The involvement of hydrogen sulphide in melatonin-induced tolerance to arsenic toxicity in pepper (Capsicum annuum L.) plants by regulating sequestration and subcellular distribution of arsenic, and antioxidant defense system

The teamwork of melatonin, ethylene and H2S in abiotic stress adaptation in plants

Abiotic stresses significantly reduce plant growth and productivity, challenging agricultural sustainability. Plants have evolved adaptive mechanisms to counter these stresses, including antioxidant defences, biochemical changes, and hormonal signaling. Among these, the hormone melatonin (MT) and signaling molecules, ethylene (ET) and hydrogen sulfide (H2S), play pivotal roles, interacting in complex ways that modulate stress responses. Melatonin, known for its antioxidant properties, interacts with ET pathways to regulate its production. While ET is essential for stress signaling, its overproduction can exacerbate oxidative damage, and MT helps modulate ET levels to prevent such detrimental effects. Moreover, MT regulates H2S synthesis by activating L-cysteine desulfhydrase (LCD) and D-cysteine desulfhydrase (DCD), enhancing its protective effects under stress. Hydrogen sulfide supports MT synthesis, indicating a bidirectional relationship. Evidence suggests that H2S plays a role in fine-tuning ET levels under stress conditions, supporting optimal signaling for resilience. This review explores the intricate interactions among MT, ET, and H2S, shedding light on potential crosstalk mechanisms that strengthen plant stress tolerance, aiming to enhance crop resilience through targeted manipulation of these pathways.

Exogenous Hydrogen sulfide attenuates cadmium toxicity to Chrysanthemum (Chrysanthemum indicum) by modulating glutathione synthesis and cadmium adsorption capacity in the cell wall

Soil cadmium (Cd) contamination leads to plant toxicity and poses a risk to human health both directly and indirectly through the food chain. Hydrogen sulfide (H2S), a novel gaseous signaling molecule, has been shown to enhance plant tolerance to various abiotic stresses. In this study, the potential of H2S in mitigating Cd toxicity in chrysanthemum (Chrysanthemum indicum) was investigated through physiological, biochemical and transcriptomic analyses. Results showed that the application of exogenous H2S resulted Cd accumulation in the roots by 21.15 %, while reducing Cd in the aboveground parts by 13.21 %. It was further found that H2S increased the pectin and hemicellulose content by 50.09 % and 49.79 %, respectively, through the regulation of cell wall polysaccharide synthesis-related genes, leading to changes in root functional group content and cell wall adsorption capacity for cadmium ions (Cd2+). Additionally, H2S also promoted the synthesis of GSH and PCs by regulating the expression of genes related to sulfur metabolism, chelating free Cd2+ in the cytoplasm, and reducing their harmful effects on the organelles. It was also found that exogenous H2S may have regulated the expression of transporter proteins by modulating the expression of transcription factors (MYB, AP2/ERF, and WRKY), thereby affecting the uptake, transport, and accumulation of Cd2+. In conclusion, exogenous H2S reduced the free Cd2+ content in the cytoplasm by promoting the adsorption of Cd2+ in the root cell walls and facilitating the synthesis of GSH and PCs in the cells, which in turn alleviated the toxic effects of Cd2+ on chrysanthemum.

Unveiling the role and crosstalk of hydrogen sulfide with other signalling molecules enhances plant tolerance to water scarcity

Drought, a major factor limiting global crop yields, disrupts plant growth, water interactions, and overall water use efficiency. Hydrogen sulfide (H2S), a key gasotransmitter, has become a crucial signalling molecule in plant biology. It promotes growth and development while significantly contributing to the plant's response to various abiotic stresses, including drought. This review explores how H₂S mitigates drought stress in plants and crosstalks with various signalling molecules such as nitric oxide, melatonin, abscisic acid, γ-aminobutyric acid, polyamines, and others. It highlights how these interactions, with H₂S acting either upstream or downstream, enhance the plant's stress response and resistance. Furthermore, H₂S signalling involves persulfidation, in which H₂S modifies protein thiol groups to protect against oxidative damage. The review underscores the key role of protein persulfidation in reducing reactive oxygen species accumulation and maintaining redox homeostasis under drought stress. The review aims to elucidate the role of H₂S in stress relief and expand our knowledge of how it contributes to plant resistance during water scarcity by examining its regulatory mechanisms and interactions. Additionally, it proposes practical strategies for enhancing agricultural practices in the face of growing drought conditions, offering methods to leverage H₂S for improving plant tolerance to water scarcity.

