Hypotaurine Research Articles

Hydrogen Sulfide and 5‐Aminolevulinic Acid Synergistically Enhance Drought Tolerance in Tomato (Solanum lycopersicum L.)

ABSTRACTEnhancing crop drought tolerance is crucial for food security amid climate change. This study examines how 5‐aminolevulinic acid (ALA) and hydrogen sulfide (H2S) can improve drought resilience in tomato plants, which are essential for sustainable food production. Drought stress was induced using 12% PEG‐6000. Plants were pre‐treated with 25 mg L−1 ALA and 0.1 mg L−1 hypotaurine (HT), followed by 0.2 mM sodium hydrosulfide (NaHS) treatment to assess the effects on plant physiological effects over 10 days. Drought stress reduced plant dry weight, chlorophylls (a and b), Fv/Fm, leaf water potential, and relative water content, while increasing glycine betaine (GB) and proline levels. Additionally, drought stress elevated NADPH oxidase (NOX) and glycolate oxidase (GOX) activities, inducing oxidative stress and membrane damage. ALA and NaHS enhanced plant growth, photosynthesis, proline, GB, ALA content, ATP synthase, and ATPase activities, while mitigating NOX and GOX activities, thereby reducing and H2O2 radicals. ALA alone boosted L‐DES activity, promoting H2S accumulation. However, ALA + HT reduced H2S levels, compromising ALA's efficacy. NaHS with ALA + HT reinstated positive effects by restoring H2S levels. Biochemical assays confirmed ALA and NaHS promoted H2S accumulation, bolstering antioxidants, mitigating lipid peroxidation, suggesting their drought resilience potential in tomatoes.

H2S is involved in drought-mediated stomatal closure through PLDα1 in Arabidopsis.

PLDα1 promoted H2S production by positively regulating the expression of LCD. Stomatal closure promoted by PLDα1 required the accumulation of H2S under drought stress. Phospholipase Dα1 (PLDα1) acting as one of the signal enzymes can respond to drought stress. It is well known that hydrogen sulfide (H2S) plays an important role in plant responding to biotic or abiotic stress. In this study, the functions and relationship between PLDα1 and H2S in drought stress resistance in Arabidopsis were explored. Our results indicated that drought stress promotes PLDα1 and H2S production by inducing the expression of PLDα1 and LCD genes. PLDα1 and LCD enhanced plant tolerance to drought by regulating membrane lipid peroxidation, proline accumulation, H2O2 content and stomatal closure. Under drought stress, the H2O2 content of PLDα1-deficient mutant (pldα1), L-cysteine desulfhydrase (LCD)-deficient mutant (lcd) was higher than that of ecotype (WT), the stomatal aperture of pldα1 and lcd was larger than that of WT. The transcriptional and translational levels of LCD were lower in pldα1 than that in WT. Exogenous application of the H2S donor NaHS or GYY reduced the stomatal aperture of WT, pldα1, PLDα1-CO, and PLDα1-OE lines, while exogenous application of the H2S scavenger hypotaurine (HT) increased the stomatal aperture. qRT-PCR analysis of stomatal movement-related genes showed that the expression of CAX1, ABCG5, SCAB1, and SLAC1 genes in pldα1 and lcd were down-regulated, while ACA1 and OST1 gene expression was significantly up-regulated. Thus, PLDα1 and LCD are required for stomatal closure to improve drought stress tolerance.

Hydrogen sulfide inhibits tomato fruit ripening by restraining fruit softening and ethylene production

Hydrogen sulfide (H2S) plays various roles in plant growth, development and stress response. However, the mechanism of action of H2S in fruit ripening remains unclear. This study investigated the roles and mechanisms of H2S in tomato (Solanum lycopersicum) fruit repining. The results showed that compared with the control (distilled water), H2S treatment significantly delayed the color and hardness transition of tomato fruit; while an H2S scavenger hypotaurine (HT) treatment promoted the color and hardness transition. H2S increased the endogenous chlorophyll content, activity of chlorophyll synthesis-related enzymes, and expression of chlorophyll synthesis-related genes and decreased the expression of chlorophyll degradation-related genes and lycopene content. In contrast, HT decreased the activity of chlorophyll synthesis-related enzymes and expression of related genes; and increased the expression of chlorophyll degradation-related genes. In addition, the activity of the softening-related enzymes, ACS and ACO, ethylene content, and the expression of softening- and ethylene biosynthesis-related genes were decreased by H2S but increased by HT. Exogenous H2S increases endogenous H2S levels. Therefore, H2S may delay tomato fruit ripening by down-regulating the expression of softening-related and ethylene synthesis-related genes and reducing the activity of softening-related and ethylene synthesis-related enzymes.

