In site bioimaging of hydrogen sulfide uncovers its pivotal role in regulating nitric oxide-induced lateral root formation

Hydrogen sulfide signaling in plants

SIGNIFICANCE

Hydrogen sulfide (H2S) is a multitasking potent regulator that facilitates plant growth, development, and responses to environmental stimuli.

RECENT ADVANCES

The important beneficial effects of H2S in various aspects of plant physiology aroused the interest of this chemical for agriculture. Protein cysteine persulfidation has been recognized as the main redox regulatory mechanism of H2S signaling. An increasing number of studies, including large-scale proteomic analyses and function characterizations, have revealed that H2S-mediated persulfidations directly regulate protein functions, altering downstream signaling in plants. To date, the importance of H2S-mediated persufidation in several abscisic acid signaling-controlling key proteins has been assessed as well as their role in stomatal movements, largely contributing to the understanding of the plant H2S-regulatory mechanism.

CRITICAL ISSUES

The molecular mechanisms of the H2S sensing and transduction in plants remain elusive. The correlation between H2S-mediated persulfidation with other oxidative posttranslational modifications of cysteines are still to be explored.

FUTURE DIRECTIONS

Implementation of advanced detection approaches for the spatiotemporal monitoring of H2S levels in cells and the current proteomic profiling strategies for the identification and quantification of the cysteine site-specific persulfidation will provide insight into the H2S signaling in plants.

H2 O2 , NO, and H2 S networks during root development and signalling under physiological and challenging environments: Beneficial or toxic?

Hydrogen peroxide (H₂ O₂ ) is a reactive oxygen species (ROS) and a key modulator of the development and architecture of the root system under physiological and adverse environmental conditions. Nitric oxide (NO) and hydrogen sulphide (H₂ S) also exert myriad functions on plant development and signalling. Accumulating pieces of evidence show that depending upon the dose and mode of applications, NO and H₂ S can have synergistic or antagonistic actions in mediating H₂ O₂ signalling during root development. Thus, H₂ O₂ -NO-H₂ S crosstalk might essentially impart tolerance to elude oxidative stress in roots. Growth and proliferation of root apex involve crucial orchestration of NO and H₂ S-mediated ROS signalling which also comprise other components including mitogen-activated protein kinase, cyclins, cyclin-dependent kinases, respiratory burst oxidase homolog (RBOH), and Ca²⁺ flux. This assessment provides a comprehensive update on the cooperative roles of NO and H₂ S in modulating H₂ O₂ homoeostasis during root development, abiotic stress tolerance, and root-microbe interaction. Furthermore, it also analyses the scopes of some fascinating future investigations associated with strigolactone and karrikins concerning H₂ O₂ -NO-H₂ S crosstalk in plant roots.

Sustained Release of Hydrogen Sulfide from Di(t-butanol)dithiophosphate Phenethylamine Salt Encapsulated into Poly(lactic acid) Microparticles to Enhance the Growth of Radish Plants

The slow release of hydrogen sulfide has been shown to be beneficial to plants by protecting them from environmental stressors, increasing germination, and extending the lifetime of harvested fruits. A major challenge in this field is controlling the amount and location of release of hydrogen sulfide so that it is available for use by plants at optimal amounts. This article reports a dual method to release hydrogen sulfide near the roots of plants by controlling its release using the hydrolysis of a dithiophosphate and the degradation of poly(lactic acid) [PLA]. Di(t-butanol)dithiophosphate phenylethylamine (tBDPA) was dissolved in a solution of PLA, and the solvent was allowed to evaporate. The resulting solid was crushed in a blender and separated into microparticles with two different size distributions of 250-500 or 500-2000 μm. The microparticles were characterized by powder X-ray diffraction to measure the presence of microcrystals of tBDPA within PLA, and images obtained using scanning electron microscopy with energy dispersive X-ray analysis confirmed the presence of these crystals. Microparticles of tBDPA loaded within PLA were characterized for their release of phosphorus and hydrogen sulfide, which both showed a burst release within 3 days, followed by a steady release. Radish plants grown with microparticles of PLA loaded with tBDPA had up to a 141% increase in harvest yield compared to plants grown in the presence of free tBDPA not loaded into PLA, PLA microparticles without tBDPA, and control plants grown without PLA or tBDPA. These experiments showed that loading hydrogen sulfide-releasing chemicals into PLA is a promising method to improve the effect of hydrogen sulfide on plants.

