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

The role of redox-active small molecules and oxidative protein post-translational modifications in seed aging

Seed vigor is a crucial indicator of seed quality. Variations in seed vigor are closely associated with seed properties and storage conditions. The vigor of mature seeds progressively declines during storage, which is called seed deterioration or aging. Seed aging induces a cascade of cellular damage, including impaired subcellular structures and macromolecules, such as lipids, proteins, and DNA. Reactive oxygen species (ROS) act as signaling molecules during seed aging causing oxidative damage and triggering programmed cell death (PCD). Mitochondria are the main site of ROS production and change morphology and function before other organelles during aging. The roles of other small redox-active molecules in regulating cell and seed vigor, such as nitric oxide (NO) and hydrogen sulfide (H2S), were identified later. ROS, NO, and H2S typically regulate protein function through post-translational modifications (PTMs), including carbonylation, S-glutathionylation, S-nitrosylation, and S-sulfhydration. These signaling molecules as well as the PTMs they induce interact to regulate cell fate and seed vigor. This review was conducted to describe the physiological changes and underlying molecular mechanisms that in seed aging and provides a comprehensive view of how ROS, NO, and H2S affect cell death and seed vigor.

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

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

Aquaporins: a vital nexus in H2O2-gasotransmitter signaling

Land plants have evolved with a complex mechanism of water uptake facilitated by the activity of aquaporins under normal and challenging environments. However, we lack a clear understanding of its interactions with reactive oxygen species, particularly hydrogen peroxide (H2O2) and the gasotransmitters nitric oxide (NO) and hydrogen sulfide (H2S), under oxidative stress. Here, we assess the crosstalk of aquaporin function, H2O2 homeostasis, and NO-H2S signaling in plants and provide a computational prediction of cysteine-based oxidative post-translational modifications (oxiPTMs) in plant aquaporins. We propose that aquaporin activity could be regulated by three major oxiPTMs, S-nitrosation, S-sulfenylation, and persulfidation, mediated by NO, H2O2, and H2S, respectively. Therefore, aquaporins might be key players in the gasotransmitter-mediated long-distance oxidative stress signals in plant cells.

The role of phytomelatonin in plant homeostasis, signaling, and crosstalk in abiotic stress mitigation

In recent years, there has been an increase in the study of phytomelatonin. Having numerous functions in animals, melatonin produced by plants (phytomelatonin) is also a multi-regulatory molecule with great potential in plant physiology and in mitigating abiotic stresses, such as drought, salinity, chilling, heat, chemical contamination, and UV-radiation stress. This review highlights the primary functions of phytomelatonin as an anti-stress molecule against abiotic stress. We discuss the role of phytomelatonin as a master regulator, oxidative stress manager, reactive oxygen species and reactive nitrogen species regulator, and defense compounds inducer. Although there exist a handful of reviews on the crosstalk of phytomelatonin with other signaling molecules like auxin, cytokinin, gibberellin, abscisic acid, ethylene, nitric oxide, jasmonic acid, and salicylic acid, this review looks at studies that have reported a few aspects of phytomelatonin with newly discovered signaling molecules along with classical signaling molecules with relation to abiotic stress tolerance. The research and applications of phytomelatonin with hydrogen sulfide, strigolactones, brassinosteroids, and polyamines are still in their nascent stage but hold a promising scope for the future. Additionally, this review states the recent developments in the signaling of phytomelatonin with nitrogen metabolism and nitrosative stress in plants.

Melatonin Mitigates Water Deficit Stress in Cenchrus alopecuroides (L.) Thunb through Up-Regulating Gene Expression Related to the Photosynthetic Rate, Flavonoid Synthesis, and the Assimilatory Sulfate Reduction Pathway

Melatonin can improve plant adaptability to water deficit stress by regulating the biosynthesis of flavonoids and improving the reactive oxygen species-scavenging enzyme system. However, it remains unclear whether melatonin mitigates the effects and causes of water deficit stress in Cenchrus alopecuroides. We conducted a PEG-simulated water stress pot experiment to determine whether and how exogenous melatonin alleviates water deficit in C. alopecuroides. The experiment was divided into four treatments: (1) normal watering (Control), (2) 40% PEG-6000 treatment (D), (3) 100 μmol·L-1 melatonin treatment (MT), and (4) both melatonin and PEG-6000 treatment (DMT). The results showed that melatonin can alleviate water deficit in C. alopecuroides by effectively inhibiting plant chlorophyll degradation and MDA accumulation while increasing antioxidant enzyme activities and photosynthetic rates under water deficit stress. The transcriptome results indicated that melatonin regulates the expression of genes with the biosynthesis pathway of flavonoids (by increasing the expression of PAL, 4CL, HCT, and CHS), photosynthesis-antenna proteins (by increasing the expression of LHC), and sulfur metabolism (the expression of PAPSS and CysC is up-regulated in the assimilatory sulfate reduction pathway), while up-regulating the transcription factors (AP2/ERF-ERF-, C2H2-, WRKY-, Tify-, bHLH-, NAC-, and MYB-related). These findings revealed the possible causes by which melatonin mitigates water deficit stress in C. alopecuroides, which provided novel insights into the role of melatonin in water deficit stress.

Gaseous signaling molecule H2S as a multitasking signal molecule in ROS metabolism of Oryza sativa under thiocyanate (SCN-) pollution

The induction of disruption in the electronic transport chain by thiocyanate (SCN-) leads to an excessive generation of reactive oxygen species (ROS) within rice (Oryza sativa). Hydrogen sulfide (H2S) assumes a crucial role as a gaseous signaling molecule, holding significant potential in alleviating SCN--related stress. Nevertheless, there remains a dearth of understanding regarding the intricate interplay between H2S and ROS in Oryza sativa amidst SCN- pollution. In this investigation, a hydroponics-based experiment was meticulously devised to explore how H2S-mediated modifications influence the genetic feedback network governing ROS metabolism within the subcellular organelles of Oryza sativa when exposed to varying effective concentrations (EC20: 24 mg SCN/L; EC50: 96 mg SCN/L; EC75: 300 mg SCN/L) of SCN-. The findings unveiled the enhanced capacity of Oryza sativa to uptake SCN- under H2S + SCN- treatments in comparison to SCN- treatments alone. Notably, the relative growth rate (RGR) of seedlings subjected to H2S + SCN- exhibited a superior performance when contrasted with seedlings exposed solely to SCN-. Furthermore, the application of exogenous H2S yielded a significant reduction in ROS levels within Oryza sativa tissues during SCN- exposure. To elucidate the intricacies of gene regulation governing ROS metabolism at the mRNA level, the 52 targeted genes were categorized into four distinct types, namely: initial regulatory ROS generation genes (ROS-I), direct ROS scavenging genes (ROS-II), indirect ROS scavenging genes (ROS-III), and lipid oxidation genes (ROS-IV). On the whole, exogenous H2S exhibited the capacity to activate the majority of ROS-I ∼ ROS-IV genes within both Oryza sativa tissues at the EC20 concentration of SCN-. However, genetic positive/negative feedback networks emphasized the pivotal role of ROS-II genes in governing ROS metabolism within Oryza sativa. Notably, these genes were predominantly activated within the cytoplasm, chloroplasts, mitochondria, peroxisomes, and the cell wall.

