Hydrogen sulfide delays GA-triggered programmed cell death in wheat aleurone layers by the modulation of glutathione homeostasis and heme oxygenase-1 expression

Hydrogen sulfide (H₂S) is considered as a cellular signaling intermediate in higher plants, but corresponding molecular mechanisms and signal transduction pathways in plant biology are still limited. In the present study, a combination of pharmacological and biochemical approaches was used to study the effect of H₂S on the alleviation of GA-induced programmed cell death (PCD) in wheat aleurone cells. The results showed that in contrast with the responses of ABA, GA brought about a gradual decrease of l-cysteine desulfhydrase (LCD) activity and H₂S production, and thereafter PCD occurred. Exogenous H₂S donor sodium hydrosulfide (NaHS) not only effectively blocked the decrease of endogenous H₂S release, but also alleviated GA-triggered PCD in wheat aleurone cells. These responses were sensitive to hypotaurine (HT), a H₂S scavenger, suggesting that this effect of NaHS was in an H₂S-dependent fashion. Further experiment confirmed that H₂S, rather than other sodium- or sulphur-containing compounds derived from the decomposing of NaHS, was attributed to the rescuing response. Importantly, the reversing effect was associated with glutathione (GSH) because the NaHS triggered increases of endogenous GSH content and the ratio of GSH/oxidized GSH (GSSG) in GA-treated layers, and the NaHS-mediated alleviation of PCD was markedly eliminated by l-buthionine-sulfoximine (BSO, a selective inhibitor of GSH biosynthesis). The inducible effect of NaHS was also ascribed to the modulation of heme oxygenase-1 (HO-1), because the specific inhibitor of HO-1 zinc protoporphyrin IX (ZnPP) significantly suppressed the NaHS-related responses. By contrast, the above inhibitory effects were reversed partially when carbon monoxide (CO) aqueous solution or bilirubin (BR), two of the by-products of HO-1, was added, respectively. NaHS-triggered HO-1 gene expression in GA-treated layers was also confirmed. Together, the above results clearly suggested that the H₂S-delayed PCD in GA-treated wheat aleurone cells was associated with the modulation of GSH homeostasis and HO-1 gene expression.     

Cadmium-Induced Hydrogen Sulfide Synthesis Is Involved in Cadmium Tolerance in Medicago sativa by Reestablishment of Reduced (Homo)glutathione and Reactive Oxygen Species Homeostases

Until now, physiological mechanisms and downstream targets responsible for the cadmium (Cd) tolerance mediated by endogenous hydrogen sulfide (H₂S) have been elusive. To address this gap, a combination of pharmacological, histochemical, biochemical and molecular approaches was applied. The perturbation of reduced (homo)glutathione homeostasis and increased H₂S production as well as the activation of two H₂S-synthetic enzymes activities, including _L-cysteine desulfhydrase (LCD) and _D-cysteine desulfhydrase (DCD), in alfalfa seedling roots were early responses to the exposure of Cd. The application of H₂S donor sodium hydrosulfide (NaHS), not only mimicked intracellular H₂S production triggered by Cd, but also alleviated Cd toxicity in a H₂S-dependent fashion. By contrast, the inhibition of H₂S production caused by the application of its synthetic inhibitor blocked NaHS-induced Cd tolerance, and destroyed reduced (homo)glutathione and reactive oxygen species (ROS) homeostases. Above mentioned inhibitory responses were further rescued by exogenously applied glutathione (GSH). Meanwhile, NaHS responses were sensitive to a (homo)glutathione synthetic inhibitor, but reversed by the cotreatment with GSH. The possible involvement of cyclic AMP (cAMP) signaling in NaHS responses was also suggested. In summary, LCD/DCD-mediated H₂S might be an important signaling molecule in the enhancement of Cd toxicity in alfalfa seedlings mainly by governing reduced (homo)glutathione and ROS homeostases.     

