H2 supplied via ammonia borane stimulates lateral root branching via phytomelatonin signaling

Research Progress of Hydrogen Rich Water in Preservation of Postharvest Horticultural Products: A Review

The perishable nature of horticultural products and unfavorable factors during storage lead to postharvest losses and shelf life limitations. As an effective hydrogen (H2) supplier, hydrogen-rich water (HRW) is regarded as a new green postharvest preservation strategy of horticultural products. This review presents a complete overview of the application advance of HRW for the preservation of horticultural products, including the potential production mechanisms of hydrogen in plants, the preparation and application methods of HRW, and potential mechanisms of HRW in improving the quality of postharvest horticultural products. The findings show that HRW can maintain the quality and stress tolerance of horticultural products by regulating metabolic pathways and molecular responses, including oxidative defense, energy homeostasis, respiration, cell-wall intergrity, ethylene biosynthesis, related gene expression and phytohormones signaling crosstalk. The information obtained in this review is expected to provide a scientific basis for the application of HRW for the preservation of postharvest horticultural products.

Hydrogen gas enhances Arabidopsis salt tolerance by modulating hydrogen peroxide-mediated redox and ion homeostasis

Hydrogen gas (H2) plays a crucial role in mitigating salt stress in plants, but the underlying mechanisms is largely unknown. Herein, we employed the pharmacological, molecular, and genetic approaches to investigate the positive roles of hydrogen peroxide (H2O2) in endogenous H2-induced salt tolerance of Arabidopsis thaliana. H2-induecd salt tolerance of CrHYD1 (hydrogenase 1 gene from Chlamydomonas reinhardtii) transgenic Arabidopsis was blocked by H2O2 scavenger or NADPH oxidase inhibitor. When RESPIRATORY BURST OXIDASE HOMOLOG (RBOH) genes (AtrbohD or AtrbohF) were mutated, salt sensitivity of CrHYD1/atrboh (especially CrHYD1/atrbohD) hybrids was increased, but diminished by exogenous H2O2 administration. Salt-stimulated endogenous H2 enrichment consequently resulted in the rapid reactive oxygen species (ROS) accumulation under early salt stress, and the expression of AtrbohD (especially) and AtrbohF in CrHYD1 plants was higher than those in the wild-type (WT), suggesting that endogenous H2 could induce Atrboh-dependent ROS burst to respond salt stress. Further, H2-induced less 3,3'-diaminobenzidine (DAB) and nitro blue tetrazolium (NBT) stain in CrHYD1 plants was reversed under salt stress when either H2O2 was removed or Atrbohs were mutated, which could be explained by higher H2O2 and thiobarbituric acid reactive substances (TBARS) levels, as well as lower antioxidant enzyme activity. Additionally, H2-induced Na+ discharge and K+ accumulation in CrHYD1 plants under salt stress were blocked by either H2O2 removal or Atrboh knockout, which was validated by higher Na+/K+ ratios and lower ion transport-related gene expression. Our findings not only elucidate that endogenous H2 enhanced Arabidopsis salt tolerance by reestablishing H2O2-dependent ion and redox homeostasis, but provide new insights into the mechanisms of plant salinity responses.

Molecular hydrogen positively influences root gravitropism involving auxin signaling and starch accumulation

Although geoscience of natural hydrogen (H2), hydrogen-producing soil bacteria, and especially plant-based H2, has been observed, it is not clear whether or how above H2 resources influence root gravitropic responses. Here, pharmacological, genetic, molecular, and cell biological tools were applied to investigate how plant-based H2 coordinates gravity responses in Arabidopsis roots. Since roots show higher H2 production than shoots, exogenous H2 supply was used to mimic this function. After H2 supplementation, the asymmetric expression of the auxin-response reporter DR5 driven by auxin influx and efflux carriers, and thereafter positive root gravitropism were observed. These positive responses in root gravitropism were sensitive to auxin polar transport inhibitors, and importantly, the defective phenotypes observed in aux1-7, pin1, and pin2 mutants were not significantly altered by exogenous H2. The observed starch accumulation was matched with the reprogramming gene expression linked to starch synthesis and degradation. Transgenic plants expressing hydrogenase1 (CrHYD1) from Chlamydomonas reinhardtii not only displayed higher endogenous H2 concentrations, the inducible AUX1 gene expression and starch accumulation, but also showed pronounced root gravitropism. Collectively, above evidence preliminarily provides a framework for understanding the molecular basis of the possible functions of both plant/soil-based and nature H2 in root architecture.

The activation of autophagy by molecular hydrogen is functionally associated with osmotic tolerance in Arabidopsis

The role of molecular hydrogen (H2) in autophagy during inflammatory response is controversial in mammalian cells. Although the stimulation of H2 production in response to osmotic stress was observed in plants, its synthetic pathway and the interrelationship between its induction and plant autophagy remain unclear. Here, the induction of autophagy was observed in Arabidopsis upon osmotic stress, assessing by the autophagosome formation and autophagy-related genes expression. Above responses were intensified by H2 fumigation. Meanwhile, the reduction in seedling growth and roots vigor was obviously abolished, accompanied by reestablishing redox balance. These H2 responses were markedly impaired in T-DNA knockout lines atg2, atg5, and atg18. Further evidence showed that the increased endogenous H2 synthesis by genetic manipulation, not only stimulated autophagosome formation, but also triggered various plant responses toward osmotic stress. By contrast, these responses were obviously abolished by the disruption of endogenous H2 synthesis with the addition of 2,6-dichloroindophenol sodium salt. Together, the integrated genetic and molecular evidence clearly illustrated the requirement of autophagy activation in H2 control of plant osmotic tolerance.

