle, the NADPH-dependent thioredoxin reductase (NTR), or the superoxide-generating NADPH oxidase. Plant cells have diverse mechanisms to generate NADPH by a group of NADP-dependent oxidoreductases including ferredoxin-NADP reductase (FNR), NADP-glyceraldehyde-3-phosphate dehydrogenase (NADP-GAPDH), NADP-dependent malic enzyme (NADP-ME), NADP-dependent isocitrate dehydrogenase (NADP-ICDH), and both enzymes of the oxidative pentose phosphate pathway, designated as glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH). These enzymes consist of different isozymes located in diverse subcellular compartments (chloroplasts, cytosol, mitochondria, and peroxisomes) which contribute to the NAPDH cellular pool. We provide a comprehensive overview of how post-translational modifications promoted by NO (tyrosine nitration and S-nitrosation), H2S (persulfidation), and glutathione (glutathionylation), affect the cellular redox status through regulation of the NADP-dependent dehydrogenases.

Hydrogen sulfide mitigates cadmium induced toxicity in Brassica rapa by modulating physiochemical attributes, osmolyte metabolism and antioxidative machinery

Hydrogen sulfide (H₂S) is helpful for maintaining plant growth under abiotic stresses. The current study elucidated the physiological and biochemical strategies by which sodium hydrosulfide (NaHS), a donor of H₂S, alleviated cadmium (Cd) toxicity in Brassica rapa. B. rapa plants growing under 50 mgkg^-1 Cd stress showed reduced leaf relative water contents (LRWC), photosynthetic pigments, total soluble proteins, minerals uptake, antioxidants and growth. Furthermore, enhanced accumulation of Cd contents caused augmentation in levels of electrolyte leakage (EL) and methylglyoxal (MG). Nevertheless, improved physiochemical parameters in B. rapa seedlings obtained from seeds primed with 1.5 mM NaHS resulted better phenotype, growth and biomass production in Cd stressed plants. Protective stimulus of H₂S regulated minerals and Cd homeostasis besides increased activity of antioxidants which decreased level of reactive oxygen species (ROS), EL, malondialdehyde (MDA) and MG in Cd regimes. Furthermore, H₂S treated seedlings exhibited reduction in Cd content and revealed an active participation in the indole acetic acid (IAA) mediated pathway during stress. The findings of current study propose that H₂S improved stress tolerance and mitigated Cd stress in B. rapa by modulating growth biomarkers and antioxidative system.

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.

Something smells bad to plant pathogens: Production of hydrogen sulfide in plants and its role in plant defence responses

Background

Sulfur and diverse sulfur-containing compounds constitute important components of plant defences against a wide array of microbial pathogens. Among them, hydrogen sulfide (H₂S) occupies a prominent position as a gaseous signalling molecule that plays multiple roles in regulation of plant growth, development and plant responses to stress conditions. Although the production of H₂S in plant cells has been discovered several decades ago, the underlying pathways of H₂S biosynthesis, metabolism and signalling were only recently uncovered.

Aim of the review

Here we review the current knowledge on the biosynthesis of H₂S in plant cells, with special attention to L-cysteine desulfhydrase (DES) as the key enzyme controlling H₂S levels biosynthesis in the cytosol of plant cells during plant growth, development and diverse abiotic and biotic stress conditions.

Key Scientific Concepts of Review

Recent advances have revealed molecular mechanisms of DES properties, functions and regulation involved in modulations of H₂S production during plant responses to abiotic and biotic stress stimuli. Studies on des mutants of the model plant Arabidopsis thaliana uncovered molecular mechanisms of H₂S action as a signalling and defence molecule in plant-pathogen interactions. Signalling pathways of H₂S include S-persulfidation of protein cysteines, a redox-based post-translational modification leading to activation of downstream components of H₂S signalling. Accumulated evidence shows DES and H2S implementation into salicylic acid signalling and activation of pathogenesis-related proteins and autophagy within plant immunity. Obtained knowledge on molecular mechanisms of H₂S action in plant defence responses opens new prospects in the search for crop varieties with increased resistance to bacterial and fungal pathogens.