Glutathione‐induced hydrogen sulfide enhances drought tolerance in sweet pepper (Capsicum annuum L.)

AbstractGlutathione (GSH) has been studied for its potential to enhance stress tolerance in plant systems, but the role of hydrogen sulfide (H2S) in GSH‐induced water stress tolerance in sweet pepper (Capsicum annuum L.) is still under investigation. This study explores how H2S and GSH modulate water stress tolerance in pepper plants, addressing a research gap. The joint effect of sodium hydrosulfide (NaHS), a donor of H2S, and GSH on water stress tolerance was determined through pre‐treatment with the H2S scavenger 0.1 mM hypotaurine (HT). Pepper seedlings were sprayed with 1.0 mM GSH or GSH + 0.2 mM NaHS once a week, with soil moisture content set at 80% and 40% for full irrigation and water stress conditions for a duration of 2 weeks. The results showed that water stress significantly reduced total plant dry weight, chlorophyll a and b content, Fv/Fm, leaf water potential, and relative water content by 50%, 56%, 33%, 27%, 52%, and 34%, while increasing hydrogen peroxide (H2O2), proline, and H2S levels by 152%, 134%, and77%, respectively. Treatment with GSH and NaHS reduced water stress‐induced H2O2 production and improved plant growth, photosynthetic traits, proline, and the activity of L‐cysteine desulfhydrase (L‐DES), leading to the generation of H2S content. GSH reduced NADPH oxidase (NOX), superoxide dismutase (SOD), and H2O2 but increased glutathione peroxidase (GPX) activities. The interaction of NaHS and GSH led to further reductions in NOX, SOD, and H2O2 values but increased GPX activity. The combined GSH and NaHS treatment increased nitric oxide (NO) production but decreased the activity of S‐nitrosoglutathione reductase (GSNOR), potentially accelerating S‐nitrosylation. Hypotaurine negated the positive impacts of GSH on water stress tolerance by reducing H2S concentration in pepper plants, but this was corrected by the concurrent application of NaHS and GSH + HT. Therefore, water stress tolerance requires H2S.

Hydrogen Sulfide Alleviates Oxidative Damage under Chilling Stress through Mitogen-Activated Protein Kinase in Tomato.

Tomato is the vegetable with the largest greenhouse area in China, and low temperature is one of the main factors affecting tomato growth, yield, and quality. Hydrogen sulfide (H2S) plays an important role in regulating plant chilling tolerance, but its downstream cascade reaction and mechanism remain unclear. Mitogen-activated protein kinases (MAPK/MPKs) are closely related to a variety of signaling substances in stress signal transmission. However, whether H2S is related to the MPK cascade pathway in response to low-temperature stress is rarely reported. In this study, NaHS treatment significantly decreased the electrolyte leakage (EL), superoxide anion (O2-) production rate, and hydrogen peroxide (H2O2) content of seedlings at low temperatures. In addition, the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were obviously increased; and the photochemical efficiency of PSII (Fv/Fm) was enhanced with treatment with NaHS, indicating that NaHS improved the seedlings' cold tolerance by alleviating the degree of membrane lipid peroxidation and oxidative damage. However, H2S scavenger hypotaurine (HT) treatment showed the opposite effect. We found that H2S content, L-cysteine desulfhydrase (LCD) activity, and mRNA expression were increased by chilling stress but reduced by MPK inhibitor PD98059; PD98059 reversed the alleviating effect of H2S via increasing the EL and H2O2 contents. The expression levels of MPK1-MPK7 at low temperatures showed that SlMPK4 was significantly induced by exogenous NaHS and showed a trend of first increasing and then decreasing, while the expression level of SlMPK4 in HT-treated seedlings was lower than that of the control. After SlMPK4 was silenced by virus-induced gene silencing, the H2S-induced upregulation of C-repeat-Binding Factor (CBF1), inducer of CBF expression 1 (ICE1), respiratory burst oxidase homologs (RBOH1, RBOH2) at low temperatures disappeared, and tomato cold tolerance decreased. In conclusion, H2S improves the cold tolerance of tomato plants by increasing the activity of antioxidant enzymes and reducing reactive oxygen species (ROS) accumulation and membrane lipid peroxidation. MPK4 may act as a downstream signaling molecule in this process.

