Characterization of Dialkyldithiophosphates as Slow Hydrogen Sulfide Releasing Chemicals and Their Effect on the Growth of Maize

The role of exogenous hydrogen sulfide in mitigating cadmium toxicity in plants: A comprehensive meta-analysis

Reducing the accumulation of cadmium (Cd) and mitigating its toxicity are pivotal strategies for addressing Cd pollution's threats to agriculture and human health. Hydrogen sulfide (H2S) serves as a signaling molecule, playing a crucial role in plant stress defense mechanisms. Nevertheless, a comprehensive assessment of the impact of exogenous H2S on plant growth, antioxidant properties, and gene expression under Cd stress remains lacking. In this meta-analysis, we synthesized 575 observations from 27 articles, revealing that exogenous H2S significantly alleviates Cd-induced growth inhibition in plants. Specifically, it enhances root length (by 8.71%), plant height (by 15.67%), fresh weight (by 15.15%), dry weight (by 22.54%), and chlorophyll content (by 27.99%) under Cd stress conditions. H2S boosts antioxidant enzyme activity, particularly catalase (CAT), by 39.51%, thereby reducing Cd-induced reactive oxygen species (ROS) accumulation. Moreover, it impedes Cd translocation from roots to shoots, resulting in a substantial 40.19% reduction in stem Cd content. Additionally, H2S influences gene expression in pathways associated with antioxidant enzymes, metal transport, heavy metal tolerance, H2S biosynthesis, and energy metabolism. However, the efficacy of exogenous H2S in alleviating Cd toxicity varies depending on factors such as plant species, concentration of the H2S donor sodium hydrosulfide (NaHS), application method, and cultivation techniques. Notably, NaHS concentrations exceeding 200 μM may adversely affect plants. Overall, our study underscores the role of exogenous H2S in mitigating Cd toxicity and elucidates its mechanism, providing insights for utilizing H2S to combat Cd pollution in agriculture.

Hydrogen sulfide signaling in plants

SIGNIFICANCE

Hydrogen sulfide (H2S) is a multitasking potent regulator that facilitates plant growth, development, and responses to environmental stimuli.

RECENT ADVANCES

The important beneficial effects of H2S in various aspects of plant physiology aroused the interest of this chemical for agriculture. Protein cysteine persulfidation has been recognized as the main redox regulatory mechanism of H2S signaling. An increasing number of studies, including large-scale proteomic analyses and function characterizations, have revealed that H2S-mediated persulfidations directly regulate protein functions, altering downstream signaling in plants. To date, the importance of H2S-mediated persufidation in several abscisic acid signaling-controlling key proteins has been assessed as well as their role in stomatal movements, largely contributing to the understanding of the plant H2S-regulatory mechanism.

CRITICAL ISSUES

The molecular mechanisms of the H2S sensing and transduction in plants remain elusive. The correlation between H2S-mediated persulfidation with other oxidative posttranslational modifications of cysteines are still to be explored.

FUTURE DIRECTIONS

Implementation of advanced detection approaches for the spatiotemporal monitoring of H2S levels in cells and the current proteomic profiling strategies for the identification and quantification of the cysteine site-specific persulfidation will provide insight into the H2S signaling in plants.

Recent advances and mechanistic interactions of hydrogen sulfide with plant growth regulators in relation to abiotic stress tolerance in plants

Adverse environmental constraints such as drought, heat, cold, salinity, and heavy metal toxicity are the primary concerns of the agricultural industry across the globe, as these stresses negatively affect yield and quality of crop production and therefore can be a major threat to world food security. Recently, it has been demonstrated that hydrogen sulfide (H₂S), which is well-known as a gasotransmitter in animals, also plays a potent role in various growth and developmental processes in plants. H₂S, as a potent signaling molecule, is involved in several plant processes such as in the regulation of stomatal pore movements, seed germination, photosynthesis and plant adaptation to environmental stress through gene regulation, post-translation modification of proteins and redox homeostasis. Moreover, a number of experimental studies have revealed that H₂S could improve the adaptation capabilities of plants against diverse environmental constraints by mitigating the toxic and damaging effects triggered by stressful environments. An attempt has been made to uncover recent development in the biosynthetic and metabolic pathways of H₂S and various physiological functions modulated in plants, H₂S donors, their functional mechanism, and application in plants. Specifically, our focus has been on how H₂S is involved in combating the destructive effects of abiotic stresses and its role in persulfidation. Furthermore, we have comprehensively elucidated the crosstalk of H₂S with plant growth regulators.

