Hydrogen sulfide and cell signaling: team player or referee?

Recent Advancements and Future Prospects in NBD-Based Fluorescent Chemosensors: Design Strategy, Sensing Mechanism, and Biological Applications

In recent years, the field of Supramolecular Chemistry has witnessed tremendous progress owing to the development of versatile optical sensors for the detection of harmful biological analytes. Nitrobenzoxadiazole (NBD) is one such scaffold that has been exploited as fluorescent probes for selective recognition of harmful analytes and their optical imaging in various cell lines including HeLa, PC3, A549, SMMC-7721, MDA-MB-231, HepG2, MFC-7, etc. The NBD-derived molecular probes are majorly synthesized from the chloro derivative of NBD via nucleophilic aromatic substitution. This general NBD moiety ligation method to nucleophiles has been leveraged to develop various derivatives for sensing analytes. NBD-derived probes are extensively used as optical sensors because of remarkable properties like excellent stability, large Stoke's shift, high efficiency and stability, visible excitation, easy use, low cost, and high quantum yield. This article reviewed NBD-based probes for the years 2017-2023 according to the sensing of analyte(s), including cations, anions, thiols, and small molecules like hydrogen sulfide. The sensing mechanism, designing of the probe, plausible binding mechanism, and biological application of chemosensors are summarized. The real-time application of optical sensors has been discussed by various methods, such as paper strips, molecular logic gates, smartphone detection, development of test kits, etc. This article will update the researchers with the in vivo and in vitro biological applicability of NBD-based molecular probes and challenges the research fraternity to design, propose, and develop better chemosensors in the future possessing commercial utility.

Sulfur nutrition and its role in plant growth and development

Sulfur is one of the essential nutrients that is required for the adequate growth and development of plants. Sulfur is a structural component of protein disulfide bonds, amino acids, vitamins, and cofactors. Most of the sulfur in soil is present in organic matter and hence not accessible to the plants. Anionic form of sulfur (SO42-) is the primary source of sulfur for plants that are generally present in minimal amounts in the soil. It is water-soluble, so readily leaches out of the soil. Sulfur and sulfur-containing compounds act as signaling molecules in stress management as well as normal metabolic processes. They also take part in crosstalk of complex signaling network as a mediator molecule. Plants uptake sulfate directly from the soil by using their dedicated sulfate transporters. In addition, plants also use the sulfur transporter of a symbiotically associated organism like bacteria and fungi to uptake sulfur from the soil especially under sulfur depleted conditions. So, sulfur is a very important component of plant metabolism and its analysis with different dimensions is highly required to improve the overall well-being of plants, and dependent animals as well as human beings. The deficiency of sulfur leads to stunted growth of plants and ultimately loss of yield. In this review, we have focused on sulfur nutrition, uptake, transport, and inter-organismic transfer to host plants. Given the strong potential for agricultural use of sulfur sources and their applications, we cover what is known about sulfur impact on the plant health. We identify opportunities to expand our understanding of how the application of soil microbes like AMF or other root endophytic fungi affects plant sulfur uptake and in turn plant growth and development.

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

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

Hydrogen Sulfide Enhances Browning Repression and Quality Maintenance in Fresh-Cut Peaches via Modulating Phenolic and Amino Acids Metabolisms

Effects of hydrogen sulfide (H₂S) on the browning and quality maintenance of fresh-cut peach fruit were studied. The results showed that H₂S treatment repressed the development of surface browning, suppressed the increase in respiration rate and weight loss, and delayed the decline of firmness while soluble solids content (SSC) and microbial growth were unaffected during storage. H₂S treatment maintained higher contents of phenolic compounds, especially neo-chlorogenic acid, catechin, and quercetin, and delayed the degradation of phenolic compounds by enhancing the activities of phenolic biosynthesis-related enzymes and inhibiting the oxidative activities of polyphenol oxidase (PPO) in comparison with control. Moreover, H₂S stimulated the accumulation of amino acids and their derivatives including proline, γ-aminobutyric acid (GABA), and polyamines (PAs) via enhancing biosynthesis and repressing degradation compared to control. These results suggested that H₂S treatment enhanced the accumulation of phenolic, amino acids, and their derivatives by modulating phenolic and amino acids metabolisms, which contributed to the higher antioxidant activity and membrane integrity maintenance, ultimately repressing browning development and maintaining the quality. Therefore, the current study speculated that H₂S might be a promising approach for browning inhibition and quality maintenance in fresh-cut peach fruit.

The role of nitric oxide and hydrogen sulfide in regulation of redox homeostasis at extreme temperatures in plants

Nitric oxide and hydrogen sulfide, as important signaling molecules (gasotransmitters), are involved in many functions of plant organism, including adaptation to stress factors of various natures. As redox-active molecules, NO and H₂S are involved in redox regulation of functional activity of many proteins. They are also involved in maintaining cell redox homeostasis due to their ability to interact directly and indirectly (functionally) with ROS, thiols, and other molecules. The review considers the involvement of nitric oxide and hydrogen sulfide in plant responses to low and high temperatures. Particular attention is paid to the role of gasotransmitters interaction with other signaling mediators (in particular, with Ca²⁺ ions and ROS) in the formation of adaptive responses to extreme temperatures. Pathways of stress-induced enhancement of NO and H₂S synthesis in plants are considered. Mechanisms of the NO and H₂S effect on the activity of some proteins of the signaling system, as well as on the state of antioxidant and osmoprotective systems during adaptation to stress temperatures, were analyzed. Possibilities of practical use of nitric oxide and hydrogen sulfide donors as inductors of plant adaptive responses are discussed.