Hydrogen sulfide in horticulture: Emerging roles in the era of climate change

Future climate change will present many plants with environmental challenges, including extreme temperatures and drought. Hydrogen sulfide (H₂S) has emerged as an important signal transmitting molecule in plants, especially important in many stress responses and it is known to regulate numerous physiological and developmental processes. Being recently suggested as a signaling molecule, research exploring the regulatory functions is continuously progressing regarding the role of H₂S in plant science, agriculture and horticulture. Biosynthesis of H₂S occurs in different cellular compartments from where it can freely translocate via membranes to where needed or be excluded where not required. H₂S interacts with related signaling molecules which together mediate stress tolerance against a plethora of harsh conditions. The H₂S induced tolerance against stresses occurs via regulation of antioxidants activities, endogenous levels of GSH, osmoregulator accumulation, cell signaling proteins, and stress-related gene expression. Overall this efficiently eliminates excessive reactive oxygen species (ROS) and maintains the intracellular redox balance. The current review summarizes the recent progress on H₂S or H₂S donor-mediated abiotic stress tolerance with special reference to climate change and horticulture crops, pre- and post-harvest. Elucidating the role of H₂S in cell signaling pathways may open new horizons towards understanding how exogenous treatments with H₂S in horticulture plants may aid in the tolerance to stress, especially as environmental conditions change, and can secure better crop yields and avoid post-harvest losses.

Crosstalk between Hydrogen Sulfide and Other Signal Molecules Regulates Plant Growth and Development

Hydrogen sulfide (H₂S), once recognized only as a poisonous gas, is now considered the third endogenous gaseous transmitter, along with nitric oxide (NO) and carbon monoxide (CO). Multiple lines of emerging evidence suggest that H₂S plays positive roles in plant growth and development when at appropriate concentrations, including seed germination, root development, photosynthesis, stomatal movement, and organ abscission under both normal and stress conditions. H₂S influences these processes by altering gene expression and enzyme activities, as well as regulating the contents of some secondary metabolites. In its regulatory roles, H₂S always interacts with either plant hormones, other gasotransmitters, or ionic signals, such as abscisic acid (ABA), ethylene, auxin, CO, NO, and Ca²⁺. Remarkably, H₂S also contributes to the post-translational modification of proteins to affect protein activities, structures, and sub-cellular localization. Here, we review the functions of H₂S at different stages of plant development, focusing on the S-sulfhydration of proteins mediated by H₂S and the crosstalk between H₂S and other signaling molecules.

H2S signaling in plants and applications in agriculture

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Hydrogen sulfide (H₂S) plays a signaling role in higher plants.

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It mediates persulfidation, a post-translational modification.

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It regulates physiological functions ranging from seed germination to fruit ripening.

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The beneficial effects of exogenous H₂S are mainly caused by the stimulation of antioxidant systems.

The signaling properties of the gasotransmitter molecule hydrogen sulfide (H₂S), which is endogenously generated in plant cells, are mainly observed during persulfidation, a protein post-translational modification (PTM) that affects redox-sensitive cysteine residues. There is growing experimental evidence that H₂S in higher plants may function as a mechanism of response to environmental stress conditions. In addition, exogenous applications of H₂S to plants appear to provide additional protection against stresses, such as salinity, drought, extreme temperatures and heavy metals, mainly through the induction of antioxidant systems, in order to palliate oxidative cellular damage. H₂S also appears to be involved in regulating physiological functions, such as seed germination, stomatal movement and fruit ripening, as well as molecules that maintain post-harvest quality and rhizobium–legume symbiosis. These properties of H₂S open up new challenges in plant research to better understand its functions as well as new opportunities for biotechnological treatments in agriculture in a changing environment.

Revealing on hydrogen sulfide and nitric oxide signals co-ordination for plant growth under stress conditions

In the recent times, plants are facing certain types of environmental stresses, which give rise to formation of reactive oxygen species (ROS) such as hydroxyl radicals, hydrogen peroxides, superoxide anions and so on. These are required by the plants at low concentrations for signal transduction and at high concentrations, they repress plant root growth. Apart from the ROS activities, hydrogen sulfide (H₂ S) and nitric oxide (NO) have major contributions in regulating growth and developmental processes in plants, as they also play key roles as signaling molecules and act as chief plant immune defense mechanisms against various biotic as well as abiotic stresses. H₂ S and NO are the two pivotal gaseous messengers involved in growth, germination and improved tolerance in plants under stressed and non-stress conditions. H₂ S and NO mediate cell signaling in plants as a response to several abiotic stresses like temperature, heavy metal exposure, water and salinity. They alter gene expression levels to induce the synthesis of antioxidant enzymes, osmolytes and also trigger their interactions with each other. However, research has been limited to only cross adaptations and signal transductions. Understanding the change and mechanism of H₂ S and NO mediated cell signaling will broaden our knowledge on the various biochemical changes that occur in plant cells related to different stresses. A clear understanding of these molecules in various environmental stresses would help to confer biotechnological applications to protect plants against abiotic stresses and to improve crop productivity.

