Impact of elevated H(2)S on metabolite levels, activity of enzymes and expression of genes involved in cysteine metabolism

Detrimental impact of sulfide on the seagrass Zostera marina in dark hypoxia

Sulfide poisoning, hypoxia events, and reduced light availability pose threats to marine ecosystems such as seagrass meadows. These threats are projected to intensify globally, largely due to accelerating eutrophication of estuaries and coastal environments. Despite the urgency, our current comprehension of the metabolic pathways that underlie the deleterious effects of sulfide toxicity and hypoxia on seagrasses remains inadequate. To address this knowledge gap, I conducted metabolomic analyses to investigate the impact of sulfide poisoning under dark-hypoxia in vitro conditions on Zostera marina, a vital habitat-forming marine plant. During the initial 45 minutes of dark-hypoxia exposure, I detected an acclimation phase characterized by the activation of anaerobic metabolic pathways and specific biochemical routes that mitigated hypoxia and sulfide toxicity. These pathways served to offset energy imbalances, cytosolic acidosis, and sulfide toxicity. Notably, one such route facilitated the transformation of toxic sulfide into non-toxic organic sulfur compounds, including cysteine and glutathione. However, this sulfide tolerance mechanism exhibited exhaustion post the initial 45-minute acclimation phase. Consequently, after 60 minutes of continuous sulfide exposure, the sulfide toxicity began to inhibit the hypoxia-mitigating pathways, culminating in leaf senescence and tissue degradation. Utilizing metabolomic approaches, I elucidated the intricate metabolic responses of seagrasses to sulfide toxicity under in vitro dark-hypoxic conditions. My findings suggest that future increases in coastal eutrophication will compromise the resilience of seagrass ecosystems to hypoxia, primarily due to the exacerbating influence of sulfide.

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.

Integrated bioinformatic and physiological analyses reveal the pivotal role of hydrogen sulfide in enhancing low-temperature tolerance in alfalfa

Hydrogen sulfide (H₂ S) is an important gaseous signal molecule that regulates plant growth and stress resistance. However, research on the H₂ S synthase (HSase) genes is still limited in the model legume plant Medicago truncatula Gaertn. In the present study, a total of 40 HSase family members were first identified and analyzed in the M. truncatula genome, and these genes distributed across eight chromosomes and were clustered into five groups (I-V) based on their conserved gene structures and protein motifs. Expression analysis revealed that the MtHSase genes were expressed in all the tested abiotic stresses, albeit with expression level differences. This study also showed that H₂ S improves low temperature tolerance of alfalfa seedlings by regulating the antioxidant defense system and enhancing photosynthetic capacity. Thus, the study provides new insights into how the H₂ S signal regulates tolerance to low-temperature stress and provides the basis for further gene function and detection.

Protective mechanisms of sulfur against arsenic phytotoxicity in Brassica napus by regulating thiol biosynthesis, sulfur-assimilation, photosynthesis, and antioxidant response

The contamination of agricultural soils with Arsenic (As) is a significant environmental stress that restricts plant growth, metabolism, and productivity worldwide. The present study examined the role of elemental sulfur (S⁰) in protecting Brassica napus plants from Arsenic (As) toxicity. Arsenic (100, and 200 mg As kg^-1 soil) in soil caused detrimental effects on five Brassica napus cultivars (Neelam, Teri-Uttam Jawahar, Him Sarson, GSC-101, and NUDB 26-11). The As toxicity inhibited the growth and photosynthesis indices in all cultivars with more deterioration effects in NUDB 26-11. Plant absorption and uptake of As caused the generation of oxidative injury by accumulating the reactive oxygen species (ROS), which simultaneously decreased the plant defence capability and ultimately the photosynthesis. Application of sulfur (S⁰, 100 or 200 mg S kg^-1 soil) alleviated the negative impacts and toxicity of As on the photosynthesis and growth matrices of plants, especially under high S level. S⁰ also boosted the antioxidant potential of plants and toned-down lipid peroxidation and ROS aggravation such as superoxide anion (O₂^•-) and H₂O₂, hydrogen peroxide, in As affected plants. In general, S⁰ at 200 mg kg^-1 soil more perceptibly increased the functionality of antioxidant enzymes, and non-enzymatic antioxidants, metal chelators and non-protein thiols. Further amendment of soil with S⁰ at fifteen days before seed sowing affected by As-induced toxic effects (added to soil at the time of sowing) considerably intensified the endogenous hydrogen sulfide (H₂S) content and its regenerating enzymes D-cysteine desulfhydrase (DCD) and L-cysteine desulfhydrase (LCD) that further strengthened the defense capability of plants to withstand As-stress. Our results suggest the role of H₂S in the S-induced defense operation of the B. napus plants in restraining As toxicity. The current study shows that S⁰ as a source of S might be used to promote the growth of B. napus plants in polluted agricultural soils.

Hydrogen Sulfide Mitigates Chilling Injury of Postharvest Banana Fruits by Regulating γ-Aminobutyric Acid Shunt Pathway and Ascorbate-Glutathione Cycle

This study aimed to determine the effect of hydrogen sulfide on chilling injury (CI) of banana (Musa spp.) during cold storage (7°C). It was observed that hydrogen sulfide application (2 mmol L^-1) markedly reduced the CI index and showed significantly higher chlorophyll contents, along with suppressed chlorophyll peroxidase and chlorophyllase enzyme activity. The treated banana fruits exhibited substantially higher peel lightness (L*), along with significantly a lower browning degree and soluble quinone content. The treated bananas had substantially a higher endogenous hydrogen sulfide content and higher activity of its biosynthesis-associated enzymes such as D-cysteine desulfhydrase (DCD) and L-cysteine desulfhydrase (LCD), along with significantly lower ion leakage, lipid peroxidation, hydrogen peroxide, and superoxide anion concentrations. Hydrogen sulfide-treated banana fruits showed an increased proline content and proline metabolism-associated enzymes including ornithine aminotransferase (OAT), Δ¹-pyrroline-5-carboxylate synthetase (P5CS), and proline dehydrogenase (PDH). In the same way, hydrogen sulfide-fumigated banana fruits accumulated higher endogenous γ-aminobutyric acid (GABA) due to enhanced activity of glutamate decarboxylase (GAD) and GABA transaminase (GABA-T) enzymes. The hydrogen sulfide-treated fruits exhibited higher total phenolics owing to lower polyphenol oxidase (PPO) and peroxidase (POD) activity and stimulated phenylalanine ammonia lyase (PAL). The treated banana exhibited higher ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), and superoxide dismutase (SOD) activity, along with higher glutathione (GSH) and ascorbic acid (AsA) concentrations and a significantly lower dehydroascorbic acid (DHA) content. In conclusion, hydrogen sulfide treatment could be utilized for CI alleviation of banana fruits during cold storage.

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.

Sulfur Starvation in Extremophilic Microalga Galdieria sulphuraria: Can Glutathione Contribute to Stress Tolerance?