Mitigating salt toxicity and overcoming phosphate deficiency alone and in combination in pepper (Capsicum annuum L.) plants through supplementation of hydrogen sulfide

While it is widely recognized that hydrogen sulfide (H2S) promotes plant stress tolerance, the precise processes through which H2S modulates this process remains unclear. The processes by which H2S promotes phosphorus deficiency (PD) and salinity stress (SS) tolerance, simulated individually or together, were examined in this study. The adverse impacts on plant biomass, total chlorophyll and chlorophyll fluorescence were more pronounced with joint occurrence of PD and SS than with individual application. Malondialdehyde (MDA), hydrogen peroxide (H2O2), and electrolyte leakage (EL) levels in plant leaves were higher in plants exposed to joint stresses than in plants grown under an individual stress. When plants were exposed to a single stress as opposed to both stressors, sodium hydrosulfide (NaHS) treatment more efficiently decreased EL, MDA, and H2O2 concentrations. Superoxide dismutase, peroxidase, glutathione reductase and ascorbate peroxidase activities were increased by SS alone or in conjunction with PD, whereas catalase activity decreased significantly. The favorable impact of NaHS on all the evaluated attributes was reversed by supplementation with 0.2 mM hypotaurine (HT), a H2S scavenger. Overall, the unfavorable effects caused to NaHS-supplied plants by a single stress were less severe compared with those caused by the combined administration of both stressors.

Molecular Regulatory Mechanism of Exogenous Hydrogen Sulfide in Alleviating Low-Temperature Stress in Pepper Seedlings.

Pepper (Capsicum annuum L.) is sensitive to low temperatures, with low-temperature stress affecting its plant growth, yield, and quality. In this study, we analyzed the effects of exogenous hydrogen sulfide (H2S) on pepper seedlings subjected to low-temperature stress. Exogenous H2S increased the content of endogenous H2S and its synthetase activity, enhanced the antioxidant capacity of membrane lipids, and protected the integrity of the membrane system. Exogenous H2S also promoted the Calvin cycle to protect the integrity of photosynthetic organs; enhanced the photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and photosynthesis; and reduced the intercellular CO2 concentration (Ci). Moreover, the activities of superoxide dismutase, peroxidase, catalase, and anti-cyclic glutathione (ASA-GSH) oxidase were improved to decompose excess reactive oxygen species (ROS), enhance the oxidative stress and detoxification ability of pepper seedlings, and improve the resistance to low-temperature chilling injury in 'Long Yun2' pepper seedlings. In addition, the H2S scavenger hypotaurine (HT) aggravated the ROS imbalance by reducing the endogenous H2S content, partially eliminating the beneficial effects of H2S on the oxidative stress and antioxidant defense system, indicating that H2S can effectively alleviate the damage of low temperature on pepper seedlings. The results of transcriptome analysis showed that H2S could induce the MAPK-signaling pathway and plant hormone signal transduction; upregulate the expression of transcription factors WRKY22 and PTI6; induce defense genes; and activate the ethylene and gibberellin synthesis receptors ERF1, GDI2, and DELLA, enhancing the resistance to low-temperature chilling injury of pepper seedlings. The plant-pathogen interaction was also significantly enriched, suggesting that exogenous H2S also promotes the expression of genes related to plant-pathogen interaction. The results of this study provide novel insights into the molecular mechanisms and genetic modifications of H2S that mitigate the hypothermic response.

Citric acid and hydrogen sulfide cooperate to mitigate chromium stress in tomato plants by modulating the ascorbate-glutathione cycle, chromium sequestration, and subcellular allocation of chromium

