Progress in the study of biological effects of hydrogen on higher plants and its promising application in agriculture

The Effect of Adjuvant Therapy with Molecular Hydrogen on Endogenous Coenzyme Q10 Levels and Platelet Mitochondrial Bioenergetics in Patients with Non-Alcoholic Fatty Liver Disease

Molecular hydrogen (H2) has been recognized as a novel medical gas with antioxidant and anti-inflammatory effects. Non-alcoholic fatty liver disease (NAFLD) is a liver pathology with increased fat accumulation in liver tissue caused by factors other than alcohol consumption. Platelet mitochondrial function is considered to reflect systemic mitochondrial health. We studied the effect of adjuvant therapy with hydrogen-rich water (HRW) on coenzyme Q10 (CoQ10) content and platelet mitochondrial bioenergetics in patients with NAFLD. A total of 30 patients with NAFLD and 15 healthy volunteers were included in this clinical trial. A total of 17 patients (H2 group) drank water three × 330 mL/day with tablets producing HRW (>4 mg/L H2) for 8 weeks, and 13 patients (P group) drank water with placebo tablets producing CO2. The concentration of CoQ10-TOTAL was determined by the HPLC method, the parameter of oxidative stress, thiobarbituric acid reactive substances (TBARS), by the spectrophotometric method, and mitochondrial bioenergetics in platelets isolated from whole blood by high-resolution respirometry. The patients with NAFLD had lower concentrations of CoQ10-TOTAL in the blood, plasma, and platelets vs. the control group. Mitochondrial CI-linked LEAK respiration was higher, and CI-linked oxidative phosphorylation (OXPHOS) and CII-linked electron transfer (ET) capacities were lower vs. the control group. Plasma TBARS concentrations were higher in the H2 group. After 8 weeks of adjuvant therapy with HRW, the concentration of CoQ10 in platelets increased, plasma TBARS decreased, and the efficiency of OXPHOS improved, while in the P group, the changes were non-significant. Long-term supplementation with HRW could be a promising strategy for the acceleration of health recovery in patients with NAFLD. The application of H2 appears to be a new treatment strategy for targeted therapy of mitochondrial disorders. Additional and longer-term studies are needed to confirm and elucidate the exact mechanisms of the mitochondria-targeted effects of H2 therapy in patients with NAFLD.

Transcriptome and Metabonomics Combined Analysis Revealed the Defense Mechanism Involved in Hydrogen-Rich Water-Regulated Cold Stress Response of Tetrastigma hemsleyanum

The poor resistance to cold stress conditions has become the bottleneck problem in Tetrastigma hemsleyanum (T. hemsleyanum) planting industry. Exogenous hydrogen (H₂) plays an important role in improving stress resistance in plants. However, the key factors and regulatory network of plants in response to hydrogen-rich water (HRW) treatment under environmental stress are not clear. Here, we conducted integrative analyses of metabolome and transcriptome profiles to reveal the defense mechanism involved in the HRW-regulated cold stress response of T. hemsleyanum. The application of 75% HRW could alleviate stress damage by decreasing stomatal apparatus density and significantly increasing photosynthetic efficiency and mitigating physiological indexes of resistance, such as Pn, Cond, MDA, SOD, etc., which were changed by cold stress conditions. A total of 7,883 DEGs and 439 DEMs were identified. DEGs were the most relevant to phenylpropanoid, isoflavonoid, monoterpenoid, and flavonoid biosynthesis pathways. Using gene co-expression analysis (WGCNA), we identified one gene module that showed a strong correlation between total antioxidant capacity and transpiration rate. Trend analysis indicated that the phenylpropanoid biosynthesis pathway played a major role in the transcription and metabolism process of HRW treatment under cold stress. Based on the integrated analysis of genes and metabolites, the results showed cold stress upregulated the expression of PAL, CHS, COMT, CCR, AtBG1, etc., resulting in the accumulation of coniferyl alcohol and eriodictyol contents in T. hemsleyanum under cold stress, but the 75% HRW treatment could attenuate the enhancement. The study not only identified the main strategy of HRW protection against cold stress but also provided candidate genes for flavonoid biosynthesis, so as to better improve cold tolerance through molecular breeding techniques.