Review on nitric oxide at the forefront of rapid systemic signaling in mitigation of salinity stress in plants: Crosstalk with calcium and hydrogen peroxide

Soil salinity is a global issue that limits plant growth in agricultural fields and contributes to food crisis. Salt stressors impede plant's ionic, osmotic, and oxidative balance, as well as a variety of physiological functions. Exposure to salinity stress manifest considerable ROS clustering, entailing modification in performance of various organelles. To deal with salinity, plants use a variety of coping strategies, such as osmoregulation, ion-homeostasis, increased antioxidant synthesis, and so on. Nitric oxide (NO) is a pivotal signalling molecule that helps facilitate salt stress-induced physiological plant responses. A variety of evidences point to NO being produced under similar stress conditions and with similar kinetics as hydrogen peroxide (H2O2). The interplay between H2O2 and NO has important functional implications for modulating plant transduction processes. Besides, NO and calcium (Ca2+)-dependent pathways also have some connection in salt stress response mechanisms. Extensive crosstalk between NO and Ca2+ signalling pathways is investigated, and it suggests that almost every type of Ca2+ channel is under the tight control of NO, and NO acts as a Ca2+ mobilising compound and aids in signal reliance. The review provides insights into understanding recent advances regarding NO's, Ca2+ and H2O2 role in salt stress reduction with entwine signaling mechanisms.

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.

Selenate triggers diverse oxidative responses in Astragalus species with diverse selenium tolerance and hyperaccumulation capacity

Selenium (Se) hyperaccumulators are capable of uptake and tolerate high Se dosages. Excess Se-induced oxidative responses were compared in Astragalus bisulcatus and Astragalus cicer. Plants were grown on media supplemented with 0, 25 or 75 μM selenate for 14 days. Both A. bisulcatus and A. cicer accumulated >2000 μg/g dry weight Se to the shoot but the translocation factors of A. cicer were below 1 suggesting its non hyperaccumulator nature. A. cicer showed Se sensitivity indicated by reduced seedling fresh weight, root growth and root apical meristem viability, altered element homeostasis in the presence of Se. In Se-exposed A. bisulcatus, less toxic organic Se forms (mainly MetSeCys, γ-Glu-MetSeCys, and a selenosugar) dominated, while these were absent from A. cicer suggesting that the majority of the accumulated Se may be present as inorganic forms. The glutathione-dependent processes were more affected, while ascorbate levels were not notably influenced by Se in either species. Exogenous Se triggered more intense accumulation of malondialdehyde in the sensitive A. cicer compared with the tolerant A. bisulcatus. The extent of protein carbonylation in the roots of the 75 μM Se-exposed A. cicer exceeded that of A. bisulcatus indicating a correlation between selenate sensitivity and the degree of protein carbonylation. Overall, our results reveal connection between oxidative processes and Se sensitivity/tolerance/hyperaccumulation and contribute to the understanding of the molecular responses to excess Se.

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.

Allicin-Loaded Intelligent Hydrogel Coating Improving Vascular Implant Performance

Coronary atherosclerosis is closely related to inflammation and oxidative stress. Owing to poor biocompatibility, lack of personalized treatment, and late toxic side effects, traditional drug-eluting stent intervention, releasing antiproliferative drugs, can delay endothelial repair and cause late thrombosis. The inflammation caused by atherosclerosis results in an acidic microenvironment and oxidative stress, which can be considered as triggers for precise and intelligent treatment. Here, we used catechol hyaluronic acid (C-HA) and cystamine (Cys) to prepare C-HA-Cys hydrogel coatings by amide reaction. The H2S-releasing donor allicin was loaded in the hydrogel to form an intelligent biomimetic coating. The disulfide bond of Cys made the cross-linked network redox-responsive to the inflammation and oxidative stress in the microenvironment by releasing the drug and H2S intelligently to combat the side effects of stent implantation. This study evaluated the hemocompatibility, anti-inflammatory capacity, vascular wall cytocompatibility, and in vivo histocompatibility of this intelligent hydrogel coating. Furthermore, the effect of H2S released from the coating on atherosclerosis-related signaling pathways such as CD31 and cystathionine γ-lyase (CSE), CD36, and ACAT-1 was investigated. Our results indicate that the C-HA-Cys-Allicin hydrogel coating could be manufactured on the surface of vascular interventional devices to achieve a precise response to the microenvironment of the lesion to release drug, which can attain the purpose of prevention of in-stent restenosis and ensure the effectiveness and safety of the application of interventional devices.

Encapsulated plant growth regulators and associative microorganisms: Nature-based solutions to mitigate the effects of climate change on plants

Over the past decades, the atmospheric CO₂ concentration and global average temperature have been increasing, and this trend is projected to soon become more severe. This scenario of climate change intensifies abiotic stress factors (such as drought, flooding, salinity, and ultraviolet radiation) that threaten forest and associated ecosystems as well as crop production. These factors can negatively affect plant growth and development with a consequent reduction in plant biomass accumulation and yield, in addition to increasing plant susceptibility to biotic stresses. Recently, biostimulants have become a hotspot as an effective and sustainable alternative to alleviate the negative effects of stresses on plants. However, the majority of biostimulants have poor stability under environmental conditions, which leads to premature degradation, shortening their biological activity. To solve these bottlenecks, micro- and nano-based formulations containing biostimulant molecules and/or microorganisms are gaining attention, as they demonstrate several advantages over their conventional formulations. In this review, we focus on the encapsulation of plant growth regulators and plant associative microorganisms as a strategy to boost their application for plant protection against abiotic stresses. We also address the potential limitations and challenges faced for the implementation of this technology, as well as possibilities regarding future research.