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.

The Defensive Role of Endogenous H2S in Brassica rapa against Mercury-Selenium Combined Stress

Plants are always exposed to the environment, polluted by multiple trace elements. Hydrogen sulfide (H₂S), an endogenous gaseous transmitter in plant cells, can help plant combat single elements with excess concentration. Until now, little has been known about the regulatory role of H₂S in response to combined stress of multiple elements. Here we found that combined exposure of mercury (Hg) and selenium (Se) triggered endogenous H₂S signal in the roots of Brasscia rapa. However, neither Hg nor Se alone worked on it. In roots upon Hg + Se exposure, the defensive role of endogenous H₂S was associated to the decrease in reactive oxygen species (ROS) level, followed by alleviating cell death and recovering root growth. Such findings extend our knowledge of plant H₂S in response to multiple stress conditions.

Fluorescence Probes for Reactive Sulfur Species in Agricultural Chemistry

Sulfur is an element that is indispensable throughout the growth of plants. In plant cells, reactive sulfur species (RSS) play a vital role in maintaining cellular redox homeostasis and signal transduction. There is demand accordingly for a simple, highly selective, and sensitive method of RSS detection and imaging for monitoring dynamic changes and clarifying the biological functions of RSS in plant systems. Fluorescent analysis based on organic small-molecule fluorescent probes is an effective and specific approach to tracking plant RSS characteristics. This perspective summarizes the recent progress regarding organic small-molecule fluorescent probes for RSS monitoring, including small-molecule biological thiols, hydrogen sulfide, and sulfane sulfurs, in plants; it also discusses their response mechanism toward RSS and their imaging applications in plants across the agricultural chemistry field.

Melatonin-ROS signal module regulates plant lateral root development

Lateral root (LR) branches from primary root. LR is vital for plants acquiring water and nutrients from soil, especially under stress conditions. LR development involves the complicated signaling network, which has not yet been fully understood. Melatonin, a novel endogenous plant regulator, plays a role in the regulation of LR development. However, we still have limited knowledge about melatonin-modulated signaling during LR development. Our recent study identifies that reactive oxygen species (ROS) acts as downstream signaling of melatonin to facilitate LR development. The recently identified receptor of melatonin in plants controls a signaling module involving G protein, ROS, and Ca²⁺. Based on these findings, we propose a novel signaling network for LR development controlled by melatonin.

Hydrogen sulfide (H2S) signaling in plant development and stress responses

ABSTRACT

Hydrogen sulfide (H₂S) was initially recognized as a toxic gas and its biological functions in mammalian cells have been gradually discovered during the past decades. In the latest decade, numerous studies have revealed that H₂S has versatile functions in plants as well. In this review, we summarize H₂S-mediated sulfur metabolic pathways, as well as the progress in the recognition of its biological functions in plant growth and development, particularly its physiological functions in biotic and abiotic stress responses. Besides direct chemical reactions, nitric oxide (NO) and hydrogen peroxide (H₂O₂) have complex relationships with H₂S in plant signaling, both of which mediate protein post-translational modification (PTM) to attack the cysteine residues. We also discuss recent progress in the research on the three types of PTMs and their biological functions in plants. Finally, we propose the relevant issues that need to be addressed in the future research.

GRAPHIC ABSTRACT

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s42994-021-00035-4.

Current approaches for detection of hydrogen sulfide and persulfidation in biological systems

The past decades have witnessed hydrogen sulfide (H₂S) serving as gaseous signaling molecule participating in diverse cellular and physiological processes in biological systems. Recently, a considerable number of studies highlight the signaling role of this redox-regulating molecule occurs via persulfidation, which is a post-translation modification of protein cysteine residues by covalent addition of thiol group form persulfide. However, our current understanding on detection of H₂S and persulfidation in biological systems still lags behind. This review aims to summarize current approaches for measuring H₂S and persulfidated levels in biological systems. Meanwhile, potential interference may exist in plant research has been proposed and discussed.