The study aimed to investigate the role of hydrogen sulfide (H2S) in regulating chromium stress (Cr–S) tolerance of tomato plants treated with citric acid (CA). Prior to the Cr treatment, tomato plants were foliar-fed with CA (100 μM) daily for 3 days. Subsequently, the plants were grown for another ten days in a hydroponic system in a 50 μM Cr (VI) solution. Chromium treatment reduced photosynthetic pigments and plant biomass, but boosted the levels of hydrogen peroxide (H2O2) malondialdehyde (MDA), H2S, phytochelatins (PCs), and glutathione (GSH), electrolyte leakage (EL), and antioxidant enzyme activity in tomato plants. However, the foliar spray of CA mitigated the levels of H2O2, MDA, and EL, promoted plant growth and chlorophyll content, enhanced antioxidant enzymes’ activities, and increased H2S production in Cr–S-tomato plants. CA also increased the levels of GSH and PCs, potentially reducing the toxicity of Cr through regulated sequestration. Additionally, the application of sodium hydrogen sulfide (NaHS), a donor of H2S, improved CA-induced Cr stress tolerance. The addition of CA promoted Cr accumulation in root cell wall and leaf vacuoles to suppress its toxicity. To assess the involvement of H2S in CA-mediated Cr–S tolerance, 0.1 mM hypotaurine (HT), an H2S scavenger, was provided to the control and Cr–S-plants along with CA and CA + NaHS. HT reduced the beneficial effects of CA by decreasing H2S production in tomato plants. However, the NaHS addition with CA + HT inverted the adverse impacts of HT, indicating that H2S is required for CA-induced Cr–S tolerance in tomato plants.

Sodium hydrosulfide-mediated upregulation of nitrogen metabolism improves drought stress tolerance in pepper plants

Although hydrogen sulfide (H2S) has been proven to promote plant tolerance to abiotic stress (including drought), the specific mechanism by which H2S mediates this process remains uncertain. The aim of the study was to fill this knowledge gap by investigating the potential of sodium hydrosulfide (NaHS) to improve drought tolerance in pepper plants through upregulating nitrogen metabolism-related enzymes and to gain insights into plant responses to drought stress. Pepper (Capsicum annuum) plants were grown at 80% and 40% of full field capacity. Reduced water availability led to a drastic decline in plant dry weight, leaf water potential (ΨI), relative water content (RWC), PSII operation efficiency (chlorophyll fluorescence Fv/Fm ratio), and chlorophyll content. Soluble protein and leaf and root nitrogen (N) levels were also lowered. Simultaneously, drought has significantly increased the levels of hydrogen peroxide (H2O2) and malondialdehyde (MDA), and resulted in increased content of nitrate (NO3-) and ammonium (NH4+). Also increased were the amount of free amino acid, soluble sugars, glycine betaine and free proline. The activities of peroxidase (POD), glutathione S-transferase (GST), and catalase (CAT) were elevated, as were those of endogenous hydrogen sulfide (H2S), L-cysteine desulfhydrase (L-DES), and methylglyoxal (MG). When 0.2 mM sodium dihydrosulfide (NaHS, a H2S donor) was sprayed on drought-affected plants, oxidative stress markers were reduced, as well as NO3-, NH4+ and free amino acid levels. Furthermore, NaHS improved endogenous H2S without changing L-DES activity. At the same time, NaHS activated nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthetase (GOGAT) and glutamine dehydrogenase (GDH) activities, as well as enzymes related to the glyoxalase system (Gly I and Gly II) thus improving nitrogen metabolism. This resulted in an increased plant growth, photosynthetic attributes, and N content. To demonstrate the causal role of H2S in drought tolerance, plants were administered an H2S scavenger, hypotaurine (HT), along with NaHS. HT treatment negated beneficial effects of NaHS by lowering H2S content without changing L-DES activity. Thus, exogenous application of NaHS could offer a simple and economical alternative for crop productivity in environments with restricted water supply.

Protective effects of 2-aminoethylthiosulfuric acid and structurally analogous organosulfur compounds against ionizing radiation.

High efficacy and minimal toxicity radioprotectors are desirable options for the hazards posed by nuclear medical and energy technologies and the dangers presented by nuclear weapons in an unstable global situation. Although cysteamine is an effective radioprotector, it has considerable toxicity. In this study, the protective effects of the less toxic organosulfur compounds 2-aminoethylthiosulfate (AETS), thiotaurine (TTAU), and hypotaurine (HTAU) against X-ray damage in mice were compared with that of cysteamine. Intraperitoneal injection of either AETS or cysteamine (2.2 mmol/kg body weight) 30 min before X-ray irradiation (7.0 Gy) provided 100% survival for 30 days, limited the decrease in erythrocytes and neutrophils over 9 days, and reduced damage to bone marrow and spleen over 9 days. Neither TTAU nor HTAU provided any protection. In mice, 30 min after AETS administration, non-protein thiol content increased in the spleen, indicating cysteamine generation by AETS hydrolysis, the active protective species of AETS. All examined compounds scavenged •OH under diffusion control in aqueous solution, which is inconsistent with the difference in the protective effects among the compounds. The results indicate that AETS protects animals from ionizing radiation by several mechanisms, including scavenging •OH as cysteamine.