Exogenous hydrogen sulfide alleviates chromium toxicity by modulating chromium, nutrients and reactive oxygen species accumulation, and antioxidant defence system in mungbean (Vigna radiata L.) seedlings

Chromium (Cr), a highly toxic redox-active metal cation in soil, seriously threatens global agriculture by affecting nutrient uptake and disturbing various physio-biochemical processes in plants, thereby reducing yields. Here, we examined the effects of different concentrations of Cr alone and in combination with hydrogen sulfide (H₂S) application on the growth and physio-biochemical performance of two mungbeans (Vigna radiata L.) varieties, viz. Pusa Vishal (PV; Cr tolerant) and Pusa Ratna (PR; Cr sensitive), growing in a pot in hydroponics. Plants were grown in the pot experiment to examine their growth, enzymatic and non-enzymatic antioxidant levels, electrolyte balance, and plasma membrane (PM) H⁺-ATPase activity. Furthermore, root anatomy and cell death were analysed 15 days after sowing both varieties in hydroponic systems. The Cr-induced accumulation of reactive oxygen species caused cell death and affected the root anatomy and growth of both varieties. However, the extent of alteration in anatomical features was less in PV than in PR. Exogenous application of H₂S promoted plant growth, thereby improving plant antioxidant activities and reducing cell death by suppressing Cr accumulation and translocation. Seedlings of both cultivars treated with H₂S exhibited enhanced photosynthesis, ion uptake, glutathione, and proline levels and reduced oxidative stress. Interestingly, H₂S restricted the translocation of Cr to aerial parts of plants by improving the nutrient profile and viability of root cells, thereby relieving plants from oxidative bursts by activating the antioxidant machinery through triggering the ascorbate-glutathione cycle. Overall, H₂S application improved the nutrient profile and ionic homeostasis of Cr-stressed mungbean plants. These results highlight the importance of H₂S application in protecting crops against Cr toxicity. Our findings can be utilised to develop management strategies to improve heavy metal tolerance among crops.

Hydrogen sulfide improves salt tolerance through persulfidation of PMA1 in Arabidopsis

KEY MESSAGE

A new interaction was found between PMA1 and GRF4. H₂S promotes the interaction through persulfidated Cys446 of PMA1. H₂S activates PMA1 to maintain K⁺/Na⁺ homeostasis through persulfidation under salt stress. Plasma membrane H⁺-ATPase (PMA) is a transmembrane transporter responsible for pumping protons, and its contribution to salt resistance is indispensable in plants. Hydrogen sulfide (H₂S), a small signaling gas molecule, plays the important roles in facilitating adaptation of plants to salt stress. However, how H₂S regulates PMA activity remains largely unclear. Here, we show a possible original mechanism for H₂S to regulate PMA activity. PMA1, a predominant member in the PMA family of Arabidopsis, has a non-conservative persulfidated cysteine (Cys) residue (Cys446), which is exposed on the surface of PMA1 and located in cation transporter/ATPase domain. A new interaction of PMA1 and GENERAL REGULATORY FACTOR 4 (GRF4, belongs to the 14-3-3 protein family) was found by chemical crosslinking coupled with mass spectrometry (CXMS) in vivo. H₂S-mediated persulfidation promoted the binding of PMA1 to GRF4. Further studies showed that H₂S enhanced instantaneous H⁺ efflux and maintained K⁺/Na⁺ homeostasis under salt stress. In light of these findings, we suggest that H₂S promotes the binding of PMA1 to GRF4 through persulfidation, and then activating PMA, thus improving the salt tolerance of Arabidopsis.

E3 ligase BRG3 persulfidation delays tomato ripening by reducing ubiquitination of the repressor WRKY71

Hydrogen sulfide (H2S) is a gaseous signaling molecule reported to play multiple roles in fruit ripening. However, the molecular mechanisms underlying H2S-mediated delay in fruit ripening remain to be established. Here, the gene encoding a WRKY transcription factor, WRKY71, was identified as substantially upregulated in H2S-treated tomato (Solanum lycopersicum) via transcriptome profiling. The expression of WRKY71 was negatively associated with that of CYANOALANINE SYNTHASE1 (CAS1). Transient and stable genetic modification experiments disclosed that WRKY71 acts as a repressor of the tomato ripening process. CAS1 appears to play an opposite role, based on the finding that the ripening process was delayed in the cas1 mutant and accelerated in CAS1-OE tomatoes. Dual-luciferase reporter assay, yeast one-hybrid, electrophoretic mobility shift assay, and transient transformation experiments showed that WRKY71 bound to the CAS1 promoter and suppressed its activation. Moreover, the persulfidation of WRKY71 enhanced its binding ability to the CAS1 promoter. Data from luciferase complementation and Y2H assays confirmed that WRKY71 interacts with a BOI-related E3 ubiquitin-protein ligase 3 (BRG3) and is ubiquitinated in vitro. Further experiments showed that modification of BRG3 via persulfidation at Cys206 and Cys212 led to reduced ubiquitination activity. Our findings support a model whereby BRG3 undergoes persulfidation at Cys206 and Cys212, leading to reduced ubiquitination activity and decreased interactions with the WRKY71 transcript, with a subsequent increase in binding activity of the persulfidated WRKY71 to the CAS1 promoter, resulting in its transcriptional inhibition and thereby delayed ripening of tomatoes. Our collective findings provide insights into a mechanism of H2S-mediated regulation of tomato fruit ripening.

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.

Transcriptome reveals the crucial role of exogenous hydrogen sulfide in alleviation of thiocyanate (SCN-) toxicity in rice seedlings

Application of exogenous hydrogen sulfide (H₂S) is a novel strategy for alleviation of the adverse effects caused by abiotic stresses. However, little is known about H₂S-mediated global molecular response of rice seedlings to thiocyanate (SCN^-) exposure. Herein, a hydroponic experiment was carried out to investigate the crucial role of exogenous H₂S in alleviation of SCN^- toxicity generated at different effective concentrations (EC₂₀: 24.0 mg SCN/L, EC₅₀: 96.0 mg SCN/L, and EC₇₅: 300.0 mg SCN/L) in rice seedlings through transcriptome analysis. The results showed that the total numbers of differentially expressed genes (DEGs, upregulated genes/downregulated genes) in rice roots were 755/313, 1114/3303, and 2184/7427, while they were 427/292, 2134/526, and 2378/890 in rice shoots at EC₂₀, EC₅₀, and EC₇₅ of SCN^-, respectively. When exogenous H₂S was supplied to rice seedlings exposed to SCN^-, the total number of DEGs (upregulated genes/downregulated genes) in rice roots was 1158/316, 1943/2959, and 1737/5392, while it was 2067/937, 2689/683, and 3492/1062 in rice shoots at EC₂₀, EC₅₀, and EC₇₅ of SCN^-, respectively. Upregulated DEGs in shoots were positively correlated with SCN^- concentration in the presence of exogenous H₂S, suggesting its crucial role in regulating the phytotoxicity of SCN^-. Gene function and pathway enrichment analyses showed that exogenous H₂S triggered "secondary metabolite synthesis," "metabolic pathways," and "signal transduction mechanisms" in rice seedlings corresponding to different effective concentrations of SCN^- exposure.