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

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

Hydrogen Sulfide Treatment Alleviates Chilling Injury in Cucumber Fruit by Regulating Antioxidant Capacity, Energy Metabolism and Proline Metabolism

Although low-temperature storage could maintain the quality of fruits and vegetables, it may also result in chilling injury (CI) in cold-sensitive produce, such as cucumbers. This can seriously affect their quality.” The antioxidant capacity, energy metabolism and proline metabolism of cucumbers treated with hydrogen sulfide (H2S) were studied in this assay. The outcomes displayed that H2S treatment effectively reduced CI and delayed the increase in electrolyte leakage (EL) and malondialdehyde (MDA) content. In addition, the H2S-treated cucumber fruit exhibited higher L* and hue angle values, as well as nutrients such as ascorbic acid (AsA). The H2S-treated fruit showed lower levels of reactive oxygen species (ROS) and higher antioxidant enzyme activities. Meanwhile, H2S treatment also increased the activities of the essential enzymes involved in energy metabolism, including cytochrome C oxidase (CCO), succinate dehydrogenase (SDH), H+-ATPase and Ca2+-ATPase, which improved the energy supply. H2S induced higher ornithine δ-aminotransferase (OAT) and Δ-1-pyrroline-5-carboxylate synthetase (P5CS) activities, and reduced proline dehydrogenase (PDH) activity, promoting the accumulation of proline. These results indicated that H2S could alleviate CI in the cucumber fruit by modulating antioxidant capacity, energy metabolism and proline metabolism, thereby extending the shelf life of postharvest cucumbers.

Hydrogen sulphide: an emerging regulator of plant defence signalling

Hydrogen sulphide (H₂ S), a gaseous signalling molecule in plants, has gained considerable attention in recent years because of its emerging roles in the regulation of plant growth and development and responses to abiotic stressors. Although the involvement of H₂ S in biotic stress is not well documented in the literature, a growing body of evidence indicates its potential role in plant defence, particularly against bacterial and fungal pathogens. Recent reports have suggested that H₂ S participates in plant defence signalling potentially by (1) regulating glutathione metabolism, (2) inducing expression of pathogenesis-related (PR) and other defence-related genes, (3) modulating enzyme activity through post-translational modifications, and (4) interacting with phytohormones such as jasmonic acid, ethylene and auxin. In this review, we discuss the biosynthesis, metabolism and interaction of H₂ S with phytohormones, and highlight evidence gathered so far to support the emerging roles of H₂ S in plant defence against invading pathogens.

Hydrogen sulfide alleviates chilling injury in peach fruit by maintaining cell structure integrity via regulating endogenous H2S, antioxidant and cell wall metabolisms

Effects of hydrogen sulfide (H₂S) on chilling injury (CI), H₂S, antioxidant and cell-wall metabolisms of refrigerated peaches treated with H₂S and hypotaurine (HT, H₂S scavenger) were investigated in present study. Results revealed that H₂S treatment enhanced endogenous H₂S content, which was associated with increased related H₂S synthase enzymes activities, while HT showed the opposite results. Moreover, H₂S treatment induced the accumulation of ascorbic acid, glutathione and the enhancement of antioxidant enzymes activities compared to control and HT, contributing to lower hydrogen peroxide content and superoxide radical production. Furthermore, H₂S suppressed the increase of cell-wall degradation enzymes accompanied by higher levels of water-insoluble pectin, 24% KOH-soluble hemicellulose and cellulose, while HT accelerated these components degradation. Therefore, results indicated that H₂S mitigated CI of refrigerated peaches by regulating H₂S, antioxidant and cell-wall metabolisms, maintaining higher H₂S and antioxidants contents, suppressing cell-wall degradation, thereby contributing to redox homeostasis maintenance and cell structure integrity.

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.

Cardiovascular benefits of Eruca sativa mill. Defatted seed meal extract: Potential role of hydrogen sulfide

Eruca sativa Mill. is an edible plant belonging to the Brassicaceae botanical family with a long story as a medicinal material, mainly linked to the presence of glucoerucin. One of the main products of this glucosinolate is erucin, a biologicallly active isothiocyanate recently recognized as a hydrogen sulfide (H₂S) donor. In this work, an Eruca sativa extract has been obtained from a defatted seed meal (DSM), achieving a powder rich in thiofunctionalized glucosinolates, glucoerucin, and glucoraphanin, accounting for 95% and 5% of the total glucosinolate content (17% on a dry weight basis), associated with 13 identified phenolic acids and flavonoids accounting for 2.5%. In a cell‐free model, Eruca sativa DSM extract slowly released H₂S. Moreover, this extract promoted significant hypotensive effects in hypertensive rats, and evoked dose‐dependent cardioprotection in in vivo model of acute myocardial infarct, obtained through a reversible coronary occlusion. This latter effect was sensitive to blockers of mitochondrial KATP and Kv7.4 potassium channels, suggesting a potential role of these mitochondrial channels in the protective effects of Eruca sativa DSM extract. Accordingly, Eruca sativa DSM extract reduced calcium uptake and apoptotic cell death in isolated cardiac mitochondria. Taken together, these results demonstrate that Eruca sativa DSM extract is endowed with an interesting nutraceutical profile on the cardiovascular system due to, at least in part, its H₂S releasing properties. These results pave the way for future investigations on active metabolites.

Physiological roles of hydrogen sulfide in mammalian cells, tissues and organs

H2S belongs to the class of molecules known as gasotransmitters, which also includes nitric oxide (NO) and carbon monoxide (CO). Three enzymes are recognized as endogenous sources of H2S in various cells and tissues: cystathionine g-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). The current article reviews the regulation of these enzymes as well as the pathways of their enzymatic and non-enzymatic degradation and elimination. The multiple interactions of H2S with other labile endogenous molecules (e.g. NO) and reactive oxygen species are also outlined. The various biological targets and signaling pathways are discussed, with special reference to H2S and oxidative posttranscriptional modification of proteins, the effect of H2S on channels and intracellular second messenger pathways, the regulation of gene transcription and translation and the regulation of cellular bioenergetics and metabolism. The pharmacological and molecular tools currently available to study H2S physiology are also reviewed, including their utility and limitations. In subsequent sections, the role of H2S in the regulation of various physiological and cellular functions is reviewed. The physiological role of H2S in various cell types and organ systems are overviewed. Finally, the role of H2S in the regulation of various organ functions is discussed as well as the characteristic bell-shaped biphasic effects of H2S. In addition, key pathophysiological aspects, debated areas, and future research and translational areas are identified A wide array of significant roles of H2S in the physiological regulation of all organ functions emerges from this review.

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.