H_2S对干旱胁迫下白三叶幼苗抗氧化防御能力的影响

以‘拉丁诺’白三叶(Trifolium repens cv.‘Ladino’)为试验材料,研究外源H2S处理对PEG6 000(聚乙二醇)模拟干旱胁迫下白三叶叶片相对含水量(RWC)、膜脂过氧化、活性氧成分、抗氧化酶、抗坏血酸-谷胱甘肽循环代谢和非酶抗氧化物质的影响,以揭示H_2S调控白三叶抗旱性的生理机制。结果显示:(1)0.2 mmol/L的外源NaHS(H_2S供体)能显著提高干旱胁迫下白三叶的叶片相对含水量,维持显著较低的电解质渗透率(EL)和丙二醛(MDA)含量。(2)与直接干旱胁迫相比,干旱胁迫下外源添加NaHS处理的白三叶叶片内超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性显著增强,抗坏血酸-谷胱甘肽循环代谢中关键酶抗坏血酸过氧化物酶(APX)、脱氢抗坏血酸还原酶(DHAR)、单脱水抗坏血酸还原酶(MDHAR)和谷胱甘肽还原酶(GR)活性及其抗氧化中间产物抗坏血酸(AsA)、谷胱甘肽(GSH)含量也显著提高。(3)叶片类黄酮、总酚和原花青素的含量在一定的胁迫时间范围内亦显著增加,并伴随着活性氧成分O_2~(-·)产生速率和H_2O_2水平降低。研究认为,外源H2S能通过促进干旱胁迫下白三叶体内的多重抗氧化防御能力来提高其幼苗的抗旱性。     

Hydrogen sulfide alleviated chromium toxicity in wheat

Effects of H₂S on seed germination under chromium (Cr) stress were investigated in wheat (Triticum aestivum L.). Under Cr stress, the percentage of germination of wheat seeds decreased, but this decrease could be alleviated by pretreatment with NaHS, an H₂S donor, in a dose-dependent manner. Furthermore, NaHS significantly enhanced the activities of amylase, esterase, superoxide dismutase, catalase, ascorbate peroxidase, and guaiacol peroxidase in Cr-stressed germinating seeds, whereas reduced the Cr-induced increase in lipoxygenase activity and over-production of malondialdehyde (MDA) and H₂O₂, and sustained slightly higher content of endogenous H₂S.     

Slow Regulated Release of H2S Inhibits Oxidative Stress Induced Cell Death by Influencing Certain Key Signaling Molecules

Hydrogen sulphide (H₂S) is one of three gaseous signaling molecules after nitric oxide and carbon monoxide. Various H₂S donor compounds have been synthesized to study its physiological function. Among these compounds sodium hydrosulphide (NaHS), a donor of releasing H₂S rapidly have shown to be protective in certain neuronal cell line but several in vivo studies have generated conflicting data. Furthermore several slow releasing H₂S donors have been shown to have positive effects on cells in culture. The intracellular concentration of H₂S and hence its rate of production may be a factor in keeping the balance between its neuroprotective and toxic effects. The present study was undertaken to deduce how a rapid releasing H₂S donor (NaHS) as opposed to a slow releasing donor (ADTOH), affect oxidative stress related intracellular components and survival of RGC-5 cells. It was concluded that when RGC-5 cells are exposed to the toxic effects of glutamate in combination with buthionine sulfoxime (Glu/BSO), ADTOH was more efficacious in inhibiting apoptosis, scavenging reactive oxygen species (ROS), stimulation of glutathione (GSH) and gluthathione-S-transferase (GST). Western blot and qPCR analysis showed ADTOH increased the levels of Nrf2, HO-1, PKCα, p-Akt, Bcl-2 and XIAP but caused a decrease of Nfκβ and xCT greater than NaHS. This study is first to compare the efficacy of two H₂S donor drugs as potential neuroprotectants and demonstrate that slow regulated release of H₂S to cell culture can be more beneficial in inhibiting oxidative stress induced cell death.     

Manganese-Induced Neurotoxicity is Differentially Enhanced by Glutathione Depletion in Astrocytoma and Neuroblastoma Cells

Manganese (Mn) is neurotoxic: the underlying mechanisms have not been fully elucidated. l-Buthionine-(S,R)-sulfoximine (BSO) is an irreversible inhibitor of γ-glutamylcysteine synthetase, an important enzyme in glutathione (GSH) synthesis. To test the hypothesis that BSO modulates Mn toxicity, we investigated the effects of treatment of U-87 or SK-N-SH cells with MnCl₂, BSO, or MnCl₂ plus BSO. We monitored cell viability using MTT assay, staining with HO-33342 to assess live and/or apoptotic cells, and staining with propidium iodide (PI) to assess necrotic cells; we also measured cellular glutathione. Our results indicate decreased viability in both cell types when treated with MnCl₂ or BSO: Mn was more toxic to SK-N-SH cells, whereas BSO was more toxic to U-87 cells. Because BSO treatment accentuated Mn toxicity in both cell lines, GSH may act to combat Mn toxicity. Thus, further investigation in oxidative stress mediated by glutathione depletion will unravel new Mn toxicity mechanism(s).     