Hydrogen Sulfide: From a Toxic Molecule to a Key Molecule of Cell Life

Hydrogen sulfide (H2S) has always been considered toxic, but a huge number of articles published more recently showed the beneficial biochemical properties of its endogenous production throughout all regna. In this review, the participation of H2S in many physiological and pathological processes in animals is described, and its importance as a signaling molecule in plant systems is underlined from an evolutionary point of view. H2S quantification methods are summarized and persulfidation is described as the underlying mechanism of action in plants, animals and bacteria. This review aims to highlight the importance of its crosstalk with other signaling molecules and its fine regulation for the proper function of the cell and its survival.

Induction of caveolin-3/eNOS complex by nitroxyl (HNO) ameliorates diabetic cardiomyopathy

Nitroxyl (HNO), one-electron reduced and protonated sibling of nitric oxide (NO), is a potential regulator of cardiovascular functions. It produces positive inotropic, lusitropic, myocardial anti-hypertrophic and vasodilator properties. Despite of these favorable actions, the significance and the possible mechanisms of HNO in diabetic hearts have yet to be fully elucidated. H9c2 cells or primary neonatal mouse cardiomyocytes were incubated with normal glucose (NG) or high glucose (HG). Male C57BL/6 mice received intraperitoneal injection of streptozotocin (STZ) to induce diabetes. Here, we demonstrated that the baseline fluorescence signals of HNO in H9c2 cells were reinforced by both HNO donor Angeli's salt (AS), and the mixture of hydrogen sulfide (H₂S) donor sodium hydrogen sulfide (NaHS) and NO donor sodium nitroprusside (SNP), but decreased by HG. Pretreatment with AS significantly reduced HG-induced cell vitality injury, apoptosis, reactive oxygen species (ROS) generation, and hypertrophy in H9c2 cells. This effect was mediated by induction of caveolin-3 (Cav-3)/endothelial nitric oxide (NO) synthase (eNOS) complex. Disruption of Cav-3/eNOS by pharmacological manipulation or small interfering RNA (siRNA) abolished the protective effects of AS in HG-incubated H9c2 cells. In STZ-induced diabetic mice, administration of AS ameliorated the development of diabetic cardiomyopathy, as evidenced by improved cardiac function and reduced cardiac hypertrophy, apoptosis, oxidative stress and myocardial fibrosis without affecting hyperglycemia. This study shed light on how interaction of NO and H₂S regulates cardiac pathology and provide new route to treat diabetic cardiomyopathy with HNO.

Signaling by hydrogen sulfide and cyanide through post-translational modification

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

Interactions between hydrogen sulphide and nitric oxide regulate two soybean citrate transporters during the alleviation of aluminium toxicity

Hydrogen sulphide (H2 S) is emerging as an important signalling molecule involved in plant resistance to various stresses. However, the underlying mechanism of H2 S in aluminium (Al) resistance and the crosstalk between H2 S and nitric oxide (NO) in Al stress signalling remain elusive. Citrate secretion is a wide-spread strategy for plants against Al toxicity. Here, two citrate transporter genes, GmMATE13 and GmMATE47, were identified and characterized in soybean. Functional analysis in Xenopus oocytes and transgenic Arabidopsis showed that GmMATE13 and GmMATE47 mediated citrate exudation and enhanced Al resistance. Al treatment triggered H2 S generation and citrate exudation in soybean roots. Pretreatment with an H2 S donor significantly elevated Al-induced citrate exudation, reduced Al accumulation in root tips, and alleviated Al-induced inhibition of root elongation, whereas application of an H2 S scavenger elicited the opposite effect. Furthermore, H2 S and NO mediated Al-induced GmMATE expression and plasma membrane (PM) H+ -ATPase activity and expression. Further investigation showed that NO induced H2 S production by regulating the key enzymes involved in biosynthesis and degradation of H2 S. These findings indicate that H2 S acts downstream of NO in mediating Al-induced citrate secretion through the upregulation of PM H+ -ATPase-coupled citrate transporter cotransport systems, thereby conferring plant resistance to Al toxicity.