This study reports the effects of sulfur (S) deprivation in cultures of Galdieria sulphuraria (Cyanidiophyceae). Galdieria is a unicellular red alga that usually grows, forming biomats on rocks, in S-rich environments. These are volcanic areas, where S is widespread since H₂S is the prevalent form of gas. The glutathione content in Galdieria sulphuraria is much higher than that found in the green algae and even under conditions of S deprivation for 7 days, it remains high. On the other hand, the S deprivation causes a decrease in the total protein content and a significant increase in soluble protein fraction. This suggests that in the conditions of S starvation, the synthesis of enzymatic proteins, that metabolically support the cell in the condition of nutritional stress, could be up regulated. Among these enzymatic proteins, those involved in cell detoxification, due to the accumulation of ROS species, have been counted.

Hydrogen Sulfide-Linked Persulfidation Maintains Protein Stability of ABSCISIC ACID-INSENSITIVE 4 and Delays Seed Germination

Hydrogen sulfide (H₂S) is an endogenous gaseous molecule that plays an important role in the plant life cycle. The multiple transcription factor ABSCISIC ACID INSENSITIVE 4 (ABI4) was precisely regulated to participate in the abscisic acid (ABA) mediated signaling cascade. However, the molecular mechanisms of how H₂S regulates ABI4 protein level to control seed germination and seedling growth have remained elusive. In this study, we demonstrated that ABI4 controls the expression of L-CYSTEINE DESULFHYDRASE1 (DES1), a critical endogenous H₂S-producing enzyme, and both ABI4 and DES1-produced H₂S have inhibitory effects on seed germination. Furthermore, the ABI4 level decreased during seed germination while H₂S triggered the enhancement of the persulfidation level of ABI4 and alleviated its degradation rate, which in turn inhibited seed germination and seedling establishment. Conversely, the mutation of ABI4 at Cys250 decreased ABI4 protein stability and facilitated seed germination. Moreover, ABI4 degradation is also regulated via the 26S proteasome pathway. Taken together, these findings suggest a molecular link between DES1 and ABI4 through the post-translational modifications of persulfidation during early seedling development.

Sulfur Compounds in Regulation of Stomatal Movement

Sulfur, widely present in the soil and atmosphere, is one of the essential elements for plants. Sulfate is a dominant form of sulfur in soils taken up by plant roots. In addition to the assimilation into sulfur compounds essential for plant growth and development, it has been reported recently that sulfate as well as other sulfur containing compounds can also induce stomatal movement. Here, we first summarized the uptake and transport of sulfate and atmospheric sulfur, including H₂O and SO₂, and then, focused on the effects of inorganic and organic sulfur on stomatal movement. We concluded all the transporters for different sulfur compounds, and compared the expression level of those transporters in guard cells and mesophyll cells. The relationship between abscisic acid and sulfur compounds in regulation of stomatal movement were also discussed.

Hydrogen sulfide improves tall fescue photosynthesis response to low-light stress by regulating chlorophyll and carotenoid metabolisms

Hydrogen sulfide (H₂S), as a gaseous messenger molecule, plays critical roles in signal transduction and biological modulation. In the present study, the roles of H₂S in regulating chlorophyll (Chl) and carotenoid (Car) contents to improve photosynthesis in tall fescue were investigated under low-light (LL) stress. Compared to control conditions, LL stress significantly reduced total biomass, net photosynthetic rate (P_n), maximal quantum yield of photosystem II (PSII) photochemistry (F_v/F_m), and the contents of Chl and Car. Under exogenous sodium hydrosulfide (NaHS, H₂S donor) application, these parameters were enhanced, ultimately increasing photosynthesis. Moreover, exogenous H₂S up-regulated the expression of chlorophyll biosynthesis genes while down-regulated chlorophyll degradation genes, resulting in increases in chlorophyll precursors. Components of carotenoids and expression of genes encoding biosynthesis and degradation enzymes varied similarly. Additionally, application exogenous H₂S up-regulated expression of FaDES1 and FaDCD. Thus, it enhanced L-cysteine desulfhydrase 1 (DES1, EC 4.4.1.1) and D-cysteine desulfhydrase (DCD, EC 4.4.1.15) activities leading to elevated endogenous H₂S. However, these responses were reversed by treatment with hypotaurine (HT, H₂S scavenger). These results suggested that H₂S is involved in regulating photosynthesis to improve LL tolerance via modulating Chl and Car metabolisms in tall fescue.

Response to Antimony Toxicity in Dittrichia viscosa Plants: ROS, NO, H2S, and the Antioxidant System

Dittrichia viscosa plants were grown hydroponically with different concentrations of Sb. There was preferential accumulation of Sb in roots. Fe and Cu decreased, while Mn decreased in roots but not in leaves. Chlorophyll content declined, but the carotenoid content increased, and photosynthetic efficiency was unaltered. O₂^●− generation increased slightly, while lipid peroxidation increased only in roots. H₂O₂, NO, ONOO⁻, S-nitrosothiols, and H₂S showed significant increases, and the enzymatic antioxidant system was altered. In roots, superoxide dismutase (SOD) and monodehydroascorbate reductase (MDAR) activities declined, dehydroscorbate reductase (DHAR) rose, and ascorbate peroxidase (APX), peroxidase (POX), and glutathione reductase (GR) were unaffected. In leaves, SOD and POX increased, MDAR decreased, and APX was unaltered, while GR increased. S-nitrosoglutathione reductase (GSNOR) and l-cysteine desulfhydrilase (l-DES) increased in activity, while glutathione S-transferase (GST) decreased in leaves but was enhanced in roots. Components of the AsA/GSH cycle decreased. The great capacity of Dittrichia roots to accumulate Sb is the reason for the differing behaviour observed in the enzymatic antioxidant systems of the two organs. Sb appears to act by binding to thiol groups, which can alter free GSH content and SOD and GST activities. The coniferyl alcohol peroxidase activity increased, possibly to lignify the roots’ cell walls. Sb altered the ROS balance, especially with respect to H₂O₂. This led to an increase in NO and H₂S acting on the antioxidant system to limit that Sb-induced redox imbalance. The interaction NO, H₂S and H₂O₂ appears key to the response to stress induced by Sb. The interaction between ROS, NO, and H₂S appears to be involved in the response to Sb.

Unraveling hydrogen sulfide-promoted lateral root development and growth in mangrove plant Kandelia obovata: insight into regulatory mechanism by TMT-based quantitative proteomic approaches

Mangroves are the main intertidal ecosystems with varieties of root types along the tropical and subtropical coastlines around the world. The typical characteristics of mangrove habitats, including the abundant organic matter and nutrients, as well as the strong reductive environment, are favor for the production of hydrogen sulfide (H2S). H2S, as a pivotal signaling molecule, has been evidenced in a wide variety of plant physiological and developmental processes. However, whether H2S functions in the mangrove root system establishment is not clear yet. Here, we reported the possible role of H2S in regulation of Kandelia obovata root development and growth by tandem mass tag (TMT)-based quantitative proteomic approaches coupled with bioinformatic methods. The results showed that H2S could induce the root morphogenesis of K. obovata in a dose-dependent manner. The proteomic results successfully identified 8075 proteins, and 697 were determined as differentially expressed proteins. Based on the functional enrichment analysis, we demonstrated that H2S could promote the lateral root development and growth by predominantly regulating the proteins associated with carbohydrate metabolism, sulfur metabolism, glutathione metabolism and other antioxidant associated proteins. In addition, transcriptional regulation and brassinosteroid signal transduction associated proteins also act as important roles in lateral root development. The protein-protein interaction analysis further unravels a complicated regulation network of carbohydrate metabolism, cellular redox homeostasis, protein metabolism, secondary metabolism, and amino acid metabolism in H2S-promoted root development and growth of K. obovata. Overall, our results revealed that H2S could contribute to the morphogenesis of the unique root system of mangrove plant K. obovata, and play a positive role in the adaption of mangrove plants to intertidal habitats.