Speciation dependant antioxidative response in roots and leaves of sorghum (Sorghum bicolor (L.) Moench cv CO 27) under Cr(III) and Cr(VI) stress

Growth, lipid peroxidation, H₂O₂ produciton and the response of the antioxidant enzymes and metabolites of the ascorbate glutathione pathway to oxidative stress caused by two concentrations (50 and 100 µM) of Cr(III) and Cr(VI) was studied in 15 day old seedlings of sorghum (Sorghum bicolor (L.) Moench cv CO 27) after 10 days of treatment. Cr accumulation in sorghum plants was concentration and organ dependant. There was no significant growth retardation of plants under 50 µM Cr(III) stress. 100 µM Cr(VI) was most toxic of all the treatments in terms of root and leaf growth and oxidative stress. 50 µM Cr(VI) treated roots exhibited high significant increase in superoxide dismutase (SOD), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) (p < 0.01) and significant increases in catalse (CAT), ascorbate peroxidase (APX) and monodehydroascorbate reductase (MDHAR) (p < 0.05). A high increase in ascorbic acid (AA) level was seen in roots of 50 µM Cr(VI) treated plants in comparison with control. Levels of reduced glutathione (GSH) showed a varied and complex response in all the treatments in both plant parts. GSH/GSSG ratio was not affected by Cr(III) treatment in leaves, in contrast, roots exhibited significant reduction in the ratio. Results indicate that GSH depletion increased sensitivity to oxidative stress (Cr(VI) roots and leaves and Cr(III) 100 µM roots) and AA in tandem with APX compensated for GSH depletion by acting directly on H₂O₂ and the mechanism of defensive response in roots as well as leaves varied in its degree and effectiveness due to the concentration dependant differences observed in translocation of the element itself, reactive oxygen species (ROS) generation and enzyme inhibition based on the oxidation state supplied to the plants.     

Regulation of apoptosis/necrosis execution in cadmium-treated human promonocytic cells under different forms of oxidative stress

Pulse-treatment of U-937 human promonocytic cells with cadmium chloride followed by recovery caused caspase-9/caspase-3-dependent, caspase-8-independent apoptosis. However, pre-incubation with the glutathione (GSH)-suppressing agent DL-buthionine-(S,R)-sulfoximine (cadmium/BSO), or co-treatment with H₂O₂ (cadmium/H₂O₂), switched the mode of death to caspase-independent necrosis. The switch from apoptosis to necrosis did not involve gross alterations in Apaf-1 and pro-caspase-9 expression, nor inhibition of cytochrome c release from mitochondria. However, cadmium/H₂O₂-induced necrosis involved ATP depletion and was prevented by 3-aminobenzamide, while cadmium/BSO-induced necrosis was ATP independent. Pre-incubation with BSO increased the intracellular cadmium accumulation, while co-treatment with H₂O₂ did not. Both treatments caused intracellular peroxide over-accumulation and disruption of mitochondrial transmembrane potential (ΔΨm). However, while post-treatment with N-acetyl-L-cysteine or butylated hydroxyanisole reduced the cadmium/BSO-mediated necrosis and ΔΨm disruption, it did not reduce the effects of cadmium/H₂O₂. Bcl-2 over-expression, which reduced peroxide accumulation without affecting the intracellular GSH content, attenuated necrosis generation by cadmium/H₂O₂ but not by cadmium/BSO. By contrast, AIF suppression, which reduced peroxide accumulation and increased the GSH content, attenuated the toxicity of both treatments. These results unravel the existence of two different oxidation-mediated necrotic pathways in cadmium-treated cells, one of them resulting from ATP-dependent apoptosis blockade, and the other involving the concurrence of multiple regulatory factors.     

