Modulation of Enhanced Antioxidant Activity by Hydrogen Sulfide Antagonization of Ethylene in Tomato Fruit Ripening

Hydrogen sulfide enhances kiwifruit resistance to soft rot by regulating jasmonic acid signaling pathway

As the third active gas signal molecule in plants, hydrogen sulfide (H2S) plays important roles in physiological metabolisms and biological process of fruits and vegetables during postharvest storage. In the present study, the effects of H2S on enhancing resistance against soft rot caused by Botryosphaeria dothidea and the involvement of jasmonic acid (JA) signaling pathway in kiwifruit during the storage were investigated. The results showed that 20 μL L-1 H2S fumigation restrained the disease incidence of B. dothidea-inoculated kiwifruit during storage, and delayed the decrease of firmness and the increase of soluble solids (SSC) content. H2S treatment increased the transcription levels of genes related to JA biosynthesis (AcLOX3, AcAOS, AcAOC2, and AcOPR) and signaling pathway (AcCOI1, AcJAZ5, AcMYC2, and AcERF1), as well as the JA accumulation. Meanwhile, H2S promoted the expression of defense-related genes (AcPPO, AcSOD, AcGLU, AcCHI, AcAPX, and AcCAT). Correlation analysis revealed that JA content was positively correlated with the expression levels of JA biosynthesis and defense-related genes. Overall, the results indicated that H2S could promote the increase of endogenous JA content and expression of defense-related genes by regulating the transcription levels of JA pathway-related genes, which contributed to the inhibition on the soft rot occurrence of kiwifruit.

Unraveling the potential of hydrogen sulfide as a signaling molecule for plant development and environmental stress responses: A state-of-the-art review

Over the past decade, a plethora of research has illuminated the multifaceted roles of hydrogen sulfide (H2S) in plant physiology. This gaseous molecule, endowed with signaling properties, plays a pivotal role in mitigating metal-induced oxidative stress and strengthening the plant's ability to withstand harsh environmental conditions. It fulfils several functions in regulating plant development while ameliorating the adverse impacts of environmental stressors. The intricate connections among nitric oxide (NO), hydrogen peroxide (H2O2), and hydrogen sulfide in plant signaling, along with their involvement in direct chemical processes, are contributory in facilitating post-translational modifications (PTMs) of proteins that target cysteine residues. Therefore, the present review offers a comprehensive overview of sulfur metabolic pathways regulated by hydrogen sulfide, alongside the advancements in understanding its biological activities in plant growth and development. Specifically, it centres on the physiological roles of H2S in responding to environmental stressors to explore the crucial significance of different exogenously administered hydrogen sulfide donors in mitigating the toxicity associated with heavy metals (HMs). These donors are of utmost importance in facilitating the plant development, stabilization of physiological and biochemical processes, and augmentation of anti-oxidative metabolic pathways. Furthermore, the review delves into the interaction between different growth regulators and endogenous hydrogen sulfide and their contributions to mitigating metal-induced phytotoxicity.

Ascorbate peroxidase in fruits and modulation of its activity by reactive species

Ascorbate peroxidase (APX) is one of the enzymes of the ascorbate-glutathione cycle and is the key enzyme that breaks down H2O2 with the aid of ascorbate as an electron source. APX is present in all photosynthetic eukaryotes from algae to higher plants and, at the cellular level, it is localized in all subcellular compartments where H2O2 is generated, including the apoplast, cytosol, plastids, mitochondria, and peroxisomes, either in soluble form or attached to the organelle membranes. APX activity can be modulated by various post-translational modifications including tyrosine nitration, S-nitrosation, persulfidation, and S-sulfenylation. This allows the connection of H2O2 metabolism with other relevant signaling molecules such as NO and H2S, thus building a complex coordination system. In both climacteric and non-climacteric fruits, APX plays a key role during the ripening process and during post-harvest, since it participates in the regulation of both H2O2 and ascorbate levels affecting fruit quality. Currently, the exogenous application of molecules such as NO, H2S, H2O2, and, more recently, melatonin is seen as a new alternative to maintain and extend the shelf life and quality of fruits because they can modulate APX activity as well as other antioxidant systems. Therefore, these molecules are being considered as new biotechnological tools to improve crop quality in the horticultural industry.

Tobacco Transcription Factor NtWRKY70b Facilitates Leaf Senescence via Inducing ROS Accumulation and Impairing Hydrogen Sulfide Biosynthesis

Leaf senescence is the terminal stage of leaf development, and its initiation and progression are closely controlled by the integration of a myriad of endogenous signals and environmental stimuli. It has been documented that WRKY transcription factors (TFs) play essential roles in regulating leaf senescence, yet the molecular mechanism of WRKY-mediated leaf senescence still lacks detailed elucidation in crop plants. In this study, we cloned and identified a tobacco WRKY TF gene, designated NtWRKY70b, acting as a positive regulator of natural leaf senescence. The expression profile analysis showed that NtWRKY70b transcript levels were induced by aging and hydrogen peroxide (H2O2) and downregulated upon hydrogen sulfide (H2S) treatment. The physiological and biochemical assays revealed that overexpression of NtWRKY70b (OE) clearly promoted leaf senescence, triggering increased levels of reactive oxygen species (ROS) and decreased H2S content, while disruption of NtWRKY70b by chimeric repressor silencing technology (SRDX) significantly delayed the onset of leaf senescence, leading to a decreased accumulation of ROS and elevated concentration of H2S. The quantitative real-time PCR analysis showed that the expression levels of various senescence-associated genes and ROS biosynthesis-related genes (NtRbohD and NtRbohE) were upregulated in OE lines, while the expression of H2S biosynthesis-related genes (NtDCD and NtCYSC1) were inhibited in OE lines. Furthermore, the Yeast one-hybrid analysis (Y1H) and dual luciferase assays showed that NtWRKY70b could directly upregulate the expression of an ROS biosynthesis-related gene (NtRbohD) and a chlorophyll degradation-related gene (NtPPH) by binding to their promoter sequences. Accordingly, these results indicated that NtWYKY70b directly activated the transcript levels of NtRbohD and NtPPH and repressed the expression of NtDCD and NtCYCS1, thereby promoting ROS accumulation and impairing the endogenous H2S production, and subsequently accelerating leaf aging. These observations improve our knowledge of the regulatory mechanisms of WRKY TFs controlling leaf senescence and provide a novel method for ensuring high agricultural crop productivity via genetic manipulation of leaf senescence in crops.