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

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

Hydrogen sulfide, a signaling molecule in plant stress responses

Gaseous molecules, such as hydrogen sulfide (H₂ S) and nitric oxide (NO), are crucial players in cellular and (patho)physiological processes in biological systems. The biological functions of these gaseous molecules, which were first discovered and identified as gasotransmitters in animals, have received unprecedented attention from plant scientists in recent decades. Researchers have arrived at the consensus that H₂ S is synthesized endogenously and serves as a signaling molecule throughout the plant life cycle. However, the mechanisms of H₂ S action in redox biology is still largely unexplored. This review highlights what we currently know about the characteristics and biosynthesis of H₂ S in plants. Additionally, we summarize the role of H₂ S in plant resistance to abiotic stress. Moreover, we propose and discuss possible redox-dependent mechanisms by which H₂ S regulates plant physiology.

Hydrogen sulfide induced by hydrogen peroxide mediates brassinosteroid-induced stomatal closure of Arabidopsis thaliana

The role of hydrogen sulfide (H2S) and its relationship with hydrogen peroxide (H2O2) in brassinosteroid-induced stomatal closure in Arabidopsis thaliana (L.) Heynh. were investigated. In the present study, 2,4-epibrassinolide (EBR, a bioactive BR) induced stomatal closure in the wild type, the effects were inhibited by H2S scavenger and synthesis inhibitors, and H2O2 scavengers and synthesis inhibitor. However, EBR failed to close the stomata of mutants Atl-cdes, Atd-cdes, AtrbohF and AtrbohD/F. Additionally, EBR induced increase of L-/D-cysteine desulfhydrase (L-/D-CDes) activity, H2S production, and H2O2 production in the wild type, and the effects were inhibited by H2S scavenger and synthesis inhibitors, and H2O2 scavengers and synthesis inhibitor respectively. Furthermore, EBR increased H2O2 levels in the guard cells of AtrbohD mutant, but couldn't raise H2O2 levels in the guard cells of AtrbohF and AtrbohD/F mutants. Next, scavengers and synthesis inhibitor of H2O2 could significantly inhibit EBR-induced rise of L-/D-CDes activity and H2S production in the wild type, but H2S scavenger and synthesis inhibitors failed to repress EBR-induced H2O2 production. EBR could increase H2O2 levels in the guard cells of Atl-cdes and Atd-cdes mutants, but EBR failed to induce increase of L-/D-CDes activity and H2S production in AtrbohF and AtrbohD/F mutants. Therefore, we conclude that H2S and H2O2 are involved in the signal transduction pathway of EBR-induced stomatal closure. Altogether, our data suggested that EBR induces AtrbohF-dependent H2O2 production and subsequent AtL-CDes-/AtD-CDes-catalysed H2S production, and finally closes stomata in A. thaliana.

Something smells bad to plant pathogens: Production of hydrogen sulfide in plants and its role in plant defence responses

Background

Sulfur and diverse sulfur-containing compounds constitute important components of plant defences against a wide array of microbial pathogens. Among them, hydrogen sulfide (H₂S) occupies a prominent position as a gaseous signalling molecule that plays multiple roles in regulation of plant growth, development and plant responses to stress conditions. Although the production of H₂S in plant cells has been discovered several decades ago, the underlying pathways of H₂S biosynthesis, metabolism and signalling were only recently uncovered.

Aim of the review

Here we review the current knowledge on the biosynthesis of H₂S in plant cells, with special attention to L-cysteine desulfhydrase (DES) as the key enzyme controlling H₂S levels biosynthesis in the cytosol of plant cells during plant growth, development and diverse abiotic and biotic stress conditions.

Key Scientific Concepts of Review

Recent advances have revealed molecular mechanisms of DES properties, functions and regulation involved in modulations of H₂S production during plant responses to abiotic and biotic stress stimuli. Studies on des mutants of the model plant Arabidopsis thaliana uncovered molecular mechanisms of H₂S action as a signalling and defence molecule in plant-pathogen interactions. Signalling pathways of H₂S include S-persulfidation of protein cysteines, a redox-based post-translational modification leading to activation of downstream components of H₂S signalling. Accumulated evidence shows DES and H2S implementation into salicylic acid signalling and activation of pathogenesis-related proteins and autophagy within plant immunity. Obtained knowledge on molecular mechanisms of H₂S action in plant defence responses opens new prospects in the search for crop varieties with increased resistance to bacterial and fungal pathogens.

Hydrogen sulfide is required for salicylic acid-induced chilling tolerance of cucumber seedlings

Salicylic acid (SA) and hydrogen sulfide (H₂S) have been proved to be multifunctional signal molecules to participate in the response of plants to abiotic stresses. However, it is still unclear whether there is interaction between SA and H₂S in response to chilling intensity of cucumber seedlings. Here, we found SA was sensitive to chilling intensity. Under normal condition, NaHS (H₂S donor) or removing endogenous H₂S with hypotaurine (HT, a specific scavenger of H₂S) and DL-propargylglycine (PAG, a specific inhibitor of H₂S) has no effect on endogenous SA level; however, SA induced endogenous H₂S content and activated the activities and mRNA level of L-/D-cysteine desulfhydrase (L-/D-CD), and inhibiting endogenous SA with paclobutrazol (PAC) or 2-aminoindan-2-phosphonic acid (AIP) blocked this effect, implying H₂S may play a role after SA signal. Further studies showed that both SA and NaHS notably alleviated chilling injury, which was evidenced by lower electrolyte leakage (EL), MDA content, and ROS accumulation, compared with H₂O treatment. Of note, SA and H₂S improved the activities and mRNA level of antioxidant enzymes (SOD, POD, CAT, APX, and GR) as well as the contents of AsA and GSH. Additionally, the chilling-response genes (ICE, CBF1, and COR) were obviously upregulated by exogenous SA and NaHS. However, the positive effect of SA on chilling tolerance was inhibited by HT, whereas PAC or AIP did not affect NaHS-induced chilling tolerance. Taken together, the data reveals that H₂S acts as a downstream signal of SA-induced chilling tolerance of cucumber via modulating antioxidant system and chilling-response genes.