Influence of sulfur and selenium application on wheat growth in arsenic-contaminated soil

Wheat could become poisoned when grown in soil with high arsenic (As) content. It is worthwhile to investigate the potential use of sulfur (S) and selenium (Se) for crop protection while detoxifying heavy metal(loid)s. In this study, a pot experiment was conducted under both single and combined application of the two elements. Their effects on wheat growth were analyzed based on As distribution in subcellular tissues and the variation in physiological and biochemical indicators. Despite wheat absorbing and enriching As under S and Se application, its growth status improved. Cell wall and vacuole sequestered majority of elevated As. Phytochelatins (PCs) content increased significantly in the roots, particularly when Se was applied alone. They could chelate with As using thiol groups. Superoxide dismutase (SOD) activity was found to be considerably lower in leaves and without any discernible increase in roots. Peroxidase (POD) activity in roots/stems and/or catalase (CAT) activity in stems increased, and exerted antioxidant effects. The leaf was well protected, and its chlorophyll content significantly increased. The application of S alone had a relatively weaker effect on reducing As content in grains, but the mixed application of Se could induce an inhibitory effect.

Synergistic interplay between melatonin and hydrogen sulfide enhances cadmium-induced oxidative stress resistance in stock (Matthiola incana L.)

Ornamental crops particularly cut flowers are considered sensitive to heavy metals (HMs) induced oxidative stress condition. Melatonin (MLT) is a versatile phytohormone with the ability to mitigate abiotic stresses induced oxidative stress in plants. Similarly, signaling molecules such as hydrogen sulfide (H2S) have emerged as potential options for resolving HMs related problems in plants. The mechanisms underlying the combined application of MLT and H2S are not yet explored. Therefore, we evaluated the ability of individual and combined applications of MLT (100 μM) and H2S in the form of sodium hydrosulfide (NaHS), a donor of H2S, (1.5 mM) to alleviate cadmium (Cd) stress (50 mg L-1) in stock (Matthiola incana L.) plants by measuring various morpho-physiological and biochemical characteristics. The results depicted that Cd-stress inhibited growth, photosynthesis and induced Cd-associated oxidative stress as depicted by excessive ROS accumulation. Combined application of MLT and H2S efficiently recovered all these attributes. Furthermore, Cd stress-induced oxidative stress markers including electrolyte leakage, malondialdehyde, and hydrogen peroxide are partially reversed in Cd-stressed plants by MLT and H2S application. This might be attributed to MLT or H2S induced antioxidant plant defense activities, which effectively reduce the severity of oxidative stress indicators. Overall, MLT and H2S supplementation, favorably regulated Cd tolerance in stock; yet, the combined use had a greater effect on Cd tolerance than the independent application.

The Ameliorative Effect of Coumarin on Copper Toxicity in Citrus sinensis: Insights from Growth, Nutrient Uptake, Oxidative Damage, and Photosynthetic Performance