Integrated Metabolomic and Transcriptomic Analyses to Understand the Effects of Hydrogen Water on the Roots of Ficus hirta Vahl

Wuzhimaotao (Ficus hirta Vahl) is an important medicinal and edible plant in China. The extract from the roots of Ficus hirta Vahl contains phenylpropanoid compounds, such as coumarins and flavonoids, which are the main active components of this Chinese herbal medicine. In this study, we analyzed the transcriptomic and metabolomic data of the hydrogen-water-treated roots of Ficus hirta Vahl and a control group. The results showed that many genes and metabolites were regulated in the roots of Ficus hirta Vahl that were treated with hydrogen water. Compared with the control group, 173 genes were downregulated and 138 genes were upregulated in the hydrogen-rich water treatment group. Differential metabolite analysis through LC-MS showed that 168 and 109 metabolites had significant differences in positive and negative ion mode, respectively. In the upregulated metabolites, the main active components of Wuzhimaotao, such as the phenylpropane compounds naringin, bergaptol, hesperidin, and benzofuran, were found. Integrated transcriptomic and metabolomic data analysis showed that four and one of the most relevant pathways were over enriched in positive and negative ion mode, respectively. In the relationship between metabolites and DEGs, phenylpropanoid biosynthesis and metabolism play an important role. This indicates that phenylpropanoid biosynthesis and metabolism may be the main metabolic pathways regulated by hydrogen water. Our transcriptome analysis showed that most of the DEGs with |log2FC| ≥ 1 are transcription factor genes, and most of them are related to plant hormone signal transduction, stress resistance, and secondary metabolism, mainly phenylpropanoid biosynthesis and metabolism. This study provides important evidence and clues for revealing the botanical effect mechanism of hydrogen and a theoretical basis for the application of hydrogen agriculture in the cultivation of Chinese herbal medicine.

An Activity-Based Ratiometric Fluorescent Probe for In Vivo Real-Time Imaging of Hydrogen Molecules

To reveal the biomedical effects and mechanisms of hydrogen molecules urgently needs hydrogen molecular imaging probes as an imperative tool, but the development of these probes is extremely challenging. In this work, a catalytic hydrogenation strategy is proposed to design and synthesize a ratiometric fluorescent probe by encapsulating Pd nanoparticles and conjugating azido-/coumarin-modified fluorophore into mesoporous silica nanoparticles, realizing in vitro and in vivo fluorescence imaging of hydrogen molecules. The developed hydrogen probe exhibits high sensitivity, rapid responsivity, high selectivity and low detection limit, enabling rapid and real-time detection of hydrogen molecules both in cells and in the body of animal and plant. By application of the developed fluorescent probe, we have directly observed superhigh transmembrane and ultrafast transport abilities of hydrogen molecules in cell, animal and plant, and discovered in vivo high diffusion of hydrogen molecules.

Molecular Hydrogen: Is This a Viable New Treatment for Plants in the UK?

Despite being trialed in other regions of the world, the use of molecular hydrogen (H₂) for enhanced plant growth and the postharvest storage of crops has yet to be widely accepted in the UK. The evidence that the treatment of plants and plant products with H₂ alleviates plant stress and slows crop senescence continues to grow. Many of these effects appear to be mediated by the alteration of the antioxidant capacity of plant cells. Some effects seem to involve heme oxygenase, whilst the reduction in the prosthetic group Fe³⁺ is also suggested as a mechanism. Although it is difficult to use as a gaseous treatment in a field setting, the use of hydrogen-rich water (HRW) has the potential to be of significant benefit to agricultural practices. However, the use of H₂ in agriculture will only be adopted if the benefits outweigh the production and application costs. HRW is safe and relatively easy to use. If H₂ gas or HRW are utilized in other countries for agricultural purposes, it is tempting to suggest that they could also be widely used in the UK in the future, particularly for postharvest storage, thus reducing food waste.