Hydrogen sulfide and nitric oxide regulate the adaptation to iron deficiency through affecting Fe homeostasis and thiol redox modification in Glycine max seedlings

Iron (Fe) is a vital microelement required for the growth and development of plants. Hydrogen sulfide (H₂S) and nitric oxide (NO), as messenger molecules, participated in the regulation of plant physiological processes. Here, we studied the interaction effects of H₂S and NO on the adaptation to Fe deficiency in Glycine max L. Physiological, biochemical and molecular approaches were conducted to analyze the role of H₂S and NO in regulating the adaptation to Fe deficiency in soybean. We found that H₂S and NO had obvious rescuing function on the Fe deficiency-induced the plant growth inhibition, which was significantly correlated with the increase in Fe content in the leaves, stems, and roots of soybean. Meanwhile, H⁺-flux, ferric chelate reductase (FCR) activity, and root apoplast Fe content were significantly affected by H₂S and NO. Under Fe deficiency conditions NO and H₂S regulated the expression of genes related to Fe homeostasis. Moreover, photosynthesis (Pn) and photosystem II (PSII) efficiency were enhanced by H₂S and NO, and thiol redox modification was important for regulating the adaptation of Fe deficiency. The aforementioned affirmative influences caused by H₂S and NO were also totally reversed by cPTIO (a NO scavenger). Our results suggested that H₂S might act upstream of NO in response to Fe deficiency by affecting the Fe homeostasis enzyme activities and gene expression, and by promoting Fe accumulation in plant tissues as well as by enhancing thiol redox modification and photosynthesis in soybean plants.

Key role of reactive oxygen species-scavenging system in nitric oxide and hydrogen sulfide crosstalk-evoked thermotolerance in maize seedlings

Nitric oxide (NO) and hydrogen sulfide (H₂S) are novel signaling molecules, which participate in plant growth, development, and response to stress. In this study root-irrigation with 0.15 mM sodium nitroprusside (SNP, NO donor) up-regulated gene expression of L-CYSTEINE DESULFHYDRASE1 (LCD1), activities of L-cysteine desulfhydrase (LCD) and D-cysteine desulfhydrase (DCD), as well as an endogenous H₂S level, compared to control seedlings. The SNP-up-regulated effects were enhanced by 0.5 mM sodium hydrosulfide (NaHS, H₂S donor), but weakened by NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) and H₂S scavenger hypotaurine (HT) alone. NaHS had no significant effect on gene expression and activity of nitrate reductase (NR, a NO candidate producing enzyme). These data indicate that NO could trigger the LCD/H₂S signaling pathway in maize seedlings. To further investigate the effect of NO and H₂S crosstalk on thermotolerance in maize seedlings, thermotolerance parameters and reactive oxygen species (ROS)-scavenging system were estimated. The results show that SNP increased survival rate and tissue viability, decreased malondialdehyde (MDA) accumulation, and electrolyte leakage in maize seedlings under heat stress (HS), implying NO could improve thermotolerance in maize seedlings. The NO-improved thermotolerance was impaired by H₂S inhibitor DL-propargylglycine (PAG) and scavenger HT alone. Similarly, SNP up-regulated the gene expression of DEHYDROASCORBATE REDUCTASE (DHAR) and GLUTATHIONE REDUCTASE1 (GR1); activities of ascorbate peroxidase, glutathione reductase, and catalase; as well as levels of ascorbic acid, glutathione, flavonoids, carotenoids, and total phenols. SNP also reduced hydrogen peroxide and superoxide radical accumulation in maize seedlings under HS compared to the control. The effects of SNP on ROS and their scavenger system were weakened by PAG and HT alone. These data hint that NO could evoke thermotolerance in maize seedlings by triggering the LCD/H₂S signaling pathway, and the ROS-scavenging system played a key role in the NO and H₂S crosstalk-evoked thermotolerance.

Review of the Mechanisms by Which Transcription Factors and Exogenous Substances Regulate ROS Metabolism under Abiotic Stress

Reactive oxygen species (ROS) are signaling molecules that regulate many biological processes in plants. However, excess ROS induced by biotic and abiotic stresses can destroy biological macromolecules and cause oxidative damage to plants. As the global environment continues to deteriorate, plants inevitably experience abiotic stress. Therefore, in-depth exploration of ROS metabolism and an improved understanding of its regulatory mechanisms are of great importance for regulating cultivated plant growth and developing cultivars that are resilient to abiotic stresses. This review presents current research on the generation and scavenging of ROS in plants and summarizes recent progress in elucidating transcription factor-mediated regulation of ROS metabolism. Most importantly, the effects of applying exogenous substances on ROS metabolism and the potential regulatory mechanisms at play under abiotic stress are summarized. Given the important role of ROS in plants and other organisms, our findings provide insights for optimizing cultivation patterns and for improving plant stress tolerance and growth regulation.

Integrating transcriptome and physiological analysis to reveal the essential responses of Daphnia magna to antimony trioxide nanoparticle

Antimony (Sb) pollution has already posed a severe threat to the aquatic ecosystem. However, the toxicity mechanisms of Sb on aquatic organisms are far from being elucidated. One of the crucial questions remaining unresolved is the characterization of molecular toxicity of Sb(III). Transcriptomics profiling combined with physiological characterizations was applied to investigate the response of Daphnia magna to nano-size antimony trioxide (nATO) and its soluble Sb(III) counterpart antimony potassium tartrate (APT) in the present study. Both nATO and APT induced the formation of oxidative stress, enhanced the activities of anti-oxidative enzymes, altered the metabolism of xenobiotics, increased the concentration of hydrogen sulfide (H₂S) and nitric oxide (NO), and triggered the self-protection mechanisms such as ubiquitin-mediated proteolysis. In addition, nATO and APT caused damage to the nervous system of D. magna, inhibited its locomotion and nutrient uptake in a concentration-dependent manner. Moreover, nATO exposure enhanced the autophagy activity, reflected by the up-regulated expression of hypoxia-inducible factor-1α, calmodulin-dependent protein kinase-β, and inositol-requiring enzyme 1. The present study, for the first time, depicted a global map of cellular response to nATO, provided essential information on Sb(III) toxicity to aquatic organisms, and is of great significance to the development of Sb management strategies.