Auxin acts as a downstream signaling molecule involved in hydrogen sulfide-induced chilling tolerance in cucumber

This report proves a cross talk between H₂S and IAA in cold stress response, which has presented strong evidence that IAA acts as a downstream signal mediating the H₂S-induced stress tolerance in cucumber seedlings. We evaluated changes in endogenous hydrogen sulfide (H₂S) and indole-3-acetic acid (IAA) emission systems, and the interactive effect of exogenous H₂S and IAA on chilling tolerance in cucumber seedlings. The results showed that chilling stress increased the activity and relative mRNA expression of L-/D-cysteine desulfhydrase (L-/D-CD), which in turn induced the accumulation of endogenous H₂S. Similarly, the endogenous IAA system was triggered by chilling stress. We found that 1.0 mM sodium hydrosulfide (NaHS, an H₂S donor) significantly enhanced the activity of flavin monooxygenase (FMO) and relative expression of FMO-like proteins (YUCCA2), which in turn elevated endogenous IAA levels in cucumber seedlings. However, IAA had little effects on activities of L-/D-CD and endogenous H₂S levels. H₂S-induced IAA production accompanied by increase in chilling tolerance, as shown by the decrease in stress-induced electrolyte leakage (EL) and reactive oxygen species (ROS) accumulation, and increase in gene expressions and enzyme activities of photosynthesis. 1-naphthylphthalamic acid (NPA, an IAA polar transport inhibitor) declined H₂S-induced chilling tolerance and defense genes' expression. However, scavenging of H₂S had a little effect on IAA-induced chilling tolerance. These results suggest that IAA acting as a downstream signaling molecule is involved in the H₂S-induced chilling tolerance in cucumber seedlings.

Physiological response and transcription profiling analysis reveal the role of glutathione in H2S-induced chilling stress tolerance of cucumber seedlings

Recent reports have uncovered the multifunctional role of H₂S in the physiological response of plants to biotic and abiotic stresses. Here, we studied whether NaHS (an H₂S donor) pretreatment could provoke the tolerance of cucumber (Cucumis sativus L.) seedlings subsequently exposed to chilling stress and whether glutathione was involved in this process. Results showed that cucumber seedlings sprayed with NaHS exhibited remarkably increased chilling tolerance, as evidenced by the observed plant tolerant phenotype, as well as the lower levels of electrolyte leakage (EL), malondialdehyde (MDA) content, hydrogen peroxide (H₂O₂) content and RBOH mRNA abundance, compared with the control plants. In addition, NaHS treatment increased the endogenous content of the reduced glutathione (GSH) and the ratio of reduced/oxidized glutathione (GSH/GSSG), meanwhile, the higher net photosynthetic rate (Anet), the light-saturated CO₂ assimilation rate (Asat), the photochemical efficiency (Fv/Fm) and the maximum photochemical efficiency of PSII in darkness (ФPSII) as well as the mRNA levels and activities of the key photosynthetic enzymes (Rubisco, TK, SBPase and FBA) were observed in NaHS-treated seedlings under chilling stress, whereas this effect of NaHS was weakened by buthionine sulfoximine (BSO, an inhibitor of glutathione) or 6-Aminonicotinamide (6-AN, a specific pentose inhibitor and thus inhibits the NADPH production), which preliminarily proved the interaction between H₂S and GSH. Moreover, transcription profiling analysis revealed that the GSH-associated genes (GST Tau, MAAI, APX, GR, GS and MDHAR) were significantly up-regulated in NaHS-treated cucumber seedlings, compared to the H₂O-treated seedlings under chilling stress. Thus, novel results highlight the importance of glutathione as a downstream signal of H₂S-induced plant tolerance to chilling stress.

Nitric oxide and hydrogen sulfide crosstalk during heavy metal stress in plants

Gases such as ethylene, hydrogen peroxide (H₂ O₂ ), nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H₂ S) have been recognized as vital signaling molecules in plants and animals. Of these gasotransmitters, NO and H₂ S have recently gained momentum mainly because of their involvement in numerous cellular processes. It is therefore important to study their various attributes including their biosynthetic and signaling pathways. The present review provides an insight into various routes for the biosynthesis of NO and H₂ S as well as their signaling role in plant cells under different conditions, more particularly under heavy metal stress. Their beneficial roles in the plant's protection against abiotic and biotic stresses as well as their adverse effects have been addressed. This review describes how H₂ S and NO, being very small-sized molecules, can quickly pass through the cell membranes and trigger a multitude of responses to various factors, notably to various stress conditions such as drought, heat, osmotic, heavy metal and multiple biotic stresses. The versatile interactions between H₂ S and NO involved in the different molecular pathways have been discussed. In addition to the signaling role of H₂ S and NO, their direct role in posttranslational modifications is also considered. The information provided here will be helpful to better understand the multifaceted roles of H₂ S and NO in plants, particularly under stress conditions.

Role of Exogenous and Endogenous Hydrogen Sulfide (H2S) on Functional Traits of Plants Under Heavy Metal Stresses: A Recent Perspective

Improving growth and productivity of plants that are vulnerable to environmental stresses, such as heavy metals, is of significant importance for meeting global food and energy demands. Because heavy metal toxicity not only causes impaired plant growth, it has also posed many concerns related to human well-being, so mitigation of heavy metal pollution is a necessary priority for a cleaner environment and healthier world. Hydrogen sulfide (H₂S), a gaseous signaling molecule, is involved in metal-related oxidative stress mitigation and increased stress tolerance in plants. It performs multifunctional roles in plant growth regulation while reducing the adverse effects of abiotic stress. Most effective function of H₂S in plants is to eliminate metal-related oxidative toxicity by regulating several key physiobiochemical processes. Soil pollution by heavy metals presents significant environmental challenge due to the absence of vegetation cover and the resulting depletion of key soil functions. However, the use of stress alleviators, such as H₂S, along with suitable crop plants, has considerable potential for an effective management of these contaminated soils. Overall, the present review examines the imperative role of exogenous application of different H₂S donors in reducing HMs toxicity, by promoting plant growth, stabilizing their physiobiochemical processes, and upregulating antioxidative metabolic activities. In addition, crosstalk of different growth regulators with endogenous H₂S and their contribution to the mitigation of metal phytotoxicity have also been explored.

Anomalous Discharge of Endogenous Gas at Lavinio (Rome, Italy) and the Lethal Accident of 5 September 2011

The Rome region contains several sites where endogenous gas is brought to the surface through deep reaching faults, creating locally hazardous conditions for people and animals. Lavinio is a touristic borough of Anzio (Rome Capital Metropolitan City) that hosts a country club with a swimming pool and an adjacent basement balance tank. In early September 2011, the pool and the tank had been emptied for cleaning. On 5 September, four men descended into the tank and immediately lost consciousness. On 12 August 2012, after a long coma the first person died, the second one reported permanent damage to his central nervous system, and the other two men recovered completely. Detailed geochemical investigations show that the site is affected by a huge release of endogenous gas (CO2 ≈ 96 vol.% and H2S ≈ 4 vol.%). High soil CO2 and H2S flux values were measured near the pool (up to 898 and 7.155 g·m-2·day-1, respectively), and a high CO2 concentration (23-25 vol.%) was found at 50-70 cm depth in the soil. We were able to demonstrate that gas had been transported into the balance tank from the swimming pool through two hubs connected to the lateral overflow channels of the pool. We show also that the time before the accident (60 hr), during which the balance tank had remained closed to external air, had been largely sufficient to reach indoor nearly lethal conditions (oxygen deficiency and high concentration of both CO2 and H2S).