Molecular hydrogen in agriculture

H₂ gas, usually in the form of H₂-saturated water, could play a useful role in improving many aspects of plant growth and productivity, including resistance to stress tolerance and improved post-harvest durability. Therefore, molecular hydrogen delivery systems should be considered as a valuable addition within agricultural practice. Agriculture and food security are both impacted by plant stresses, whether that is directly from human impact or through climate change. A continuously increasing human population and rising food consumption means that there is need to search for agriculturally useful and environment friendly strategies to ensure future food security. Molecular hydrogen (H₂) research has gained momentum in plant and agricultural science owing to its multifaceted and diverse roles in plants. H₂ application can mitigate against a range of stresses, including salinity, heavy metals and drought. Therefore, knowing how endogenous, or exogenously applied, H₂ enhances the growth and tolerance against numerous plant stresses will enhance our understanding of how H₂ may be useful for future to agriculture and horticulture. In this review, recent progress and future implication of H₂ in agriculture is highlighted, focusing on how H₂ impacts on plant cell function and how it can be applied for better plant performance. Although the exact molecular action of H₂ in plants remains elusive, this safe and easy to apply treatment should have a future in agricultural practice.

Downstream Signalling from Molecular Hydrogen

Molecular hydrogen (H2) is now considered part of the suite of small molecules that can control cellular activity. As such, H2 has been suggested to be used in the therapy of diseases in humans and in plant science to enhance the growth and productivity of plants. Treatments of plants may involve the creation of hydrogen-rich water (HRW), which can then be applied to the foliage or roots systems of the plants. However, the molecular action of H2 remains elusive. It has been suggested that the presence of H2 may act as an antioxidant or on the antioxidant capacity of cells, perhaps through the scavenging of hydroxyl radicals. H2 may act through influencing heme oxygenase activity or through the interaction with reactive nitrogen species. However, controversy exists around all the mechanisms suggested. Here, the downstream mechanisms in which H2 may be involved are critically reviewed, with a particular emphasis on the H2 mitigation of stress responses. Hopefully, this review will provide insight that may inform future research in this area.

Nitric oxide, other reactive signalling compounds, redox, and reductive stress

Nitric oxide (NO) and other reactive nitrogen species (RNS) are key signalling molecules in plants, but they do not work in isolation. NO is produced in cells, often increased in response to stress conditions, but many other reactive compounds used in signalling are generated and accumulate spatially and temporally together. This includes the reactive oxygen species (ROS), such as hydrogen peroxide (H2O2), and hydrogen sulfide (H2S). Here, the interactions with such other reactive molecules is briefly reviewed. Furthermore, along with ROS and H2S, NO will potentially contribute to the overall intracellular redox of the cell. However, RNS will exist in redox couples and therefore the influence of the cellular redox on such couples will be explored. In discussions of the aberrations in intracellular redox it is usually oxidation, so-called oxidative stress, which is discussed. Here, we consider the notion of reductive stress and how this may influence the signalling which may be mediated by NO. By getting a more holistic view of NO biology, the influence on cell activity of NO and other RNS can be more fully understood, and may lead to the elucidation of methods for NO-based manipulation of plant physiology, leading to better stress responses and improved crops in the future.

Hydrogenases and the Role of Molecular Hydrogen in Plants

Molecular hydrogen (H2) has been suggested to be a beneficial treatment for a range of species, from humans to plants. Hydrogenases catalyze the reversible oxidation of H2, and are found in many organisms, including plants. One of the cellular effects of H2 is the selective removal of reactive oxygen species (ROS) and reactive nitrogen species (RNS), specifically hydroxyl radicals and peroxynitrite. Therefore, the function of hydrogenases and the action of H2 needs to be reviewed in the context of the signalling roles of a range of redox active compounds. Enzymes can be controlled by the covalent modification of thiol groups, and although motifs targeted by nitric oxide (NO) can be predicted in hydrogenases sequences it is likely that the metal prosthetic groups are the target of inhibition. Here, a selection of hydrogenases, and the possibility of their control by molecules involved in redox signalling are investigated using a bioinformatics approach. Methods of treating plants with H2 along with the role of H2 in plants is also briefly reviewed. It is clear that studies report significant effects of H2 on plants, improving growth and stress responses, and therefore future work needs to focus on the molecular mechanisms involved.