Protein S-sulfhydration: Unraveling the prospective of hydrogen sulfide in the brain, vasculature and neurological manifestations

Hydrogen sulfide (H₂S) and hydrogen polysulfides (H₂S_n) are essential regulatory signaling molecules generated by the entire body, including the central nervous system. Researchers have focused on the classical H₂S signaling from the past several decades, whereas the last decade has shown the emergence of H₂S-induced protein S-sulfhydration signaling as a potential therapeutic approach. Cysteine S-persulfidation is a critical paradigm of post-translational modification in the process of H₂S signaling. Additionally, studies have shown the cross-relationship between S-sulfhydration and other cysteine-induced post-translational modifications, namely nitrosylation and carbonylation. In the central nervous system, S-sulfhydration is involved in the cytoprotection through various signaling pathways, viz. inflammatory response, oxidative stress, endoplasmic reticulum stress, atherosclerosis, thrombosis, and angiogenesis. Further, studies have demonstrated H₂S-induced S-sulfhydration in regulating different biological processes, such as mitochondrial integrity, calcium homeostasis, blood-brain permeability, cerebral blood flow, and long-term potentiation. Thus, protein S-sulfhydration becomes a crucial regulatory molecule in cerebrovascular and neurodegenerative diseases. Herein, we first described the generation of intracellular H₂S followed by the application of H₂S in the regulation of cerebral blood flow and blood-brain permeability. Further, we described the involvement of S-sulfhydration in different biological and cellular functions, such as inflammatory response, mitochondrial integrity, calcium imbalance, and oxidative stress. Moreover, we highlighted the importance of S-sulfhydration in cerebrovascular and neurodegenerative diseases.

Sodium thiosulfate-supplemented UW solution protects renal grafts against prolonged cold ischemia-reperfusion injury in a murine model of syngeneic kidney transplantation

INTRODUCTION

Cold ischemia-reperfusion injury (IRI) is an inevitable event that increases post-transplant complications. We have previously demonstrated that supplementation of University of Wisconsin (UW) solution with non-FDA-approved hydrogen sulfide (H₂S) donor molecules minimizes cold IRI and improves renal graft function after transplantation. The present study investigates whether an FDA-approved H₂S donor molecule, sodium thiosulfate (STS), will have the same or superior effect in a clinically relevant rat model of syngeneic orthotopic kidney transplantation.

METHOD

Thirty Lewis rats underwent bilateral nephrectomy followed by syngeneic orthotopic transplantation of the left kidney after 24-hour preservation in either UW or UW+STS solution at 4 °C. Rats were monitored to post-transplant day 14 and sacrificed to assess renal function (urine output, serum creatinine and blood urea nitrogen). Kidney sections were stained with H&E, TUNEL, CD68, and myeloperoxidase (MPO) to detect acute tubular necrosis (ATN), apoptosis, macrophage infiltration, and neutrophil infiltration.

RESULT

UW+STS grafts showed significantly improved graft function immediately after transplantation, with improved recipient survival compared to UW grafts (p < 0.05). Histopathological examination revealed significantly reduced ATN, apoptosis, macrophage and neutrophil infiltration and downregulation of pro-inflammatory and pro-apoptotic genes in UW+STS grafts compared to UW grafts (p < 0.05).

CONCLUSION

We show for the first time that preservation of renal grafts in STS-supplemented UW solution protects against prolonged cold IRI by suppressing apoptotic and inflammatory pathways, and thereby improving graft function and prolonging recipient survival. This could represent a novel clinically applicable therapeutic strategy to minimize the detrimental clinical outcome of prolonged cold IRI in kidney transplantation.

Molecular Hydrogen: Is This a Viable New Treatment for Plants in the UK?

Despite being trialed in other regions of the world, the use of molecular hydrogen (H₂) for enhanced plant growth and the postharvest storage of crops has yet to be widely accepted in the UK. The evidence that the treatment of plants and plant products with H₂ alleviates plant stress and slows crop senescence continues to grow. Many of these effects appear to be mediated by the alteration of the antioxidant capacity of plant cells. Some effects seem to involve heme oxygenase, whilst the reduction in the prosthetic group Fe³⁺ is also suggested as a mechanism. Although it is difficult to use as a gaseous treatment in a field setting, the use of hydrogen-rich water (HRW) has the potential to be of significant benefit to agricultural practices. However, the use of H₂ in agriculture will only be adopted if the benefits outweigh the production and application costs. HRW is safe and relatively easy to use. If H₂ gas or HRW are utilized in other countries for agricultural purposes, it is tempting to suggest that they could also be widely used in the UK in the future, particularly for postharvest storage, thus reducing food waste.

Interplay Among Hydrogen Sulfide, Nitric Oxide, Reactive Oxygen Species, and Mitochondrial DNA Oxidative Damage

Hydrogen sulfide (H2S), nitric oxide (NO), and reactive oxygen species (ROS) play essential signaling roles in cells by oxidative post-translational modification within suitable ranges of concentration. All of them contribute to the balance of redox and are involved in the DNA damage and repair pathways. However, the damage and repair pathways of mitochondrial DNA (mtDNA) are complicated, and the interactions among NO, H2S, ROS, and mtDNA damage are also intricate. This article summarized the current knowledge about the metabolism of H2S, NO, and ROS and their roles in maintaining redox balance and regulating the repair pathway of mtDNA damage in plants. The three reactive species may likely influence each other in their generation, elimination, and signaling actions, indicating a crosstalk relationship between them. In addition, NO and H2S are reported to be involved in epigenetic variations by participating in various cell metabolisms, including (nuclear and mitochondrial) DNA damage and repair. Nevertheless, the research on the details of NO and H2S in regulating DNA damage repair of plants is in its infancy, especially in mtDNA.

Preservation of pancreas in the University of Wisconsin solution supplemented with AP39 reduces reactive oxygen species production and improves islet graft function

Ischemia-reperfusion injury (IRI) results in increased rates of delayed graft function and early graft loss. It has recently been reported that hydrogen sulfide (H₂ S) protects organ grafts against prolonged IRI. Here, we investigated whether the preservation of pancreas in University of Wisconsin (UW) solution supplemented with AP39, which is a mitochondrial-targeted H₂ S donor, protected pancreatic islets against IRI and improved islet function. Porcine pancreata were preserved in the UW solution with AP39 (UW + AP39) or the vehicle (UW) for 18 h, followed by islet isolation. The islet yields before and after purification were significantly higher in the UW + AP39 group than in the UW group. The islets isolated from the pancreas preserved in UW + AP39 exhibited significantly decreased levels of reactive oxygen species (ROS) production and a significantly increased mitochondrial membrane potential as compared to the islets isolated from the pancreas preserved in the vehicle. We found that the pancreas preserved in UW + AP39 improved the outcome of islet transplantation in streptozotocin-induced diabetic mice. These results suggest that the preservation of pancreas in UW + AP39 protects the islet grafts against IRI and could thus serve as a novel clinical strategy for improving islet transplantation outcomes.