Potassium in plant physiological adaptation to abiotic stresses

Potassium (K) is an integral part of plant nutrition, playing essential roles in plant growth and development. Despite its abundance in soils, the limitedly available form of K ion (K⁺) for plant uptake is a critical factor for agricultural production. Plants have evolved complex transport systems to maintain appropriate K⁺ levels in tissues under changing environmental conditions. Adequate stimulation and coordinated actions of multiple K⁺-channels and K⁺-transporters are required for nutrient homeostasis, reproductive growth, cellular signaling and stress adaptation responses in plants. Various contemporary studies revealed that K⁺-homeostasis plays a substantial role in plant responses and tolerance to abiotic stresses. The beneficial effects of K⁺ in plant responses to abiotic stresses include its roles in physiological and biochemical mechanisms involved in photosynthesis, osmoprotection, stomatal regulation, water-nutrient absorption, nutrient translocation and enzyme activation. Over the last decade, we have seen considerable breakthroughs in K research, owing to the advances in omics technologies. In this aspect, omics investigations (e.g., transcriptomics, metabolomics, and proteomics) in systems biology manner have broadened our understanding of how K⁺ signals are perceived, conveyed, and integrated for improving plant physiological resilience to abiotic stresses. Here, we update on how K⁺-uptake and K⁺-distribution are regulated under various types of abiotic stress. We discuss the effects of K⁺ on several physiological functions and the interaction of K⁺ with other nutrients to improve plant potential against abiotic stress-induced adverse consequences. Understanding of how K⁺ orchestrates physiological mechanisms and contributes to abiotic stress tolerance in plants is essential for practicing sustainable agriculture amidst the climate crisis in global agriculture.

Hydrogen Sulfide, Ethylene, and Nitric Oxide Regulate Redox Homeostasis and Protect Photosynthetic Metabolism under High Temperature Stress in Rice Plants

Rising temperatures worldwide due to global climate change are a major scientific issue at present. The present study reports the effects of gaseous signaling molecules, ethylene (200 µL L⁻¹; 2-chloroethylphosphonic acid; ethephon, Eth), nitric oxide (NO; 100 µM sodium nitroprusside; SNP), and hydrogen sulfide (H₂S; 200 µM sodium hydrosulfide, NaHS) in high temperature stress (HS) tolerance, and whether or not H₂S contributes to ethylene or NO-induced thermo-tolerance and photosynthetic protection in rice (Oryza sativa L.) cultivars, i.e., Taipei-309, and Rasi. Plants exposed to an HS of 40 °C for six h per day for 15 days caused a reduction in rice biomass, associated with decreased photosynthesis and leaf water status. High temperature stress increased oxidative stress by increasing the content of hydrogen peroxide (H₂O₂) and thiobarbituric acid reactive substance (TBARS) in rice leaves. These signaling molecules increased biomass, leaf water status, osmolytes, antioxidants, and photosynthesis of plants under non-stress and high temperature stress. However, the effect was more conspicuous with ethylene than NO and H₂S. The application of H₂S scavenger hypotaurine (HT) reversed the effect of ethylene or NO on photosynthesis under HS. This supports the findings that the ameliorating effects of Eth or SNP involved H₂S. Thus, the presence of H₂S with ethylene or NO can enhance thermo-tolerance while also protecting plant photosynthesis.

Hydrogen Sulfide Mitigates Chilling Injury of Postharvest Banana Fruits by Regulating γ-Aminobutyric Acid Shunt Pathway and Ascorbate-Glutathione Cycle

This study aimed to determine the effect of hydrogen sulfide on chilling injury (CI) of banana (Musa spp.) during cold storage (7°C). It was observed that hydrogen sulfide application (2 mmol L^-1) markedly reduced the CI index and showed significantly higher chlorophyll contents, along with suppressed chlorophyll peroxidase and chlorophyllase enzyme activity. The treated banana fruits exhibited substantially higher peel lightness (L*), along with significantly a lower browning degree and soluble quinone content. The treated bananas had substantially a higher endogenous hydrogen sulfide content and higher activity of its biosynthesis-associated enzymes such as D-cysteine desulfhydrase (DCD) and L-cysteine desulfhydrase (LCD), along with significantly lower ion leakage, lipid peroxidation, hydrogen peroxide, and superoxide anion concentrations. Hydrogen sulfide-treated banana fruits showed an increased proline content and proline metabolism-associated enzymes including ornithine aminotransferase (OAT), Δ¹-pyrroline-5-carboxylate synthetase (P5CS), and proline dehydrogenase (PDH). In the same way, hydrogen sulfide-fumigated banana fruits accumulated higher endogenous γ-aminobutyric acid (GABA) due to enhanced activity of glutamate decarboxylase (GAD) and GABA transaminase (GABA-T) enzymes. The hydrogen sulfide-treated fruits exhibited higher total phenolics owing to lower polyphenol oxidase (PPO) and peroxidase (POD) activity and stimulated phenylalanine ammonia lyase (PAL). The treated banana exhibited higher ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), and superoxide dismutase (SOD) activity, along with higher glutathione (GSH) and ascorbic acid (AsA) concentrations and a significantly lower dehydroascorbic acid (DHA) content. In conclusion, hydrogen sulfide treatment could be utilized for CI alleviation of banana fruits during cold storage.

Hydrogen sulfide reduces cell death through regulating autophagy during submergence in Arabidopsis

Hydrogen sulfide positively regulates autophagy and the expression of hypoxia response-related genes under submergence to enhance the submergence tolerance of Arabidopsis. Flooding seriously endangers agricultural production, and it is quite necessary to explore the mechanism of plant response to submergence for improving crop yield. Both hydrogen sulfide (H₂S) and autophagy are involved in the plant response to submergence. However, the mechanisms by which H₂S and autophagy interact and influence submergence tolerance have not been thoroughly elucidated. Here, we reported that exogenous H₂S pretreatment increased the level of endogenous H₂S and alleviated plant cell death under submergence. And transgenic lines decreased in the level of endogenous H₂S, L-cysteine desulfurase 1 (des1) mutant and 35S::GFP-O-acetyl-L-serine(thiol)lyase A1 (OASA1)/des1-#56/#61, were sensitive to submergence, along with the lower transcript levels of hypoxia response genes, LOB DOMAIN 41 (LBD41) and HYPOXIA RESPONSIVE UNKNOWN PROTEIN 43 (HUP43). Submergence induced the formation of autophagosomes, and the autophagy-related (ATG) mutants (atg4a/4b, atg5, atg7) displayed sensitive phenotypes to submergence. Simultaneously, H₂S pretreatment repressed the autophagosome producing under normal conditions, but enhanced this process under submergence by regulating the expression of ATG genes. Moreover, the mutation of DES1 aggravated the sensitivity of des1/atg5 to submergence by reducing the formation of autophagosomes under submergence. Taken together, our results demonstrated that H₂S alleviated cell death through regulating autophagy and the expression of hypoxia response genes during submergence in Arabidopsis.