Magnesium Hydride Confers Osmotic Tolerance in Mung Bean Seedlings by Promoting Ascorbate-Glutathione Cycle

Despite substantial evidence suggesting that hydrogen gas (H2) can enhance osmotic tolerance in plants, the conventional supply method of hydrogen-rich water (HRW) poses challenges for large-scale agricultural applications. Recently, magnesium hydride (MgH2), a hydrogen storage material in industry, has been reported to yield beneficial effects in plants. This study aimed to investigate the effects and underlying mechanisms of MgH2 in plants under osmotic stress. Mung bean seedlings were cultured under control conditions or with 20% polyethylene glycol (PEG)-6000, with or without MgH2 addition (0.01 g L-1). Under our experimental conditions, the MgH2 solution maintained a higher H2 content and longer retention time than HRW. Importantly, PEG-stimulated endogenous H2 production was further triggered by MgH2 application. Further results revealed that MgH2 significantly alleviated the inhibition of seedling growth and reduced oxidative damage induced by osmotic stress. Pharmacological evidence suggests the MgH2-reestablished redox homeostasis was associated with activated antioxidant systems, particularly the ascorbate-glutathione cycle. The above observations were further supported by the enhanced activities and gene transcriptional levels of ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase. Overall, this study demonstrates the importance of MgH2 in mitigating osmotic stress in mung bean seedlings, providing novel insights into the potential agricultural applications of hydrogen storage materials.

Phytomelatonin: From Intracellular Signaling to Global Horticulture Market

Melatonin (N-acetyl-5-methoxytryptamine), a well-known mammalian hormone, has been having a great relevance in the Plant World in recent years. Many of its physiological actions in plants are leading to possible features of agronomic interest, especially those related to improvements in tolerance to stressors and in the postharvest life of fruits and vegetables. Thus, through the exogenous application of melatonin or by modifying the endogenous biosynthesis of phytomelatonin, some change can be made in the functional levels of melatonin in tissues and their responses. Also, acting in the respective phytomelatonin biosynthesis enzymes, regulating the expression of tryptophan decarboxylase (TDC), tryptamine 5-hydroxylase (T5H), serotonin N-acetyltransferase (SNAT), N-acetylserotonin O-methyltransferase (ASMT), and caffeic acid O-methyltransferase (COMT), and recently the possible action of deacetylases on some intermediates offers promising opportunities for improving fruits and vegetables in postharvest and its marketability. Other regulators/effectors such as different transcription factors, protein kinases, phosphatases, miRNAs, protein-protein interactions, and some gasotransmitters such as nitric oxide or hydrogen sulfide were also considered in an exhaustive vision. Other interesting aspects such as the role of phytomelatonin in autophagic responses, the posttranslational reprogramming by protein-phosphorylation, ubiquitylation, SUMOylation, PARylation, persulfidation, and nitrosylation described in the phytomelatonin-mediated responses were also discussed, including the relationship of phytomelatonin and several plant hormones, for chilling injury and fungal decay alleviating. The current data about the phytomelatonin receptor in plants (CAND2/PMTR1), the effect of UV-B light and cold storage on the postharvest damage are presented and discussed. All this on the focus of a possible new action in the preservation of the quality of fruits and vegetables.

Hydrogen Fertilization with Hydrogen Nanobubble Water Improves Yield and Quality of Cherry Tomatoes Compared to the Conventional Fertilizers

Although hydrogen gas (H2)-treated soil improves crop biomass, this approach appears difficult for field application due to the flammability of H2 gas. In this report, we investigated whether and how H2 applied in hydrogen nanobubble water (HNW) improves the yield and quality of cherry tomato (Lycopersicon esculentum var. cerasiforme) with and without fertilizers. Two-year-long field trials showed that compared to corresponding controls, HNW without and with fertilizers improved the cherry tomato yield per plant by 39.7% and 26.5% in 2021 (Shanghai), respectively, and by 39.4% and 28.2% in 2023 (Nanjing), respectively. Compared to surface water (SW), HNW increased the soil available nitrogen (N), phosphorus (P), and potassium (K) consumption regardless of fertilizer application, which may be attributed to the increased NPK transport-related genes in roots (LeAMT2, LePT2, LePT5, and SlHKT1,1). Furthermore, HNW-irrigated cherry tomatoes displayed a higher sugar-acid ratio (8.6%) and lycopene content (22.3%) than SW-irrigated plants without fertilizers. Importantly, the beneficial effects of HNW without fertilizers on the yield per plant (9.1%), sugar-acid ratio (31.1%), and volatiles (20.0%) and lycopene contents (54.3%) were stronger than those achieved using fertilizers alone. In short, this study clearly indicated that HNW-supplied H2 not only exhibited a fertilization effect on enhancing the tomato yield, but also improved the fruit's quality with a lower carbon footprint.