Hydrogen sulfide regulates arsenic-induced cell death in yeast cells by modulating the antioxidative system

Arsenic (As) is a metal with potentially toxic effects on different organisms. Hydrogen sulfide (H2S) plays a vital role in mitigating heavy metal toxicity by reducing oxidative stress in plants and animals. However, the role of H2S in alleviating arsenic toxicity in yeast cells remains unclear. In this study, the role of NaHS (exogenous physiological H2S) in alleviating As-induced yeast cell death was investigated. Yeast cells in the logarithmic phase were pretreated with 0.05 mmol/L NaHS for 6 h, and then incubated in the YPD medium with or without 1 mmol/L As. After 12 h of treatment, relative survival rate, H2S content, oxidative stress biomarkers, and antioxidant machinery were measured. Our results showed that sodium arsenite-induced yeast cell death and pretreatment with 0.05 mmol/L NaHS significantly alleviated sodium arsenite-induced cell death. Under sodium arsenite conditions, the levels of intracellular reactive oxygen species (ROS) and malondialdehyde (MDA) increased, accompanied by the inhibition of the catalase (CAT) activity and the downregulation of CTT1 expression. However, the activities of the superoxide dismutase (SOD) and glutathion peroxidase (GPX) increased, and the expression of SOD1 and GPX2 was markedly upregulated in the group treated with sodium arsenite. When yeast cells were pretreated with NaHS, the intracellular ROS and MDA levels decreased significantly, and the activities of SOD, CAT, and GPX increased significantly. This was associated with a significant increase in relative survival rate and H2S content compared to the arsenic treatment alone. Our findings indicate that NaHS alleviates sodium arsenite-induced yeast cell death, mainly by enhancing the antioxidant defense system.

Hydrogen Peroxide Promotes Tomato Leaf Senescence by Regulating Antioxidant System and Hydrogen Sulfide Metabolism

Hydrogen peroxide (H2O2) is relatively stable among ROS (reactive oxygen species) and could act as a signal in plant cells. In the present work, detached tomato leaves were treated with exogenous H2O2 at 10 mmol/L for 8 h to study the mechanism of how H2O2 regulates leaf senescence. The data indicated that H2O2 treatment significantly accelerated the degradation of chlorophyll and led to the upregulation of the expression of leaf senescence-related genes (NYC1, PAO, PPH, SGR1, SAG12 and SAG15) during leaf senescence. H2O2 treatment also induced the accumulation of H2O2 and malondialdehyde (MDA), decreased POD and SOD enzyme activities and inhibited H2S production by reducing the expression of LCD1/2 and DCD1/2. A correlation analysis indicated that H2O2 was significantly and negatively correlated with chlorophyll, the expression of leaf senescence-related genes, and LCD1/2 and DCD1/2. The principal component analysis (PCA) results show that H2S showed the highest load value followed by O2•-, H2O2, DCD1, SAG15, etc. Therefore, these findings provide a basis for studying the role of H2O2 in regulating detached tomato leaf senescence and demonstrated that H2O2 plays a positive role in the senescence of detached leaves by repressing antioxidant enzymes and H2S production.

Uncovering the Role of Hormones in Enhancing Antioxidant Defense Systems in Stressed Tomato (Solanum lycopersicum) Plants

Tomato is one of the most important fruits worldwide. It is widely consumed due to its sensory and nutritional attributes. However, like many other industrial crops, it is affected by biotic and abiotic stress factors, reducing its metabolic and physiological processes. Tomato plants possess different mechanisms of stress responses in which hormones have a pivotal role. They are responsible for a complex signaling network, where the antioxidant system (enzymatic and non-enzymatic antioxidants) is crucial for avoiding the excessive damage caused by stress factors. In this sense, it seems that hormones such as ethylene, auxins, brassinosteroids, and salicylic, jasmonic, abscisic, and gibberellic acids, play important roles in increasing antioxidant system and reducing oxidative damage caused by different stressors. Although several studies have been conducted on the stress factors, hormones, and primary metabolites of tomato plants, the effect of endogenous and/or exogenous hormones on the secondary metabolism is still poorly studied, which is paramount for tomato growing management and secondary metabolites production. Thus, this review offers an updated overview of both endogenous biosynthesis and exogenous hormone application in the antioxidant system of tomato plants as a response to biotic and abiotic stress factors.