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.

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 Alleviates Manganese Stress in Arabidopsis.

Hydrogen sulfide (H2S) has been shown to participate in various stress responses in plants, including drought, salinity, extreme temperatures, osmotic stress, and heavy metal stress. Manganese (Mn), as a necessary nutrient for plant growth, plays an important role in photosynthesis, growth, development, and enzymatic activation of plants. However, excessive Mn2+ in the soil can critically affect plant growth, particularly in acidic soil. In this study, the model plant Arabidopsis thaliana was used to explore the mechanism of H2S participation and alleviation of Mn stress. First, using wild-type Arabidopsis with excessive Mn2+ treatment, the following factors were increased: H2S content, the main H2S synthetase L-cysteine desulfhydrase enzyme (AtLCD) activity, and the expression level of the AtLCD gene. Further, using the wild-type, AtLCD deletion mutant (lcd) and overexpression lines (OE5 and OE32) as materials, the phenotype of Arabidopsis seedlings was observed by exogenous application of hydrogen sulfide donor sodium hydrosulfide (NaHS) and scavenger hypotaurine (HT) under excessive Mn2+ treatment. The results showed that NaHS can significantly alleviate the stress caused by Mn2+, whereas HT aggravates this stress. The lcd mutant is more sensitive to Mn stress than the wild type, and the overexpression lines are more resistant. Moreover, the mechanism of H2S alleviating Mn stress was determined. The Mn2+ content and the expression of the Mn transporter gene in the mutant were significantly higher than those of the wild-type and overexpression lines. The accumulation of reactive oxygen species was significantly reduced in NaHS-treated Arabidopsis seedlings and AtLCD overexpression lines, and the activities of various antioxidant enzymes (SOD, POD, CAT, APX) also significantly increased. In summary, H2S is involved in the response of Arabidopsis to Mn stress and may alleviate the inhibition of Mn stress on Arabidopsis seedling growth by reducing Mn2+ content, reducing reactive oxygen species content, and enhancing antioxidant enzyme activity. This study provides an important basis for further study of plant resistance to heavy metal stress.

Exogenous hydrogen sulfide mediates Na+ and K+ fluxes of salt gland in salt-secreting mangrove plant Avicennia marina.

Hydrogen sulfide (H2S), is a crucial biological player in plants. Here, we primarily explored the interaction between sodium hydrosulfide (NaHS, a H2S donor) and the fluxes of Na+ and K+ from the salt glands of mangrove species Avicennia marina (Forsk.) Vierh. with non-invasive micro-test technology (NMT) and quantitative real-time PCR (qRT-PCR) approaches under salinity treatments. The results showed that under 400-mM NaCl treatment, the addition of 200-μM NaHS markedly increased the quantity of salt crystals in the adaxial epidermis of A. marina leaves, accompanied by an increase in the K+/Na+ ratio. Meanwhile, the endogenous content of H2S was dramatically elevated in this process. The NMT result revealed that the Na+ efflux was increased from salt glands, whereas K+ efflux was decreased with NaHS application. On the contrary, the effects of NaHS were reversed by H2S scavenger hypotaurine (HT), and DL-propargylglycine (PAG), an inhibitor of cystathionine-γ-lyase (CES, a H2S synthase). Moreover, enzymic assay revealed that NaHS increased the activities of plasma membrane and tonoplast H+-ATPase. qRT-PCR analysis revealed that NaHS significantly increased the genes transcript levels of tonoplast Na+/H+ antiporter (NHX1), plasma membrane Na+/H+ antiporter (SOS1), plasma membrane H+-ATPase (AHA1) and tonoplast H+-ATPase subunit c (VHA-c1), while suppressed above-mentioned gene expressions by the application of HT and PAG. Overall, H2S promotes Na+ secretion from the salt glands of A. marina by up-regulating the plasma membrane and tonoplast Na+/H+ antiporter and H+-ATPase.