Hydrogen sulfide acts downstream of jasmonic acid to inhibit stomatal development in Arabidopsis

Main conclusion: Jasmonic acid (JA) negatively regulates stomatal development by promoting LCD expression and hydrogen sulfide (H₂S) biosynthesis. H₂S inhibits the initiation of stomata formation and acts upstream of SPEECHLESS. Abstract: Stomatal development is strictly regulated by endogenous signals and environmental cues. We recently revealed that jasmonic acid (JA) negatively regulates stomatal development in Arabidopsis thaliana cotyledons (Han et al., Plant Physiol 176:2871-2885, 2018), but the underlying molecular mechanism remains largely unknown. Here, we uncovered a role for H₂S in regulating stomatal development. The H₂S scavenger hypotaurine reversed the JA-induced repression of stomatal development in the epidermis of wild-type Arabidopsis. The H₂S-deficient mutant lcd displayed increased stomatal density and stomatal index values, which were rescued by treatment with sodium hydrosulfide (NaHS; an H₂S donor) but not JA, suggesting that JA-mediated repression of stomatal development is dependent on H₂S biosynthesis. The high stomatal density of JA-deficient mutants was rescued by exogenous NaHS treatment. Further analysis indicated that JA positively regulates LCD expression, L-cysteine desulfhydrases (L-CDes) activity, and endogenous H₂S content. Furthermore, H₂S represses the expression of stomate-associated genes and functions downstream of stomate-related signaling pathway components TOO MANY MOUTHS (TMM) and STOMATAL DENSITY AND DISTRIBUTION1 (SDD1) and upstream of SPEECHLESS (SPCH). Therefore, H₂S acts downstream of JA signaling to regulate stomatal development in Arabidopsis cotyledons.

Role of Exogenous and Endogenous Hydrogen Sulfide (H2S) on Functional Traits of Plants Under Heavy Metal Stresses: A Recent Perspective

Improving growth and productivity of plants that are vulnerable to environmental stresses, such as heavy metals, is of significant importance for meeting global food and energy demands. Because heavy metal toxicity not only causes impaired plant growth, it has also posed many concerns related to human well-being, so mitigation of heavy metal pollution is a necessary priority for a cleaner environment and healthier world. Hydrogen sulfide (H₂S), a gaseous signaling molecule, is involved in metal-related oxidative stress mitigation and increased stress tolerance in plants. It performs multifunctional roles in plant growth regulation while reducing the adverse effects of abiotic stress. Most effective function of H₂S in plants is to eliminate metal-related oxidative toxicity by regulating several key physiobiochemical processes. Soil pollution by heavy metals presents significant environmental challenge due to the absence of vegetation cover and the resulting depletion of key soil functions. However, the use of stress alleviators, such as H₂S, along with suitable crop plants, has considerable potential for an effective management of these contaminated soils. Overall, the present review examines the imperative role of exogenous application of different H₂S donors in reducing HMs toxicity, by promoting plant growth, stabilizing their physiobiochemical processes, and upregulating antioxidative metabolic activities. In addition, crosstalk of different growth regulators with endogenous H₂S and their contribution to the mitigation of metal phytotoxicity have also been explored.

Regulation of Hydrogen Sulfide Metabolism by Nitric Oxide Inhibitors and the Quality of Peaches during Cold Storage

Both nitric oxide (NO) and hydrogen sulfide (H2S) have been shown to have positive effects on the maintenance of fruit quality during storage; however, the mechanisms by which NO regulates the endogenous H2S metabolism remain unknown. In this experiment, peaches were immersed in solutions of NO, potassium 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO, as an NO scavenger), N-nitro-l-arginine methyl ester (l-NAME, as an inhibitor of nitric oxide synthase (NOS)-like activity), and sodium tungstate (as an inhibitor of nitrate reductase), and the resulting changes in the H2S metabolism of peaches were studied. The results showed that exogenous NO reduced the contents of endogenous H2S, Cys, and sulfite; decreased the activities of l-/d-cysteine desulfhydrase (l-/d-CD), O-acetylserine (thiol)lyase (OAS-TL), and sulfite reductase (SiR); and increased the activity of β-cyanoalanine synthase (β-CAS). Both c-PTIO and sodium tungstate had similar roles in increasing the H2S content by sustaining the activities of l-/d-CDs, OAS-TL, and SiR. l-NAME increased the H2S content, mainly by maintaining the d-CD activity. The results suggest that NO, c-PTIO, l-NAME, and sodium tungstate differently regulate the H2S metabolism of peaches during storage.