Hydrogen sulfide: A novel component in Arabidopsis peroxisomes which triggers catalase inhibition

Plant peroxisomes have the capacity to generate different reactive oxygen and nitrogen species (ROS and RNS), such as H₂ O₂ , superoxide radical (O₂ ^· - ), nitric oxide and peroxynitrite (ONOO^- ). These organelles have an active nitro-oxidative metabolism which can be exacerbated by adverse stress conditions. Hydrogen sulfide (H₂ S) is a new signaling gasotransmitter which can mediate the posttranslational modification (PTM) persulfidation. We used Arabidopsis thaliana transgenic seedlings expressing cyan fluorescent protein (CFP) fused to a canonical peroxisome targeting signal 1 (PTS1) to visualize peroxisomes in living cells, as well as a specific fluorescent probe which showed that peroxisomes contain H₂ S. H₂ S was also detected in chloroplasts under glyphosate-induced oxidative stress conditions. Peroxisomal enzyme activities, including catalase, photorespiratory H₂ O₂ -generating glycolate oxidase (GOX) and hydroxypyruvate reductase (HPR), were assayed in vitro with a H₂ S donor. In line with the persulfidation of this enzyme, catalase activity declined significantly in the presence of the H₂ S donor. To corroborate the inhibitory effect of H₂ S on catalase activity, we also assayed pure catalase from bovine liver and pepper fruit-enriched samples, in which catalase activity was inhibited. Taken together, these data provide evidence of the presence of H₂ S in plant peroxisomes which appears to regulate catalase activity and, consequently, the peroxisomal H₂ O₂ metabolism.

Eugenol Confers Cadmium Tolerance via Intensifying Endogenous Hydrogen Sulfide Signaling in Brassica rapa

Eugenol, a plant-derived small compound, shows great medicinal potential. However, whether and how eugenol regulates crop physiology remains elusive. Here we reported that eugenol induced Cd (cadmium) tolerance in the root of Brassica rapa. Roots were treated with eugenol and CdCl₂ simultaneously (eugenol + Cd) or pretreated with eugenol followed by CdCl₂ treatment (eugenol → Cd). Eugenol significantly attenuated Cd-induced growth inhibition, ROS accumulation, oxidative injury, and cell death, which were confirmed by in vivo histochemical analysis. Eugenol remarkably decreased free Cd²⁺ accumulation in root. Eugenol intensified GSH (glutathione) accumulation in roots upon CdCl₂ exposure, which explained the decrease in free Cd²⁺ and attenuation of oxidative injury. Eugenol stimulated endogenous H₂S (hydrogen sulfide) generation by upregulating the expression of BrLCD ( l-cysteine desulfhydrase) and BrDCD ( d-cysteine desulfhydrase) as well as their enzymatic activities in CdCl₂-treated root. Application of H₂S biosynthesis inhibitor or H₂S scavenger led to the decrease in endogenous H₂S level in Cd-treated root, which further compromised all the above effects of eugenol. These findings suggested that eugenol triggered H₂S → GSH signaling cassette in plants to combat Cd stress, which shed new light on eugenol-modulated plant physiology and the interaction between eugenol and H₂S.

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

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

Cadmium Disrupts the Balance between Hydrogen Peroxide and Superoxide Radical by Regulating Endogenous Hydrogen Sulfide in the Root Tip of Brassica rapa