Regulation of Hydrogen Sulfide Metabolism by Nitric Oxide Inhibitors and the Quality of Peaches during Cold Storage

Both nitric oxide (NO) and hydrogen sulfide (H2S) have been shown to have positive effects on the maintenance of fruit quality during storage; however, the mechanisms by which NO regulates the endogenous H2S metabolism remain unknown. In this experiment, peaches were immersed in solutions of NO, potassium 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO, as an NO scavenger), N-nitro-l-arginine methyl ester (l-NAME, as an inhibitor of nitric oxide synthase (NOS)-like activity), and sodium tungstate (as an inhibitor of nitrate reductase), and the resulting changes in the H2S metabolism of peaches were studied. The results showed that exogenous NO reduced the contents of endogenous H2S, Cys, and sulfite; decreased the activities of l-/d-cysteine desulfhydrase (l-/d-CD), O-acetylserine (thiol)lyase (OAS-TL), and sulfite reductase (SiR); and increased the activity of β-cyanoalanine synthase (β-CAS). Both c-PTIO and sodium tungstate had similar roles in increasing the H2S content by sustaining the activities of l-/d-CDs, OAS-TL, and SiR. l-NAME increased the H2S content, mainly by maintaining the d-CD activity. The results suggest that NO, c-PTIO, l-NAME, and sodium tungstate differently regulate the H2S metabolism of peaches during storage.

Differential effects of NaCl and Na2SO4 on the halophyte Prosopis strombulifera are explained by different responses of photosynthesis and metabolism

Prosopis strombulifera (Lam.) Benth. is a halophytic shrub found in highly saline soils in Argentina, with high tolerance against NaCl but strong growth inhibition by Na₂SO_4. In the present study, the differences in the physiological responses caused by these salts and an iso-osmotic combination thereof on photosynthesis, mineral composition and metabolism were analyzed. Na₂SO₄ treated plants were the most affected by salinity, showing a significant decrease in several photosynthetic parameters. Proline and cysteine accumulated significantly in the plants in response to salt stress. These results show by the first time that the SO₄^2- anion is triggering damage in the photosynthetic apparatus and consequently affecting the photosynthetic process, which may explain the strong growth inhibition in these plants at high salinity. Moreover, the SO₄^2- anion provoke challenges in the incorporation of nutrients, decreasing the levels of K, Ca, P and Mg, and inducing a strong antioxidant activity in P. strombulifera.

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

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

Atmospheric H2S: Impact on Plant Functioning

Hydrogen sulfide (H2S) is an air pollutant present at high levels in various regions. Plants actively take up H2S via the foliage, though the impact of the gas on the physiological functioning of plants is paradoxical. Whereas elevated H2S levels may be phytotoxic, H2S levels realistic for polluted areas can also significantly contribute to the sulfur requirement of the vegetation. Plants can even grow with H2S as sole sulfur source. There is no relation between the rate of H2S metabolism and the H2S susceptibility of a plant, which suggests that the metabolism of H2S does not contribute to the detoxification of absorbed sulfide. By contrast, there may be a strong relation between the rate of H2S metabolism and the rate of sulfate metabolism: foliar H2S absorbance may downregulate the metabolism of sulfate, taken up by the root. Studies with plants from the Brassica genus clarified the background of this downregulation. Simultaneously, these studies illustrated that H2S fumigation may be a useful tool for obtaining insight in the regulation of sulfur homeostasis and the (signal) functions of sulfur-containing compounds in plants.

Interaction between the signaling molecules hydrogen sulfide and hydrogen peroxide and their role in vacuolar H+ -ATPase regulation in cadmium-stressed cucumber roots

Vacuolar H⁺ -ATPase (V-ATPase; EC 3.6.3.14) is the main enzyme responsible for generating a proton gradient across the tonoplast. Under cadmium (Cd) stress conditions, V-ATPase activity is inhibited. In the present work, hydrogen sulfide (H₂ S) and hydrogen peroxide (H₂ O₂ ) cross-talk was analyzed in cucumber (Cucumis sativus L.) seedlings exposed to Cd to explain the role of both signaling molecules in the control of V-ATPase. V-ATPase activity and gene expression as well as H₂ S and H₂ O₂ content and endogenous production were determined in roots of plants treated with 100 μM CdCl₂ and different inhibitors or scavengers. It was found that H₂ S donor improved photosynthetic parameters in Cd-stressed cucumber seedlings. Cd-induced stimulation of H₂ S level was correlated with the increased activities of the H₂ S-generating desulfhydrases. Increased H₂ O₂ and lowered H₂ S contents in roots were able to reduce V-ATPase activities similar to Cd. H₂ O₂ and H₂ S-induced modulations in V-ATPase activities were not closely related to the transcript level of encoding genes, suggesting posttranslational modifications of enzyme protein. On the other hand, exogenous H₂ O₂ raised H₂ S content in root tissues independently from the desulfhydrase activity. Although treatment of control plants with H₂ S significantly stimulated NADPH oxidase activity and gene expression, H₂ S did not affect H₂ O₂ accumulation in roots exposed to Cd. The results suggest the existence of two pathways of H₂ S generation in Cd-stressed cucumber roots. One involves desulfhydrase activity, as was previously demonstrated in different plant species. The other, the desulfhydrase-independent pathway induced by H₂ O₂ /NADPH oxidase, may protect V-ATPase from inhibition by Cd.

H2S Alleviates Salinity Stress in Cucumber by Maintaining the Na+/K+ Balance and Regulating H2S Metabolism and Oxidative Stress Response

Salinity stress from soil or irrigation water can significantly limit the growth and development of plants. Emerging evidence suggests that hydrogen sulfide (H2S), as a versatile signal molecule, can ameliorate salt stress-induced adverse effects. However, the possible physiological mechanism underlying H2S-alleviated salt stress in cucumber remains unclear. Here, a pot experiment was conducted with an aim to examine the possible mechanism of H2S in enhancement of cucumber salt stress tolerance. The results showed that H2S ameliorated salt-induced growth inhibition and alleviated the reduction in photosynthetic attributes, chlorophyll fluorescence and stomatal parameters. Meanwhile H2S increased the endogenous H2S level concomitant with increased activities of D/L-cysteine desulfhydrase and β-cyanoalanine synthase and decreased activities of O-acetyl-L-serine(thiol)lyase under excess NaCl. Notably, H2S maintained Na+ and K+ homeostasis via regulation of the expression of PM H+-ATPase, SOS1 and SKOR at the transcriptional level under excess NaCl. Moreover, H2S alleviated salt-induced oxidative stress as indicated by lowered lipid peroxidation and reactive oxygen species accumulation through an enhanced antioxidant system. Altogether, these results demonstrated that application of H2S could protect cucumber seedlings against salinity stress, likely by keeping the Na+/K+ balance, controlling the endogenous H2S level by regulating the H2S synthetic and decomposition enzymes, and preventing oxidative stress by enhancing the antioxidant system under salinity stress.

