Activity Of L-cysteine Desulfhydrase Research Articles

Sodium nitroprusside modulates oxidative and nitrosative processes in Lycopersicum esculentum L. under drought stress

Key messageSodium nitroprusside mediates drought stress responses in tomatoes by modulating nitrosative and oxidative pathways, highlighting the interplay between nitric oxide, hydrogen sulfide, and antioxidant systems for enhanced drought tolerance.While nitric oxide (NO), a signalling molecule, enhances plant tolerance to abiotic stresses, its precise contribution to improving tomato tolerance to drought stress (DS) through modulating oxide-nitrosative processes is not yet fully understood. We aimed to examine the interaction of NO and nitrosative signaling, revealing how sodium nitroprusside (SNP) could mitigate the effects of DS on tomatoes. DS-seedlings endured 12% polyethylene glycol (PEG) in a 10% nutrient solution (NS) for 2 days, then transitioned to half-strength NS for 10 days alongside control plants. DS reduced total plant dry weight, chlorophyll a and b, Fv/Fm, leaf water potential (ΨI), and relative water content, but improved hydrogen peroxide (H2O2), proline, and NO content. The SNP reduced the DS-induced H2O2 generation by reducing thiol (–SH) and the carbonyl (–CO) groups. SNP increased not only NO but also the activity of l-cysteine desulfhydrase (L-DES), leading to the generation of H2S. Decreases in S-nitrosoglutathione reductase (GSNOR) and NADPH oxidase (NOX) suggest a potential regulatory mechanism in which S-nitrosylation [formation of S-nitrosothiol (SNO)] may influence protein function and signaling pathways during DS. Moreover, SNP improved ascorbate (AsA) and glutathione (GSH) and reduced oxidized glutathione (GSSG) levels in tomato plants under drought. Furthermore, the interaction of NO and H2S, mediated by L-DES activity, may serve as a vital cross-talk mechanism impacting plant responses to DS. Understanding these signaling interactions is crucial for developing innovative drought-tolerance strategies in crops.

Exploring the synergistic effects of melatonin and salicylic acid in enhancing drought stress tolerance in tomato plants through fine-tuning oxidative-nitrosative processes and methylglyoxal metabolism

Enhancement of drought stress (DS) tolerance in plants has been reported with the separate applications of melatonin (MT) and salicylic acid (SA). However, the synergistic effects of their combined application and the exact mechanisms through which they enhance drought tolerance are still not fully understood. The study explored the joint effects of MT and SA on DS tolerance and their implications for oxide-nitrosative processes and methylglyoxal metabolism in tomato plants. To impose DS in tomato plants, they were treated with a 6% polyethylene glycol solution (PEG-6000) in a half-strength nutrient solution. The plants underwent a treatment consisting of individual or combined spraying with 0.5 mM SA and/or 0.1 mM MT every two days for 14 days to relieve the after effects of the PEG-induced stress. The combined MT and SA treatment improved plant drought tolerance, resulting in significant increases in shoot (75%) and root (204%) dry weights. Other improvements included a 141% increase in total chlorophyll content, a 61% increase in Fv/Fm, a 39% increase in Ψl, a 50% increase in RWC, and a 76% increase in proline content compared to DS alone. It also increased non-enzymatic antioxidants (ascorbate and glutathione) and decreased oxidized glutathione under DS. The combined treatment also led to decreased levels of hydrogen peroxide, carbonyl (-CO), and thiol (-SH) groups, indicating the activation of the oxide-nitrosative system. Additionally, the treatment with MT and SA together increased the activity of l-cysteine desulfhydrase (L-CD), resulting in the production of hydrogen sulfide (H2S) and nitric oxide (NO), while decreasing the activity of S-nitroso glutathione reductase, which may have accelerated S-nitrosylation. The synthesis of methylglyoxal (MG) was also reduced by the combined treatment, possibly through the upregulation of the glyoxalase system. Overall, our study presents evidence that the combination of MT and SA treatment can enhance tomato plant tolerance to DS by regulating the oxidative-nitrosative processes and methylglyoxal metabolism.