Persulfidation of transcription factor MYB10 inhibits anthocyanin synthesis in red-skinned pear

Hydrogen sulfide (H2S) is a gaseous signaling molecule that delays color change during fruit ripening. Whether H2S affects anthocyanin biosynthesis in red-skinned pears (Pyrus L.) remains unclear. Here, we found that H2S substantially inhibits anthocyanin accumulation in red-skinned pears and the expression of several genes encoding transcription factors is affected in response to H2S signaling. For example, PyMYB10 and PyMYB73 were down-regulated, whereas PyMYB114 and PyMYB6 were up-regulated. Bioinformatics analysis showed that PyMYB73 and PyMYB6, each containing an EAR motif, may negatively regulate anthocyanin accumulation. Transient expression analysis showed that PyMYB73 substantially promotes anthocyanin biosynthesis by co-transforming with PyMYB10/PyMYB114 + PybHLH3; however, PyMYB6 inhibited anthocyanin biosynthesis in strawberry (Fragaria vesca) receptacles and pear fruits, and PyMYB73 interacted with PyMYB10 and PyMYB6 but not PyMYB114 or PybHLH3. Further investigation showed that Cys194 and Cys218 of PyMYB10 were modified by persulfidation and that PyMYB10Cys218Ala substantially increased anthocyanin accumulation by a transient transformation system. Co-transformation of PyMYB10Cys218Ala + PyMYB73/PyMYB6 also promoted anthocyanin accumulation in pear fruits. Yeast two-hybrid assays showed that the mutation of PyMYB10 did not affect the interaction between PyMYB10 and PyMYB73, but it inhibited interaction with PyMYB6. Moreover, H2S weakened the interaction between PyMYB10 and PyMYB73 but enhanced the interaction with PyMYB6. Thus, we provided a model in which PyMYB10 undergoes persulfidation at Cys218, enhancing the interaction with PyMYB6 and reducing the interaction with PyMYB73. These subsequently results in lower expression of the anthocyanin biosynthesis-related genes Pyrus dihydroflavonol 4-reductase (PyDFR), Pyrus anthocyanidin synthase (PyANS), Pyrus UDP-glucose: flavonoid 3-glucosyl transferase (PyUFGT) and Pyrus glutathione S-transferase (PyGST), thereby inhibiting anthocyanin accumulation in red-skinned pears. Our findings provided a molecular mechanism for H2S-mediated anthocyanin biosynthesis in red-skinned pears.

E3 ligase BRG3 persulfidation delays tomato ripening by reducing ubiquitination of the repressor WRKY71

Hydrogen sulfide (H2S) is a gaseous signaling molecule reported to play multiple roles in fruit ripening. However, the molecular mechanisms underlying H2S-mediated delay in fruit ripening remain to be established. Here, the gene encoding a WRKY transcription factor, WRKY71, was identified as substantially upregulated in H2S-treated tomato (Solanum lycopersicum) via transcriptome profiling. The expression of WRKY71 was negatively associated with that of CYANOALANINE SYNTHASE1 (CAS1). Transient and stable genetic modification experiments disclosed that WRKY71 acts as a repressor of the tomato ripening process. CAS1 appears to play an opposite role, based on the finding that the ripening process was delayed in the cas1 mutant and accelerated in CAS1-OE tomatoes. Dual-luciferase reporter assay, yeast one-hybrid, electrophoretic mobility shift assay, and transient transformation experiments showed that WRKY71 bound to the CAS1 promoter and suppressed its activation. Moreover, the persulfidation of WRKY71 enhanced its binding ability to the CAS1 promoter. Data from luciferase complementation and Y2H assays confirmed that WRKY71 interacts with a BOI-related E3 ubiquitin-protein ligase 3 (BRG3) and is ubiquitinated in vitro. Further experiments showed that modification of BRG3 via persulfidation at Cys206 and Cys212 led to reduced ubiquitination activity. Our findings support a model whereby BRG3 undergoes persulfidation at Cys206 and Cys212, leading to reduced ubiquitination activity and decreased interactions with the WRKY71 transcript, with a subsequent increase in binding activity of the persulfidated WRKY71 to the CAS1 promoter, resulting in its transcriptional inhibition and thereby delayed ripening of tomatoes. Our collective findings provide insights into a mechanism of H2S-mediated regulation of tomato fruit ripening.

Novel insight into the role of sulfur dioxide in fruits and vegetables: Chemical interactions, biological activity, metabolism, applications, and safety

Sulfur dioxide (SO₂) are a category of chemical compounds widely used as additives in food industry. So far, the use of SO₂ in fruit and vegetable industry has been indispensable although its safety concerns have been controversial. This article comprehensively reviews the chemical interactions of SO₂ with the components of fruit and vegetable products, elaborates its mechanism of antimicrobial, anti-browning, and antioxidation, discusses its roles in regulation of sulfur metabolism, reactive oxygen species (ROS)/redox, resistance induction, and quality maintenance in fruits and vegetables, summarizes the application technology of SO₂ and its safety in human (absorption, metabolism, toxicity, regulation), and emphasizes the intrinsic metabolism of SO₂ and its consequences for the postharvest physiology and safety of fresh fruits and vegetables. In order to fully understand the benefits and risks of SO₂, more research is needed to evaluate the molecular mechanisms of SO₂ metabolism in the cells and tissues of fruits and vegetables, and to uncover the interaction mechanisms between SO₂ and the components of fruits and vegetables as well as the efficacy and safety of bound SO₂. This review has important guiding significance for adjusting an applicable definition of maximum residue limit of SO₂ in food.