The role of H2S in low temperature-induced cucurbitacin C increases in cucumber

In this study, we first linked the signal molecule H₂S with cucurbitacin C, which can cause the bitter taste of cucumber leaves and fruit, and specifically discuss its molecular mechanism. Cucurbitacin C (CuC), a triterpenoid secondary metabolite, enhances the resistance of cucumber plants to pathogenic bacteria and insect herbivores, but results in bitter-tasting fruits. CuC can be induced in some varieties of cucumber on exposure to plant stressors. The gasotransmitter hydrogen sulfide (H₂S) participates in multiple physiological processes relating to plant stress resistance. This study focused on the effect of H₂S on low temperature-induced CuC synthesis in cucumber. The results showed that treatment of cucumber leaves at 4 °C for 12 h enhanced the content and production rate of H₂S and increased the expression of genes encoding enzymes involved in H₂S generation, Csa2G034800.1 (CsaLCD), Csa1G574800.1 (CsaDES1), and Csa1G574810.1 (CsaDES2). In addition, treatment at 4 °C or with exogenous H₂S upregulated the expression of CuC synthetase-encoding genes and the resulting CuC content in cucumber leaves, whereas pretreatment with hypotaurine (HT, a H₂S scavenger) before treatment at 4 °C offset these effects. In vitro, H₂S could increase the S-sulfhydration level of His-Csa5G156220 and His-Csa5G157230 (both bHLH transcription factors), as well as their binding activity to the promoter of Csa6G088690, which encodes the key synthetase for CuC generation. H₂S pretreatment enhanced the cucumber leaves resistance to the Phytophthora melonis. Together, these results demonstrated that H₂S acts as a positive regulator of CuC synthesis as a result of the modification of proteins by S-sulfhydration, also providing indirect evidence for the role of H₂S in improving the resistance of plants to abiotic stresses and biotic stresses by regulating the synthesis of secondary metabolites.

Hydrogen sulfide may function downstream of hydrogen peroxide in salt stress-induced stomatal closure in Vicia faba

The roles of hydrogen sulfide (H2S) and hydrogen peroxide (H2O2) in signalling transduction of stomatal closure induced by salt stress were examined by using pharmacological, spectrophotographic and laser scanning confocal microscopic (LSCM) approaches in Vicia faba L. Salt stress resulted in stomatal closure, and this effect was blocked by H2S modulators hypotaurine (HT), aminooxy acetic acid (AOA), hydroxylamine (NH2OH), potassium pyruvate (C3H3KO3) and ammonia (NH3) and H2O2 modulators ascorbic acid (ASA), catalase (CAT), diphenylene iodonium (DPI). Additionally, salt stress induced H2S generation and increased L-/D-cysteine desulfhydrase (L-/D-CDes, pyridoxalphosphate-dependent enzyme) activity in leaves, and caused H2O2 production in guard cells, and these effects were significantly suppressed by H2S modulators and H2O2 modulators respectively. Moreover, H2O2 modulators suppressed salt stress-induced increase of H2S levels and L-/D-CDes activity in leaves as well as stomatal closure of V. faba. However, H2S modulators had no effects on salt stress-induced H2O2 production in guard cells. Altogether, our data suggested that H2S and H2O2 probably are involved in salt stress-induced stomatal closure, and H2S may function downstream of H2O2 in salt stress-induced stomatal movement in V. faba.

Characterization of the O-acetylserine(thiol)lyase gene family in Solanum lycopersicum L

This research demonstrated the conservation and diversification of the functions of the O-acetylserine-(thiol) lyase gene family genes in Solanum lycopersicum L. Cysteine is the first sulfur-containing organic molecule generated by plants and is the precursor of many important biomolecules and defense compounds. Cysteine and its derivatives are also essential in various redox signaling-related processes. O-acetylserine(thiol)lyase (OASTL) proteins catalyze the last step of cysteine biosynthesis. Previously, researches focused mainly on OASTL proteins which were the most abundant or possessed the authentic OASTL activity, whereas few studies have ever given a comprehensive view of the functions of all the OASTL members in one specific species. Here, we characterized 8 genes belonging to the OASTL gene family from tomato genome (SlOAS2 to SlOAS9), including the sequence analyses, subcellular localization, enzymatic activity assays, expression patterns, as well as the interaction property with SATs. Apart from SlOAS3, all the other genes encoded OASTL-like proteins. Tomato OASTLs were differentially expressed during the development of tomato plants, and their encoded proteins had diverse compartmental distributions and functions. SlOAS5 and SlOAS6 catalyzed the biogenesis of cysteine in chloroplasts and in the cytosol, respectively, and this was in consistent with their interaction abilities with SlSATs. SlOAS4 catalyzed the generation of hydrogen sulfide, similar to its Arabidopsis ortholog, DES1. SlOAS2 also functioned as an L-cysteine desulfhydrase, but its expression pattern was very different from that of SlOAS4. Additionally, SlOAS8 might be a β-cyanoalanine synthase in mitochondria, and the S-sulfocysteine synthase activity appeared lost in tomato plants. SlOAS7 exhibited a transactivational ability in yeast; while the subcellular localization of SlOAS9 was in the peroxisome and correlated with the process of leaf senescence, indicating that these two genes might have novel roles.

Hydrogen sulfide may function downstream of hydrogen peroxide in mediating darkness-induced stomatal closure in Vicia faba

The relationship between hydrogen sulfide (H2S) and hydrogen peroxide (H2O2) during darkness-induced stomatal closure in Vicia faba L. was investigated by using pharmacological, spectrophotographic and lasers canning confocal microscopic approaches. Darkness-induced stomatal closure was inhibited by H2S scavenger hypotaurine (HT), H2S synthesis inhibitors aminooxy acetic acid (AOA) and hydroxylamine (NH2OH) and potassium pyruvate (N3H3KO3) and ammonia (NH3), which are the products of L-/D-cysteine desulfhydrase (L-/D-CDes). Moreover, darkness induced H2S generation and increased L-/D-CDes activity in leaves of V. faba. H2O2 scavenger and synthesis inhibitors suppressed darkness-induced increase of H2S levels and L-/D-CDes activity as well as stomatal closure in leaves of V. faba. However, H2S scavenger and synthesis inhibitors had no effect on darkness-induced H2O2 accumulation in guard cells of V. faba. From these data it can be deduced that H2S is involved in darkness-induced stomatal closure and acts downstream of H2O2 in V. faba.

Accumulated substancies and calorific capacity in adipose tissue: Physical and chemical clinical trial

Aim

To study physical and chemical structures and properties including calorific value of human adipose tissue in different anatomical location in autopsy-assigned clinical trial.

Methods

A pilot physical and chemical descriptive randomized autopsy-assigned trial. Adipose tissue 252 sampled from 36 individuals at autopsy who between 36 and 63 years old died from road accidents. Interventions: Chemical functional groups and calorific value were studied using infrared and atomic adsorptive spectrometries, elemental chemical analysis and differential scanning calorimetry. Adipose tissue was sampled from the 7 various anatomical locations.

Results

The highest levels of the analysed chemical substancies were found in dense atherosclerotic plaque. Dense atherosclerotic plaque contains the most of metabolic products, organic and inorganic elements. Dense atherosclerotic plaque has the most of calorific value. The lowest calorific capacity has a pararenal fat.

Conclusions

Human body lipids serve as a harbor for various organic substances, they may absorb different metabolic products, and they have different calorific capacity depending on their location and forms. Atherosclerotic plaque contains the most of organic and inorganic elements, and brings the highest energy potential.

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The body adipose tissue is heterogeneous in content and in property.

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Atherosclerosis plaque contains the largest amount of organic/inorganic functional groups.

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Atherosclerosis plaque is a harbor for various organic substances.