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.

Hydrogen sulfide delays yellowing and softening, inhibits nutrient loss in postharvest celery

Celery is an important leafy vegetable crop and is widely used in fresh food consumption and processing. Therefore, the preservation of fresh cut celery is warranted. As a food preservative, sodium hydrosulfide has been used to maintain postharvest quality of crops. However, the role of sodium hydrosulfide in the preservation of postharvest celery remains unclear. Here, by regulating endogenous hydrogen sulfide content with sodium hydrosulfide and hypotaurine, we evaluated the effects of sodium hydrosulfide on postharvest celery quality. Sodium hydrosulfide treatment promoted endogenous hydrogen sulfide accumulation by triggering AgLCD and AgSAT expression, as well as increased activity of L-cysteine desulfhydrase, D-cysteine desulfhydrase, O-acetylserine (thiol)lyase, and serine acetyltransferase. Simultaneously, sodium hydrosulfide treatment enhanced the expression of AgSOD1, AgPOD, and AgCAT, improved the activities of superoxide dismutase, peroxidase, and catalase, and inhibited the accumulation of malondialdehyde, hydrogen peroxide, and superoxide anion, thereby reducing electrolyte leakage of the cell membrane. AgPAL and AgCAD expressions were up-regulated, and phenylalanine ammonia-lyase and cinnamyl alcohol dehydrogenase activities were increased to promote lignin synthesis and alleviate the softening process. AgPAO and AgPPH expression was down-regulated, polyamine oxidases and pheophytinase activities were decreased to inhibit chlorophyll degradation and delay yellowing. Meanwhile, sodium hydrosulfide treatment effectively inhibited nutrient loss, including soluble sugar, soluble protein, vitamin C, carotenoids, and total phenols. Our findings suggest that hydrogen sulfide plays an essential role in delaying quality deterioration of postharvest celery, while sodium hydrosulfide treatment is a promising method for celery preservation.

Synergistic regulation of Chitosan and NaHS on energy metabolism and endogenous H2S metabolism of postharvest nectarines

Chitosan (CS) and sodium sulphate (NaHS), as common chemical preservatives, are widely used in postharvest storage of fruit, but the synergistic effect of the combination of the two for fruit preservation remains unclear. The study aimed to investigate the synergistic regulation of CS and NaHS on energy metabolism and endogenous H2S metabolism of postharvest fruit. “Linqu” nectarine was used as experimental material, and treated with 5 g·L−1 chitosan and different concentrations of NaHS (0, 0.3, 0.4, 0.5 mmol·L−1). The endogenous H2S content and related enzyme activities of nectarine fruits during storage, as well as the activities of energy metabolism related enzymes were measured. The results showed that the synergistic treatment of chitosan and NaHS increased the activities of L-cysteine desulfhydrase, O-acetylserine sulfur lyase and serine acetyltransferase, and promoted the production of endogenous H2S in nectarine fruit. At the same time, the activities of succinate dehydrogenase, cytochrome oxidase, H+-ATPase and Ca2+-ATPase were increased by the synergistic treatment of chitosan and NaHS, so that the nectarine fruit maintained a higher ATP and ADP content and energy level. By comparison, it was found that the synergistic treatment of chitosan and 0.4 mmol·L−1 had the best preservation effect on nectarine fruit.

Differential Water Deficit in Leaves Is a Principal Factor Modifying Barley Response to Drought Stress

In response to environmental stress, plants activate complex signalling, including being dependent on reactive oxygen-nitrogen-sulphur species. One of the key abiotic stresses is drought. As a result of drought, changes in the level of hydration of the plant occur, which obviously entails various metabolic alternations. The primary aim of this study was to determine the relationship between the response of barley to drought and the intensity of stress, therefore investigations were performed under various levels of water saturation deficit (WSD) in leaves at 15%, 30%, and 50%. In barley subjected to drought, most significant changes occurred under a slight dehydration level at 15%. It was observed that the gene expression of 9-cis-epoxycarotenoid dioxygenases, enzymes involved in ABA biosynthesis, increased significantly, and led to a higher concentration of ABA. This was most likely the result of an increase in the gene expression and enzyme activity of L-cysteine desulfhydrase, which is responsible for H2S synthesis. Our results suggest that the differential water deficit in leaves underlies the activation of an appropriate defence, with ABA metabolism at the centre of these processes. Furthermore, at 15% WSD, a dominant contribution of H2O2-dependent signalling was noted, but at 30% and 50% WSD, significant NO-dependent signalling occurred.