Synthesis and Hydrogen Sulfide Releasing Properties of Diaminodisulfides and Dialkoxydisulfides

Heterosubstituted disulfides are an understudied class of molecules that have been used in biological studies, but they have not been investigated for their ability to release hydrogen sulfide (H₂S). The synthesis of two sets of chemicals with the diaminodisulfide (NSSN) and dialkoxydisulfide (OSSO) functional groups was reported. These chemicals were synthesized from commercially available sulfur monochloride or a simple disulfur transfer reagent. Both the diaminodisulfide and dialkoxydisulfide functional groups were found to have rapid rates of H₂S release in the presence of excess thiol. The release of H₂S was complete with 10 min, and the only byproducts were conversion of the thiols into disulfides and the amines or alcohols originally used in the synthesis of the diaminodisulfide or dialkoxydisulfide functional groups. These results will allow the design of H₂S releasing chemicals that also release natural, biocompatible alcohols or amines. Chemicals with the diaminodisulfide and dialkoxydisulfide functional groups may find applications in medicine where a controlled, burst release of H₂S is needed.

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.

Patterns of Expression of H2S-Producing Enzyme in Human Renal Cell Carcinoma Specimens: Potential Avenue for Future Therapeutics

BACKGROUND

Renal cell carcinoma (RCC) is the most common cancer of the kidney. The most common histotype is clear-cell (cc) RCC. Hydrogen sulfide (H₂S) is an angiogenic and anti-apoptotic gasotransmitter that is elevated under pseudohypoxic conditions. H₂S is endogenously produced by three enzymes: Cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS), and 3-mercaptopyruvate sulfurtransferase (MPST). Seeing as increased expression of these enzymes has been observed in other human cancer types, this study aimed to quantify H₂S-producing enzyme expression in human RCC samples and evaluate whether it correlated with clinical outcomes.

PATIENTS AND METHODS

Eighty-eight human kidney tissue specimens, with healthy and cancerous tissue components, were immunohistochemically stained for CSE, CBS, and MPST. The mean pixel intensity of positively stained areas was quantified. A retrospective analysis was conducted to obtain patient demographics, rates of metastasis/recurrence, and prognostic characteristics. Statistical correlations between enzyme expressions and subsequent patient outcomes were evaluated.

RESULTS

There was significantly greater expression of CSE, CBS, and MPST in cc-RCC compared to paired healthy tissue (p<0.0001). The difference in expression of CSE in cancerous versus normal tissue was significantly greater than that for CBS and MPST (p<0.0001 and p<0.01, respectively). Enzyme expression patterns in cancerous versus normal tissue did not correlate with nuclear grade, stage, histological type or cancer recurrence/metastasis.

CONCLUSION

To our knowledge, this is the first report of the differential increase in expression of CSE, CBS, and MPST in human RCC. Although these patterns do not appear to correlate with cancer recurrence, metastasis, size or nuclear grade, their differential increase suggests a potential therapeutic target.

Downstream Signalling from Molecular Hydrogen

Molecular hydrogen (H2) is now considered part of the suite of small molecules that can control cellular activity. As such, H2 has been suggested to be used in the therapy of diseases in humans and in plant science to enhance the growth and productivity of plants. Treatments of plants may involve the creation of hydrogen-rich water (HRW), which can then be applied to the foliage or roots systems of the plants. However, the molecular action of H2 remains elusive. It has been suggested that the presence of H2 may act as an antioxidant or on the antioxidant capacity of cells, perhaps through the scavenging of hydroxyl radicals. H2 may act through influencing heme oxygenase activity or through the interaction with reactive nitrogen species. However, controversy exists around all the mechanisms suggested. Here, the downstream mechanisms in which H2 may be involved are critically reviewed, with a particular emphasis on the H2 mitigation of stress responses. Hopefully, this review will provide insight that may inform future research in this area.

Nitric oxide, other reactive signalling compounds, redox, and reductive stress

Nitric oxide (NO) and other reactive nitrogen species (RNS) are key signalling molecules in plants, but they do not work in isolation. NO is produced in cells, often increased in response to stress conditions, but many other reactive compounds used in signalling are generated and accumulate spatially and temporally together. This includes the reactive oxygen species (ROS), such as hydrogen peroxide (H2O2), and hydrogen sulfide (H2S). Here, the interactions with such other reactive molecules is briefly reviewed. Furthermore, along with ROS and H2S, NO will potentially contribute to the overall intracellular redox of the cell. However, RNS will exist in redox couples and therefore the influence of the cellular redox on such couples will be explored. In discussions of the aberrations in intracellular redox it is usually oxidation, so-called oxidative stress, which is discussed. Here, we consider the notion of reductive stress and how this may influence the signalling which may be mediated by NO. By getting a more holistic view of NO biology, the influence on cell activity of NO and other RNS can be more fully understood, and may lead to the elucidation of methods for NO-based manipulation of plant physiology, leading to better stress responses and improved crops in the future.

Hydrogen sulfide: A versatile gaseous molecule in plants

Hydrogen sulfide (H₂S) is a gasotransmitter and signaling molecule associated with seed germination, plant growth, organogenesis, photosynthesis, stomatal conductance, senescence, and post-harvesting. H₂S is produced in plants via both enzymatic and non-enzymatic pathways in different subcellular compartments. Exogenous application of H₂S facilitates versatile metabolic processes and antioxidant machinery in plants under normal and environmental stresses. This compound interacts with phytohormones like auxins, abscisic acid, gibberellins, ethylene, jasmonic acid, and salicylic acid. Furthermore, H₂S participates in signal transductions of other signaling molecules like nitric oxide, carbon monoxide, calcium, methylglyoxal, and hydrogen peroxide. It also mediates post-translational modification, which is a protective mechanism against oxidative damage of proteins. This review summarizes the roles of H₂S as intriguing molecule in plants.