Effect of different concentrations of hypotaurine on melanosis and quality of Pacific white shrimp (Penaeus vannamei) during refrigeration

Effect of different concentrations of hypotaurine (HTU) on melanosis and quality of shrimps during 10 d storage in ice were studied. During refrigeration, the total plate count and total volatile basic nitrogen of shrimps treated with 20 g/L HTU were the lowest, and the hardness and microstructure were the best. Moreover, the score of melanoses, pH and total bile acid of shrimps treated with 20 g/L HTU were also low. Sensory evaluation showed that HTU treatment could make the shelf life of shrimps 3-4 days longer compared with the control. Based on the above physical and chemical indexes, 20 g/L HTU showed great potential as a safe inhibitor in the treatment of shrimps’ melanosis.

Hydrogen Sulfide Promotes Adventitious Root Development in Cucumber under Salt Stress by Enhancing Antioxidant Ability.

As a gas signal molecule, hydrogen sulfide (H2S) can enhance plant stress resistance. Here, cucumber (Cucumis sativus ‘Xinchun NO. 4’) explants were used to investigate the role of H2S in adventitious root development under salt stress. The results show that sodium chloride (NaCl) at 10 mM produced moderate salt stress. The 100 µM sodium hydrosulfide (NaHS) treatment, a H2S donor, increased root number and root length by 38.37% and 66.75%, respectively, indicating that H2S effectively promoted the occurrence of adventitious roots in cucumber explants under salt stress. The results show that under salt stress, NaHS treatment reduced free proline content and increased the soluble sugar and soluble protein content during rooting. Meanwhile, NaHS treatment enhanced the activities of antioxidant enzymes [peroxidase (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT)], increased the content of ascorbic (ASA) and glutathione (GSH), reduced the content of hydrogen peroxide (H2O2) and the rate of superoxide radical (O2−) production, and decreased relative electrical conductivity (REC) and the content of malondialdehyde (MDA). However, the NaHS scavenger hypotaurine (HT) reversed the above effects of NaHS under salt stress. In summary, H2S promoted adventitious root development under salt stress through regulating osmotic substance content and enhancing antioxidant ability in explants.

ROS scavenger Hypotaurine delays postharvest softening of ‘Kyoho’ grape by regulating pectin and cell metabolism pathway

The rapid softening of postharvest fruit has a serious detrimental effect on quality and market value. In this study, postharvest grape berries treated with hypotaurine (HT) or H2O2 were employed to explore the dynamic physical and transcriptional changes after the treatment. The berry firmness and the content of propectin were higher in the berries with HT treatment compared to the control (CK) and H2O2 treatment. A total of 1774 differentially expressed genes (DEGs) were identified from comparisons of CK_vs_HT (1,020) and CK_vs_H2O2 (1,072). Weighted gene coexpression network analysis (WGCNA) showed that genes assigned to ‘MEgreen’ were predicted to be highly correlated to fruit firmness and propectin content. Based on transcriptome and quantitative real-time polymerase chain reaction (RT-qPCR), expression levels of VvMYB-like, VvNAC22, VvPEI and VvCESA-like were upregulated whereas VvMADS-box and VvPG were downregulated in HT-treated berries compared to H2O2 treatment. Dual luciferase reporter assay confirmed that VvMYB-like and VvNAC22 upregulate the expression of VvPEI and VvCESA respectively by binding to the corresponding sites of their promoters. Meanwhile, HT treatment triggered the differential expression of Accelerated Cell Death 6 (VvACD6), VvXyloglucan galactosyltransferase (VvXyG galactosyltransferase) and Cell wall/Vacuolar Inhibitor of Fructosidase 1-like (VvC/VIF1-like). Finally, a possible regulatory model that HT delays berry softening by regulating pectin and cell metabolism pathway through VvMYB-like and VvNAC22 was proposed. This study laid a foundation for understanding the molecular mechanisms of delaying berry softening which HT mediated.

The role of hydrogen sulfide and its relationship with hydrogen peroxide and nitric oxide in brassinosteroid-induced stomatal closure of Vicia faba L.