外源H_2S对NO_3~-胁迫下番茄幼苗生理生化特性的影响

采用营养液水培方法,通过外源施加H2S供体NaHS(100μmol/L),研究了信号分子H2S对100mmol/L NO3-胁迫下番茄幼苗生理生化特性的影响。结果表明:(1)NO3-胁迫下,随着处理时间的延长,番茄幼苗的株高、根长、鲜重和干重显著降低,叶绿素(a、b)含量、净光合速率、气孔导度、蒸腾速率均显著降低,而胞间CO2浓度以及丙二醛(MDA)、H2O2含量增加,超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)活性显著降低,抗坏血酸(AsA)和还原性谷胱甘肽(GSH)含量显著降低。(2)与NO3-胁迫处理相比,外源NaHS处理1、3、5d后,番茄幼苗的株高、根长、鲜重和干重显著增加,叶绿素(a、b)含量、净光合速率、气孔导度、蒸腾速率均显著升高,而胞间CO2浓度显著降低;MDA和H2O2含量降低,SOD、POD、CAT和APX活性显著增强,AsA和GSH含量显著增加,而且幼苗的硝酸还原酶、谷氨酰胺合成酶、谷氨酸合酶的活性显著增强;L-半胱氨酸脱巯基酶活性和内源H2S含量增加。研究认为,外源H2S可能通过提高抗氧化物酶的活性和增加抗氧化物质含量来缓解NO3-对番茄幼苗造成的伤害,从而增强其对NO3-胁迫耐性。     

Hydrogen sulfide attenuates homocysteine-induced osteoblast dysfunction by inhibiting mitochondrial toxicity

Homocysteine (Hcy) is detrimental to bone health in a mouse model of diet-induced hyperhomocysteinemia (HHcy). However, little is known about Hcy-mediated osteoblast dysfunction via mitochondrial oxidative damage. Hydrogen sulfide (H₂S) has potent antioxidant, anti-inflammatory, and antiapoptotic effects. In this study, we hypothesized that the H₂S mediated recovery of osteoblast dysfunction by maintaining mitochondrial biogenesis in Hcy-treated osteoblast cultures in vitro. MC3T3-E1 osteoblastic cells were exposed to Hcy treatment in the presence or absence of an H₂S donor (NaHS). Cell viability, osteogenic differentiation, reactive oxygen species (ROS) production were determined. Mitochondrial DNA copy number, adenosine triphosphate (ATP) production, and oxygen consumption were also measured. Our results demonstrated that administration of Hcy increases the intracellular Hcy level and decreases intracellular H₂S level and expression of the cystathionine β-synthase/Cystathionine γ-lyase system, thereby inhibiting osteogenic differentiation. Pretreatment with NaHS attenuated Hcy-induced mitochondrial toxicity (production of total ROS and mito-ROS, ratio of mitochondrial fission (DRP-1)/fusion (Mfn-2)) and restored ATP production and mitochondrial DNA copy numbers as well as oxygen consumption in the osteoblast as compared with the control, indicating its protective effects against Hcy-induced mitochondrial toxicity. In addition, NaHS also decreased the release of cytochrome c from the mitochondria to the cytosol, which induces cell apoptosis. Finally, flow cytometry confirmed that NaHS can rescue cells from apoptosis induced by Hcy. Our studies strongly suggest that NaHS has beneficial effects on mitochondrial toxicity, and could be developed as a potential therapeutic agent against HHcy-induced mitochondrial dysfunction in cultured osteoblasts in vitro.     

Chromium effect on ROS generation and detoxification in pea (Pisum sativum) leaf chloroplasts

Pea plants were exposed to 0, 20, 50, and 100 µM chromium [Cr(VI)] to investigate oxidative stress in isolated chloroplasts. Leaf area and biomass accumulation were significantly reduced at higher Cr supply. Generation of superoxide, hydrogen peroxide, and ·OH radical generation was enhanced in the chloroplasts isolated from Cr-exposed pea plants. Cr(VI) significantly reduced F _v/F _m ratio of chlorophyll (Chl) fluorescence, Chl content, and whole chain electron transport rate. Superoxide dismutase (SOD) activity increased at lower Cr supply while it decreased at higher Cr supply. Ascorbate peroxidase (APX) was found to be most sensitive to Cr stress. Monodehydroascorbate reductase activity remained higher at 20 and 50 µM Cr but decreased at 100 µM Cr. Increased activities of dehydroascorbate reductase (DHAR) and glutathione reductase (GR) in the isolated chloroplasts were observed during the initial 3 days of Cr exposure of pea plants. Activities of DHAR and GR were increased up to day 3 only. Ascorbate and glutathione (GSH) pools showed similar decrease that was more evident in the GSH pool as the duration of Cr treatment increased. Observed changes in reactive oxygen species concentration, photosynthetic characteristics, and antioxidant system indicate that chloroplasts in Cr-exposed pea plants are an important target of oxidative stress.     