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 negatively regulates cd-induced cell death in cucumber (Cucumis sativus L) root tip cells

BACKGROUND

Hydrogen sulfide (H₂S) is a gas signal molecule involved in regulating plants tolerance to heavy metals stress. In this study, we investigated the role of H₂S in cadmium-(Cd-) induced cell death of root tips of cucumber seedlings.

RESULTS

The results showed that the application of 200 μM Cd caused cell death, increased the content of reactive oxygen species (ROS), chromatin condensation, the release of Cytochrome c (Cyt c) from mitochondria and activated caspase-3-like protease. Pretreatment of seedlings with 100 μM sodium hydrogen sulfide (NaHS, a H₂S donor) effectively alleviated the growth inhibition and reduced cell death of root tips caused by Cd stress. Additionally, NaHS + Cd treatment could decrease the ROS level and enhanced antioxidant enzyme activity. Pretreatment with NaHS also inhibited the release of Cyt c from the mitochondria, the opening of the mitochondrial permeability transition pore (MPTP), and the activity of caspase-3-like protease in the root tips of cucumber seedling under Cd stress.

CONCLUSION

H₂S inhibited Cd-induced cell death in cucumber root tips by reducing ROS accumulation, activating the antioxidant system, inhibiting mitochondrial Cyt c release and reducing the opening of the MPTP. The results suggest that H₂S is a negative regulator of Cd-induced cell death in the root tips of cucumber seedling.

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.

Hydrogenases and the Role of Molecular Hydrogen in Plants

Molecular hydrogen (H2) has been suggested to be a beneficial treatment for a range of species, from humans to plants. Hydrogenases catalyze the reversible oxidation of H2, and are found in many organisms, including plants. One of the cellular effects of H2 is the selective removal of reactive oxygen species (ROS) and reactive nitrogen species (RNS), specifically hydroxyl radicals and peroxynitrite. Therefore, the function of hydrogenases and the action of H2 needs to be reviewed in the context of the signalling roles of a range of redox active compounds. Enzymes can be controlled by the covalent modification of thiol groups, and although motifs targeted by nitric oxide (NO) can be predicted in hydrogenases sequences it is likely that the metal prosthetic groups are the target of inhibition. Here, a selection of hydrogenases, and the possibility of their control by molecules involved in redox signalling are investigated using a bioinformatics approach. Methods of treating plants with H2 along with the role of H2 in plants is also briefly reviewed. It is clear that studies report significant effects of H2 on plants, improving growth and stress responses, and therefore future work needs to focus on the molecular mechanisms involved.

Interplay between hydrogen sulfide and methylglyoxal initiates thermotolerance in maize seedlings by modulating reactive oxidative species and osmolyte metabolism

Hydrogen sulfide (H₂S) and methylglyoxal (MG) were supposed to be novel signaling molecules in plants. However, whether interplay between H₂S and MG can initiate thermotolerance in maize seedlings and in relation to metabolism of reactive oxygen species (ROS) and osmolytes is little known. In this study, watering with MG and NaHS (H₂S donor) alone or in combination elevated survival and tissue vigor of maize seedlings under heat stress and coped with an increase in the biomembrane injury (as indicated in membrane lipid peroxidation and electrolyte leakage). The above-mentioned effects were separately weakened by MG scavengers (N-acetyl cysteine: NAC; aminoguanidine: AG) and H₂S inhibitor (DL-propargylglycine, PAG) and scavenger (hypotaurine, HT). These suggested that the interplay between H₂S and MG initiated the thermotolerance in maize seedlings. The further data indicated that, under non-heat stress and heat stress conditions, MG and NaHS alone or in combination modulated ROS metabolism by regulating the activities of antioxidant enzymes (catalase, ascorbate peroxidase, guaiacol peroxidase, glutathione reductase, monodehydroascorbate reductase, and dehydroascorbate reductase) and the contents of non-enzymatic antioxidants (ascorbic acid, glutathione, flavonoids, and carotenoids) in maize seedlings. In addition, MG and NaHS alone or in combination also separately modulated the metabolism of osmolytes (proline, trehalose, glycine betaine, and total soluble sugar), H₂S (L-cysteine desulfhydrase and O-acetylserine (thione) lyase), and MG (glyoxalase I, glyoxalase II, and MG reductase). These physiological effects also were separately impaired by NAC, AG, PAG, and HT. The current data illustrated that the interplay between H₂S and MG initiated the thermotolerance in maize seedlings by modulating ROS, osmolyte, H₂S, and MG metabolism.

Dietary methionine restriction attenuates renal ischaemia/reperfusion-induced myocardial injury by activating the CSE/H2S/ERS pathway in diabetic mice

Methionine restrictive diet may alleviate ischaemia/reperfusion (I/R)‐induced myocardial injury, but its underlying mechanism remains unclear. HE staining was performed to evaluate the myocardial injury caused by I/R and the effect of methionine‐restricted diet (MRD) in I/R mice. IHC and Western blot were carried out to analyse the expression of CSE, CHOP and active caspase3 in I/R mice and hypoxia/reoxygenation (H/R) cells. TUNEL assay and flow cytometry were used to assess the apoptotic status of I/R mice and H/R cells. MTT was performed to analyse the proliferation of H/R cells. H2S assay was used to evaluate the concentration of H2S in the myocardial tissues and peripheral blood of I/R mice. I/R‐induced mediated myocardial injury and apoptosis were partially reversed by methionine‐restricted diet (MRD) via the down‐regulation of CSE expression and up‐regulation of CHOP and active caspase3 expression. The decreased H2S concentration in myocardial tissues and peripheral blood of I/R mice was increased by MRD. Accordingly, in a cellular model of I/R injury established with H9C2 cells, cell proliferation was inhibited, cell apoptosis was increased, and the expressions of CSE, CHOP and active caspase3 were dysregulated, whereas NaHS treatment alleviated the effect of I/R injury in H9C2 cells in a dose‐dependent manner. This study provided a deep insight into the mechanism underlying the role of MRD in I/R‐induced myocardial injury.