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.

Gasotransmitter H2S accelerates seed germination via activating AOX mediated cyanide-resistant respiration pathway

Hydrogen sulfide (H2S) has been witnessed as a crucial gasotransmitter involving in various physiological processes in plants. H2S signaling has been reported to involve in regulating seed germination, but the underlying mechanism remains poorly understood. Here, we found that endogenous H2S production was activated in germinating Arabidopsis seeds, correlating with upregulated both the transcription and the activity of L-cysteine desulfhydrase (EC 4.4.1.28, LCD and DES1) responsible for H2S production. Moreover, seed germination could be significantly accelerated by exogenous NaHS (the H2S donor) fumigation and over-expressing DES1, while H2S-generation defective (lcd/des1) seeds exhibited decreased germination speed. We also confirmed that the alternative oxidase (AOX), a cyanide-insensitive terminal oxidase, can be stimulated by imbibition. Furthermore, exogenous H2S fumigation and over-expressing DES1 could significantly reinforced imbibition induced increase of both the AOX1A expression and AOX protein abundance, while this increase could be obviously weakened in lcd/des1. Additionally, exogenous H2S fumigation mediated post-translational modification to keep AOX in its reduced and active state, which might involve H2S induced improvement of the reduced GSH content and the cell reducing power. The promotive effect of H2S on germination was clearly impaired by inducing aox1a mutation, indicating that AOX acts downstream of H2S signaling to accelerate seed germination. Consequently, H2S signaling was activated during germination then acted as a trigger to induce AOX mediated cyanide-resistant respiration to accelerate seed germination. Our study correlates H2S signaling to cyanide-resistant respiration, providing evidence for more extensive studies of H2S signaling.

Sodium hydrosulfite together with silicon detoxifies arsenic toxicity in tomato plants by modulating the AsA-GSH cycle

The main intent of the current research was to appraise if combined application of hydrogen sulfide (H2S, 0.2 mM) and silicon (Si 2.0 mM) could improve tolerance of tomato plants to arsenic (As as sodium hydrogen arsenate heptahydrate, 0.2 mM) stress. Plant growth, chlorophylls (Chl), PSII maximum efficiency (Fv/Fm), H2S concentration and L-cysteine desulfhydrase activity were found to be suppressed, but leaf and root As, leaf proline content, phytochelatins, malondialdehyde (MDA) and H2O2 as well as the activity of lipoxygenase (LOX) increased under As stress. H2S and Si supplied together or alone enhanced the concentrations of key antioxidant biomolecules such as ascorbic acid, and reduced glutathione and the activities of key antioxidant system enzymes including catalase (CAT), superoxide dismutase (SOD), dehydroascorbate reductase (DHAR), glutathione reductase (GR), and glutathione S-transferase (GST). In comparison with individual application of H2S or Si, the joint supplementation of both had better effect in improving growth and key biochemical processes, and reducing tissue As content, suggesting a putative collaborative role of both molecules in improving tolerance to As-toxicity in tomato plants.

Exogenous melatonin-mediated regulation of K+ /Na+ transport, H+ -ATPase activity and enzymatic antioxidative defence operate through endogenous hydrogen sulphide signalling in NaCl-stressed tomato seedling roots.