A D-cysteine desulfhydrase, SlDCD2, participates in tomato fruit ripening by modulating ROS homoeostasis and ethylene biosynthesis

Hydrogen sulfide (H₂S) is involved in multiple processes during plant growth and development. D-cysteine desulfhydrase (DCD) can produce H₂S with D-cysteine as the substrate; however, the potential developmental roles of DCD have not been explored during the tomato lifecycle. In the present study, SlDCD2 showed increasing expression during fruit ripening. Compared with the control fruits, the silencing of SlDCD2 by pTRV2-SlDCD2 accelerated fruit ripening. A SlDCD2 gene-edited mutant was constructed by CRISPR/Cas9 transformation, and the mutant exhibited accelerated fruit ripening, decreased H₂S release, higher total cysteine and ethylene contents, enhanced chlorophyll degradation and increased carotenoid accumulation. Additionally, the expression of multiple ripening-related genes, including NYC1, PAO, SGR1, PDS, PSY1, ACO1, ACS2, E4, CEL2, and EXP was enhanced during the dcd2 mutant tomato fruit ripening. Compared with the wild-type fruits, SlDCD2 mutation induced H₂O₂ and malondialdehyde (MDA) accumulation in fruits, which led to an imbalance in reactive oxygen species (ROS) metabolism. A correlation analysis indicated that H₂O₂ content was strongly positively correlated with carotenoids content, ethylene content and ripening-related gene expression and negatively correlated with the chlorophyll content. Additionally, the dcd2 mutant showed earlier leaf senescence, which may be due to disturbed ROS homeostasis. In short, our findings show that SlDCD2 is involved in H₂S generation and that the reduction in endogenous H₂S production in the dcd2 mutant causes accelerated fruit ripening and premature leaf senescence. Additionally, decreased H₂S in the dcd2 mutant causes excessive H₂O₂ accumulation and increased ethylene release, suggesting a role of H₂S and SlDCD2 in modulating ROS homeostasis and ethylene biosynthesis.

Crosstalk between melatonin and reactive oxygen species in fruits and vegetables post-harvest preservation: An update

Fruits and vegetables contain numerous nutrients, such as vitamins, minerals, phenolic compounds, and dietary fibers. They reduce the incidence of cardiovascular diseases and the risk of certain chronic diseases, and improve the antioxidant and anti-inflammatory capacity. Moreover, melatonin was found in various fruits and vegetables species. Melatonin acts as a multifunctional compound to participate in various physiological processes. In recent years, many advances have been found that melatonin is also appraised as a key modulator on the fruits and vegetables post-harvest preservation. Fruits and vegetables post-harvest usually elicit reactive oxygen species (ROS) generation and accumulation. Excess ROS stimulate cell damage, protein structure destruction, and tissue aging, and thereby reducing their quality. Numerous studies find that exogenous application of melatonin modulates ROS homeostasis by regulating the antioxidant enzymes and non-enzymatic antioxidants systems. Further evidences reveal that melatonin often interacts with hormones and other signaling molecules, such as ROS, nitric oxide (NO), hydrogen sulfide (H₂S), and etc. Among these 'new' molecules, crosstalks of melatonin and ROS, especially the H₂O₂ produced by RBOHs, are provided in fruits and vegetables post-harvest preservation in this review. It will provide reference for complicated integration of both melatonin and ROS as signal molecules in future study.

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

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

Hydrogen Sulfide, Ethylene, and Nitric Oxide Regulate Redox Homeostasis and Protect Photosynthetic Metabolism under High Temperature Stress in Rice Plants

Rising temperatures worldwide due to global climate change are a major scientific issue at present. The present study reports the effects of gaseous signaling molecules, ethylene (200 µL L⁻¹; 2-chloroethylphosphonic acid; ethephon, Eth), nitric oxide (NO; 100 µM sodium nitroprusside; SNP), and hydrogen sulfide (H₂S; 200 µM sodium hydrosulfide, NaHS) in high temperature stress (HS) tolerance, and whether or not H₂S contributes to ethylene or NO-induced thermo-tolerance and photosynthetic protection in rice (Oryza sativa L.) cultivars, i.e., Taipei-309, and Rasi. Plants exposed to an HS of 40 °C for six h per day for 15 days caused a reduction in rice biomass, associated with decreased photosynthesis and leaf water status. High temperature stress increased oxidative stress by increasing the content of hydrogen peroxide (H₂O₂) and thiobarbituric acid reactive substance (TBARS) in rice leaves. These signaling molecules increased biomass, leaf water status, osmolytes, antioxidants, and photosynthesis of plants under non-stress and high temperature stress. However, the effect was more conspicuous with ethylene than NO and H₂S. The application of H₂S scavenger hypotaurine (HT) reversed the effect of ethylene or NO on photosynthesis under HS. This supports the findings that the ameliorating effects of Eth or SNP involved H₂S. Thus, the presence of H₂S with ethylene or NO can enhance thermo-tolerance while also protecting plant photosynthesis.

The secret of H2 S to keep plants young and fresh and its products

Recently, accumulating evidence has shown that hydrogen sulphide (H₂ S), a newly determined gasotransmitter, plays important roles in senescence, which is an essential biological process for plant fitness and an important agricultural trait that is critical for the yield and quality of farm produce. Here, in this review, we summarize the roles of H₂ S in senescence, both before and after the harvesting of agricultural products, and the underlying mechanism is also discussed. During the plant growth process, the function of H₂ S in the leaf senescence process has been studied extensively, and H₂ S plays roles during the whole process, including the initiation, reorganization and terminal stages. While during the postharvest stage, H₂ S can prevents farm products from deterioration resulting from over-ripening, pathogen attack and incorrect storage. The underlying H₂ S-related mechanisms during different stages of the senescence process are summarized and compared. The most prominent interaction occurs between H₂ S and reactive oxygen species, and the molecular mechanism is explored. Additionally, the conserved action mode of H₂ S in different life processes and different species is also discussed. In the future, multi-omics analyses over time will be needed to investigate the detailed mechanisms of H₂ S, and a safety attribute analysis of H₂ S is also required before it can be used in agricultural production.

