Gasotransmitter H2S accelerates seed germination via activating AOX mediated cyanide-resistant respiration pathway

An overview of analytical methods for detecting endogenous hydrogen sulfide (H2S) in plants

The significance of hydrogen sulfide (H2S) as a crucial gasotransmitter has been shown extensively in plants, and endogenous H2S is often modulated to activate H2S signaling when plants respond to numerous developmental and environmental cues. Consequently, elucidating the H2S physiological concentrations and the H2S generation intensity of plants is key to understanding the activation mechanism of H2S signaling, which has attracted increasing attention. Currently, a variety of reaction-based methods have been reported for monitoring H2S concentration in vivo and in vitro. In this review, we summarize and describe in detail several methods for quantifying and bioimaging endogenous H2S in plants systems, mainly the spectrophotometer-dependent methylene blue (MB) method and fluorescence probes, including the reaction mechanisms, design strategies, response principles, and application details. Moreover, we also summarize the advantages and disadvantages of these methods as well as the research scenarios in which they are applicable. We expect that this review will provide some guidelines on the selection of methods for H2S sensing and the comprehensive investigations into H2S signaling in plants.

Revealing how plants utilize H2S to relay drought stress signals

Hydrogen sulfide (H2S) has been proposed to regulate plant-environment interactions. Here, we compare its distinct pathways in plants with those in animals, summarizing recently uncovered mechanisms that govern plant H2S production in subcellular compartments. We underscore the importance of H2S and its role in drought stress and guard cell (GC) signaling.

Hydrogen sulfide maintains mitochondrial homeostasis and regulates ganoderic acids biosynthesis by SQR under heat stress in Ganoderma lucidum

Hydrogen sulfide (H2S) has recently been recognized as an important gaseous transmitter with multiple physiological effects in various species. Previous studies have shown that H2S alleviated heat-induced ganoderic acids (GAs) biosynthesis, an important quality index of Ganoderma lucidum. However, a comprehensive understanding of the physiological effects and molecular mechanisms of H2S in G. lucidum remains unexplored. In this study, we found that heat treatment reduced the mitochondrial membrane potential (MMP) and mitochondrial DNA copy number (mtDNAcn) in G. lucidum. Increasing the intracellular H2S concentration through pharmacological and genetic means increased the MMP level, mtDNAcn, oxygen consumption rate level and ATP content under heat treatment, suggesting a role for H2S in mitigating heat-caused mitochondrial damage in G. lucidum. Further results indicated that H2S activates sulfide-quinone oxidoreductase (SQR) and complex III (Com III), thereby maintaining mitochondrial homeostasis under heat stress in G. lucidum. Moreover, SQR also mediated the negative regulation of H2S to GAs biosynthesis under heat stress. Furthermore, SQR might be persulfidated under heat stress in G. lucidum. Thus, our study reveals a novel physiological function and molecular mechanism of H2S signalling under heat stress in G. lucidum with broad implications for research on the environmental response of microorganisms.

Persulfidome of Sweet Pepper Fruits during Ripening: The Case Study of Leucine Aminopeptidase That Is Positively Modulated by H2S

Protein persulfidation is a thiol-based oxidative posttranslational modification (oxiPTM) that involves the modification of susceptible cysteine thiol groups present in peptides and proteins through hydrogen sulfide (H2S), thus affecting their function. Using sweet pepper (Capsicum annuum L.) fruits as a model material at different stages of ripening (immature green and ripe red), endogenous persulfidated proteins (persulfidome) were labeled using the dimedone switch method and identified using liquid chromatography and mass spectrometry analysis (LC-MS/MS). A total of 891 persulfidated proteins were found in pepper fruits, either immature green or ripe red. Among these, 370 proteins were exclusively present in green pepper, 237 proteins were exclusively present in red pepper, and 284 proteins were shared between both stages of ripening. A comparative analysis of the pepper persulfidome with that described in Arabidopsis leaves allowed the identification of 25% of common proteins. Among these proteins, glutathione reductase (GR) and leucine aminopeptidase (LAP) were selected to evaluate the effect of persulfidation using an in vitro approach. GR activity was unaffected, whereas LAP activity increased by 3-fold after persulfidation. Furthermore, this effect was reverted through treatment with dithiothreitol (DTT). To our knowledge, this is the first persulfidome described in fruits, which opens new avenues to study H2S metabolism. Additionally, the results obtained lead us to hypothesize that LAP could be involved in glutathione (GSH) recycling in pepper fruits.