Excessive copper (Cu) has become a common physiological disorder restricting the sustainable production of citrus. Coumarin (COU) is a hydroxycinnamic acid that can protect plants from heavy metal toxicity. No data to date are available on the ameliorative effect of COU on plant Cu toxicity. 'Xuegan' (Citrus sinensis (L.) Osbeck) seedlings were treated for 24 weeks with nutrient solution containing two Cu levels (0.5 (Cu0.5) and 400 (Cu400) μM CuCl2) × four COU levels (0 (COU0), 10 (COU10), 50 (COU50), and 100 (COU100) μM COU). There were eight treatments in total. COU supply alleviated Cu400-induced increase in Cu absorption and oxidative injury in roots and leaves, decrease in growth, nutrient uptake, and leaf pigment concentrations and CO2 assimilation (ACO2), and photo-inhibitory impairment to the whole photosynthetic electron transport chain (PETC) in leaves, as revealed by chlorophyll a fluorescence (OJIP) transient. Further analysis suggested that the COU-mediated improvement of nutrient status (decreased competition of Cu2+ with Mg2+ and Fe2+, increased uptake of nutrients, and elevated ability to maintain nutrient balance) and mitigation of oxidative damage (decreased formation of reactive oxygen species and efficient detoxification system in leaves and roots) might lower the damage of Cu400 to roots and leaves (chloroplast ultrastructure and PETC), thereby improving the leaf pigment levels, ACO2, and growth of Cu400-treated seedlings.

Functional interaction of melatonin with gasotransmitters and ROS in plant adaptation to abiotic stresses

Melatonin is considered a multifunctional stress metabolite and a novel plant hormone affecting seed germination, root architecture, circadian rhythms, leaf senescence, and fruit ripening. Melatonin functions related to plant adaptation to stress stimuli of various natures are considered especially important. One of the key components of melatonin's stress-protective action is its ability to neutralise reactive oxygen species (ROS) and reactive nitrogen species directly. However, many of its effects are related to its involvement in the signalling network of plant cells and its influence on the expression of a large number of genes important for adaptation to adverse factors. Insights into the functional relationships of melatonin with gasotransmitters (GT) - gaseous molecules performing signalling functions - are still emerging. This review has analysed and summarised the experimental data that testify to the participation of the main GTs - nitric oxide, hydrogen sulfide, and carbon monoxide - in the implementation of the protective effect of melatonin when plants are exposed to abiotic stimuli of various nature. In addition, modulation by melatonin of one of the most important components in the action of GTs and ROS - post-translational modifications of proteins and the influence of ROS and GTs on melatonin synthesis in plants under stress conditions and the specific physiological effects of exogenous melatonin and GTs have been reviewed. Finally, the prospects of the GTs' practical application to achieve synergistic stress-protective effects on plants have been considered.

Melatonin attenuates degenerative disc degression by downregulating DLX5 via the TGF/Smad2/3 pathway in nucleus pulposus cells

Background

Intervertebral disc degeneration (IVDD) is the leading cause of low back pain, and apoptosis plays a key role in its pathogenesis. Distal-less homeobox 5 (Dlx5) has been reported to induce cell apoptosis. Melatonin, as a powerful antiapoptotic agent, has been widely reported.

Aim

This study aimed to investigate the role of DLX5 in the pathogenesis of IVDD and the potential therapeutic role of melatonin in targeting DLX5 in IVDD.

Materials & Methods

Western blotting, RT-qPCR, immunohistochemistry, si-DLX5, Ex-DLX5, flow cytometry, and immunofluorescence were used to examine the regulatory effect of DLX5 on apoptosis. Therapeutic efficacy was assessed by the intraperitoneal injection of melatonin into IVDD mice.

Results

The expression level of DLX5 is significantly increased in IVDD, and the expression levels were positively correlated with the grade of IVDD. DLX5 was significantly upregulated in TNF-α-induced degenerative NP cells. Degenerative NP cells transfected with si-DLX5 exhibited significantly less apoptosis than control cells. Melatonin significantly alleviated IVDD in surgically induced IVDD model mice.

Discussion

The results revealed that the expression of DLX5 was positively correlated with the severity of IVDD and that melatonin ameliorated DLX5-induced apoptosis and extracellular matrix imbalance by inhibiting the TGF-β/Smad signaling pathway. This study may provide therapeutic strategies to alleviate inflammation-induced apoptosis IVDD-associated inflammation-induced apoptosis.

Conclusion

DLX5 plays an important role in IVDD progression by promoting apoptosis, and melatonin represents a promising therapeutic strategy for alleviating IVDD-associated inflammation and apoptosis.