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

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

Hydrogen sulphide signalling in plant response to abiotic stress

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

Hydrogen sulfide: an emerging component against abiotic stress in plants

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

Crosstalk between Melatonin and Reactive Oxygen Species in Plant Abiotic Stress Responses: An Update

Melatonin acts as a multifunctional molecule that takes part in various physiological processes, especially in the protection against abiotic stresses, such as salinity, drought, heat, cold, heavy metals, etc. These stresses typically elicit reactive oxygen species (ROS) accumulation. Excessive ROS induce oxidative stress and decrease crop growth and productivity. Significant advances in melatonin initiate a complex antioxidant system that modulates ROS homeostasis in plants. Numerous evidences further reveal that melatonin often cooperates with other signaling molecules, such as ROS, nitric oxide (NO), and hydrogen sulfide (H₂S). The interaction among melatonin, NO, H₂S, and ROS orchestrates the responses to abiotic stresses via signaling networks, thus conferring the plant tolerance. In this review, we summarize the roles of melatonin in establishing redox homeostasis through the antioxidant system and the current progress of complex interactions among melatonin, NO, H₂S, and ROS in higher plant responses to abiotic stresses. We further highlight the vital role of respiratory burst oxidase homologs (RBOHs) during these processes. The complicated integration that occurs between ROS and melatonin in plants is also discussed.

The Functional Interplay between Ethylene, Hydrogen Sulfide, and Sulfur in Plant Heat Stress Tolerance

Plants encounter several abiotic stresses, among which heat stress is gaining paramount attention because of the changing climatic conditions. Severe heat stress conspicuously reduces crop productivity through changes in metabolic processes and in growth and development. Ethylene and hydrogen sulfide (H2S) are signaling molecules involved in defense against heat stress through modulation of biomolecule synthesis, the antioxidant system, and post-translational modifications. Other compounds containing the essential mineral nutrient sulfur (S) also play pivotal roles in these defense mechanisms. As biosynthesis of ethylene and H2S is connected to the S-assimilation pathway, it is logical to consider the existence of a functional interplay between ethylene, H2S, and S in relation to heat stress tolerance. The present review focuses on the crosstalk between ethylene, H2S, and S to highlight their joint involvement in heat stress tolerance.

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

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

Putrescine: A Key Metabolite Involved in Plant Development, Tolerance and Resistance Responses to Stress

Putrescine (Put) is the starting point of the polyamines (PAs) pathway and the most common PA in higher plants. It is synthesized by two main pathways (from ornithine and arginine), but recently a third pathway from citrulline was reported in sesame plants. There is strong evidence that Put may play a crucial role not only in plant growth and development but also in the tolerance responses to the major stresses affecting crop production. The main strategies to investigate the involvement of PA in plant systems are based on the application of competitive inhibitors, exogenous PAs treatments, and the most efficient approaches based on mutant and transgenic plants. Thus, in this article, the recent advances in understanding the role of this metabolite in plant growth promotion and protection against abiotic and biotic stresses will be discussed to provide an overview for future research.

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.

Exogenous Melatonin Promotes the Salt Tolerance by Removing Active Oxygen and Maintaining Ion Balance in Wheat (Triticum aestivum L.)

Melatonin (MT) is a small molecule indole hormone that plays an important role in the regulation of biological processes and abiotic stress resistance. Previous studies have confirmed that MT promotes the normal development of plants under stress by mediating physiological regulation mechanisms. However, the physiological mechanism of exogenous MT regulating seed germination and seedling growth of wheat under salt stress is still unclear. In this study, NaCl stress decreased germination rate and inhibited seedling growth of wheat, but shoot length, root length, and plant weight of SM15 did not change significantly. The addition of 300 μM MT in the cultivation solution directly promoted the germination rate of SM15 and ZM18, and lateral root production, but decreased the germination rate of JM22 and inhibited the length of germ and radicle of three varieties under salt stress. For wheat seedling, application of MT could increase proline content, soluble protein, soluble sugar, Ca2+ content, and vital amino acid content in leaves to keep high water content, low level of H2O2 content, and low [K+]/[Na+] ratio. MT increased root vigor and [K+]/[Na+] ratio and decreased H2O2 content in root induced by salt stress. In conclusion, MT enhanced salt tolerance in wheat seeds and seedlings by regulating the synthesis of soluble protein and sugar, ion compartmentation in roots and leaves, enhancement of enzymatic systems, and changes in amino acid levels. Salt resistance varied with different varieties under the same environmental condition. SM15 was a higher salt-resistant variety and JM22 was a salt-sensitive one. In wheat production, the application of exogenous MT should consider the differences among varieties of wheat during the sowing and seedling stages.

The Role of Hydrogen Sulfide in Plant Roots during Development and in Response to Abiotic Stress

Hydrogen sulfide (H₂S) is regarded as a “New Warrior” for managing plant stress. It also plays an important role in plant growth and development. The regulation of root system architecture (RSA) by H₂S has been widely recognized. Plants are dependent on the RSA to meet their water and nutritional requirements. They are also partially dependent on the RSA for adapting to environment change. Therefore, a good understanding of how H₂S affects the RSA could lead to improvements in both crop function and resistance to environmental change. In this review, we summarized the regulating effects of H₂S on the RSA in terms of primary root growth, lateral and adventitious root formation, root hair development, and the formation of nodules. We also discussed the genes involved in the regulation of the RSA by H₂S, and the relationships with other signal pathways. In addition, we discussed how H₂S regulates root growth in response to abiotic stress. This review could provide a comprehensive understanding of the role of H₂S in roots during development and under abiotic stress.

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

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

Improving oxidative stress resilience in plants

Originally conceived as harmful metabolic byproducts, reactive oxygen species (ROS) are now recognized as an integral part of numerous cellular programs. Thanks to their diverse physicochemical properties, compartmentalized production, and tight control exerted by the antioxidant machinery they activate signaling pathways that govern plant growth, development, and defense. Excessive ROS levels are often driven by adverse changes in environmental conditions, ultimately causing oxidative stress. The associated negative impact on cellular constituents have been a major focus of decade-long research efforts to improve the oxidative stress resilience by boosting the antioxidant machinery in model and crop species. We highlight the role of enzymatic and non-enzymatic antioxidants as integral factors of multiple signaling cascades beyond their mere function to prevent oxidative damage under adverse abiotic stress conditions.

A Comprehensive Review on the Heavy Metal Toxicity and Sequestration in Plants

Heavy metal (HM) toxicity has become a global concern in recent years and is imposing a severe threat to the environment and human health. In the case of plants, a higher concentration of HMs, above a threshold, adversely affects cellular metabolism because of the generation of reactive oxygen species (ROS) which target the key biological molecules. Moreover, some of the HMs such as mercury and arsenic, among others, can directly alter the protein/enzyme activities by targeting their –SH group to further impede the cellular metabolism. Particularly, inhibition of photosynthesis has been reported under HM toxicity because HMs trigger the degradation of chlorophyll molecules by enhancing the chlorophyllase activity and by replacing the central Mg ion in the porphyrin ring which affects overall plant growth and yield. Consequently, plants utilize various strategies to mitigate the negative impact of HM toxicity by limiting the uptake of these HMs and their sequestration into the vacuoles with the help of various molecules including proteins such as phytochelatins, metallothionein, compatible solutes, and secondary metabolites. In this comprehensive review, we provided insights towards a wider aspect of HM toxicity, ranging from their negative impact on plant growth to the mechanisms employed by the plants to alleviate the HM toxicity and presented the molecular mechanism of HMs toxicity and sequestration in plants.