Gene expression and metabolite levels converge in the thermogenic spadix of skunk cabbage

The inflorescence (spadix) of skunk cabbage (Symplocarpus renifolius) is strongly thermogenic and can regulate its temperature at around 23 °C even when the ambient temperature drops below freezing. To elucidate the mechanisms underlying developmentally controlled thermogenesis and thermoregulation in skunk cabbage, we conducted a comprehensive transcriptome and metabolome analysis across 3 developmental stages of spadix development. Our RNA-seq analysis revealed distinct groups of expressed genes, with selenium-binding protein 1/methanethiol oxidase (SBP1/MTO) exhibiting the highest levels in thermogenic florets. Notably, the expression of alternative oxidase (AOX) was consistently high from the prethermogenic stage through the thermogenic stage in the florets. Metabolome analysis showed that alterations in nucleotide levels correspond with the developmentally controlled and tissue-specific thermogenesis of skunk cabbage, evident by a substantial increase in AMP levels in thermogenic florets. Our study also reveals that hydrogen sulfide, a product of SBP1/MTO, inhibits cytochrome c oxidase (COX)-mediated mitochondrial respiration, while AOX-mediated respiration remains relatively unaffected. Specifically, at lower temperatures, the inhibitory effect of hydrogen sulfide on COX-mediated respiration increases, promoting a shift toward the dominance of AOX-mediated respiration. Finally, despite the differential regulation of genes and metabolites throughout spadix development, we observed a convergence of gene expression and metabolite accumulation patterns during thermogenesis. This synchrony may play a key role in developmentally regulated thermogenesis. Moreover, such convergence during the thermogenic stage in the spadix may provide a solid molecular basis for thermoregulation in skunk cabbage.

Hydrogen sulfide-mitigated salinity stress impact in sunflower seedlings was associated with improved photosynthesis performance and osmoregulation

BACKGROUND

Salinity is one major abiotic stress affecting photosynthesis, plant growth, and development, resulting in low-input crops. Although photosynthesis underlies the substantial productivity and biomass storage of crop yield, the response of the sunflower photosynthetic machinery to salinity imposition and how H2S mitigates the salinity-induced photosynthetic injury remains largely unclear. Seed priming with 0.5 mM NaHS, as a donor of H2S, was adopted to analyze this issue under NaCl stress. Primed and nonprime seeds were established in nonsaline soil irrigated with tape water for 14 d, and then the seedlings were exposed to 150 mM NaCl for 7 d under controlled growth conditions.

RESULTS

Salinity stress significantly harmed plant growth, photosynthetic parameters, the structural integrity of chloroplasts, and mesophyll cells. H2S priming improved the growth parameters, relative water content, stomatal density and aperture, photosynthetic pigments, photochemical efficiency of PSII, photosynthetic performance, soluble sugar as well as soluble protein contents while reducing proline and ABA under salinity. H2S also boosted the transcriptional level of ribulose 1,5-bisphosphate carboxylase small subunit gene (HaRBCS). Further, the transmission electron microscope showed that under H2S priming and salinity stress, mesophyll cells maintained their cell membrane integrity and integrated chloroplasts with well-developed thylakoid membranes.

CONCLUSION

The results underscore the importance of H2S priming in maintaining photochemical efficiency, Rubisco activity, and preserving the chloroplast structure which participates in salinity stress adaptation, and possibly sunflower productivity under salinity imposition. This underpins retaining and minimizing the injury to the photosynthetic machinery to be a crucial trait in response of sunflower to salinity stress.