Biochemical Characterization of the Fusarium graminearum Candidate ACC-Deaminases and Virulence Testing of Knockout Mutant Strains

Fusarium graminearum is a plant pathogenic fungus which is able to infect wheat and other economically important cereal crop species. The role of ethylene in the interaction with host plants is unclear and controversial. We have analyzed the inventory of genes with a putative function in ethylene production or degradation of the ethylene precursor 1-aminocyclopropane carboxylic acid (ACC). F. graminearum, in contrast to other species, does not contain a candidate gene encoding ethylene-forming enzyme. Three genes with similarity to ACC synthases exist; heterologous expression of these did not reveal enzymatic activity. The F. graminearum genome contains in addition two ACC deaminase candidate genes. We have expressed both genes in E. coli and characterized the enzymatic properties of the affinity-purified products. One of the proteins had indeed ACC deaminase activity, with kinetic properties similar to ethylene-stress reducing enzymes of plant growth promoting bacteria. The other candidate was inactive with ACC but turned out to be a d-cysteine desulfhydrase. Since it had been reported that ethylene insensitivity in transgenic wheat increased Fusarium resistance and reduced the content of the mycotoxin deoxynivalenol (DON) in infected wheat, we generated single and double knockout mutants of both genes in the F. graminearum strain PH-1. No statistically significant effect of the gene disruptions on fungal spread or mycotoxin content was detected, indicating that the ability of the fungus to manipulate the production of the gaseous plant hormones ethylene and H₂S is dispensable for full virulence.

Nitric oxide and hydrogen sulfide in plants: which comes first?

Nitric oxide (NO) is a signal molecule regarded as being involved in myriad functions in plants under physiological, pathogenic, and adverse environmental conditions. Hydrogen sulfide (H2S) has also recently been recognized as a new gasotransmitter with a diverse range of functions similar to those of NO. Depending on their respective concentrations, both these molecules act synergistically or antagonistically as signals or damage promoters in plants. Nevertheless, available evidence shows that the complex biological connections between NO and H2S involve multiple pathways and depend on the plant organ and species, as well as on experimental conditions. Cysteine-based redox switches are prone to reversible modification; proteomic and biochemical analyses have demonstrated that certain target proteins undergo post-translational modifications such as S-nitrosation, caused by NO, and persulfidation, caused by H2S, both of which affect functionality. This review provides a comprehensive update on NO and H2S in physiological processes (seed germination, root development, stomatal movement, leaf senescence, and fruit ripening) and under adverse environmental conditions. Existing data suggest that H2S acts upstream or downstream of the NO signaling cascade, depending on processes such as stomatal closure or in response to abiotic stress, respectively.

Nitric oxide in the physiology and quality of fleshy fruits

Fruits are unique to flowering plants and confer a selective advantage as they facilitate seed maturation and dispersal. In fleshy fruits, development and ripening are associated with numerous structural, biochemical, and physiological changes, including modifications in the general appearance, texture, flavor, and aroma, which ultimately convert the immature fruit into a considerably more attractive and palatable structure for seed dispersal by animals. Treatment with exogenous nitric oxide (NO) delays fruit ripening, prevents chilling damage, promotes disease resistance, and enhances the nutritional value. The ripening process is influenced by NO, which operates antagonistically to ethylene, but it also interacts with other regulatory molecules such as abscisic acid, auxin, jasmonic acid, salicylic acid, melatonin, and hydrogen sulfide. NO content progressively declines during fruit ripening, with concomitant increases in protein nitration and nitrosation, two post-translational modifications that are promoted by reactive nitrogen species. Dissecting the intimate interactions of NO with other ripening-associated factors, including reactive oxygen species, antioxidants, and the aforementioned phytohormones, remains a challenging subject of research. In this context, integrative 'omics' and gene-editing approaches may provide additional knowledge of the impact of NO in the regulatory processes involved in controlling physiology and quality traits in both climacteric and non-climacteric fruits.

