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

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.

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

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

Interplay between hydrogen sulfide and other signaling molecules in the regulation of guard cell signaling and abiotic/biotic stress response

Stomatal aperture controls the balance between transpirational water loss and photosynthetic carbon dioxide (CO2) uptake. Stomata are surrounded by pairs of guard cells that sense and transduce environmental or stress signals to induce diverse endogenous responses for adaptation to environmental changes. In a recent decade, hydrogen sulfide (H2S) has been recognized as a signaling molecule that regulates stomatal movement. In this review, we summarize recent progress in research on the regulatory role of H2S in stomatal movement, including the dynamic regulation of phytohormones, ion homeostasis, and cell structural components. We focus especially on the cross talk among H2S, nitric oxide (NO), and hydrogen peroxide (H2O2) in guard cells, as well as on H2S-mediated post-translational protein modification (cysteine thiol persulfidation). Finally, we summarize the mechanisms by which H2S interacts with other signaling molecules in plants under abiotic or biotic stress. Based on evidence and clues from existing research, we propose some issues that need to be addressed in the future.

Plant Nitric Oxide Signaling under Drought Stress

Water deficit caused by drought is a significant threat to crop growth and production. Nitric oxide (NO), a water- and lipid-soluble free radical, plays an important role in cytoprotection. Apart from a few studies supporting the role of NO in drought responses, little is known about this pivotal molecular amendment in the regulation of abiotic stress signaling. In this review, we highlight the knowledge gaps in NO roles under drought stress and the technical challenges underlying NO detection and measurements, and we provide recommendations regarding potential avenues for future investigation. The modulation of NO production to alleviate abiotic stress disturbances in higher plants highlights the potential of genetic manipulation to influence NO metabolism as a tool with which plant fitness can be improved under adverse growth conditions.