SQR mediates therapeutic effects of H2S by targeting mitochondrial electron transport to induce mitochondrial uncoupling

Hydrogen sulfide (H₂S) is a gasotransmitter and a potential therapeutic agent. However, molecular targets relevant to its therapeutic actions remain enigmatic. Sulfide-quinone oxidoreductase (SQR) irreversibly oxidizes H₂S. Therefore, SQR is assumed to inhibit H₂S signaling. We now report that SQR-mediated oxidation of H₂S drives reverse electron transport (RET) at mitochondrial complex I, which, in turn, repurposes mitochondrial function to superoxide production. Unexpectedly, complex I RET, a process dependent on high mitochondrial membrane potential, induces superoxide-dependent mitochondrial uncoupling and downstream activation of adenosine monophosphate-activated protein kinase (AMPK). SQR-induced mitochondrial uncoupling is separated from the inhibition of mitochondrial complex IV by H₂S. Moreover, deletion of SQR, complex I, or AMPK abolishes therapeutic effects of H₂S following intracerebral hemorrhage. To conclude, SQR mediates H₂S signaling and therapeutic effects by targeting mitochondrial electron transport to induce mitochondrial uncoupling. Moreover, SQR is a previously unrecognized target for developing non-protonophore uncouplers with broad clinical implications.

Highly efficient H2S scavengers via thiolysis of positively-charged NBD amines

H2S is a well-known toxic gas and also a gaseous signaling molecule involved in many biological processes. Advanced chemical tools that can regulate H2S levels in vivo are useful for understanding H2S biology as well as its potential therapeutic effects. To this end, we have developed a series of 7-nitro-1,2,3-benzoxadiazole (NBD) amines as potential H2S scavengers. The kinetic studies of thiolysis reactions revealed that incorporation of positively-charged groups onto the NBD amines greatly increased the rate of the H2S-specific thiolysis reaction. We demonstrate that these reactions proceed effectively, with second order rate constants (k 2) of >116 M-1 s-1 at 37 °C for NBD-S8. Additionally, we demonstrate that NBD-S8 can effectively scavenge enzymatically-produced and endogenous H2S in live cells. Furthering the biological significance, we demonstrate NBD-S8 mediates scavenging of H2S in mice.

Hydrogen Sulfide and Endoplasmic Reticulum Stress: A Potential Therapeutic Target for Central Nervous System Degeneration Diseases

There are three members of the endogenous gas transmitter family. The first two are nitric oxide and carbon monoxide, and the third newly added member is hydrogen sulfide (H₂S). They all have similar functions: relaxing blood vessels, smoothing muscles, and getting involved in the regulation of neuronal excitation, learning, and memory. The cystathionine β-synthase (CBS), 3-mercaptopyruvate sulfur transferase acts together with cysteine aminotransferase (3-MST/CAT), cystathionine γ-lyase (CSE), and 3-mercaptopyruvate sulfur transferase with D-amino acid oxidase (3-MST/DAO) pathways are involved in the enzymatic production of H₂S. More and more researches focus on the role of H₂S in the central nervous system (CNS), and H₂S plays a significant function in neuroprotection processes, regulating the function of the nervous system as a signaling molecule in the CNS. Endoplasmic reticulum stress (ERS) and protein misfolding in its mechanism are related to neurodegenerative diseases. H₂S exhibits a wide variety of cytoprotective and physiological functions in the CNS degenerative diseases by regulating ERS. This review summarized on the neuroprotective effect of H₂S for ERS played in several CNS diseases including Alzheimer’s disease, Parkinson’s disease, and depression disorder, and discussed the corresponding possible signaling pathways or mechanisms as well.

Hydrogen sulfide (H2S) and nitric oxide (NO) alleviate cobalt toxicity in wheat (Triticum aestivum L.) by modulating photosynthesis, chloroplastic redox and antioxidant capacity

The role of hydrogen sulfide (H₂S)/nitric oxide (NO) in mitigating stress-induced damages has gained interest in the past few years. However, the protective mechanism H₂S and/or NO has towards the chloroplast system through the regulation of redox status and activation of antioxidant capacity in cobalt-treated wheat remain largely unanswered. Triticum aestivum L. cv. Ekiz was treated with alone/in combination of a H₂S donor (sodium hydrosulfide (NaHS,600μM)), a NO donor (sodium nitroprusside (SNP,100μM)) and a NO scavenger (rutin hydrate (RTN,50μM)) to assess how the donors affect growth, water relations, redox and antioxidant capacity in chloroplasts, under cobalt (Co) concentrations of 150-300 μM. Stress decreased a number of parameters (growth, water content (RWC), osmotic potential (Ψ_Π), carbon assimilation rate, stomatal conductance, intercellular CO₂ concentrations, transpiration rate and the transcript levels of rubisco, which subsequently disrupt the photosynthetic capacity). However, SNP/NaHS counteracted the negative effects of stress on these aforementioned parameters and RTN application with stress/non-stress was reversed these effects. Hydrogen peroxide (H₂O₂) and TBARS were induced under stress in spite of activated ascorbate peroxidase (APX). SNP/NaHS under stress increased activation of superoxide dismutase (SOD), peroxidase (POX), APX, glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), ascorbate (tAsA) and glutathione (GSH). In conclusion, NaHS/SNP are involved in the regulation and modification of growth, water content, rubisco activity and up-regulation of ascorbate-glutathione cycle (AsA-GSH) in chloroplast under stress.

Therapeutic importance of hydrogen sulfide in age-associated neurodegenerative diseases

Hydrogen sulfide (H2S) is a gasotransmitter that acts as an antioxidant and exhibits a wide variety of cytoprotective and physiological functions in age-associated diseases. One of the major causes of age-related diseases is oxidative stress. In recent years, the importance of H2S has become clear, although its antioxidant function has not yet been fully explored. The enzymes cystathionine β-synthase, cystathionine γ-lya-se, and 3-mercaptopyruvate sulfurtransferase are involved in the enzymatic production of H2S. Previously, H2S was considered a neuromodulator, given its role in long-term hippocampal potentiation, but it is now also recognized as an antioxidant in age-related neurodegeneration. Due to aerobic metabolism, the central nervous system is vulnerable to oxidative stress in brain aging, resulting in age-associated degenerative diseases. H2S exerts its antioxidant effect by limiting free radical reactions through the activation of antioxidant enzymes, including superoxide dismutase, catalase, and glutathione peroxidase, which protect against the effects of aging by regulating apoptosis-related genes, including p53, Bax, and Bcl-2. This review explores the implications and mechanisms of H2S as an antioxidant in age-associated neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease, and Down syndrome.