Signaling by hydrogen sulfide and cyanide through post-translational modification

Two cysteine metabolism-related molecules, hydrogen sulfide and hydrogen cyanide, which are considered toxic, have now been considered as signaling molecules. Hydrogen sulfide is produced in chloroplasts through the activity of sulfite reductase and in the cytosol and mitochondria by the action of sulfide-generating enzymes, and regulates/affects essential plant processes such as plant adaptation, development, photosynthesis, autophagy, and stomatal movement, where interplay with other signaling molecules occurs. The mechanism of action of sulfide, which modifies protein cysteine thiols to form persulfides, is related to its chemical features. This post-translational modification, called persulfidation, could play a protective role for thiols against oxidative damage. Hydrogen cyanide is produced during the biosynthesis of ethylene and camalexin in non-cyanogenic plants, and is detoxified by the action of sulfur-related enzymes. Cyanide functions include the breaking of seed dormancy, modifying the plant responses to biotic stress, and inhibition of root hair elongation. The mode of action of cyanide is under investigation, although it has recently been demonstrated to perform post-translational modification of protein cysteine thiols to form thiocyanate, a process called S-cyanylation. Therefore, the signaling roles of sulfide and most probably of cyanide are performed through the modification of specific cysteine residues, altering protein functions.

Gasotransmitters in Action: Nitric Oxide-Ethylene Crosstalk during Plant Growth and Abiotic Stress Responses

Since their first description as atmospheric gases, it turned out that both nitric oxide (NO) and ethylene (ET) are multifunctional plant signals. ET and polyamines (PAs) use the same precursor for their synthesis, and NO can be produced from PA oxidation. Therefore, an indirect metabolic link between NO and ET synthesis can be considered. NO signal is perceived primarily through S-nitrosation without the involvement of a specific receptor, while ET signal is sensed by a well-characterized receptor complex. Both NO and ET are synthetized by plants at various developmental stages (e.g., seeds, fruits) and as a response to numerous environmental factors (e.g., heat, heavy metals) and they mutually regulate each other's levels. Most of the growth and developmental processes (e.g., fruit ripening, de-etiolation) are regulated by NO-ET antagonism, while in abiotic stress responses, both antagonistic (e.g., dark-induced stomatal opening, cadmium-induced cell death) and synergistic (e.g., UV-B-induced stomatal closure, iron deficiency-induced expression of iron acquisition genes) NO-ET interplays have been revealed. Despite the numerous pieces of experimental evidence revealing NO-ET relationships in plants, the picture is far from complete. Understanding the mechanisms of NO-ET interactions may contribute to the increment of yield and intensification of stress tolerance of crop plants in changing environments.

Signaling Molecule Hydrogen Sulfide Improves Seed Germination and Seedling Growth of Maize (Zea mays L.) Under High Temperature by Inducing Antioxidant System and Osmolyte Biosynthesis

Hydrogen sulfide (H2S) is a novel type signaling molecule in plants. Seed germination is a key stage of life cycle of plants, which is vulnerable to environmental stress including high temperature. However, under high temperature stress, whether pre-soaking of maize seeds with NaHS (a H2S donor) could improve seed germination and seedling growth and the possible mechanisms are not completely clear. In this study, maize seeds pre-soaked with NaHS enhanced germination percentage, sprout length, root length, and fresh weight compared with the control without NaHS treatment, illustrating that H2S could improve maize seed germination and seedling growth under high temperature. In addition, in comparison to the control, NaHS pre-soaking stimulated antioxidant enzymes [ascorbate peroxidase (APX), glutathione reductase (GR), guaiacol peroxidase (GPX), superoxide dismutase (SOD), and catalase (CAT)] activities and the contents of water soluble non-enzymatic antioxidants [ascorbic acid (AsA) and glutathione (GSH)], as well as the ratio of reduced antioxidant to oxidized antioxidant. Moreover, pre-soaking with NaHS activated Δ1-pyrroline-5-carboxylate synthetase (P5CS) and ornithine aminotransferase [OAT; both are rate-limiting enzymes in proline (Pro) synthesis], betaine aldehyde dehydrogenase [BADH; a key enzyme in glycine betaine (GB)], and trehalose (Tre)-6-phosphate phosphatase (a key step in Tre synthesis), which in turn accumulated Pro, GB, and Tre in germinating seeds compared with the control. Also, an improved germination by NaHS under high temperature was reinforced by the above osmotic adjustment substances (osmolytes) alone, while deteriorated by the inhibitors of osmolyte biosynthesis [gabaculine (GAB), disulfiram (DSF), and sodium citrate (SC)]. These results imply that H2S could improve maize seed germination and seedling growth under high temperature by inducing antioxidant system and osmolyte biosynthesis.