Arbuscular mycorrhizal fungi alleviate Mn phytotoxicity by altering Mn subcellular distribution and chemical forms in Lespedeza davidii

Introduction

Arbuscular mycorrhizal fungi (AMF) can relieve manganese (Mn) phytotoxicity and promote plant growth under Mn stress, but their roles remain unclear.

Methods

In this study, Lespedeza davidii inoculated with or without AMF (Glomus mosseae) under different Mn concentrations (0 mmol/L, 1 mmol/L, 5 mmol/L, 10 mmol/L, and 20 mmol/L) was cultivated via a pot experiment, and plant biomass, physiological and biochemical characteristics, manganese absorption, subcellular distribution, and chemical forms of Mn were examined.

Results

The results showed that root biomass, stem biomass, leaf biomass, and total individual biomass decreased under high Mn concentrations (above 10 mmol/L), and the inoculated plants had higher biomass than the uninoculated plants. With the increasing Mn concentration, the contents of soluble sugar, soluble protein, free proline, superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) increased first and then decreased, while the malondialdehyde (MDA) content increased. The contents of soluble sugar, soluble protein, free proline, SOD, POD, and CAT in the inoculated group were higher than those in the uninoculated group at the Mn concentration of 20 mmol/L. The content of MDA in the inoculated plants was lower than that in the uninoculated plants. AMF inoculation enriched most of the manganese in the root system when compared with the non-mycorrhizal treatment. Subcellular distribution of Mn indicated that most of the Mn ions were stored in the cell wall and the vacuoles (the soluble fractions), and the proportion of Mn content in the cell wall components and the vacuole components in leaves in the inoculated group was higher than that in the uninoculated group. Furthermore, the proportions of Mn extracted using ethanol and deionized water in the uninoculated group in stems and roots were higher than those in the inoculated group, which suggested that AMF could convert Mn into inactive forms.

Discussion

The present study demonstrated that AMF could improve the resistance of L. davidii to Mn toxicity by increasing the activity of antioxidant enzymes and altering the subcellular distribution and chemical forms of Mn.

Chitosan nanoparticles alleviate chromium toxicity by modulating metabolic homeostasis and promoting chromium sequestration in Zea mays L

Chitosan nanoparticles (CSNPs) have been proposed as a potential alternative in alleviating chromium (Cr) toxicity. However, the mechanisms underlying remains poorly understood. This study investigates the effects of CSNPs on carbon/nitrogen metabolism, cell wall Cr binding capacity, and antioxidant activity in Zea mays L. under Cr stress. Cr stress decreased the total dry weight (DW) by 48.5 %. By contrast, the total DW was reduced by only 26.2 % in CSNPs-treated plants. Analysis of transcriptomic, enzyme activity, and metabolite content data, CSNPs-treated plants exhibited a higher level of relatively stable Carbon and Nitrogen metabolism than untreated plants. CSNPs application resulted in a substantial increase in the levels of sucrose and soluble protein by 78.0 % and 19.4 % in the leaves, and 60.0 % and 59.7 % in the roots, respectively. Meanwhile, CSNPs increased the contents of glutathione, phytochelatin, and cell wall polysaccharide. This increase resulted in a higher retention of Cr in vacuole and cell wall. Additionally, CSNPs alleviated the oxidative damage by improving antioxidant activity. Overall, our results suggest that CSNPs alleviates Cr toxicity by modulating metabolic homeostasis and promoting Cr sequestration in maize plants. This study provides new insights into the mechanisms underlying CSNPs-mediated Cr stress response with potential implications for crop production.

Ionic and nano calcium to reduce cadmium and arsenic toxicity in plants: Review of mechanisms and potentials