Melatonin (Mel) and hydrogen sulphide (H2 S) have emerged as potential regulators of plant metabolism during abiotic stress. Presence of excess NaCl in the soil is one of the main causes of reduced crop productivity worldwide. The present investigation examines the role of exogenous Mel and endogenous H2 S in tomato seedlings grown under NaCl stress. Effect of 30µm Mel on endogenous synthesis of H2 S was examined in roots of NaCl-stressed (200mm) tomato seedlings. Also, the impact of treatments on the oxidative stress markers, transport of K+ and Na+ , and activity of H+ -ATPase and antioxidant enzymes was assessed. Results show that NaCl-stressed seedlings supplemented with 30µm Mel had increased levels of endogenous H2 S through enhanced L-cysteine desulfhydrase activity. Mel in association with H2 S overcame the deleterious effect of NaCl and induced retention of K+ that maintained a higher K+ /Na+ ratio. Use of plasma membrane inhibitors and an H2 S scavenger revealed that Mel-induced regulation of K+ /Na+ homeostasis in NaCl-stressed seedling roots operates through endogenous H2 S signalling. Synergistic effects of Mel and H2 S also reduced the generation of ROS and oxidative destruction through the enhanced activity of antioxidant enzymes. Thus, it is suggested that the protective function of Mel against NaCl stress operates through an endogenous H2 S-dependent pathway, wherein H+ -ATPase-energized secondary active transport regulates K+ /Na+ homeostasis.

Delaying Broccoli Floret Yellowing by Phytosulfokine α Application During Cold Storage.

During postharvest life, broccoli suffers from floret yellowing confining its economic and nutritional value. The objective of the present study was to explore the mechanisms employed by phytosulfokine α (PSKα) at 150 nM for delaying floret yellowing in broccoli during storage at 4°C for 28 days. Our results showed that the higher endogenous accumulation of hydrogen sulfide (H2S) resulting from the higher gene expression and activities of l-cysteine desulfhydrase (LCD) and d-cysteine desulfhydrase (DCD) in broccoli floret treated with 150 nM PSKα may serve as an endogenous signaling molecule for delaying senescence. Moreover, the suppressed ethylene biosynthesis in broccoli floret treated with 150 nM PSKα might be ascribed to lower gene expression and activities of ACC synthase (ACS) and ACC oxidase (ACO). Furthermore, lower gene expression and activities of Mg2+ dechelatase (MDC), pheophytinase (PPH), and pheophorbide a oxygenase (PaO) might be the reasons for the higher accumulation of chlorophyll in broccoli floret treated with 150 nM PSKα. Based on our findings, exogenous PSKα application could be employed as signaling bioactive hormone for retarding floret yellowing of broccoli during storage at 4°C for 28 days.

Exogenous Melatonin Modulates Endogenous H2S Homeostasis and L-Cysteine Desulfhydrase Activity in Salt-Stressed Tomato (Solanum lycopersicum L. var. cherry) Seedling Cotyledons

Although melatonin has been reported to function as a stress signaling molecule, not much information is available on the biochemical and molecular events associated with probable melatonin-hydrogen sulfide crosstalk in plants. Present work provides evidence on the role of melatonin in the modulation of H2S homoeostasis during NaCl stress in dark-grown tomato (Solanum lycopersicum L. var. cherry) seedlings. NaCl stress (120 mM) inhibits hypocotyl elongation, promotes primary root growth and enhances electrolytic leakage from tomato seedlings. Treatment with H2S donor (100 µM; NaHS) tends to reverse these effects, all the more so (additive effect) in the presence of melatonin. NaCl stress and exogenous melatonin (30 µM) treatments modulate endogenous H2S accumulation and positively upregulate the activity of L-cysteine desulfhydrase (L-DES; EC 4.4.1.15; cytosolic). Melatonin has been observed to temporally modulate the activity of specific isoforms of H2S biosynthesizing enzyme, L-DES in seedling cotyledons. Zymographic analysis of L-DES isoforms in tomato seedling cotyledons has provided novel findings in plant system. Melatonin treatment decreases H2S accumulation in NaCl-stressed seedling cotyledons which is accompanied by a contrasting increase in L-DES activity. Melatonin, therefore, regulates endogenous H2S concentration in seedling cotyledons (NaCl treated), thus indicating the role of H2S catabolism pathways in H2S homoeostasis. Present findings thus reveal that exogenous melatonin modulates early H2S signaling in cotyledons of tomato seedlings subjected to NaCl stress. Furthermore, exogenous melatonin and H2S in combination (additive effect) ameliorate NaCl stress-induced growth changes in tomato seedlings.