Cd (cadmium) stress always alters the homeostasis of ROS (reactive oxygen species) including H₂O₂ (hydrogen sulfide) and [Formula: see text] (superoxide radical), leading to the oxidative injury and growth inhibition in plants. In addition to triggering oxidative injury, ROS has been suggested as important regulators modulating root elongation. However, whether and how Cd stress induces the inhibition of root elongation by differentially regulating endogenous H₂O₂ and [Formula: see text], rather than by inducing oxidative injury, remains elusive. To address these gaps, histochemical, physiological, and biochemical approaches were applied to investigate the mechanism for Cd to fine-tune the balance between H₂O₂ and [Formula: see text] in the root tip of Brassica rapa. Treatment with Cd at 4 and 16 μM significantly inhibited root elongation, while only 16 μM but not 4 μM of Cd induced oxidative injury and cell death in root tip. Fluorescent and pharmaceutical tests suggested that H₂O₂ and [Formula: see text] played negative and positive roles, respectively, in the regulation of root elongation in the presence of Cd (4 μM) or not. Treatment with Cd at 4 μM led to the increase in H₂O₂ and the decrease in [Formula: see text] in root tip, which may be attributed to the up-regulation of Br_UPB1s and the down-regulation of their predicted targets (four peroxidase genes). Cd at 4 μM resulted in the increase in endogenous H₂S in root tip by inducing the up-regulation of LCDs and DCDs. Treatment with H₂S biosynthesis inhibitor or H₂S scavenger significantly blocked Cd (4 μM)-induced increase in endogenous H₂S level, coinciding with the recovery of root elongation, the altered balance between H₂O₂ and [Formula: see text], and the expression of Br_UPB1s and two peroxidase genes. Taken together, it can be proposed that endogenous H₂S mediated the phytotoxicity of Cd at low concentration by regulating Br_UPB1s-modulated balance between H₂O₂ and [Formula: see text] in root tip. Such findings shed new light on the regulatory role of endogenous H₂S in plant adaptions to Cd stress.

Cinnamaldehyde Ameliorates Cadmium-Inhibited Root Elongation in Tobacco Seedlings via Decreasing Endogenous Hydrogen Sulfide Production

Cinnamaldehyde (CA) is natural plant-derived compound that has been highly appreciated for its medicinal properties. However, little information is known about the regulation of plant intrinsic physiology by CA. To address these gaps, physiological, histochemical, and biochemical approaches were applied to investigate CA-facilitated cadmium (Cd) tolerance in the roots of tobacco (Nicotiana tabacum) seedlings. Treatment with CdCl₂ at 20 μM for 72 h resulted in the significant decrease in root elongation by 40.39% as compared to control. CA alleviated Cd-inhibited root elongation in dose- and time-dependent manners. The addition of CA at 20 μM induced significant increase in root elongation by 42.58% as compared to Cd treatment alone. CA abolished Cd-induced ROS (reactive oxygen species) accumulation, lipid peroxidation, loss of membrane integrity, cell death, and free Cd2+ accumulation in roots. CA blocked the Cd-induced increase in the endogenous H₂S level through the down-regulation of d-cysteine desulfhydrase (DCD) expression. H₂S scavenger hypotaurine (HT) or potent H₂S-biosynthetic inhibitor dl-propargylglicine (PAG) were able mimic the action of CA on the blockade of Cd-induced H₂S accumulation, cell death, and growth inhibition. Enhancement of the endogenous H₂S level with NaHS (H₂S donor) abrogated all the beneficial capabilities of CA, HT, and PAG. Collectively, these results suggest that CA has great potential to confer plant tolerance against Cd stress, which is closely associated with its capability to inhibit Cd-induced H₂S production. This study not only provides evidences for the regulation of plant physiology by CA but also sheds new light on the cross-talk between CA and H₂S in physiological modulations.

Hydrogen sulfide enhances nitric oxide-induced tolerance of hypoxia in maize (Zea mays L.)

Our data present H ₂ S in a new role, serving as a multi-faceted transducer to different response mechanisms during NO-induced acquisition of tolerance to flooding-induced hypoxia in maize seedling roots. Nitric oxide (NO), serving as a secondary messenger, modulates physiological processes in plants. Recently, hydrogen sulfide (H₂S) has been demonstrated to have similar signaling functions. This study focused on the effects of treatment with H₂S on NO-induced hypoxia tolerance in maize seedlings. The results showed that treatment with the NO donor sodium nitroprusside (SNP) enhanced survival rate of submerged maize roots through induced accumulation of endogenous H₂S. The induced H₂S then enhanced endogenous Ca²⁺ levels as well as the Ca²⁺-dependent activity of alcohol dehydrogenase (ADH), improving the capacity for antioxidant defense and, ultimately, the hypoxia tolerance in maize seedlings. In addition, NO induced the activities of key enzymes in H₂S biosynthesis, such as L-cysteine desulfhydrases (L-CDs), O-acetyl-L-serine (thiol)lyase (OAS-TL), and β-Cyanoalanine Synthase (CAS). SNP-induced hypoxia tolerance was enhanced by the application of NaHS, but was eliminated by the H₂S-synthesis inhibitor hydroxylamine (HA) and the H₂S-scavenger hypotaurine (HT). H₂S concurrently enhanced the transcriptional levels of relative hypoxia-induced genes. Together, our findings indicated that H₂S serves as a multi-faceted transducer that enhances the nitric oxide-induced hypoxia tolerance in maize (Zea mays L.).