Hydrogen Sulfide Improves the Cold Stress Resistance through the CsARF5-CsDREB3 Module in Cucumber

As an important gas signaling molecule, hydrogen sulfide (H₂S) plays a crucial role in regulating cold tolerance. H₂S cooperates with phytohormones such as abscisic acid, ethylene, and salicylic acid to regulate the plant stress response. However, the synergistic regulation of H₂S and auxin in the plant response to cold stress has not been reported. This study showed that sodium hydrosulfide (NaHS, an H₂S donor) treatment enhanced the cold stress tolerance of cucumber seedlings and increased the level of auxin. CsARF5, a cucumber auxin response factor (ARF) gene, was isolated, and its role in regulating H₂S-mediated cold stress tolerance was described. Transgenic cucumber leaves overexpressing CsARF5 were obtained. Physiological analysis indicated that overexpression of CsARF5 enhanced the cold stress tolerance of cucumber and the regulation of the cold stress response by CsARF5 depends on H₂S. In addition, molecular assays showed that CsARF5 modulated cold stress response by directly activating the expression of the dehydration-responsive element-binding (DREB)/C-repeat binding factor (CBF) gene CsDREB3, which was identified as a positive regulator of cold stress. Taken together, the above results suggest that CsARF5 plays an important role in H₂S-mediated cold stress in cucumber. These results shed light on the molecular mechanism by which H₂S regulates cold stress response by mediating auxin signaling; this will provide insights for further studies on the molecular mechanism by which H₂S regulates cold stress. The aim of this study was to explore the molecular mechanism of H₂S regulating cold tolerance of cucumber seedlings and provide a theoretical basis for the further study of cucumber cultivation and environmental adaptability technology in winter.

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

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

H2O2 Functions as a Downstream Signal of IAA to Mediate H2S-Induced Chilling Tolerance in Cucumber

Hydrogen sulfide (H₂S) plays a crucial role in regulating chilling tolerance. However, the role of hydrogen peroxide (H₂O₂) and auxin in H₂S-induced signal transduction in the chilling stress response of plants was unclear. In this study, 1.0 mM exogenous H₂O₂ and 75 μM indole-3-acetic acid (IAA) significantly improved the chilling tolerance of cucumber seedlings, as demonstrated by the mild plant chilling injury symptoms, lower chilling injury index (CI), electrolyte leakage (EL), and malondialdehyde content (MDA) as well as higher levels of photosynthesis and cold-responsive genes under chilling stress. IAA-induced chilling tolerance was weakened by N, N′-dimethylthiourea (DMTU, a scavenger of H₂O₂), but the polar transport inhibitor of IAA (1-naphthylphthalamic acid, NPA) did not affect H₂O₂-induced mitigation of chilling stress. IAA significantly enhanced endogenous H₂O₂ synthesis, but H₂O₂ had minimal effects on endogenous IAA content in cucumber seedlings. In addition, the H₂O₂ scavenger DMTU, inhibitor of H₂O₂ synthesis (diphenyleneiodonium chloride, DPI), and IAA polar transport inhibitor NPA reduced H₂S-induced chilling tolerance. Sodium hydrosulfide (NaHS) increased H₂O₂ and IAA levels, flavin monooxygenase (FMO) activity, and respiratory burst oxidase homolog (RBOH1) and FMO-like protein (YUCCA2) mRNA levels in cucumber seedlings. DMTU, DPI, and NPA diminished NaHS-induced H₂O₂ production, but DMTU and DPI did not affect IAA levels induced by NaHS during chilling stress. Taken together, the present data indicate that H₂O₂ as a downstream signal of IAA mediates H₂S-induced chilling tolerance in cucumber seedlings.

Hydrogen Sulfide in Plants: Crosstalk with Other Signal Molecules in Response to Abiotic Stresses

Hydrogen sulfide (H₂S) has recently been considered as a crucial gaseous transmitter occupying extensive roles in physiological and biochemical processes throughout the life of plant species. Furthermore, plenty of achievements have been announced regarding H₂S working in combination with other signal molecules to mitigate environmental damage, such as nitric oxide (NO), abscisic acid (ABA), calcium ion (Ca²⁺), hydrogen peroxide (H₂O₂), salicylic acid (SA), ethylene (ETH), jasmonic acid (JA), proline (Pro), and melatonin (MT). This review summarizes the current knowledge within the mechanism of H₂S and the above signal compounds in response to abiotic stresses in plants, including maintaining cellular redox homeostasis, exchanging metal ion transport, regulating stomatal aperture, and altering gene expression and enzyme activities. The potential relationship between H₂S and other signal transmitters is also proposed and discussed.

Melatonin Confers Plant Cadmium Tolerance: An Update

Cadmium (Cd) is one of the most injurious heavy metals, affecting plant growth and development. Melatonin (N-acetyl-5-methoxytryptamine) was discovered in plants in 1995, and it is since known to act as a multifunctional molecule to alleviate abiotic and biotic stresses, especially Cd stress. Endogenously triggered or exogenously applied melatonin re-establishes the redox homeostasis by the improvement of the antioxidant defense system. It can also affect the Cd transportation and sequestration by regulating the transcripts of genes related to the major metal transport system, as well as the increase in glutathione (GSH) and phytochelatins (PCs). Melatonin activates several downstream signals, such as nitric oxide (NO), hydrogen peroxide (H₂O₂), and salicylic acid (SA), which are required for plant Cd tolerance. Similar to the physiological functions of NO, hydrogen sulfide (H₂S) is also involved in the abiotic stress-related processes in plants. Moreover, exogenous melatonin induces H₂S generation in plants under salinity or heat stress. However, the involvement of H₂S action in melatonin-induced Cd tolerance is still largely unknown. In this review, we summarize the progresses in various physiological and molecular mechanisms regulated by melatonin in plants under Cd stress. The complex interactions between melatonin and H₂S in acquisition of Cd stress tolerance are also discussed.