Poly(dithiophosphate)s, a New Class of Phosphorus- and Sulfur-Containing Functional Polymers by a Catalyst-Free Facile Reaction between Diols and Phosphorus Pentasulfide

Novel poly(dithiophosphate)s (PDTPs) were successfully synthesized under mild conditions without any additive in the presence of THF or toluene diluents at 60 °C by a direct, catalyst-free reaction between the abundant phosphorus pentasulfide (P₄S₁₀) and glycols such as ethylene glycol (EG), 1,6-hexanediol (HD) and poly(ethylene glycol) (PEG). GPC, FTIR, ¹H and ³¹P NMR analyses proved the formation of macromolecules with dithiophosphate coupling groups having P=S and P-SH pendant functionalities. Surprisingly, the ring-opening of THF by the P-SH group and its pendant incorporation as a branching point occur during polymerization. This process is absent with toluene, providing conditions to obtain linear chains. ³¹P NMR measurements indicate long-time partial hydrolysis and esterification, resulting in the formation of a thiophosphoric acid moiety and branching points. Copolymerization, i.e., using mixtures of EG or HD with PEG, results in polymers with broadly varying viscoelastic properties. TGA shows the lower thermal stability of PDTPs than that of PEG due to the relatively low thermal stability of the P-O-C moieties. The low T_gs of these polymers, from -4 to -50 °C, and a lack of PEG crystallites were found by DSC. This polymerization process and the resulting novel PDTPs enable various new routes for polymer synthesis and application possibilities.

Biological Functions of Hydrogen Sulfide in Plants

Hydrogen sulfide (H₂S), which is a gasotransmitter, can be biosynthesized and participates in various physiological and biochemical processes in plants. H₂S also positively affects plants' adaptation to abiotic stresses. Here, we summarize the specific ways in which H₂S is endogenously synthesized and metabolized in plants, along with the agents and methods used for H₂S research, and outline the progress of research on the regulation of H₂S on plant metabolism and morphogenesis, abiotic stress tolerance, and the series of different post-translational modifications (PTMs) in which H₂S is involved, to provide a reference for future research on the mechanism of H₂S action.

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.

The Interplay between Hydrogen Sulfide and Phytohormone Signaling Pathways under Challenging Environments

Hydrogen sulfide (H₂S) serves as an important gaseous signaling molecule that is involved in intra- and intercellular signal transduction in plant–environment interactions. In plants, H₂S is formed in sulfate/cysteine reduction pathways. The activation of endogenous H₂S and its exogenous application has been found to be highly effective in ameliorating a wide variety of stress conditions in plants. The H₂S interferes with the cellular redox regulatory network and prevents the degradation of proteins from oxidative stress via post-translational modifications (PTMs). H₂S-mediated persulfidation allows the rapid response of proteins in signaling networks to environmental stimuli. In addition, regulatory crosstalk of H₂S with other gaseous signals and plant growth regulators enable the activation of multiple signaling cascades that drive cellular adaptation. In this review, we summarize and discuss the current understanding of the molecular mechanisms of H₂S-induced cellular adjustments and the interactions between H₂S and various signaling pathways in plants, emphasizing the recent progress in our understanding of the effects of H₂S on the PTMs of proteins. We also discuss future directions that would advance our understanding of H₂S interactions to ultimately mitigate the impacts of environmental stresses in the plants.

Synthesis, Stability, and Kinetics of Hydrogen Sulfide Release of Dithiophosphates

The development of chemicals to slowly release hydrogen sulfide would aid the survival of plants under environmental stressors as well as increase harvest yields. We report a series of dialkyldithiophosphates and disulfidedithiophosphates that slowly degrade to release hydrogen sulfide in the presence of water. Kinetics of the degradation of these chemicals were obtained at 85 °C and room temperature, and it was shown that the identity of the alkyl or sulfide group had a large impact on the rate of hydrolysis, and the rate constant varied by more than 10⁴×. For example, using tert-butanol as the nucleophile yielded a dithiophosphate (8) that hydrolyzed 13,750× faster than the dithiophosphate synthesized from n-butanol (1), indicating that the rate of hydrolysis is structure-dependent. The rates of hydrolysis at 85 °C varied from a low value of 6.9 × 10^-4 h^-1 to a high value of 14.1 h^-1. Hydrogen sulfide release in water was also quantified using a hydrogen sulfide-sensitive electrode. Corn was grown on an industrial scale and dosed with dibutyldithiophosphate to show that these dithiophosphates have potential applications in agriculture. At a loading of 2 kg per acre, a 6.4% increase in the harvest yield of corn was observed.

Synthesis and Hydrogen Sulfide Releasing Properties of Diaminodisulfides and Dialkoxydisulfides

Heterosubstituted disulfides are an understudied class of molecules that have been used in biological studies, but they have not been investigated for their ability to release hydrogen sulfide (H₂S). The synthesis of two sets of chemicals with the diaminodisulfide (NSSN) and dialkoxydisulfide (OSSO) functional groups was reported. These chemicals were synthesized from commercially available sulfur monochloride or a simple disulfur transfer reagent. Both the diaminodisulfide and dialkoxydisulfide functional groups were found to have rapid rates of H₂S release in the presence of excess thiol. The release of H₂S was complete with 10 min, and the only byproducts were conversion of the thiols into disulfides and the amines or alcohols originally used in the synthesis of the diaminodisulfide or dialkoxydisulfide functional groups. These results will allow the design of H₂S releasing chemicals that also release natural, biocompatible alcohols or amines. Chemicals with the diaminodisulfide and dialkoxydisulfide functional groups may find applications in medicine where a controlled, burst release of H₂S is needed.