Trivalent chromium pretreatment alleviates the toxicity of oxidative damage in wheat plants exposed to hexavalent chromium

Treating plants with abiotic or biotic factors can lead to the establishment of a unique primed state of defense. Primed plants display enhanced defense reactions upon further challenge with environmental stressors. Here, we report that trivalent chromium (Cr(III)) pretreatment can alleviate hexavalent chromium (Cr(VI)) toxicity in 2-week-old wheat plants. The data indicate that Cr(III)-pretreated wheat displayed longer survival times and less heavy metal toxicity symptoms under Cr(VI) exposure than the control. To investigate the possible mechanism from an antioxidant defense perspective, we determined the H₂O₂ and lipid peroxide content (TBARS), the activities of antioxidant enzymes (SOD, CAT, APX and GR) and the antioxidant metabolite content (ascorbate and glutathione content, AsA/DHA and GSH/GSSG ratios) in pretreated wheat roots. The results showed that 0.5 μM Cr(III) pretreatment can alleviate oxidative damage, such as H₂O₂ and TBARS accumulation, in root tissues compared to the control during the first 3 days of Cr(VI) exposure. Furthermore, we determined that this pretreatment can significantly increase the antioxidant enzyme activities and total ascorbate and glutathione contents compared to the control treatment. In addition, redox homeostasis declined slightly in pretreated wheat compared to the control in the presence of Cr(VI). We discuss a possible mechanism for Cr(III)-mediated protection of wheat.     

Involvement of glutathione in heat shock– and hydrogen peroxide–induced cadmium tolerance of rice (Oryza sativa L.) seedlings

The role of reduced glutathione (GSH) in heat shock (HS)- and H₂O₂-induced protection of rice (Oryza sativa L., cv. Taichung 1) seedlings from Cd stress was investigated. HS- and H₂O₂-pretreatment resulted in an increase in GSH content in leaves of rice seedlings. Addition of exogenous GSH under non-HS conditions, which resulted in an increase in GSH in leaves, enhanced subsequent Cd tolerance of rice seedlings. Pretreatment with buthionine sulfoximine (BSO), a specific inhibitor of GSH synthesis, which effectively inhibited GSH content induced by HS and H₂O₂, reduced subsequent Cd tolerance. Furthermore, the effect of BSO on HS- and H₂O₂-induced GSH accumulation and toxicity by subsequent Cd stress can be reversed by the addition of GSH. The time-course analyses of HS in rice seedlings demonstrated that the accumulation of H₂O₂ preceded the increase in GSH. Based on the data obtained in this study, it could be concluded that the early accumulation of H₂O₂ during HS signals the increase in GSH content, which in turn protects rice seedlings from oxidative damage caused by Cd.     

Uptake and Translocation of Tri- and Hexa-Valent Chromium and Their Effects on Black Gram (Vigna mungo L. Hepper cv. Co4) Roots