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Adipose tissue has different calorific capacity depending on its locations and forms.

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Plaques bring the highest of energy potential in compare to other fats.

Endogenous Hydrogen Sulfide Homeostasis Is Responsible for the Alleviation of Senescence of Postharvest Daylily Flower via Increasing Antioxidant Capacity and Maintained Energy Status

There are limited data concerning the role of endogenous H₂S in prolonging the postharvest of vegetables and fruits. Using a fluorescence microscope with a specific probe, we discovered that, during the senescence of postharvest daylily flower, endogenous H₂S homeostasis was impaired. The activities of two important synthetic enzymes of H₂S, l- and d-cysteine desulfhydrase, exhibited decreasing tendencies. However, NaHS (a H₂S donor) not only blocked the decreased H₂S production but also extended the postharvest life of daylilies. These beneficial roles were verified by the alleviation of lipid peroxidation and the increased activities of antioxidant enzymes. Meanwhile, the energy status was sustained, and the respiration rate was decreased. In contrast to NaHS, the addition of an inhibitor of H₂S synthesis alone aggravated lipid peroxidation and lowered energy charge. Together, the present study implies that endogenous H₂S alleviates senescence of postharvest daylilies via increasing antioxidant capacity and maintained energy status.

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

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

Impact of Sulfur Starvation in Autotrophic and Heterotrophic Cultures of the Extremophilic Microalga Galdieria phlegrea (Cyanidiophyceae)

In plants and algae, sulfate assimilation and cysteine synthesis are regulated by sulfur (S) accessibility from the environment. This study reports the effects of S deprivation in autotrophic and heterotrophic cultures of Galdieria phlegrea (Cyanidiophyceae), a unicellular red alga isolated in the Solfatara crater located in Campi Flegrei (Naples, Italy), where H2S is the prevalent form of gaseous S in the fumarolic fluids and S is widespread in the soils near the fumaroles. This is the first report on the effects of S deprivation on a sulfurous microalga that is also able to grow heterotrophically in the dark. The removal of S from the culture medium of illuminated cells caused a decrease in the soluble protein content and a significant decrease in the intracellular levels of glutathione. Cells from heterotrophic cultures of G. phlegrea exhibited high levels of internal proteins and high glutathione content, which did not diminish during S starvation, but rather glutathione significantly increased. The activity of O-acetylserine(thiol)lyase (OASTL), the enzyme synthesizing cysteine, was enhanced under S deprivation in a time-dependent manner in autotrophic but not in heterotrophic cells. Analysis of the transcript abundance of the OASTL gene supports the OASTL activity increase in autotrophic cultures under S deprivation.

The function of hydrogen sulphide in iron availability: Sulfur nutrient or signaling molecule?

Hydrogen sulphide (H2S) has traditionally been considered as a phytotoxin, having deleterious effects on the plant growth and survival. Recently, it was recongnized as a potential signaling molecule involving in physiological regulation similar to nitric oxide (NO) and carbon monoxide (CO) in plants. In a recent study, we mainly focused on the signaling function of H2S in improving adaptation of Zea mays seedlings to iron deficiency. We reported that H2S was closely related to iron uptake, transport, and accumulation, and consequently increased chlorophyll biosynthesis, chloroplast development, and photosynthesis in Z. mays seedlings. Here, we provide more commentary on the signaling roles of H2S in coping with Fe deficiency in plants through increasing sulfur containing metabolites and regulating the expression level of iron homeostasis and sulfur metabolism-related genes in maize seedlings.

Cinnamaldehyde promotes root branching by regulating endogenous hydrogen sulfide

BACKGROUND

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

RESULTS

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

CONCLUSION

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

The Significance of Hydrogen Sulfide for Arabidopsis Seed Germination

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

Hydrogen sulphide improves adaptation of Zea mays seedlings to iron deficiency

Hydrogen sulphide (H2S) is emerging as a potential molecule involved in physiological regulation in plants. However, whether H2S regulates iron-shortage responses in plants is largely unknown. Here, the role of H2S in modulating iron availability in maize (Zea mays L. cv Canner) seedlings grown in iron-deficient culture solution is reported. The main results are as follows: Firstly, NaHS, a donor of H2S, completely prevented leaf interveinal chlorosis in maize seedlings grown in iron-deficient culture solution. Secondly, electron micrographs of mesophyll cells from iron-deficient maize seedlings revealed plastids with few photosynthetic lamellae and rudimentary grana. On the contrary, mesophyll chloroplasts appeared completely developed in H2S-treated maize seedlings. Thirdly, H2S treatment increased iron accumulation in maize seedlings by changing the expression levels of iron homeostasis- and sulphur metabolism-related genes. Fourthly, phytosiderophore (PS) accumulation and secretion were enhanced by H2S treatment in seedlings grown in iron-deficient solution. Indeed, the gene expression of ferric-phytosiderophore transporter (ZmYS1) was specifically induced by iron deficiency in maize leaves and roots, whereas their abundance was decreased by NaHS treatment. Lastly, H2S significantly enhanced photosynthesis through promoting the protein expression of ribulose-1,5-bisphosphate carboxylase large subunit (RuBISCO LSU) and phosphoenolpyruvate carboxylase (PEPC) and the expression of genes encoding RuBISCO large subunit (RBCL), small subunit (RBCS), D1 protein (psbA), and PEPC in maize seedlings grown in iron-deficient solution. These results indicate that H2S is closely related to iron uptake, transport, and accumulation, and consequently increases chlorophyll biosynthesis, chloroplast development, and photosynthesis in plants.

Roles of sodium hydrosulfide and sodium nitroprusside as priming molecules during drought acclimation in citrus plants

Emerging evidence suggests that the gaseous molecules hydrogen sulfide (H2S) and nitric oxide (NO) enhances plant acclimation to stress; however, the underlying mechanism remains unclear. In this work, we explored if pretreatment of citrus roots with NaHS (a H2S donor) or sodium nitroprusside (SNP, a NO donor) for 2 days (d) could elicit long-lasting priming effects to subsequent exposure to PEG-associated drought stress for 21 d following a 5 d acclimation period. Detailed physiological study documented that both pretreatments primed plants against drought stress. Analysis of the level of nitrite, NOx, S-nitrosoglutahione reductase, Tyr-nitration and S-nitrosylation along with the expression of genes involved in NO-generation suggested that the nitrosative status of leaves and roots was altered by NaHS and SNP. Using a proteomic approach we characterized S-nitrosylated proteins in citrus leaves exposed to chemical treatments, including well known and novel S-nitrosylated targets. Mass spectrometry analysis also enabled the identification of 42 differentially expressed proteins in PEG alone-treated plants. Several PEG-responsive proteins were down-regulated, especially photosynthetic proteins. Finally, the identification of specific proteins that were regulated by NaHS and SNP under PEG conditions provides novel insight into long-term drought priming in plants and in a fruit crop such as citrus in particular.