Hydrogen sulfide promotes rice drought tolerance via reestablishing redox homeostasis and activation of ABA biosynthesis and signaling

Hydrogen sulfide (H2S) has been explored as the third biologically gasotransmitter regulating plant adaptation response, however, its possible mechanisms on drought tolerance are not completely clear yet. Here, we discovered that during dehydration treatment, the activities of L-cysteine desulfhydrase (LCD), the important synthetic enzymes of H2S in rice, was enhanced in rice seedling leaves, further leading to continuous increasing of endogenous H2S production. Pretreatment with NaHS, a well-known H2S donor, significantly improved rice performance under drought stress. The beneficial roles of NaHS were confirmed by the alleviation of lipid peroxidation, and the activation of antioxidant defence system. Importantly, besides repressing its degradation pathway, NaHS pretreatment promoted ABA de-novo synthesis as well. This resulted in an increase of ABA accumulation and the expression of downstream ABA-responsive genes in rice seedling upon drought stress. Together, the present study illustrated that H2S improve drought tolerance via reestablishing redox homeostasis and triggering ABA signaling.

Abscisic acid-triggered guard cell l-cysteine desulfhydrase function and in situ hydrogen sulfide production contributes to heme oxygenase-modulated stomatal closure.

Recent studies have demonstrated that hydrogen sulfide (H2 S) produced through the activity of l-cysteine desulfhydrase (DES1) is an important gaseous signaling molecule in plants that could participate in abscisic acid (ABA)-induced stomatal closure. However, the coupling of the DES1/H2 S signaling pathways to guard cell movement has not been thoroughly elucidated. The results presented here provide genetic evidence for a physiologically relevant signaling pathway that governs guard cell in situ DES1/H2 S function in stomatal closure. We discovered that ABA-activated DES1 produces H2 S in guard cells. The impaired guard cell ABA phenotype of the des1 mutant can be fully complemented when DES1/H2 S function has been specifically rescued in guard cells and epidermal cells, but not mesophyll cells. This research further characterized DES1/H2 S function in the regulation of LONG HYPOCOTYL1 (HY1, a member of the heme oxygenase family) signaling. ABA-induced DES1 expression and H2 S production are hyper-activated in the hy1 mutant, both of which can be fully abolished by the addition of H2 S scavenger. Impaired guard cell ABA phenotype of des1/hy1 can be restored by H2 S donors. Taken together, this research indicated that guard cell in situ DES1 function is involved in ABA-induced stomatal closure, which also acts as a pivotal hub in regulating HY1 signaling.

L-Cysteine desulfhydrase-dependent hydrogen sulfide is required for methane-induced lateral root formation.

Methane-triggered lateral root formation is not only a universal event, but also dependent on L-cysteine desulfhydrase-dependent hydrogen sulfide signaling. Whether or how methane (CH4) triggers lateral root (LR) formation has not been elucidated. In this report, CH4 induction of lateral rooting and the role of hydrogen sulfide (H2S) were dissected in tomato and Arabidopsis by using physiological, anatomical, molecular, and genetic approaches. First, we discovered that CH4 induction of lateral rooting is a universal event. Exogenously applied CH4 not only triggered tomato lateral rooting, but also increased activities of L-cysteine desulfhydrase (DES; a major synthetic enzyme of H2S) and induced endogenous H2S production, and contrasting responses were observed in the presence of hypotaurine (HT; a scavenger of H2S) or DL-propargylglycine (PAG; an inhibitor of DES) alone. CH4-triggered lateral rooting were sensitive to the inhibition of endogenous H2S with HT or PAG. The changes in the transcripts of representative cell cycle regulatory genes, miRNA and its target genes were matched with above phenotypes. In the presence of CH4, Arabidopsis mutant Atdes1 exhibited defects in lateral rooting, compared with the wild-type. Molecular evidence showed that the transcriptional profiles of representative target genes modulated by CH4 in wild-type plants were impaired in Atdes1 mutant. Overall, our data demonstrate the main branch of the DES-dependent H2S signaling cascade in CH4-triggered LR formation.