An equal concentration (100 μM) of Cr(III)- and Cr(VI)-induced changes in activities of antioxidative enzymes and metabolites of ascorbate-glutathione cycle was studied in 7-d-old black gram (Vigna mungo L Hepper cv. Co4) seedlings for 5-d after infliction of Cr stress. Seeds were germinated and grown in the presence or absence of Cr under controlled environmental conditions. Uptake and translocation of Cr rate was relatively higher during first 12 h of treatment with both speciation of Cr, Cr(III)- and Cr(VI)-treated black gram roots retained 15 times more Cr than the shoots. Significantly increased lipid peroxidation was observed in the form of accumulation of malondialdehyde (MDA) and production of hydrogen peroxide (H₂O₂) molecule and superoxide (O₂ ) radical after 6 h of infliction with Cr(VI) and after 12 h in Cr(III)-treated black gram roots. Superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities were significantly increased under Cr(VI)-treatment after 12 and 6 h, respectively. However, catalase (CAT) and monodehydroascorbate reductase (MDHAR) activities were not significantly increased under Cr(Ill)-treatment. There was a steep increase of 2.71 μmol g^-1 FW in ascorbic acid (AA) content was observed between 6 and 24 h of Cr(VI)-treatment. Oxidized glutathione (GSSG) content was steadily increased through the course of Cr(III)- and Cr(VI)-treatments, where as reduced glutathione (GSH) level was decreased after 24 h of treatment. GSH/GSSG ratio was rapidly decreased in treatment with Cr(III) than the Cr(VI). There was significant increase of 99 nmol g^-1 FW in non-protein thiol (NPT) content was recorded between 6 and 24 h of Cr(VI)-treatment. The present results showed differential response to AA and H₂O₂ signaling by Cr(III) and Cr(VI), AA in combination with APX was more effective in mitigating oxidative stress as against the role of GSH as an antioxidant.     

Effect of pretreatment with hydrogen sulfide donor sodium hydrosulfide on heat tolerance in relation to antioxidant system in maize (Zea mays) seedlings

Hydrogen sulfide (H₂S) is a signal molecule that is involved in plant growth, development and the acquisition of stress tolerance including heat tolerance, but the mechanism of H₂S-induced heat tolerance is not completely clear. In present study, the effect of sodium hydrosulfide (NaHS), a H₂S donor, treatment on heat tolerance of maize seedlings in relation to antioxidant system was investigated. The results showed that NaHS treatment improved survival percentage of maize seedlings under heat stress in a concentration-dependent manner, indicating that H₂S treatment could improve heat tolerance of maize seedlings. To further study mechanism of NaHS-induced heat tolerance, catalase (CAT), guaiacol peroxidase (GPX), superoxide dismutase (SOD), glutathione reductase (GR) and ascorbate peroxidase (APX) activities, and glutathione (GSH) and ascorbic acid (AsA) contents in maize seedlings were determined. The results showed that NaHS treatment increased the activities of CAT, GPX, SOD and GR, and GSH and AsA contents as well as the ratio of reduced antioxidants to total antioxidants [AsA/(AsA+DHA) and GSH/(GSH +GSSG)] in maize seedlings under normal culture conditions compared with the control. Under heat stress, antioxidant enzymes activities, antioxidants contents and the ratio of the reduced antioxidants to total antioxidants in control and treated seedlings all decreased, but NaHS-treated seedlings maintained higher antioxidant enzymes activities and antioxidants levels as well as the ratio of reduced antioxidants to total antioxidants. All of above-mentioned results suggested that NaHS treatment could improve heat tolerance of maize seedlings, and the acquisition of this heat tolerance may be relation to enhanced antioxidant system activity.     

Involvement of ERK in NMDA receptor-independent cortical neurotoxicity of hydrogen sulfide

Hydrogen sulfide (H₂S), a gasotransmitter, exerts both neurotoxicity and neuroprotection, and targets multiple molecules including NMDA receptors, T-type calcium channels and NO synthase (NOS) that might affect neuronal viability. Here, we determined and characterized effects of NaHS, an H₂S donor, on cell viability in the primary cultures of mouse fetal cortical neurons. NaHS caused neuronal death, as assessed by LDH release and trypan blue staining, but did not significantly reduce the glutamate toxicity. The neurotoxicity of NaHS was resistant to inhibitors of NMDA receptors, T-type calcium channels and NOS, and was blocked by inhibitors of MEK, but not JNK, p38 MAP kinase, PKC and Src. NaHS caused prompt phosphorylation of ERK and upregulation of Bad, followed by translocation of Bax to mitochondria and release of mitochondrial cytochrome c, leading to the nuclear condensation/fragmentation. These effects of NaHS were suppressed by the MEK inhibitor. Our data suggest that the NMDA receptor-independent neurotoxicity of H₂S involves activation of the MEK/ERK pathway and some apoptotic mechanisms.     