Hydrogen-rich water promotes elongation of hypocotyls and roots in plants through mediating the level of endogenous gibberellin and auxin

The aim of this study was to investigate effects of the hydrogen-rich water (HRW) on the vegetable growth, and explore the possibility of applying HRW for protected cultivation of vegetables. Results showed that compared with control, HRW treatment significantly promoted fresh weight, hypocotyl length and root length of mung bean seedlings. The strongest stimulation was observed for 480 μM H2 (60% of saturated HRW concentration) treatment. This concentration was used in the following experiments. The enhanced cell elongation was correlated with the changes in the level of endogenous phytohormones. In the dark-grown hypocotyls and roots of mung bean seedlings, HRW significantly increased the content of IAA and GA3. Addition of GA3 enhanced the hypocotyl elongation only. uniconazole, an inhibitor of GA3 biosynthesis, inhibited HRW-induced hypocotyl elongation, but did not affect root elongation. Exogenous application of IAA promoted HRW effects on elongation of both the hypocotyl and the root, while the IAA biosynthesis inhibitor TIBA negated the above affects. The general nature of HRW-induced growth-promoting effects was further confirmed in experiments involving cucumber and radish seedlings. Taken together, HRW treatment promoted growth of seedlings, by stimulating elongation of hypocotyl and root cells, via HRW-induced increase in GA and IAA content in the hypocotyl and the root respectively.

Calcium-Dependent Hydrogen Peroxide Mediates Hydrogen-Rich Water-Reduced Cadmium Uptake in Plant Roots

Hydrogen gas (H₂) has a possible signaling role in many developmental and adaptive plant responses, including mitigating the harmful effects of cadmium (Cd) uptake from soil. We used electrophysiological and molecular approaches to understand how H₂ ameliorates Cd toxicity in pak choi (Brassica campestris ssp. chinensis). Exposure of pak choi roots to Cd resulted in a rapid increase in the intracellular H₂ production. Exogenous application of hydrogen-rich water (HRW) resulted in a Cd-tolerant phenotype, with reduced net Cd uptake and accumulation. We showed that this is dependent upon the transport of calcium ions (Ca²⁺) across the plasma membrane and apoplastic generation of hydrogen peroxide (H₂O₂) by respiratory burst oxidase homolog (BcRbohD). The reduction in root Cd uptake was associated with the application of exogenous HRW or H₂O₂ This reduction was abolished in the iron-regulated transporter1 (Atirt1) mutant of Arabidopsis (Arabidopsis thaliana), and pak choi pretreated with HRW showed decreased BcIRT1 transcript levels. Roots exposed to HRW had rapid Ca²⁺ influx, and Cd-induced Ca²⁺ leakage was alleviated. Two Ca²⁺ channel blockers, gadolinium ion (Gd³⁺) and lanthanum ion (La³⁺), eliminated the HRW-induced increase in BcRbohD expression, H₂O₂ production, and Cd²⁺ influx inhibition. Collectively, our results suggest that the Cd-protective effect of H₂ in plants may be explained by its control of the plasma membrane-based NADPH oxidase encoded by RbohD, which operates upstream of IRT1 and regulates root Cd uptake at both the transcriptional and functional levels. These findings provide a mechanistic explanation for the alleviatory role of H₂ in Cd accumulation and toxicity in plants.

The role and proteomic analysis of ethylene in hydrogen gas-induced adventitious rooting development in cucumber (Cucumis sativus L.) explants

Previous studies have shown that both hydrogen gas (H₂) and ethylene (ETH) play positive roles in plant adventitious rooting. However, the relationship between H₂and ETH during this process has not been explored and remains insufficiently understood. In this study, cucumber (Cucumis sativus L.) was used to explore the proteomic changes in ETH-H₂-induced rooting. Our results show that hydrogen-rich water (HRW) and ethylene-releasing compound (ethephon) at proper concentrations promote adventitious rooting, with maximal biological responses occurring at 50% HRW or 0.5 µM ethephon. ETH inhibitors aminoethoxyvinylglycine (AVG) and AgNO₃ cause partial inhibition of adventitious rooting induced by H₂, suggesting that ETH might be involved in H₂-induced adventitious rooting. According to two-dimensional electrophoresis (2-DE) and mass spectrometric analyses, compared with the control, 9 proteins were up-regulated while 15 proteins were down-regulated in HRW treatment; four proteins were up-regulated while 10 proteins were down-regulated in ethephon treatment; and one protein was up-regulated while nine proteins were down-regulated in HRW+AVG treatment. Six of these differentially accumulated proteins were further analyzed, including photosynthesis -related proteins (ribulose-1,5-bisphosphate carall boxylase smsubunit (Rubisco), sedoheptulose-1,7-bisphosphatase (SBPase), oxygen-evolving enhancer protein (OEE1)), amino and metabolism-related protein (threonine dehydratase (TDH)), stress response-related protein (cytosolic ascorbate peroxidase (CAPX)), and folding, modification and degradation-related protein (protein disulfide-isomerase (PDI)). Moreover, the results of real-time PCR about the mRNA levels of these genes in various treatments were consistent with the 2-DE results. Therefore, ETH may be the downstream signaling molecule during H₂- induced adventitious rooting and proteins Rubisco, SBPase, OEE1, TDH, CAPX and PDI may play important roles during the process.