Modulation of growth and oxidative stress by seed priming with salicylic acid in Zea mays L. under lead stress

ABSTRACT Lead is an important environmental pollutant, extremely toxic to plants and other living organisms. In the present study, possible ameliorating effects of salicylic acid (SA) were investigated at biochemical levels in maize exposed to lead stress. The elevation in hydrogen peroxide and malondialdehyde contents and the decline in protein thiol (PT) level were revealed under lead stress. The SA pretreatment prevented a lead-induced decrease in chlorophyll and PT contents, as well as an increase in lipid peroxidation and hydrogen peroxide levels. Lead stressed plants which are pretreated with salicylic acid accumulated more ascorbic acid, glutathione and stimulated more antioxidant enzymes activity than plants treated with lead alone. In addition, SA pretreatment of seed enhanced l-cysteine desulfhydrase activity and endogenous hydrogen sulfide content. The results indicate that SA regulates the response of plants to lead stress and suggest hydrogen sulfide as a downstream signal molecule which might be involved in SA-induced lead tolerance.

Endogenous hydrogen sulfide (H2S) is up-regulated during sweet pepper (Capsicum annuum L.) fruit ripening. In vitro analysis shows that NADP-dependent isocitrate dehydrogenase (ICDH) activity is inhibited by H2S and NO

Like nitric oxide (NO), hydrogen sulfide (H2S) has been recognized as a new gasotransmitter which plays an important role as a signaling molecule in many physiological processes in higher plants. Although fruit ripening is a complex process associated with the metabolism of reactive oxygen species (ROS) and nitrogen oxygen species (RNS), little is known about the potential involvement of endogenous H2S. Using sweet pepper (Capsicum annuum L.) as a model non-climacteric fruit during the green and red ripening stages, we studied endogenous H2S content and cytosolic l-cysteine desulfhydrase (L-DES) activity which increased by 14% and 28%, respectively, in red pepper fruits. NADPH is a redox compound and key cofactor required for cell growth, proliferation and detoxification. We studied the NADPH-regenerating enzyme, NADP-isocitrate dehydrogenase (NADP-ICDH), whose activity decreased by 34% during ripening. To gain a better understanding of its potential regulation by H2S, we obtained a 50–75% ammonium sulfate-enriched protein fraction containing the NADP-ICDH protein; with the aid of in vitro assays in the presence of H2S, we observed that 2 and 10 mM NaHS used as H2S donors resulted in a decrease of up to 36% and 45%, respectively, in NADP-ICDH activity, which was unaffected by reduced glutathione (GSH). On the other hand, peroxynitrite (ONOO−), S-nitrosocyteine (CysNO) and DETA-NONOate, with the last two acting as NO donors, also inhibited NADP-ICDH activity. In silico analysis of the tertiary structure of sweet pepper NADP-ICDH activity (UniProtKB ID A0A2G2Y555) suggests that residues Cys133 and Tyr450 are the most likely potential targets for S-nitrosation and nitration, respectively. Taken together, the data reveal that the increase in the H2S production capacity of red fruits is due to higher L-DES activity during non-climacteric pepper fruit ripening. In vitro assays appear to show that H2S inhibits NADP-ICDH activity, thus suggesting that this enzyme may be regulated by persulfidation, as well as by S-nitrosation and nitration. NO and H2S may therefore regulate NADPH production and consequently cellular redox status during pepper fruit ripening.