Methods for the Addition of Redox Compounds

Often in redox biology experiments there is a need to add compounds which impinge on the redox of the cellular environment cell. Such compounds may include reactive oxygen species (ROS), such as hydrogen peroxide (H₂O₂), reactive nitrogen species such as nitric oxide (NO), hydrogen sulfide (H₂S), or even hydrogen gas (H₂). It is not always easy or obvious how such compounds should be used. Gases may be supplied and used in the gaseous form, but this is often not convenient. Alternative methods may involve donor molecules that release into solution the relevant compound, but the actual compound released needs to be considered, along with the kinetics of that release and the by-products that might be remain. Therefore, the method of delivery of redox active compounds needs to have careful consideration before more complex experiments are undertaken. This chapter covers some of the more common methods employed and discusses some of the pros and cons of such methods.

Reactive Sulfur Species Interact with Other Signal Molecules in Root Nodule Symbiosis in Lotus japonicus

Reactive sulfur species (RSS) function as strong antioxidants and are involved in various biological responses in animals and bacteria. Few studies; however, have examined RSS in plants. In the present study, we clarified that RSS are involved in root nodule symbiosis in the model legume Lotus japonicus. Polysulfides, a type of RSS, were detected in the roots by using a sulfane sulfur-specific fluorescent probe, SSP4. Supplying the sulfane sulfur donor Na₂S₃ to the roots increased the amounts of both polysulfides and hydrogen sulfide (H₂S) in the roots and simultaneously decreased the amounts of nitric oxide (NO) and reactive oxygen species (ROS). RSS were also detected in infection threads in the root hairs and in infected cells of nodules. Supplying the sulfane sulfur donor significantly increased the numbers of infection threads and nodules. When nodules were immersed in the sulfane sulfur donor, their nitrogenase activity was significantly reduced, without significant changes in the amounts of NO, ROS, and H₂S. These results suggest that polysulfides interact with signal molecules such as NO, ROS, and H₂S in root nodule symbiosis in L. japonicus. SSP4 and Na₂S₃ are useful tools for study of RSS in plants.

Stress responsive gene regulation in relation to hydrogen sulfide in plants under abiotic stress

Plants often face a variety of abiotic stresses, which affects them negatively and lead to yield loss. The antioxidant system efficiently removes excessive reactive oxygen species and maintains redox homeostasis in plants. With better understanding of these protective mechanisms, recently the concept of hydrogen sulfide (H₂ S) and its role in cell signaling has become the center of attention. H₂ S has been recognized as a third gasotransmitter and a potent regulator of growth and development processes such as germination, maturation, senescence and defense mechanism in plants. Because of its gaseous nature, H₂ S can diffuse to different part of the cells and balance the antioxidant pools by supplying sulfur to cells. H₂ S showed tolerance against a plethora of adverse environmental conditions like drought, salt, high temperature, cold, heavy metals and flood via changing in level of osmolytes, malonaldialdehyde, Na⁺ /K⁺ uptake, activities of H₂ S biosynthesis and antioxidative enzymes. It also promotes cross adaptation through persulfidation. H₂ S along with calcium, methylglyoxal and nitric oxide, and their cross talk induces the expression of mitogen activated protein kinases as well as other genes in response to stress. Therefore, it is sensible to evaluate and explore the stress responsive genes involved in H₂ S regulated homeostasis and stress tolerance. The current article is aimed to summarize the recent updates on H₂ S-mediated gene regulation in special reference to abiotic stress tolerance mechanism, and cross adaptation in plants. Moreover, new insights into the H₂ S-associated signal transduction pathway have also been explored.

Integrative roles of nitric oxide and hydrogen sulfide in melatonin-induced tolerance of pepper (Capsicum annuum L.) plants to iron deficiency and salt stress alone or in combination

There seems to be no report in the literature on the effect of melatonin (MT) in relieving the detrimental effects of combined application of salt stress (SS) and iron deficiency (ID). Therefore, the effect of MT on the accumulation/synthesis of endogenous nitric oxide (NO) and hydrogen sulphide (H₂ S) and how far these molecules are involved in MT-improved tolerance to the combined application of ID and SS in pepper (Capsicum annuum L) were tested. Hence, two individual trials were set up. The treatments in the first experiment comprised: Control, ID (0.1 mM FeSO₄ ), SS (100 mM NaCl) and ID + SS. The detrimental effects of combined stresses were more prominent than those by either of the single stress, with respect to growth, oxidative stress and antioxidant defense attributes. Single stress or both in combination improved the endogenous H₂ S and NO, and foliar-applied MT (100 µM) led to a further increase in NO and H₂ S levels. In the second experiment, 0.1 mM scavenger of NO, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt (cPTIO) and that of H₂ S, hypotuarine (HT) were applied along with MT to get further evidence whether NO and H₂ S are involved in MT-induced tolerance to ID and SS. MT combined with cPTIO and HT under a single or combined stress showed that NO effect was reversed by the NO scavenger, cPTIO, alone but the H₂ S effect was inhibited by both scavengers. These findings suggested that tolerance to ID and SS induced by MT may be involved in downstream signal crosstalk between NO and H₂ S.

Regulation of physiological aspects in plants by hydrogen sulfide and nitric oxide under challenging environment

Plants are exposed to a plethora of abiotic stresses such as drought, salinity, heavy metal and temperature stresses at different stages of their life cycle, from germination to seedling till the reproductive phase. As protective mechanisms, plants release signaling molecules that initiate a cascade of stress-signaling events, leading either to programmed cell death or plant acclimation. Hydrogen sulfide (H₂ S) and nitric oxide (NO) are considered as new 'gasotransmitter' molecules that play key roles in regulating gene expression, posttranslational modification (PTM), as well as cross-talk with other hormones. Although the exact role of NO in plants remains unclear and is species dependent, various studies have suggested a positive correlation between NO accumulation and environmental stress in plants. These molecules are also involved in a large array of stress responses and act synergistically or antagonistically as signaling components, depending on their respective concentration. This study provides a comprehensive update on the signaling interplay between H₂ S and NO in the regulation of various physiological processes under multiple abiotic stresses, modes of action and effects of exogenous application of these two molecules under drought, salt, heat and heavy metal stresses. However, the complete picture of the signaling cascades mediated by H₂ S and NO is still elusive. Recent researches indicate that during certain plant processes, such as stomatal closure, H₂ S could act upstream of NO signaling or downstream of NO in response to abiotic stresses by improving antioxidant activity in most plant species. In addition, PTMs of antioxidative pathways by these two molecules are also discussed.