8-Mercapto-Cyclic GMP Mediates Hydrogen Sulfide-Induced Stomatal Closure in Arabidopsis

Plants are exposed to hydrogen sulfide (H2S) both exogenously, as it exists as a pollutant gas in the environment, and endogenously, as it is synthesized in cells. H2S has recently been found to function as a gaseous signaling molecule, but its signaling cascade remains unknown. Here, we examined H2S-mediated guard cell signaling in Arabidopsis. The H2S donor GYY4137 (morpholin-4-ium-4-methoxyphenyl [morpholino] phosphinodithioate) induced stomatal closure, which peaked after 150 min at 1 µM or after 90 min at 10 and 100 µM. After reaching maximal closure, stomatal apertures gradually increased in size in response to further exposure to GYY4137. GYY4137 induced nitric oxide (NO) generation in guard cells, and GYY4137-induced stomatal closure was reduced by an NO scavenger and inhibitors of NO-producing enzymes. Mass spectrometry analyses showed that GYY4137 induces the synthesis of 8-nitro-cGMP and 8-mercapto-cGMP and that this synthesis is mediated by NO. In addition, 8-mercapto-cGMP triggered stomatal closure. Moreover, inhibitor and genetic studies showed that calcium, cADP ribose and slow anion channel 1 act downstream of 8-mercapto-cGMP. This study therefore demonstrates that 8-mercapto-cGMP mediates the H2S signaling cascade in guard cells.

Hydrogen sulfide regulates inward-rectifying K+ channels in conjunction with stomatal closure

Hydrogen sulfide (H2S) is the third biological gasotransmitter, and in animals, it affects many physiological processes by modulating ion channels. H2S has been reported to protect plants from oxidative stress in diverse physiological responses. H2S closes stomata, but the underlying mechanism remains elusive. Here, we report the selective inactivation of current carried by inward-rectifying K(+) channels of tobacco (Nicotiana tabacum) guard cells and show its close parallel with stomatal closure evoked by submicromolar concentrations of H2S. Experiments to scavenge H2S suggested an effect that is separable from that of abscisic acid, which is associated with water stress. Thus, H2S seems to define a unique and unresolved signaling pathway that selectively targets inward-rectifying K(+) channels.

Brassica napus L. cultivars show a broad variability in their morphology, physiology and metabolite levels in response to sulfur limitations and to pathogen attack

Under adequate sulfur supply, plants accumulate sulfate in the vacuoles and use sulfur-containing metabolites as storage compounds. Under sulfur-limiting conditions, these pools of stored sulfur-compounds are depleted in order to balance the nitrogen to sulfur ratio for protein synthesis. Stress conditions like sulfur limitation and/or pathogen attack induce changes in the sulfate pool and the levels of sulfur-containing metabolites, which often depend on the ecotypes or cultivars. We are interested in investigating the influence of the genetic background of canola (Brassica napus) cultivars in sulfur-limiting conditions on the resistance against Verticillium longisporum. Therefore, four commercially available B. napus cultivars were analyzed. These high-performing cultivars differ in some characteristics described in their cultivar pass, such as several agronomic traits, differences in the size of the root system, and resistance to certain pathogens, such as Phoma and Verticillium. The objectives of the study were to examine and explore the patterns of morphological, physiological and metabolic diversity in these B. napus cultivars at different sulfur concentrations and in the context of plant defense. Results indicate that the root systems are influenced differently by sulfur deficiency in the cultivars. Total root dry mass and length of root hairs differ not only among the cultivars but also vary in their reaction to sulfur limitation and pathogen attack. As a sensitive indicator of stress, several parameters of photosynthetic activity determined by PAM imaging showed a broad variability among the treatments. These results were supported by thermographic analysis. Levels of sulfur-containing metabolites also showed large variations. The data were interrelated to predict the specific behavior during sulfur limitation and/or pathogen attack. Advice for farming are discussed.

Spatial gene expression analysis in tomato hypocotyls suggests cysteine as key precursor of vascular sulfur accumulation implicated in Verticillium dahliae defense

Verticillium dahliae is a prominent generator of plant vascular wilting disease and sulfur (S)-enhanced defense (SED) mechanisms contribute to its in-planta elimination. The accumulation of S-containing defense compounds (SDCs) including elemental S (S(0) ) has been described based on the comparison of two near-isogenic tomato (Solanum lycopersicum) lines differing in fungal susceptibility. To better understand the effect of S nutrition on V. dahliae resistance both lines were supplied with low, optimal or supraoptimal sulfate-S. An absolute quantification demonstrated a most effective fungal elimination due to luxury plant S nutrition. High-pressure liquid chromatography (HPLC) showed a strong regulation of Cys levels and an S-responsive GSH pool rise in the bulk hypocotyl. High-frequency S peak accumulations were detected in vascular bundles of resistant tomato plants after fungal colonization by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Global transcriptomic analysis suggested that early steps of the primary S metabolism did not promote the SDCs synthesis in the whole hypocotyl as gene expression was downregulated after infection. Enhanced S fertilization mostly alleviated the repressive fungal effect but did not reverse it. Upregulation of glutathione (GSH)-associated genes in bulk hypocotyls but not in vascular bundles indicated a global antioxidative role of GSH. To finally assign the contribution of S metabolism-associated genes to high S(0) accumulations exclusively found in the resistant tomato line, a spatial gene expression approach was applied. Laser microdissection of infected vascular bundles revealed a switch toward transcription of genes connected with cysteine (Cys) synthesis. The upregulation of LeOASTLp1 suggests a role for Cys as key precursor for local S accumulations (possibly S(0) ) in the vascular bundles of the V. dahliae-resistant tomato line.

Hydrogen sulfide alleviates the aluminum-induced changes in Brassica napus as revealed by physiochemical and ultrastructural study of plant

In the present study, ameliorating role of hydrogen sulfide (H2S) in oilseed rape (Brassica napus L.) was studied with or without application of H2S donor sodium hydrosulfide (NaHS) (0.3 mM) in hydroponic conditions under three levels (0, 0.1 and 0.3 mM) of aluminum (Al). Results showed that addition of H2S significantly improved the plant growth, photosynthetic gas exchange, and nutrients concentration in the leaves and roots of B. napus plants under Al stress. Exogenously applied H2S significantly lowered the Al concentration in different plant parts, and reduced the production of malondialdehyde and reactive oxygen species by improving antioxidant enzyme activities in the leaves and roots under Al stress. Moreover, the present study indicated that exogenously applied H2S improved the cell structure and displayed clean mesophyll and root tip cells. The chloroplast with well-developed thylakoid membranes could be observed in the micrographs. Under the combined application of H2S and Al, a number of modifications could be observed in root tip cell, such as mitochondria, endoplasmic reticulum, and golgi bodies. Thus, it can be concluded that exogenous application of H2S under Al stress improved the plant growth, photosynthetic parameters, elements concentration, and biochemical and ultrastructural changes in leaves and roots of B. napus.

Roles of H2S in adaptation of alpine plants Lamiophlomis rotata to altitude gradients

Hydrogen sulfide (H2S) is an important gaseous transmitter in organisims. It widespreads in the organs and tissues of animals and participates in the biological process of cardiovascular relaxation, cell apoptosis and protection, inflammation and neuromodulation. H2S also can be synthesized in plants system and is involved in stress responses and the biological process of growth and development. This review describes the synthesis and biological function of H2S in plants. Based on our research for the adaptation of Lamiophlomis rotata to different altitude gradients, we firstly proposed H2S plays an important role in the adaptation of Lamiophlomis rotata to alpine environment.