Pharmacological induction of mesenchymal-epithelial transition via inhibition of H2S biosynthesis and consequent suppression of ACLY activity in colon cancer cells

Hydrogen sulfide (H₂S) is an important endogenous gaseous transmitter mediator, which regulates a variety of cellular functions in autocrine and paracrine manner. The enzymes responsible for the biological generation of H₂S include cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST). Increased expression of these enzymes and overproduction of H₂S has been implicated in essential processes of various cancer cells, including the stimulation of metabolism, maintenance of cell proliferation and cytoprotection. Cancer cell identity is characterized by so-called "transition states". The progression from normal (epithelial) to transformed (mesenchymal) state is termed epithelial-to-mesenchymal transition (EMT) whereby epithelial cells lose their cell-to-cell adhesion capacity and gain mesenchymal characteristics. The transition process can also proceed in the opposite direction, and this process is termed mesenchymal-to-epithelial transition (MET). The current project was designed to determine whether inhibition of endogenous H₂S production in colon cancer cells affects the EMT/MET balance in vitro. Inhibition of H₂S biosynthesis in HCT116 human colon cancer cells was achieved either with aminooxyacetic acid (AOAA) or 2-[(4-hydroxy-6-methylpyrimidin-2-yl)sulfanyl]-1-(naphthalen-1-yl)ethan-1-one (HMPSNE). These inhibitors induced an upregulation of E-cadherin and Zonula occludens-1 (ZO-1) expression and downregulation of fibronectin expression, demonstrating that H₂S biosynthesis inhibitors can produce a pharmacological induction of MET in colon cancer cells. These actions were functionally reflected in an inhibition of cell migration, as demonstrated in an in vitro "scratch wound" assay. The mechanisms involved in the action of endogenously produced H₂S in cancer cells in promoting (or maintaining) EMT (or tonically inhibiting MET) relate, at least in part, in the induction of ATP citrate lyase (ACLY) protein expression, which occurs via upregulation of ACLY mRNA (via activation of the ACLY promoter). ACLY in turn, regulates the Wnt-β-catenin pathway, an essential regulator of the EMT/MET balance. Taken together, pharmacological inhibition of endogenous H₂S biosynthesis in cancer cells induces MET. We hypothesize that this may contribute to anti-cancer / anti-metastatic effects of H₂S biosynthesis inhibitors.

Hydrogen sulfide: Roles in plant abiotic stress response and crosstalk with other signals

Hydrogen sulfide (H₂S) has been recently recognized as an endogenous gas transmitter alongside nitric oxide and carbon monoxide. Exposure of plants to H₂S, for example through applicating H₂S donors, reveals that H₂S play important roles in plant response to abiotic stresses such as heavy metals, salinity, drought and extreme temperatures. Sodium hydrosulfide is the most widely used donor in plants due to its direct and instantaneous release of H₂S, followed by GYY4137. H₂S can enhance plant tolerance to salt and heavy metal stresses through regulating Na⁺/K⁺ homeostasis and the uptake and transport of metal ions. H₂S also promotes the H₂S-Cys cycle balance under abiotic stress and enhances its roles in regulation of the antioxidant system, alternative respiratory pathway, and heavy metal chelators synthesis. H₂S coordinates with gaseous signal molecules, reactive oxygen species and nitric oxide to respond to stress directly through influencing their generation or competing for the regulation of the downstream signaling. Moreover, H₂S interacts with phytohormones including abscisic acid, ethylene, salicylic acid and melatonin as well as polyamines to regulate plant response to abiotic stresses. In this review, the application of H₂S donors and their functional mechanism are summarized. We propose promising new research directions, which can lead to new insights on the role of this gastrasmitter during plant growth and development.

Crosstalk among hydrogen sulfide (H2S), nitric oxide (NO) and carbon monoxide (CO) in root-system development and its rhizosphere interactions: A gaseous interactome

Root development in higher plants is achieved by a precise intercellular communication which determines cell fate in the primary embryonic meristem where the gasotransmitters H₂S, NO and CO participate dynamically. Furthermore, the rhizosphere interaction of these molecules with microbial and soil metabolism also affects root development. NO regulates root growth and architecture in association with several other biomolecules like auxin indole-3-acetic acid (IAA), ethylene, jasmonic acid (JA), strigolactones, alkamides and melatonin. The CO-mediated signal transduction pathway in roots is closely linked to the NO-mediated signal cascades. Interestingly, H₂S acts also as an upstream component in IAA and NO-mediated crosstalk during root development. Heme oxygenase (HO) 1 generates CO and functions as a downstream component in H₂S-mediated adventitious rooting and H₂S-CO crosstalk. Likewise, reactive oxygen species (ROS), H₂S and NO crosstalk are important components in the regulation of root architecture. Deciphering these interactions will be a potential biotechnological tool which could provide benefits in crop management in soils, especially under adverse environmental conditions. This review aims to provide a comprehensive update of the complex networks of these gasotransmitters during the development of roots.

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.