Harnessing the power of hydrogen sulphide (H2 S) for improving fruit quality traits

Hydrogen sulphide (H₂ S) is a gaseous molecule and originates endogenously in plants. It is considered a potential signalling agent in various physiological processes of plants. Numerous reports have examined the role of H₂ S in fruit ripening and in enhancing fruit quality traits. H₂ S coordinates the fruit antioxidant system, fruit ripening phytohormones, such as ethylene and abscisic acid, together with other ripening-related signalling molecules, including nitric oxide and hydrogen peroxide. Although many studies have increased understanding of various aspects of this complex network, there is a gap in understanding crosstalk of H₂ S with key players of fruit ripening, postharvest senescence and fruit metabolism. This review focused on deciphering fruit H₂ S metabolism, signalling and its interaction with other ripening-related signalling molecules during fruit ripening and postharvest storage. Moreover, we also discuss how H₂ S can be used as a tool for improving fruit quality and productivity and reducing postharvest loss of perishable fruits.

The Fruit Proteome Response to the Ripening Stages in Three Tomato Genotypes

The tomato is a horticultural crop that appears in various colors as it ripens. Differences in the proteome expression abundance of a tomato depend on its genotype and ripening stage. Thus, this study aimed to confirm the differences in changes in the proteome according to four ripening stages (green, breaker, turning, and mature) of three tomato genotypes, i.e., yellow, black, and red tomatoes, using a gel-based proteomic technique. The number of protein spots shown as two-dimensional electrophoresis (2-DE) gels differed according to tomato genotype and ripening stage. A total of 286 variant proteins were determined using matrix-assisted laser desorption-time of flight (MALDI-TOF) mass spectrometry (MS) analysis, confirming 233 identified protein functions. In three tomato genotypes in each ripening stage, grouping according to the Munich Information Center for Protein Sequences (MIPS) functional categories confirmed the variant proteins involved in the following: energy processes (21%); metabolism (20%); protein fate (15%); protein synthesis (10%); a protein with a binding function or cofactor requirement (8%); cell rescue, defense, and virulence (8%); cellular transport, transport facilitation, and transport routes (6%); the biogenesis of cellular components (5%); cell cycle and DNA processing (2%); others (5%). Among the identified protein spots in the function category, two proteins related to metabolism, four related to energy, four related to protein synthesis, and two related to interaction with the cellular environment showed significantly different changes according to the fruit color by the ripening stage. This study reveals the physiological changes in different types of tomatoes according to their ripening stage and provides information on the proteome for further improvement.

Roles of a Cysteine Desulfhydrase LCD1 in Regulating Leaf Senescence in Tomato

Hydrogen sulfide (H2S), a novel gasotransmitter in both mammals and plants, plays important roles in plant development and stress responses. Leaf senescence represents the final stage of leaf development. The role of H2S-producing enzyme L-cysteine desulfhydrase in regulating tomato leaf senescence is still unknown. In the present study, the effect of an L-cysteine desulfhydrase LCD1 on leaf senescence in tomato was explored by physiological analysis. LCD1 mutation caused earlier leaf senescence, whereas LCD1 overexpression significantly delayed leaf senescence compared with the wild type in 10-week tomato seedlings. Moreover, LCD1 overexpression was found to delay dark-induced senescence in detached tomato leaves, and the lcd1 mutant showed accelerated senescence. An increasing trend of H2S production was observed in leaves during storage in darkness, while LCD1 deletion reduced H2S production and LCD1 overexpression produced more H2S compared with the wild-type control. Further investigations showed that LCD1 overexpression delayed dark-triggered chlorophyll degradation and reactive oxygen species (ROS) accumulation in detached tomato leaves, and the increase in the expression of chlorophyll degradation genes NYC1, PAO, PPH, SGR1, and senescence-associated genes (SAGs) during senescence was attenuated by LCD1 overexpression, whereas lcd1 mutants showed enhanced senescence-related parameters. Moreover, a correlation analysis indicated that chlorophyll content was negatively correlated with H2O2 and malondialdehyde (MDA) content, and also negatively correlated with the expression of chlorophyll degradation-related genes and SAGs. Therefore, these findings increase our understanding of the physiological functions of the H2S-generating enzyme LCD1 in regulating leaf senescence in tomato.