Contamination of agricultural soils with heavy metal(loid)s like arsenic (As) and cadmium (Cd) is an ever increasing concern for crop production, quality, and global food security. Numerous in-situ and ex-situ remediation approaches have been developed to reduce As and Cd contamination in soils. However, field-scale applications of conventional remediation techniques are limited due to the associated environmental risks, low efficacy, and large capital investments. Recently, calcium (Ca) and Ca-based nano-formulations have emerged as promising solutions with the large potential to mitigate As and Cd toxicity in soil for plants. This review provides comprehensive insights into the phytotoxic effects of As and Cd stress/toxicity and discusses the applications of Ca-based ionic and nano-agrochemicals to alleviate As and Cd toxicity in important crops such as rice, wheat, maize, and barley. Further, various molecular and physiological mechanisms induced by ionic and nano Ca to mitigate As and Cd stress/toxicity in plants are discussed. This review also critically analyzes the efficiency of these emerging Ca-based approaches, both ionic and nano-formulations, in mitigating As and Cd toxicity in comparison to conventional remediation techniques. Additionally, future perspectives and ecological concerns of the remediation approaches encompassing ionic and nano Ca have been discussed. Overall, the review provides an updated and in-depth knowledge for developing sustainable and effective strategies to address the challenges posed by As and Cd contamination in agricultural crops.

Regulation of arsenate stress by nitric oxide and hydrogen sulfide in Oryza sativa seedlings: Implication of sulfur assimilation, glutathione biosynthesis, and the ascorbate-glutathione cycle and its genes

Seed priming by nitric oxide (NO) and hydrogen sulphide (H2S) in combating against abiotic stress in plants is well documented. However, knowledge of fundamental mechanisms of their crosstalk is scrambled. Therefore, the reported study examined the probable role of NO and H2S in the mitigation of arsenate toxicity (As(V)) in rice seedlings and whether their potential signalling routes crossover. Results report that As(V) toxicity limited shoot and root length growth with more As accumulation in roots. As(V) further caused elevated reactive oxygen species levels, inhibited ascorbate-glutathione cycle enzymes and relative gene expression of its enzymes and thus, causing lipid and protein oxidation. These results correlate with reduced nitric oxide synthase-like and L-cysteine desulfhydrase activity along with endogenous NO and H2S. While, L-NAME or PAG augmented As(V) toxicity, and addition of SNP or NaHS effectively reversed their respective effects. Furthermore, SNP under PAG or NaHS under L-NAME were able to pacify As(V) stress, implicating that endogenous NO and H2S efficiently ameliorate As(V) toxicity but without their shared signaling in rice seedlings.

An Overview of the Mechanisms through Which Plants Regulate ROS Homeostasis under Cadmium Stress

Cadmium (Cd2+) is a non-essential and highly toxic element to all organic life forms, including plants and humans. In response to Cd stress, plants have evolved multiple protective mechanisms, such as Cd2+ chelation, vesicle sequestration, the regulation of Cd2+ uptake, and enhanced antioxidant defenses. When Cd2+ accumulates in plants to a certain level, it triggers a burst of reactive oxygen species (ROS), leading to chlorosis, growth retardation, and potentially death. To counteract this, plants utilize a complex network of enzymatic and non-enzymatic antioxidant systems to manage ROS and protect cells from oxidative damage. This review systematically summarizes how various elements, including nitrogen, phosphorus, calcium, iron, and zinc, as well as phytohormones such as abscisic acid, auxin, brassinosteroids, and ethylene, and signaling molecules like nitric oxide, hydrogen peroxide, and hydrogen sulfide, regulate the antioxidant system under Cd stress. Furthermore, it explores the mechanisms by which exogenous regulators can enhance the antioxidant capacity and mitigate Cd toxicity.

Relative effects of melatonin and hydrogen sulfide treatments in mitigating salt damage in wheat

Soil salinity poses a significant threat to agricultural productivity, impacting the growth and yield of wheat (Triticum aestivum L.) plants. This study investigates the potential of melatonin (MT; 100 µM) and hydrogen sulfide (H2S; 200 µM sodium hydrosulfide, NaHS) to confer the tolerance of wheat plants to 100 mM NaCl. Salinity stress induced the outburst of reactive oxygen species (ROS) resulting in damage to the chloroplast structure, growth, photosynthesis, and yield. Application of either MT or NaHS augmented the activity of antioxidant enzymes, superoxide dismutase, ascorbate peroxidase, glutathione reductase, and reduced glutathione (GSH) levels, upregulated the expression of Na+ transport genes (SOS1, SOS2, SOS3, NHX1), resulting in mitigation of salinity stress. Thus, improved stomatal behavior, gas-exchange parameters, and maintenance of chloroplast structure resulted in enhanced activity of the Calvin cycle enzymes and overall enhancement of growth, photosynthetic, and yield performance of plants under salinity stress. The use of DL-propargylglycine (PAG, an inhibitor of hydrogen sulfide biosynthesis) and p-chlorophenyl alanine (p-CPA, an inhibitor of melatonin biosynthesis) to plants under salt stress showed the comparative necessity of MT and H2S in mitigation of salinity stress. In the presence of PAG, more pronounced detrimental effects were observed than in the presence of p-CPA, emphasizing that MT was involved in mitigating salinity through various potential pathways, one of which was through H2S.