Methods for the Addition of Redox Compounds

Often in redox biology experiments there is a need to add compounds which impinge on the redox of the cellular environment cell. Such compounds may include reactive oxygen species (ROS), such as hydrogen peroxide (H₂O₂), reactive nitrogen species such as nitric oxide (NO), hydrogen sulfide (H₂S), or even hydrogen gas (H₂). It is not always easy or obvious how such compounds should be used. Gases may be supplied and used in the gaseous form, but this is often not convenient. Alternative methods may involve donor molecules that release into solution the relevant compound, but the actual compound released needs to be considered, along with the kinetics of that release and the by-products that might be remain. Therefore, the method of delivery of redox active compounds needs to have careful consideration before more complex experiments are undertaken. This chapter covers some of the more common methods employed and discusses some of the pros and cons of such methods.

Acid-Responsive H2 -Releasing 2D MgB2 Nanosheet for Therapeutic Synergy and Side Effect Attenuation of Gastric Cancer Chemotherapy

The hydrogen molecule is recognized as a high potential to attenuate toxic side effects of chemotherapy and also enhance chemotherapeutic efficacy, and the development of a novel hydrogen-generating prodrug for facile, safe, and efficient hydrogen delivery is vitally important for combined hydrogenochemotherapy but is still challenging. Here, targeting gastric cancer, a 2D magnesium boride nanosheet (MBN) is synthesized as a new type of acid-responsive hydrogen-releasing prodrug by an ultrasound-assisted chemical etching route, which is used to realize hydrogenochemotherapy by combination of facile oral administration of polyvinylpyrrolidone (PVP)-encapsulating MBN (MBN@PVP) pills with routine intravenous injection of doxorubicin (DOX). The MBN@PVP pill has high stability in normal tissues/blood environments as well as high gastric acid-responsiveness with sustained release behavior, which matches well with its metabolism rate in the stomach in great favor of continuous and long-term hydrogen administration. Hydrogenochemotherapy with DOX+MBN@PVP has remarkably prolonged the survival time of gastric tumor-bearing mice by reducing the toxic side effects of chemotherapy. The mechanism for therapeutic synergy and side effect attenuation of hydrogenochemotherapy is discovered to be derived from the selectivity of hydrogen molecules in inhibiting aerobic respiration of gastric cells but activating aerobic respiration of normal cells including marrow mesenchymal stem cells and cardiac, hepatic, and splenic cells.

Nitric Oxide: Its Generation and Interactions with Other Reactive Signaling Compounds

Nitric oxide (NO) is an immensely important signaling molecule in animals and plants. It is involved in plant reproduction, development, key physiological responses such as stomatal closure, and cell death. One of the controversies of NO metabolism in plants is the identification of enzymatic sources. Although there is little doubt that nitrate reductase (NR) is involved, the identification of a nitric oxide synthase (NOS)-like enzyme remains elusive, and it is becoming increasingly clear that such a protein does not exist in higher plants, even though homologues have been found in algae. Downstream from its production, NO can have several potential actions, but none of these will be in isolation from other reactive signaling molecules which have similar chemistry to NO. Therefore, NO metabolism will take place in an environment containing reactive oxygen species (ROS), hydrogen sulfide (H₂S), glutathione, other antioxidants and within a reducing redox state. Direct reactions with NO are likely to produce new signaling molecules such as peroxynitrite and nitrosothiols, and it is probable that chemical competitions will exist which will determine the ultimate end result of signaling responses. How NO is generated in plants cells and how NO fits into this complex cellular environment needs to be understood.