Transcriptomics Reveals the ERF2-bHLH2-CML5 Module Responses to H2S and ROS in Postharvest Calcium Deficiency Apples

Calcium deficiency usually causes accelerated quality deterioration in postharvest fruit, whereas the underlining mechanism is still unclear. Here, we report that calcium deficiency induced the development of bitter pit on the surface of apple peels compared with the healthy appearance in control apples during postharvest storage. Physiological analysis indicates that calcium-deficient peels contained higher levels of superoxide anion (O₂^•−), malondialdehyde (MDA), total phenol, flavonoid contents and polyphenol oxidase (PPO) activity, and reduced calcium, H₂S production, anthocyanin, soluble protein content, and peroxidase (POD) activity compared with those in calcium-sufficient peels. The principal component analysis (PCA) results show that calcium content, ROS, and H₂S production were the main factors between calcium-deficient and calcium-sufficient apple peels. Transcriptome data indicated that four calmodulin-like proteins (CMLs), seven AP2/ERFs, and three bHLHs transcripts were significantly differentially expressed in calcium-deficient apple peels. RT-qPCR and correlation analyses further revealed that CML5 expression was significantly positively correlated with the expression of ERF2/17, bHLH2, and H₂S production related genes. In addition, transcriptional co-activation of CML5 by ERF2 and bHLH2 was demonstrated by apple transient expression assays and dual-luciferase reporter system experiments. Therefore, these findings provide a basis for studying the molecular mechanism of postharvest quality decline in calcium-deficient apples and the potential interaction between Ca²⁺ and endogenous H₂S.

Rosmarinic Acid Delays Tomato Fruit Ripening by Regulating Ripening-Associated Traits

Fruits are excellent sources of essential vitamins and health-boosting minerals. Recently, regulation of fruit ripening by both internal and external cues for the improvement of fruit quality and shelf life has received considerable attention. Rosmarinic acid (RA) is a kind of natural plant-derived polyphenol, widely used in the drug therapy and food industry due to its distinct physiological functions. However, the role of RA in plant growth and development, especially at the postharvest period of fruits, remains largely unknown. Here, we demonstrated that postharvest RA treatment delayed the ripening in tomato fruits. Exogenous application of RA decreased ripening-associated ethylene production and inhibited the fruit color change from green to red based on the decline in lycopene accumulation. We also found that the degradation of sucrose and malic acid during ripening was significantly suppressed in RA-treated tomato fruits. The results of metabolite profiling showed that RA application promoted the accumulation of multiple amino acids in tomato fruits, such as aspartic acid, serine, tyrosine, and proline. Meanwhile, RA application also strengthened the antioxidant system by increasing both the activity of antioxidant enzymes and the contents of reduced forms of antioxidants. These findings not only unveiled a novel function of RA in fruit ripening, but also indicated an attractive strategy to manage and improve shelf life, flavor, and sensory evolution of tomato fruits.

Gibberellic acid maintains postharvest quality of Agaricus bisporus mushroom by enhancing antioxidative system and hydrogen sulfide synthesis

The application of gibberellic acid (GA₃ ) treatment to the postharvest quality maintenance of white button mushroom (Agaricus bisporus) was investigated. The optimum concentration of exogenous GA₃ was 100 mg/L. At this concentration, the color change was inhibited, the firmness was maintained, and the weight loss and respiratory rates were reduced. The GA₃ group had significantly lower malonaldehyde (MDA) content and membrane permeability. Reactive oxygen species accumulation was reduced due to the regulation of polyphenol oxidase (PPO), peroxidase (POD), and superoxide dismutase (SOD) enzyme activities. Moreover, the production of endogenous gaseous signaling molecule hydrogen sulfide (H₂ S) was triggered by GA₃ treatment, which enhanced cystathionine γ-lyase (AbCSE) and cystathionine β-synthase (AbCBS) activities alongside the corresponding gene expressions. The preservation of button mushroom postharvest storage quality by GA₃ was most likely due to the regulation of reactive oxygen species metabolism and hydrogen sulfide biosynthesis. PRACTICAL APPLICATIONS: Mushroom is rich in nutrients and functional substances. However, due to the lack of cuticle, high respiration rate, and moisture content, mushroom's postharvest quality deteriorates rapidly. A safe and effective reagent that prevents the senescence and quality deterioration of harvested mushroom is urgently needed. The effects of plant hormone GA₃ on the postharvest quality of edible fungi remain unclear. The present study provided convincing evidence that 100 mg L^-1 of GA₃ effectively maintained postharvest button mushroom quality by regulating reactive oxygen species metabolism and hydrogen sulfide biosynthesis.

Interplay between hydrogen sulfide and other signaling molecules in the regulation of guard cell signaling and abiotic/biotic stress response

Stomatal aperture controls the balance between transpirational water loss and photosynthetic carbon dioxide (CO2) uptake. Stomata are surrounded by pairs of guard cells that sense and transduce environmental or stress signals to induce diverse endogenous responses for adaptation to environmental changes. In a recent decade, hydrogen sulfide (H2S) has been recognized as a signaling molecule that regulates stomatal movement. In this review, we summarize recent progress in research on the regulatory role of H2S in stomatal movement, including the dynamic regulation of phytohormones, ion homeostasis, and cell structural components. We focus especially on the cross talk among H2S, nitric oxide (NO), and hydrogen peroxide (H2O2) in guard cells, as well as on H2S-mediated post-translational protein modification (cysteine thiol persulfidation). Finally, we summarize the mechanisms by which H2S interacts with other signaling molecules in plants under abiotic or biotic stress. Based on evidence and clues from existing research, we propose some issues that need to be addressed in the future.