The role of exogenous hydrogen sulfide in mitigating cadmium toxicity in plants: A comprehensive meta-analysis

Reducing the accumulation of cadmium (Cd) and mitigating its toxicity are pivotal strategies for addressing Cd pollution's threats to agriculture and human health. Hydrogen sulfide (H2S) serves as a signaling molecule, playing a crucial role in plant stress defense mechanisms. Nevertheless, a comprehensive assessment of the impact of exogenous H2S on plant growth, antioxidant properties, and gene expression under Cd stress remains lacking. In this meta-analysis, we synthesized 575 observations from 27 articles, revealing that exogenous H2S significantly alleviates Cd-induced growth inhibition in plants. Specifically, it enhances root length (by 8.71%), plant height (by 15.67%), fresh weight (by 15.15%), dry weight (by 22.54%), and chlorophyll content (by 27.99%) under Cd stress conditions. H2S boosts antioxidant enzyme activity, particularly catalase (CAT), by 39.51%, thereby reducing Cd-induced reactive oxygen species (ROS) accumulation. Moreover, it impedes Cd translocation from roots to shoots, resulting in a substantial 40.19% reduction in stem Cd content. Additionally, H2S influences gene expression in pathways associated with antioxidant enzymes, metal transport, heavy metal tolerance, H2S biosynthesis, and energy metabolism. However, the efficacy of exogenous H2S in alleviating Cd toxicity varies depending on factors such as plant species, concentration of the H2S donor sodium hydrosulfide (NaHS), application method, and cultivation techniques. Notably, NaHS concentrations exceeding 200 μM may adversely affect plants. Overall, our study underscores the role of exogenous H2S in mitigating Cd toxicity and elucidates its mechanism, providing insights for utilizing H2S to combat Cd pollution in agriculture.

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

BACKGROUND

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

RESULTS

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

CONCLUSIONS

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

Germination of Pisum sativum L. Seeds Is Associated with the Alternative Respiratory Pathway

The alternative oxidase (AOX) is a ubiquinol oxidase with a crucial role in the mitochondrial alternative respiratory pathway, which is associated with various processes in plants. In this study, the activity of AOX in pea seed germination was determined in two pea cultivars, 'Maravilha d'América' (MA) and 'Torta de Quebrar' (TQ), during a germination trial using cytochrome oxidase (COX) and AOX inhibitors [rotenone (RT) and salicylic hydroxamic acid (SHAM), respectively]. Calorespirometry was used to assess respiratory changes during germination. In both cultivars, SHAM had a greater inhibitory effect on germination than RT, demonstrating the involvement of AOX in germination. Although calorespirometry did not provide direct information on the involvement of the alternative pathway in seed germination, this methodology was valuable for distinguishing cultivars. To gain deeper insights into the role of AOX in seed germination, the AOX gene family was characterized, and the gene expression pattern was evaluated. Three PsAOX members were identified-PsAOX1, PsAOX2a and PsAOX2b-and their expression revealed a marked genotype effect. This study emphasizes the importance of AOX in seed germination, contributing to the understanding of the role of the alternative respiratory pathway in plants.

Transcription factor TERF1 promotes seed germination through HEXOKINASE 1 (HXK1)-mediated signaling pathway

Seed germination, a vital process for plant growth and development, is regulated by ethylene. Previously, we showed that Tomato Ethylene Responsive Factor 1 (TERF1), an ethylene-responsive factor (ERF) transcription factor, could significantly promote seed germination by increasing glucose content. As glucose can function as a signaling molecule to regulate plant growth and development through HEXOKINASE 1 (HXK1), we aim to illustrate how TERF1 promotes seed germination through the HXK1-mediated signaling pathway. We showed that seeds overexpressing TERF1 exhibited more resistance to N-acetylglucosamine (NAG), an inhibitor of the HXK1- mediated signaling pathway. We identified genes regulated by TERF1 through HXK1 based on transcriptome analysis. Gene expression and phenotype analysis demonstrated that TERF1 repressed the ABA signaling pathway through HXK1, which promoted germination through activating the plasma membrane (PM) H+-ATPase. TERF1 also alleviated the endoplasmic reticulum (ER) stress to accelerate germination by maintaining reactive oxygen species (ROS) homeostasis through HXK1. Our findings provide new insights into the mechanism regulated by ethylene through the glucose-HXK1 signaling pathway during seed germination.