The role of hydrogen sulfide (H2S) and its relationship with hydrogen peroxide (H2O2) and nitric oxide (NO) in brassinosteroid-induced stomatal closure by using pharmacological, spectrophotographic and fluorescence microscope approaches in Vicia faba L. were investigated. In the present study, 2, 4-epibrassinolide (EBR, a bioactive BR) induced stomatal closure in a dose- and time-dependent manner, and the effects were inhibited by H2S modulators hypotaurine (HT), aminooxy acetic acid (AOA), hydroxylamine (NH2OH), potassium pyruvate (C3H3KO3) and ammonia (NH3), H2O2 modulators ascorbic acid (ASA), catalase (CAT), diphenylene iodonium(DPI) and salicylhydroxamic acid (SHAM), and NO modulators 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO), NG-Nitro-L-arginine methyl ester, hydrochloride (L-NAME) and sodium tungstate (Na2WO4), respectively. Additionally, EBR caused increase of L-/D-cysteine desulfhydrase (L-/D-CDes) activity and H2S production in leaves, H2O2 and NO generation in guard cells, and the effects were significantly inhibited by H2S modulators, H2O2 modulators and NO modulators, respectively. Moreover, H2O2 modulators and NO modulators could significantly inhibit EBR-induced rise of L-/D-CDes activity and H2S production in the leaves of V. faba. However, H2S modulators failed to repress EBR-induced H2O2 and NO production in guard cells of V. faba. Together, our results suggested that H2S, H2O2 and NO probably participate in the signal transduction pathway of EBR-induced stomatal closure, and H2S may represent a novel component downstream of H2O2 and NO in EBR-induced stomatal closure of V. faba.

The hypotaurine-taurine pathway as an antioxidative mechanism in patients with acute liver failure.

The liver has been thought to protect against oxidative stress through mechanisms involving reduced glutathione (GSH) that consumes high-energy phosphor-nucleotides on its synthesis. However, hepatoprotective mechanisms in acute liver failure (ALF) where the phosphor-nucleotides are decreased in remain to be solved. Liver tissues were collected from patients with ALF and liver cirrhosis (LC) and living donors (HD) who had undergone liver transplantation. Tissues were used for metabolomic analyses to determine metabolites belonging to the central carbon metabolism, and to determine sulfur-containing metabolites. ALF and LC exhibited a significant decline in metabolites of glycolysis and pentose phosphate pathways and high-energy phosphor-nucleotides such as adenosine triphosphate as compared with HD. Conversely, methionine, S-adenosyl-l-methionine, and the ratio of serine to 3-phosphoglycerate were elevated significantly in ALF as compared with LC and HD, suggesting a metabolic boost from glycolysis towards trans-sulfuration. Notably in ALF, the increases in hypotaurine (HTU) + taurine (TU) coincided with decreases in the total amounts of reduced and oxidized glutathione (GSH + 2GSSG). Plasma NH3 levels correlated with the ratio of HTU + TU to GSH + 2GSSG. Increased tissue levels of HTU + TU vs total glutathione appear to serve as a biomarker correlating with hyperammonemia, suggesting putative roles of the HTU-TU pathway in anti-oxidative protective mechanisms.

Molecular cloning and expression analysis of hydrogen peroxide sensors under H2O2 and ROS inhibitor treatment in ‘Kyoho’ grape berry

Hydrogen peroxide is an important factor involved in the senescence and quality deterioration of postharvest fruit. However, few studies have examined hydrogen peroxide sensors and their expression patterns in grape. Here, postharvest grape berries were treated with H2O2 and the ROS inhibitor hypotaurine (HT). HT reduced the H2O2 content by increasing ROS-scavenging enzyme activity, whereas H2O2 accelerated senescence. Four hydrogen peroxide sensors (VvHPCA1, 2, 3, and 4) were identified and isolated from the grape genome. Sequence analysis indicated that VvHPCAs shared a conserved structure, including the LRR-RK and hydrogen peroxide (HP) domains, with other homologous hydrogen peroxide sensor genes. Furthermore, the expression patterns of the four VvHPCAs were investigated under H2O2 and HT treatment in grape. The expression levels of the four VvHPCAs were lower in grape berries treated with HT than in grape berries treated with H2O2 or water treatment (Control) in at least one of the sampling points during storage. VvHPCAs are cytomembrane proteins with stress-responsive cis-acting elements in their promoters, indicating that these four identified VvHPCAs might function as hydrogen peroxide sensors in grape and regulate hydrogen peroxide signaling and metabolism. Thus, VvHPCAs are capable of responding to postharvest ROS stress. These findings provided new insight into the function of these four VvHPCAs, which are potential candidate genes involved in regulating ROS stress in grape.