Response to Antimony Toxicity in Dittrichia viscosa Plants: ROS, NO, H2S, and the Antioxidant System

Dittrichia viscosa plants were grown hydroponically with different concentrations of Sb. There was preferential accumulation of Sb in roots. Fe and Cu decreased, while Mn decreased in roots but not in leaves. Chlorophyll content declined, but the carotenoid content increased, and photosynthetic efficiency was unaltered. O₂^●− generation increased slightly, while lipid peroxidation increased only in roots. H₂O₂, NO, ONOO⁻, S-nitrosothiols, and H₂S showed significant increases, and the enzymatic antioxidant system was altered. In roots, superoxide dismutase (SOD) and monodehydroascorbate reductase (MDAR) activities declined, dehydroscorbate reductase (DHAR) rose, and ascorbate peroxidase (APX), peroxidase (POX), and glutathione reductase (GR) were unaffected. In leaves, SOD and POX increased, MDAR decreased, and APX was unaltered, while GR increased. S-nitrosoglutathione reductase (GSNOR) and l-cysteine desulfhydrilase (l-DES) increased in activity, while glutathione S-transferase (GST) decreased in leaves but was enhanced in roots. Components of the AsA/GSH cycle decreased. The great capacity of Dittrichia roots to accumulate Sb is the reason for the differing behaviour observed in the enzymatic antioxidant systems of the two organs. Sb appears to act by binding to thiol groups, which can alter free GSH content and SOD and GST activities. The coniferyl alcohol peroxidase activity increased, possibly to lignify the roots’ cell walls. Sb altered the ROS balance, especially with respect to H₂O₂. This led to an increase in NO and H₂S acting on the antioxidant system to limit that Sb-induced redox imbalance. The interaction NO, H₂S and H₂O₂ appears key to the response to stress induced by Sb. The interaction between ROS, NO, and H₂S appears to be involved in the response to Sb.

Hydrogen Sulfide Enhances Plant Tolerance to Waterlogging Stress

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

Crucial Cell Signaling Compounds Crosstalk and Integrative Multi-Omics Techniques for Salinity Stress Tolerance in Plants

In the era of rapid climate change, abiotic stresses are the primary cause for yield gap in major agricultural crops. Among them, salinity is considered a calamitous stress due to its global distribution and consequences. Salinity affects plant processes and growth by imposing osmotic stress and destroys ionic and redox signaling. It also affects phytohormone homeostasis, which leads to oxidative stress and eventually imbalances metabolic activity. In this situation, signaling compound crosstalk such as gasotransmitters [nitric oxide (NO), hydrogen sulfide (H2S), hydrogen peroxide (H2O2), calcium (Ca), reactive oxygen species (ROS)] and plant growth regulators (auxin, ethylene, abscisic acid, and salicylic acid) have a decisive role in regulating plant stress signaling and administer unfavorable circumstances including salinity stress. Moreover, recent significant progress in omics techniques (transcriptomics, genomics, proteomics, and metabolomics) have helped to reinforce the deep understanding of molecular insight in multiple stress tolerance. Currently, there is very little information on gasotransmitters and plant growth regulator crosstalk and inadequacy of information regarding the integration of multi-omics technology during salinity stress. Therefore, there is an urgent need to understand the crucial cell signaling crosstalk mechanisms and integrative multi-omics techniques to provide a more direct approach for salinity stress tolerance. To address the above-mentioned words, this review covers the common mechanisms of signaling compounds and role of different signaling crosstalk under salinity stress tolerance. Thereafter, we mention the integration of different omics technology and compile recent information with respect to salinity stress tolerance.

Hydrogen Sulfide: A Robust Combatant against Abiotic Stresses in Plants

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

Hydrogen sulfide and calcium effects on cadmium removal and resistance in the white-rot fungus Phanerochaete chrysosporium

Hydrogen sulfide (H₂S), an emerging gas transmitter, has been shown to be involved in multiple intracellular physiological and biochemical processes. In this study, the effects of hydrogen sulfide coupled with calcium on cadmium removal and resistance in Phanerochaete chrysosporium were examined. The results revealed that H₂S enhanced the uptake of calcium by P. chrysosporium to resist cadmium stress. The removal and accumulation of cadmium by the mycelium was reduced by H₂S and Ca²⁺ pretreatment. Moreover, oxidative damage and membrane integrity were alleviated by H₂S and Ca²⁺. Corresponding antioxidative enzyme activities and glutathione were also found to positively respond to H₂S and Ca²⁺, which played an important role in the resistance to cadmium-induced oxidative stress. The effects of hydroxylamine (HA; a hydrogen sulfide inhibitor) and ethylene glycol-bis-(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA; a calcium chelator) toward H₂S and Ca²⁺ and their cross-interactions confirmed the positive roles and the potential crosstalk of H₂S and Ca²⁺ in cadmium stress resistance. These findings imply that the protective effects of H₂S in P. chrysosporium under cadmium stress may occur through a reduction in the accumulation of cadmium and promotion of the antioxidant system, and the H₂S-regulated pathway may be associated with the intracellular calcium signaling system.Key points• Altered monoterpenoid tolerance mainly related to altered activity of efflux pumps.• Increased tolerance to geranic acid surprisingly caused by decreased export activity.• Reduction of export activity can be beneficial for biotechnological conversions.

Hydrogen sulfide (H2S) and potassium (K+) synergistically induce drought stress tolerance through regulation of H+-ATPase activity, sugar metabolism, and antioxidative defense in tomato seedlings

Exogenous potassium (K⁺) and endogenous hydrogen sulfide (H₂S) synergistically alleviate drought stress through regulating H⁺-ATPase activity, sugar metabolism and redox homoeostasis in tomato seedlings. Present work evaluates the role of K⁺ in the regulation of endogenous H₂S signaling in modulating the tolerance of tomato (Solanum lycopersicum L. Mill.) seedlings to drought stress. The findings reveal that exposure of seedlings to 15% (w/v) polyethylene glycol 8000 (PEG) led to a substantial decrease in leaf K⁺ content which was associated with reduced H⁺-ATPase activity. Treatment with sodium orthovanadate (SOV, PM H⁺-ATPase inhibitor) and tetraethylammonium chloride (TEA, K⁺ channel blocker) suggests that exogenous K⁺ stimulated H⁺-ATPase activity that further regulated endogenous K⁺ content in tomato seedlings subjected to drought stress. Moreover, reduction in H⁺-ATPase activity by hypotaurine (HT; H₂S scavenger) substantiates the role of endogenous H₂S in the regulation of H⁺-ATPase activity. Elevation in endogenous K⁺ content enhanced the biosynthesis of H₂S through enhancing the synthesis of cysteine, the H₂S precursor. Synergistic action of H₂S and K⁺ effectively neutralized drought stress by regulating sugar metabolism and redox homoeostasis that resulted in osmotic adjustment, as witnessed by reduced water loss, and improved hydration level of the stressed seedlings. The integrative role of endogenous H₂S in K⁺ homeostasis was validated using HT and TEA which weakened the protection against drought stress induced impairments. In conclusion, exogenous K⁺ and endogenous H₂S regulate H⁺-ATPase activity which plays a decisive role in the maintenance of endogenous K⁺ homeostasis. Thus, present work reveals that K⁺ and H₂S crosstalk is essential for modulation of drought stress tolerance in tomato seedlings.