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.

Melatonin improves drought stress tolerance of pepper (Capsicum annuum) plants via upregulating nitrogen metabolism

While ameliorating effects of melatonin (MT) on abiotic stress tolerance in plants are widely reported, the mechanism that underlies this process remains elusive. This work investigated mechanisms by which MT improved drought tolerance in pepper (Capsicum annuum ) plants. A foliar spray of 0.1mM MT treatment was applied to plants grown at 80% and 40% of full field capacity for 3days. Drought stress caused a significant decrease in plant dry weight, relative water content, leaf water potential, PSII efficiency (F v /F m ratio), chlorophyll, soluble protein, leaf and root nitrogen content. Drought increased hydrogen peroxide, malondialdehyde (MDA), nitrate, ammonium, free amino acids, soluble sugars, proline and glycine betaine. Drought also increased peroxidase (POD), glutathione S-transferase (GST) and catalase (CAT) activities, electrolyte leakage (EL) and methylglyoxal (MG). MT pre-treatment reduced oxidative stress and improved nitrogen metabolism by activating various enzymes such as nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthetase (GOGAT) and glutamine dehydrogenase (GDH) activities. It also activated enzymes related to the glyoxalase system (Gly I and Gly II) and decreased NO3 - , NH4 + and free amino acid content. Our study suggests a cost-effective and sustainable solution to improve crop productivity in water-limited conditions, by enhancing plant growth, photosynthesis and nitrogen content.

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

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

Melatonin alleviates chromium toxicity by altering chromium subcellular distribution and enhancing antioxidant metabolism in wheat seedlings

The endogenous stimulating molecule melatonin (N-acetyl-5-methoxytryptamine, MT) has an important function in mitigating the impact of multiple abiotic stressors. However, the ameliorating effect of MT on chromium (Cr) stress and its mechanisms remains unclear. Therefore, the present study aimed to clarify the mitigating effect of exogenous MT (0 μM and 100 μM) on wheat seedlings under Cr (0 μM and 50 μM) stress stemming from the growth and physiological characteristics, phytochelatin (PC) biosynthesis, Cr subcellular distribution, and antioxidant system of the plants in these treatments. The results showed that endogenous MT application significantly promoted plant growth and improved root morphology of wheat seedlings under Cr stress due to decreased Cr and reactive oxygen species (ROS) accumulation in both roots and leaves. Accumulation and transport of Cr from roots to leaves were reduced by MT, because enhanced vacuolar sequestration via upregulated PC accumulation, took place, derived from the fact that MT upregulated the expression of key genes for PC synthesis (TaPCS and Taγ-ECS). Furthermore, MT pre-treatment alleviated Cr-induced oxidative damage by diminishing lipid peroxidation and cell apoptosis, profiting from the enhanced scavenging ability of ROS as a result of the MT-induced increase in the activities of superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase, and the related encoding gene expression levels of TaSOD2, TaCAT, TaAPX, and TaGR. In conclusion, endogenous MT application improved the growth traits, antioxidant system, and decreased Cr accumulation especially at the leaf level in wheat seedlings under Cr stress mainly through enhancing antioxidant enzyme activities and altering Cr subcellular distribution via strengthening PC biosynthesis. The mechanisms of MT-induced plant tolerance to Cr stress could help develop new strategies for secure crop production in Cr-polluted soils.

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.