Multifaceted roles of nitric oxide in tomato fruit ripening: NO-induced metabolic rewiring and consequences for fruit quality traits

Nitric oxide (NO) has been implicated as part of the ripening regulatory network in fleshy fruits. However, very little is known about the simultaneous action of NO on the network of regulatory events and metabolic reactions behind ripening-related changes in fruit color, taste, aroma and nutritional value. Here, we performed an in-depth characterization of the concomitant changes in tomato (Solanum lycopersicum) fruit transcriptome and metabolome associated with the delayed-ripening phenotype caused by NO supplementation at the pre-climacteric stage. Approximately one-third of the fruit transcriptome was altered in response to NO, including a multilevel down-regulation of ripening regulatory genes, which in turn restricted the production and tissue sensitivity to ethylene. NO also repressed hydrogen peroxide-scavenging enzymes, intensifying nitro-oxidative stress and S-nitrosation and nitration events throughout ripening. Carotenoid, tocopherol, flavonoid and ascorbate biosynthesis were differentially affected by NO, resulting in overaccumulation of ascorbate (25%) and flavonoids (60%), and impaired lycopene production. In contrast, the biosynthesis of compounds related to tomato taste (sugars, organic acids, amino acids) and aroma (volatiles) was slightly affected by NO. Our findings indicate that NO triggers extensive transcriptional and metabolic rewiring at the early ripening stage, modifying tomato antioxidant composition with minimal impact on fruit taste and aroma.

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

ABSTRACT

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

GRAPHIC ABSTRACT

SUPPLEMENTARY INFORMATION

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

A nuclear-localized cysteine desulfhydrase plays a role in fruit ripening in tomato

Hydrogen sulfide (H₂S) is a gaseous signaling molecule that plays multiple roles in plant development. However, whether endogenous H₂S plays a role in fruit ripening in tomato is still unknown. In this study, we show that the H₂S-producing enzyme L-cysteine desulfhydrase SlLCD1 localizes to the nucleus. By constructing mutated forms of SlLCD1, we show that the amino acid residue K24 of SlLCD1 is the key amino acid that determines nuclear localization. Silencing of SlLCD1 by TRV-SlLCD1 accelerated fruit ripening and reduced H₂S production compared with the control. A SlLCD1 gene-edited mutant obtained through CRISPR/Cas9 modification displayed a slightly dwarfed phenotype and accelerated fruit ripening. This mutant also showed increased cysteine content and produced less H₂S, suggesting a role of SlLCD1 in H₂S generation. Chlorophyll degradation and carotenoid accumulation were enhanced in the SlLCD1 mutant. Other ripening-related genes that play roles in chlorophyll degradation, carotenoid biosynthesis, cell wall degradation, ethylene biosynthesis, and the ethylene signaling pathway were enhanced at the transcriptional level in the lcd1 mutant. Total RNA was sequenced from unripe tomato fruit treated with exogenous H₂S, and transcriptome analysis showed that ripening-related gene expression was suppressed. Based on the results for a SlLCD1 gene-edited mutant and exogenous H₂S application, we propose that the nuclear-localized cysteine desulfhydrase SlLCD1 is required for endogenous H₂S generation and participates in the regulation of tomato fruit ripening.

H2S pretreatment mitigates the alkaline salt stress on Malus hupehensis roots by regulating Na+/K+ homeostasis and oxidative stress

Hydrogen sulfide (H₂S) plays an important role in the plant salt stress response. The main component of salt stress is neutral salt (NaCl); NaHCO₃ and Na₂CO₃ play a key role in soil alkaline due to the influence of pH. Malus hupehensis Rehd. var. pingyiensis Jiang (Pingyi Tiancha, PYTC) is a salt-sensitive apple rootstock. Seedlings of PYTC pretreated with NaHS (an H₂S donor) were exposed to an alkaline salt solution, and then the plant growth, root architecture, oxidative damage, Na⁺/K⁺ homeostasis and gene expression of MhSOS1 and MhSKOR were investigated. The results showed that NaHS pretreatment increased the endogenous H₂S content in seedlings, significantly alleviated the alkaline salt stress-induced growth inhibition and oxidative damage by inducing antioxidant enzymes activities, and sustained the root activity and root architecture of PYTC in the alkaline salt solution. NaHS pretreatment significantly decreased the root Na⁺ content and increased K⁺ content to maintain the homeostasis of Na⁺/K⁺, and effect the expression of MhSOS1 and MhSKOR at the transcription level in the presence of the alkaline salt. Our study reveals that application of H₂S could mitigate the toxic effect of alkaline salt stress on Malus hupehensis seedlings, thus providing a foundation for improved plant tolerance to alkaline salt stress.

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

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

Crosstalk between Hydrogen Sulfide and Other Signal Molecules Regulates Plant Growth and Development

Hydrogen sulfide (H₂S), once recognized only as a poisonous gas, is now considered the third endogenous gaseous transmitter, along with nitric oxide (NO) and carbon monoxide (CO). Multiple lines of emerging evidence suggest that H₂S plays positive roles in plant growth and development when at appropriate concentrations, including seed germination, root development, photosynthesis, stomatal movement, and organ abscission under both normal and stress conditions. H₂S influences these processes by altering gene expression and enzyme activities, as well as regulating the contents of some secondary metabolites. In its regulatory roles, H₂S always interacts with either plant hormones, other gasotransmitters, or ionic signals, such as abscisic acid (ABA), ethylene, auxin, CO, NO, and Ca²⁺. Remarkably, H₂S also contributes to the post-translational modification of proteins to affect protein activities, structures, and sub-cellular localization. Here, we review the functions of H₂S at different stages of plant development, focusing on the S-sulfhydration of proteins mediated by H₂S and the crosstalk between H₂S and other signaling molecules.

H2S signaling in plants and applications in agriculture

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Hydrogen sulfide (H₂S) plays a signaling role in higher plants.

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It mediates persulfidation, a post-translational modification.

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It regulates physiological functions ranging from seed germination to fruit ripening.