Regulation of Mitochondrial Respiration by Hydrogen Sulfide

Hydrogen sulfide (H2S), the third gasotransmitter, has positive roles in animals and plants. Mitochondria are the source and the target of H2S and the regulatory hub in metabolism, stress, and disease. Mitochondrial bioenergetics is a vital process that produces ATP and provides energy to support the physiological and biochemical processes. H2S regulates mitochondrial bioenergetic functions and mitochondrial oxidative phosphorylation. The article summarizes the recent knowledge of the chemical and biological characteristics, the mitochondrial biosynthesis of H2S, and the regulatory effects of H2S on the tricarboxylic acid cycle and the mitochondrial respiratory chain complexes. The roles of H2S on the tricarboxylic acid cycle and mitochondrial respiratory complexes in mammals have been widely studied. The biological function of H2S is now a hot topic in plants. Mitochondria are also vital organelles regulating plant processes. The regulation of H2S in plant mitochondrial functions is gaining more and more attention. This paper mainly summarizes the current knowledge on the regulatory effects of H2S on the tricarboxylic acid cycle (TCA) and the mitochondrial respiratory chain. A study of the roles of H2S in mitochondrial respiration in plants to elucidate the botanical function of H2S in plants would be highly desirable.

Transcriptomic analysis reveals the functions of H2S as a gasotransmitter independently of Cys in Arabidopsis

Numerous studies have revealed the gasotransmitter functions of hydrogen sulfide (H₂S) in various biological processes. However, the involvement of H₂S in sulfur metabolism and/or Cys synthesis makes its role as a signaling molecule ambiguous. The generation of endogenous H₂S in plants is closely related to the metabolism of Cys, which play roles in a variety of signaling pathway occurring in various cellular processes. Here, we found that exogenous H₂S fumigation and Cys treatment modulated the production rate and content of endogenous H₂S and Cys to various degrees. Furthermore, we provided comprehensive transcriptomic analysis to support the gasotransmitter role of H₂S besides as a substrate for Cys synthesis. Comparison of the differentially expressed genes (DEGs) between H₂S and Cys treated seedlings indicated that H₂S fumigation and Cys treatment caused different influences on gene profiles during seedlings development. A total of 261 genes were identified to respond to H₂S fumigation, among which 72 genes were co-regulated by Cys treatment. GO and KEGG enrichment analysis of the 189 genes, H₂S but not Cys regulated DEGs, indicated that these genes mainly involved in plant hormone signal transduction, plant-pathogen interaction, phenylpropanoid biosynthesis, and MAPK signaling pathway. Most of these genes encoded proteins having DNA binding and transcription factor activities that play roles in a variety of plant developmental and environmental responses. Many stress-responsive genes and some Ca²⁺ signal associated genes were also included. Consequently, H₂S regulated gene expression through its role as a gasotransmitter, rather than just as a substrate for Cys biogenesis, and these 189 genes were far more likely to function in H₂S signal transduction independently of Cys. Our data will provide insights for revealing and enriching H₂S signaling networks.

Hydrogen sulfide upregulates the alternative respiratory pathway in mangrove plant Avicennia marina to attenuate waterlogging-induced oxidative stress and mitochondrial damage in a calcium-dependent manner

Hydrogen sulfide (H₂ S) is considered to mediate plant growth and development. However, whether H₂ S regulates the adaptation of mangrove plant to intertidal flooding habitats is not well understood. In this study, sodium hydrosulfide (NaHS) was used as an H₂ S donor to investigate the effect of H₂ S on the responses of mangrove plant Avicennia marina to waterlogging. The results showed that 24-h waterlogging increased reactive oxygen species (ROS) and cell death in roots. Excessive mitochondrial ROS accumulation is highly oxidative and leads to mitochondrial structural and functional damage. However, the application of NaHS counteracted the oxidative damage caused by waterlogging. The mitochondrial ROS production was reduced by H₂ S through increasing the expressions of the alternative oxidase genes and increasing the proportion of alternative respiratory pathway in the total mitochondrial respiration. Secondly, H₂ S enhanced the capacity of the antioxidant system. Meanwhile, H₂ S induced Ca²⁺ influx and activated the expression of intracellular Ca²⁺ -sensing-related genes. In addition, the alleviating effect of H₂ S on waterlogging can be reversed by Ca²⁺ chelator and Ca²⁺ channel blockers. In conclusion, this study provides the first evidence to explain the role of H₂ S in waterlogging adaptation in mangrove plants from the mitochondrial aspect.

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.