Azolla pinnata, Aspergillus terreus and Eisenia fetida for enhancing agronomic value of paddy straw

In the present study rice straw (R, control) was mixed with Cowdung (C), Azolla (A) and cellulolytic fungus Aspergillus terreus (F) in different combinations viz. RC, RA, RF, RCF, RCA, RFA and RCFA and subjected to aerobic composting (Acom) and vermicomposting (Vcom - with Eisenia fetida). It was found that addition of azolla and cattledung to two parts straw(RCA-666: 314:20 g) caused fastest degradation (105 days), gave maximum population buildup of E. fetida (cocoons, hatchlings and worm biomass), highest decline in pH, EC, TOC and C/N ratio and maximum increase over control in N(17.72%), P(44.64%), K(43.17%), H (7.93%), S (14.85%), Ca(10.16%), Na(145.97%), Fe(68.56%), Zn(12.10%) and Cu(32.24%). Rice straw (R) took longest time for degradation i.e. 120 and 140 days and had lowest content of nutrients in Vcom as well as Acom group. RCFA was also converted into Vcom at the same time but other parameters were less than RCA except for highest content of B (19.87%), Mg(21.27%) and Mn (5.58%). Bioconversion of three parts straw (RCA-735:245:20 g) was also faster (110 days) with vermicomposting than all the mixtures of Acom group (130–140 days) but nutrient content was slightly less than RCA with 2 parts straw. The results show that azolla reduces dependence on cattledung for recycling the carbon rich rice straw and enhances its agronomic value.

Roles of hydrogen gas in plants: a review

Hydrogen gas (H2) was first identified as a unique molecular messenger in animals. Since H2 was reported as a novel antioxidant, it has been proven effective in treating many diseases. However, the studies concerning H2 in plants are just beginning to emerge. Here, two paths of H2 production in plants have been reported, namely, hydrogenase and nitrogenase. H2 has positive effects on seed germination, seedling growth, adventitious rooting, root elongation, harvest freshness, stomatal closure and anthocyanin synthesis. H2 also can enhance plant symbiotic stress resistance commonly through the enhancement of antioxidant defence system. Moreover, H2 shows cross talk with nitric oxide, carbon monoxide and other signalling molecules (for example, abscisic acid, ethylene and jasmonate acid). H2 can regulate the expression of responsive genes under abiotic stress and during adventitious roots formation and anthocyanin biosynthesis. Future work will need to focus on the molecular mechanism of H2 and its crosstalk with other signalling molecules in plants. With its promising application in agriculture, hydrogen agriculture will be welcomed in the near future.

Hydrogen-rich water regulates effects of ROS balance on morphology, growth and secondary metabolism via glutathione peroxidase in Ganoderma lucidum

Ganoderma lucidum is one of the most important medicinal fungi, but the lack of basic study on the fungus has hindered the further development of its value. To investigate the roles of the redox system in G. lucidum, acetic acid (HAc) was applied as a reactive oxygen species (ROS) stress inducer, and hydrogen-rich water (HRW) was used to relieve the ROS stress in this study. Our results demonstrate that the treatment of 5% HRW significantly decreased the ROS content, maintained biomass and polar growth morphology of mycelium, and decreased secondary metabolism under HAc-induced oxidative stress. Furthermore, the roles of HRW were largely dependent on restoring the glutathione system under HAc stress in G. lucidum. To provide further evidence, we used two glutathione peroxidase (GPX)-defective strains, the gpxi strain, the mercaptosuccinic acid (MS, a GPX inhibitor)-treated wide-type (WT) strain, and gpx overexpression strains for further research. The results show that HRW was unable to relieve the HAc-induced ROS overproduction, decreased biomass, mycelium morphology change and increased secondary metabolism biosynthesis in the absence of GPX function. The gpx overexpression strains exhibited resistance to HAc-induced oxidative stress. Thus, we propose that HRW regulates morphology, growth and secondary metabolism via glutathione peroxidase under HAc stress in the fungus G. lucidum. Furthermore, our research also provides a method to study the ROS system in other fungi.