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The beneficial effects of exogenous H₂S are mainly caused by the stimulation of antioxidant systems.

The signaling properties of the gasotransmitter molecule hydrogen sulfide (H₂S), which is endogenously generated in plant cells, are mainly observed during persulfidation, a protein post-translational modification (PTM) that affects redox-sensitive cysteine residues. There is growing experimental evidence that H₂S in higher plants may function as a mechanism of response to environmental stress conditions. In addition, exogenous applications of H₂S to plants appear to provide additional protection against stresses, such as salinity, drought, extreme temperatures and heavy metals, mainly through the induction of antioxidant systems, in order to palliate oxidative cellular damage. H₂S also appears to be involved in regulating physiological functions, such as seed germination, stomatal movement and fruit ripening, as well as molecules that maintain post-harvest quality and rhizobium–legume symbiosis. These properties of H₂S open up new challenges in plant research to better understand its functions as well as new opportunities for biotechnological treatments in agriculture in a changing environment.

Hydrogen sulfide inhibits ethylene-induced petiole abscission in tomato (Solanum lycopersicum L.)

Abscission is a dynamic physiological process that is ubiquitous in plants and can also be an essential agronomic trait in crops, thus attracting attention from plant growers and breeders. In general, the process of plant organ abscission can be divided into four steps, among which the step to obtain the competence to respond to abscission signals (step 2) is the most complex; however, the molecular mechanism underlying this process remains unclear. In this study, we found that hydrogen sulfide (H2S) inhibited the abscission of the tomato petiole in a dose-dependent manner, and the abscission of the petiole was accelerated when an H2S scavenger was applied. Further enzymatic activity and gene expression analyses showed that H2S suppressed the activity of enzymes capable of modifying the cell wall by inhibiting the usual upregulation of the transcription of the corresponding genes during the abscission process but not by affecting the activities of these enzymes by direct posttranslational modification. H2S treatment upregulated the expression levels of SlIAA3 and SlIAA4 but downregulated the transcription of ILR-L3 and ILR-L4 in the earlier stages of the abscission process, indicating that H2S probably functioned in the second step of the abscission process by preventing the abscission zone cells from obtaining the competence to respond to abscission signals by modulating the content of the bioactive-free auxin in these cells. Moreover, similar H2S inhibitory effects were also demonstrated in the process of floral organ abscission and anther dehiscence in other plant species, suggesting a ubiquitous role for H2S in cell separation processes.

Hydrogen Sulfide Maintained the Good Appearance and Nutrition in Post-harvest Tomato Fruits by Antagonizing the Effect of Ethylene

Hydrogen sulfide (H₂S) could act as a versatile signaling molecule in delaying fruit ripening and senescence. Ethylene (C₂H₄) also plays a key role in climacteric fruit ripening, but little attention has been given to its interaction with H₂S in modulating fruit ripening and senescence. To study the role of H₂S treatment on the fruit quality and nutrient metabolism, tomato fruits at white mature stage were treated with ethylene and ethylene plus H₂S. By comparing to C₂H₄ treatment, we found that additional H₂S significantly delayed the color change of tomato fruit, and maintained higher chlorophyll and lower flavonoids during storage. Moreover, H₂S could inhibit the activity of protease, maintained higher levels of nutritional-related metabolites, such as anthocyanin, starch, soluble protein, ascorbic acid by comparing to C₂H₄ treatment. Gene expression analysis showed that additional H₂S attenuated the expression of beta-amylase encoding gene BAM3, UDP-glycosyltransferase encoding genes, ethylene-responsive transcription factor ERF003 and DOF22. Furthermore, principal component analysis suggested that starch, titratable acids, and ascorbic acid were important factors for affecting the tomato storage quality, and the correlation analysis further showed that H₂S affected pigments metabolism and the transformation of macromolecular to small molecular metabolites. These results showed that additional H₂S could maintain the better appearance and nutritional quality than C₂H₄ treatment alone, and prolong the storage period of post-harvest tomato fruits.

Impact of Silicon Nanoparticles on the Antioxidant Compounds of Tomato Fruits Stressed by Arsenic

Tomato fruit is rich in antioxidant compounds such as lycopene and β-carotene. The beneficial effects of the bioactive compounds of tomato fruit have been documented as anticancer activities. The objective of this research was to determine whether arsenic (As) causes changes in the content of antioxidant compounds in tomato fruits and whether Silicon nanoparticles (SiO₂ NPs) positively influence them. The effects on fruit quality and non-enzymatic antioxidant compounds were determined. The results showed that As decreased the oxide-reduction potential (ORP), while lycopene and β-carotene were increased by exposure to As at a low dose (0.2 mg L^-1), and proteins and vitamin C decreased due to high doses of As in the interaction with SiO₂ NPs. A dose of 250 mg L^-1 of SiO₂ NPs increased glutathione and hydrogen peroxide (H₂O₂), and phenols decreased with low doses of As and when they interacted with the NPs. As for the flavonoids, they increased with exposure to As and SiO₂ NPs. The total antioxidant capacity, determined by the ABTS (2,2´-azino-bis[3-ethylbenzthiazolin-6-sulfonic acid]) test, showed an increase with the highest dose of As in the interaction with SiO₂ NPs. The application of As at low doses induced a greater accumulation of bioactive compounds in tomato fruit; however, these compounds decreased in high doses as well as via interaction with SiO₂ NPs, indicating that there was an oxidative burst.

Signaling by hydrogen sulfide and cyanide through post-translational modification

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