Cinnamaldehyde promotes root branching by regulating endogenous hydrogen sulfide

BACKGROUND

Cinnamaldehyde (CA) has been widely applied in medicine and food preservation. However, whether and how CA regulates plant physiology is largely unknown. To address these gaps, the present study investigated the beneficial effect of CA on root branching and its possible biochemical mechanism.

RESULTS

The lateral root (LR) formation of pepper seedlings could be markedly induced by CA at specific concentrations without any inhibitory effect on primary root (PR) growth. CA could induce the generation of endogenous hydrogen sulfide (H2S) by increasing the activity of L-cysteine desulfhydrase in roots. By fluorescently tracking endogenous H2S in situ, it could be clearly observed that H2S accumulated in the outer layer cells of the PR where LRs emerge. Sodium hydrosulfide (H2S donor) treatment induced LR formation, while hypotaurine (H2S scavenger) showed an adverse effect. The addition of hypotaurine mitigated the CA-induced increase in endogenous H2S level, which in turn counteracted the inducible effect of CA on LR formation.

CONCLUSION

CA showed great potential in promoting LR formation, which was mediated by endogenous H2S. These results not only shed new light on the application of CA in agriculture but also extend the knowledge of H2S signaling in the regulation of root branching.

Eugenol confers resistance to Tomato yellow leaf curl virus (TYLCV) by regulating the expression of SlPer1 in tomato plants

Tomato yellow leaf curl virus (TYLCV) is one of the most devastating plant diseases, and poses a significant agricultural concern because of the lack of an efficient control method. Eugenol is a plant-derived natural compound that has been widely used as a food additive and in medicine. In the present study, we demonstrated the potential of eugenol to enhance the resistance of tomato plants to TYLCV. The anti-TYLCV efficiency of eugenol was significantly higher than that of moroxydine hydrochloride (MH), a widely used commercial antiviral agent. Eugenol application stimulated the production of endogenous nitric oxide (NO) and salicylic acid (SA) in tomato plants. The full-length cDNA of SlPer1, which has been suggested to be a host R gene specific to TYLCV, was isolated from tomato plants. A sequence analysis suggested that SlPer1 might be a nucleobase-ascorbate transporter (NAT) belonging to the permease family. The transcript levels of SlPer1 increased markedly in response to treatment with eugenol or TYLCV inoculation. The results of this study also showed that SlPer1 expression was strongly induced by SA, MeJA (jasmonic acid methyl ester), and NO. Thus, we propose that the increased transcription of SlPer1 contributed to the high anti-TYLCV efficiency of eugenol, which might involve in the generation of endogenous SA and NO. Such findings provide the basis for the development of eugenol as an environmental-friendly agricultural antiviral agent.

The Significance of Hydrogen Sulfide for Arabidopsis Seed Germination

Hydrogen sulfide (H2S) recently emerged as an important gaseous signaling molecule in plants. In this study, we investigated the possible functions of H2S in regulating Arabidopsis seed germination. NaHS treatments delayed seed germination in a dose-dependent manner and were ineffective in releasing seed dormancy. Interestingly, endogenous H2S content was enhanced in germinating seeds. This increase was correlated with higher activity of three enzymes (L-cysteine desulfhydrase, D-cysteine desulfhydrase, and β-cyanoalanine synthase) known as sources of H2S in plants. The H2S scavenger hypotaurine and the D/L cysteine desulfhydrase inhibitor propargylglycine significantly delayed seed germination. We analyzed the germinative capacity of des1 seeds mutated in Arabidopsis cytosolic L-cysteine desulfhydrase. Although the mutant seeds do not exhibit germination-evoked H2S formation, they retained similar germination capacity as the wild-type seeds. In addition, des1 seeds responded similarly to temperature and were as sensitive to ABA as wild type seeds. Taken together, these data suggest that, although its metabolism is stimulated upon seed imbibition, H2S plays, if any, a marginal role in regulating Arabidopsis seed germination under standard conditions.