Effects of exogenous hydrogen sulfide on the redox states of ascorbate and glutathione in maize leaves under salt stress

This study investigated the effects of exogenous hydrogen sulfide (H₂S) on the redox states of ascorbate (AsA) and glutathione (GSH) in maize leaves under NaCl (100 mM) stress. Salt stress increased the activities of ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), Γ-glutamylcysteine synthetase (Γ-ECS), and L-galactono-1,4-lactone dehydrogenase (GalLDH), malondialdehyde content and electrolyte leakage, and reduced the ratios of reduced and oxidised forms of AsA (AsA/DHA) and GSH (GSH/GSSG) compared with control. Pretreatment with NaHS (H₂S donor) further enhanced the activities of the above enzymes except MDHAR and ameliorated the decrease in the ratios of AsA/DHA and GSH/GSSG compared with the salt stress alone. Pretreatment with NaHS significantly reduced the malondialdehyde content and electrolyte leakage induced by the salt stress. Pretreatment with NaHS alone did not affect any of the above mentioned parameters compared with the control. Our results suggest that exogenous H2S could maintain the redox states of ascorbate and glutathione by up-regulating the ascorbate and glutathione metabolism and thus play an important role for acquisition of salt stress tolerance in maize.     

Responses of nitric oxide and hydrogen sulfide in regulating oxidative defence system in wheat plants grown under cadmium stress

We conducted a study to evaluate the interactive effect of NO and H₂S on the cadmium (Cd) tolerance of wheat. Cadmium stress considerably reduced total dry weight, chlorophyll a and b content and ratio of Fv/Fm by 36.7, 48.6, 26.7 and 19.5%, respectively, but significantly enhanced the levels of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), endogenous H₂S and NO, and the activities of antioxidant enzymes. Exogenously applied sodium nitroprusside (SNP) and sodium hydrosulfide (NaHS), donors of NO and H₂S, respectively, enhanced total plant dry matter by 47.8 and 39.1%, chlorophyll a by 92.3 and 61.5%, chlorophyll b content by 29.1 and 27.2%, Fv/Fm ratio by 19.7 and 15.2%, respectively, and the activities of antioxidant enzymes, but lowered oxidative stress and proline content in Cd-stressed wheat plants. NaHS and SNP also considerably limited both the uptake and translocation of Cd, thereby improving the levels of some key mineral nutrients in the plants. Enhanced levels of NO and H₂S induced by NaHS were reversed by hypotuarine application, but they were substantially reduced almost to 50% by cPTIO (a NO scavenger) application. Hypotuarine was not effective, but cPTIO was highly effective in reducing the levels of NO and H₂S produced by SNP in the roots of Cd-stressed plants. The results showed that interactive effect of NO and H₂S can considerably improve plant resistance against Cd toxicity by reducing oxidative stress and uptake of Cd in plants as well as by enhancing antioxidative defence system and uptake of some essential mineral nutrients.     

Boron toxicity is alleviated by hydrogen sulfide in cucumber (Cucumis sativus L.) seedlings

Boron (B) is an essential micronutrient for plants, which when occurs in excess in the growth medium, becomes toxic to plants. Rapid inhibition of root elongation is one of the most distinct symptoms of B toxicity. Hydrogen sulfide (H₂S) is emerging as a potential messenger molecule involved in modulation of physiological processes in plants. In the present study, we investigated the role of H₂S in B toxicity in cucumber (Cucumis sativus) seedlings. Root elongation was significantly inhibited by exposure of cucumber seedlings to solutions containing 5 mM B. The inhibitory effect of B on root elongation was substantially alleviated by treatment with H₂S donor sodium hydrosulfide (NaHS). There was an increase in the activity of pectin methylesterase (PME) and up-regulated expression of genes encoding PME (CsPME) and expansin (CsExp) on exposure to high B concentration. The increase in PME activity and up-regulation of expression of CsPME and CsExp induced by high B concentration were markedly reduced in the presence of H₂S donor. There was a rapid increase in soluble B concentrations in roots on exposure to high concentration B solutions. Treatment with H₂S donor led to a transient reduction in soluble B concentration in roots such that no differences in soluble B concentrations in roots in the absence and presence of NaHS were found after 8 h exposure to the high concentration B solutions. These findings suggest that increases in activities of PME and expansin may underlie the inhibition of root elongation by toxic B, and that H₂S plays an ameliorative role in protection of plants from B toxicity by counteracting B-induced up-regulation of cell wall-associated proteins of PME and expansins.