Hydrogen sulfide is involved in the regulation of ascorbate and glutathione metabolism by jasmonic acid in Arabidopsis thaliana

This study investigated the role of hydrogen sulfide (H2S) in the regulation of the ascorbate (AsA) and glutathione (GSH) metabolism by jasmonic acid (JA) in the leaves of Arabidopsis thaliana by using H2S scavenger hypotaurine (HT) and H2S synthetic mutant (SALK_041918, designated Atl-cdes). The results showed that JA significantly increased the H2S content, the activities of L-cysteine desulfhydrase (L-CDes), D-cysteine desulfhydrase (D-CDes), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), L-galactono-1,4-lactone dehydrogenase (GalLDH) and γ-glutamylcysteine synthetase (γ-ECS), the ratio of AsA to dehydroascorbate (DHA), and decreased the content of malondialdehyde (MDA) and H2O2 in the wild type of A. thaliana, compared to control. The above effects of JA except the increased activities of L-CDes and D-CDes were suppressed by addition of HT. However, JA and HT+JA had no significant effects on the ratio of reduced GSH to oxidized GSH (GSSG) in the wild type of A. thaliana. Application of HT to the control decreased H2S content, AsA/DHA ratio, and activities of APX, GR, DHAR, MDHAR, γ-ECS, and GalLDH, but had no effects on MDA content, activities of L-CDes and D-CDes, and GSH/GSSG ratio. In the H2S synthetic mutant, JA had no obvious effects on above mentioned parameters except the D-CDes activity compared with the control. Our results suggest that JA-induced H2S, which is a signal that leads to the up-regulation of the AsA and GSH metabolism.

Hydrogen sulfide as a signal molecule in hematin-induced heat tolerance of tobacco cell suspension

Carbon monoxide (CO) is considered as a new emerging cell signal molecule which is involved in plant growth, development, and acquisition of stress tolerance. In recent years, hydrogen sulfide (H2S) has been found to have similar functions, but crosstalk between CO and H2S in the acquisition of heat tolerance in plants is not clear. In this study, pretreatment of tobacco (Nicotiana tabaccum L.) cells cultured in a suspension with a CO donor hematin significantly increased survival percentage of cells under a heat stress and regrowth ability after the heat stress, alleviated a decrease in cell vitality, and accumulation of malondialdehyde. In addition, treatment with hematin enhanced the activity of L-cysteine desulfhydrase, a key enzyme in H2S biosynthesis, which in turn induced accumulation of endogenous H2S in tobacco cells. Interestingly, hematin-induced heat tolerance was enhanced by addition of NaHS, a H2S donor, but weakened by specific inhibitors of H2S biosynthesis DL-propargylglycine or its scavenger hypotaurine. Furthermore, pretreatment with hemoglobin (a CO scavenger) and zinc protoporphyrin IX (a CO specific synthetic inhibitor) had no significant effect on NaHS-induced heat tolerance of tobacco cells. These results suggest that CO pretreatment could improve the heat tolerance of tobacco suspension cultured cells, and H2S might exert its signal role downstream to CO-induced heat tolerance.

Hydrogen sulfide partly mediates abscisic acid-induced heat tolerance in tobacco (Nicotiana tabacum L.) suspension cultured cells

Abscisic acid (ABA), a plant hormone, plays crucial roles in plant growth, development and response to environmental stress. Recently, hydrogen sulfide (H2S) also has emerged similar functions, but interaction between ABA and H2S in the acquisition of heat tolerance is not clear. In this study, pretreatment of tobacco suspension cultured cells with ABA improved the survival percentage and regrowth ability, alleviated a decrease in cell vitality, increase in malondialdehyde content and electrolyte leakage of cells under heat stress, suggesting that ABA pretreatment could improve the heat tolerance of tobacco cells. In addition, treatment with ABA induced the accumulation of endogenous H2S in both tobacco cells and culture medium, increased the activity of l-cysteine desulfhydrase, a key enzyme in H2S biosynthesis. Also, ABA-induced heat tolerance was enhanced by addition of NaHS, a H2S donor, but weakened by dl-propargylglycine (specific inhibitor of H2S biosynthesis) and hypotaurine (H2S scavenger) respectively. These results suggest that ABA pretreatment could improve the heat tolerance of tobacco suspension cultured cells, and H2S, at least partly, mediated the acquisition of heat tolerance induced by ABA.