Selenium inhibits root elongation by repressing the generation of endogenous hydrogen sulfide in Brassica rapa

Selenium (Se) has been becoming an emerging pollutant causing severe phytotoxicity, which the biochemical mechanism is rarely known. Although hydrogen sulfide (H2S) has been suggested as an important exogenous regulator modulating plant physiological adaptions in response to heavy metal stress, whether and how the endogenous H2S regulates Se-induce phytotoxicity remains unclear. In this work, a self-developed specific fluorescent probe (WSP-1) was applied to track endogenous H2S in situ in the roots of Brassica rapa under Se(IV) stress. Se(IV)-induced root growth stunt was closely correlated with the inhibition of endogenous H2S generation in root tips. Se(IV) stress dampened the expression of most LCD and DCD homologues in the roots of B. rapa. By using various specific fluorescent probes for bio-imaging root tips in situ, we found that the increase in endogenous H2S by the application of H2S donor NaHS could significantly alleviate Se(IV)-induced reactive oxygen species (ROS) over-accumulation, oxidative impairment, and cell death in root tips, which further resulted in the recovery of root growth under Se(IV) stress. However, dampening the endogenous H2S could block the alleviated effect of NaHS on Se(IV)-induced phytotoxicity. Finally, the increase in endogenous H2S resulted in the enhancement of glutathione (GSH) in Se(IV)-treated roots, which may share the similar molecular mechanism for the dominant role of H2S in removing ROS by activating GSH biosynthesis in mammals. Altogether, these data provide the first direct evidences confirming the pivotal role of endogenous H2S in modulating Se(IV)-induced phytotoxicity in roots.

Hydrogen sulfide is a novel gasotransmitter with pivotal role in regulating lateral root formation in plants

Hydrogen sulfide (H 2S), the third gasotransmitter after nitric oxide (NO) and carbon monoxide (CO), is a critical neuromodulator in the pathogenesis of various diseases from neurodegenerative diseases to diabetes or heart failure. The crosstalk between NO and H 2S has been well established in mammalian physiology. In planta, NO is demonstrated to regulate lateral root formation by acting downstream of auxin. The recent reports revealed that H 2S is a novel inducer of lateral root (LR) formation by stimulating the expression of cell cycle regulatory genes (CCRGs), acting similarly with NO, CO, and IAA. Interestingly, during the initiation of lateral root primordia, IAA is a potent inducer of endogenous H 2S and CO, which is produced by L-cysteine desulfhydrase (LCD) and heme oxygenase-1 (HO-1), respectively. The increasing evidences suggest that H 2S-promoted LR growth is dependent on the endogenous production of CO. In addition, our results indicate that the H 2S signaling in the regulation of LR formation can be associated to NO and Ca 2+. In this addendum, we advanced a proposed schematic model for H 2S-mediated signaling pathway of plant LR development.

Hydrogen sulfide is a novel gasotransmitter with pivotal role in regulating lateral root formation in plants

Hydrogen sulfide (H ₂S), the third gasotransmitter after nitric oxide (NO) and carbon monoxide (CO), is a critical neuromodulator in the pathogenesis of various diseases from neurodegenerative diseases to diabetes or heart failure. The crosstalk between NO and H ₂S has been well established in mammalian physiology. In planta, NO is demonstrated to regulate lateral root formation by acting downstream of auxin. The recent reports revealed that H ₂S is a novel inducer of lateral root (LR) formation by stimulating the expression of cell cycle regulatory genes (CCRGs), acting similarly with NO, CO, and IAA. Interestingly, during the initiation of lateral root primordia, IAA is a potent inducer of endogenous H ₂S and CO, which is produced by _L-cysteine desulfhydrase (LCD) and heme oxygenase-1 (HO-1), respectively. The increasing evidences suggest that H ₂S-promoted LR growth is dependent on the endogenous production of CO. In addition, our results indicate that the H ₂S signaling in the regulation of LR formation can be associated to NO and Ca ²⁺. In this addendum, we advanced a proposed schematic model for H ₂S-mediated signaling pathway of plant LR development.