A Fast-Response Red Shifted Fluorescent Probe for Detection of H2S in Living Cells

Near-infrared (NIR) fluorescent probes are attractive tools for bioimaging applications because of their low auto-fluorescence interference, minimal damage to living samples, and deep tissue penetration. H2S is a gaseous signaling molecule that is involved in redox homeostasis and numerous biological processes in vivo. To this end, we have developed a new red shifted fluorescent probe 1 to detect physiological H2S in live cells. The probe 1 is based on a rhodamine derivative as the red shifted fluorophore and the thiolysis of 7-nitro 1,2,3-benzoxadiazole (NBD) amine as the H2S receptor. The probe 1 displays fast fluorescent enhancement at 660 nm (about 10-fold turn-ons, k2 = 29.8 M-1s-1) after reacting with H2S in buffer (pH 7.4), and the fluorescence quantum yield of the activated red shifted product can reach 0.29. The probe 1 also exhibits high selectivity and sensitivity towards H2S. Moreover, 1 is cell-membrane-permeable and mitochondria-targeting, and can be used for imaging of endogenous H2S in living cells. We believe that this red shifted fluorescent probe can be a useful tool for studies of H2S biology.

Construction of ratiometric hydrogen sulfide probe with two reaction sites and its applications in solution and in live cells

Hydrogen sulfide (H₂S), as the third multifunctional signaling biomolecule, it acts as a neuromodulator in the human brain and is recognized as an important gas transmitter in human physiology. The abnormal concentrations of H₂S in human cells can result in several common diseases. Therefore, accurate, fast, and reliable methodologies are required for measuring the in vitro and in vivo concentrations of H₂S to further investigate its function. In this study, a novel DR-SO₂N₃ fluorescent probe containing the fluorophore Disperse Red 277 and a sulfonyl azide group was developed and exploited based on the structural characteristic of Disperse Red 277 that contains the active site easily can be attacked by HS^-. Therefore, this probe featured two reaction sites that involved the reduction and Michael addition of H₂S and exhibited rapid ratiometric fluorescence changes and high selectivity towards H₂S with a 619-fold enhancement factor. Further, the density functional theory (DFT)/time-dependent density functional theory (TDDFT) studies are conducted to understand the photophysical properties of DR-SO₂N₃ and the final product DRHS-SO₂NH₂, which makes the proposed mechanism more reasonable. Furthermore, the probe was successfully applied for the ratiometric fluorescence imaging of exogenous H₂S in living cells.

Research Progress on the Functions of Gasotransmitters in Plant Responses to Abiotic Stresses

Abiotic stress is one of the major threats affecting plant growth and production. The harm of abiotic stresses includes the disruption of cellular redox homeostasis, reactive oxygen species (ROS) production, and oxidative stress in the plant. Plants have different mechanisms to fight stress, and these mechanisms are responsible for maintaining the required homeostasis in plants. Recently, the study of gasotransmitters in plants has attracted much attention, especially for abiotic stress. In the present review, abiotic stressors were mostly found to induce gasotransmitter production in plants. Meanwhile, these gasotransmitters can enhance the activity of several antioxidant enzymes, alleviate the harmfulness of ROS, and enhance plant tolerance under various stress conditions. In addition, we introduced the interaction of gasotransmitters in plants under abiotic stress. With their promising applications in agriculture, gasotransmitters will be adopted in the near future.

The Effect of Hydrogen Sulfide on Different Parameters of Human Plasma in the Presence or Absence of Exogenous Reactive Oxygen Species

The main aim of the study is to examine the effect of sodium hydrosulfide (NaHS), an H₂S donor, on the oxidative stress in human plasma in vitro. It also examined the effects of very high concentrations of exogenous hydrogen sulfide on the hemostatic parameters (coagulation and fibrinolytic activity) of human plasma. Plasma was incubated for 5-30 min with different concentrations of NaHS from 0.01 to 10 mM. Following this, lipid peroxidation was measured as a thiobarbituric acid reactive substance (TBARS) concentration and the oxidation of amino acid residues in proteins was measured by determining the amounts of thiol groups and carbonyl groups. Hydrogen peroxide (H₂O₂) and the hydroxyl radical generating oxidation system (Fe/H₂O₂) were used as oxidative stress inducers. Hemostatic factors, such as the maximum velocity of clot formation, fibrin lysis half-time, the activated partial thromboplastin time (APTT), thrombin time (TT), and international normalized ratio (INR), were estimated. Changes in lipid peroxidation, carbonyl group formation, and thiol group oxidation were detected at high concentrations of H₂S (0.1-10 mM), and these results indicate that NaHS (as the precursor of H₂S) may have pro-oxidative effects in human plasma in vitro. Moreover, considering the data presented in this study, we suggest that the oxidative stress stimulated by NaHS (at high concentrations: 1-10 mM) is not involved in changes of the hemostatic activity of plasma.

Hydrogen Sulfide: Emerging Role in Bladder, Kidney, and Prostate Malignancies

Hydrogen sulfide (H₂S) is the latest member of the gasotransmitter family and known to play essential roles in cancer pathophysiology. H₂S is produced endogenously and can be administered exogenously. Recent studies showed that H₂S in cancers has both pro- and antitumor roles. Understanding the difference in the expression and localization of tissue-specific H₂S-producing enzymes in healthy and cancer tissues allows us to develop tools for cancer diagnosis and treatment. Urological malignancies are some of the most common cancers in both men and women, and their early detection is vital since advanced cancers are recurrent, metastatic, and often resistant to treatment. This review summarizes the roles of H₂S in cancer and looks at current studies investigating H₂S activity and expression of H₂S-producing enzymes in urinary cancers. We specifically focused on urothelial carcinoma, renal cell carcinoma, and prostate cancer, as they form the majority of newly diagnosed urinary cancers. Recent studies show that besides the physiological activity of H₂S in cancer cells, there are patterns between the development and prognosis of urinary cancers and the expression of H₂S-producing enzymes and indirectly the H₂S levels. Though controversial and not completely understood, studying the expression of H₂S-producing enzymes in cancer tissue may represent an avenue for novel diagnostic and therapeutic strategies for addressing urological malignancies.