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Hydrogen peroxide (H2O2) is a compound involved in some mammalian reactions and processes. It modulates and signals the redox metabolism of cells by acting as a messenger together with hydrogen sulfide (H2S) and the nitric oxide radical (•NO), activating specific oxidations that determine the metabolic response. The reaction triggered determines cell survival or apoptosis, depending on which downstream metabolic pathways are activated. There are several ways to produce H2O2 in cells, and cellular systems tightly control its concentration. At the cellular level, the accumulation of hydrogen peroxide can trigger inflammation and even apoptosis, and when its concentration in the blood reaches toxic levels, it can lead to bioenergetic failure. This review summarizes existing research from a chemical perspective on the role of H2O2 in various enzymatic pathways and how this biochemistry leads to physiological or pathological responses.

Photocatalytic H2O2 production based on graphitic carbon nitride (g-C3N4) materials has been attracting increasing attention. However, it is difficult to reveal the inner relationships among the structure, properties and performance of a g-C3N4-based photocatalyst by simply summarizing preparation methods, properties and performances in previous works. In this review, the three most important issues for improving H2O2 generation based on the band diagram and physicochemical properties of pristine g-C3N4 are proposed. Improvement of the charge separation, promotion of the light absorption and introduction of active sites for 2e– oxygen reduction reaction to suppress side reactions are the most three attractive strategies for enhancing the activities. Following discussion of these strategies, representative functionalization methods are summarized on the basis of the most desired properties for improving the photocatalytic activities for H2O2 production. Other influence factors for improving H2O2 production such as addition of electron donors and adjustment of pH value of the solution are also discussed. Future challenges for photocatalytic H2O2 based on g-C3N4 materials are also summarized to provide future directions in this field.

The two‐electron oxygen reduction reaction (2e‐ORR) for the sustainable synthesis of hydrogen peroxide (H2O2) has demonstrated considerable potential for local production of this environmentally friendly chemical oxidant on small, medium, and large scales. This method offers a promising alternative to the energy‐intensive anthraquinone approach, placing a primary emphasis on the development of efficient electrocatalysts. Improving the efficiency of electrocatalysts and uncovering their catalytic mechanisms are essential steps in achieving high 2e‐ORR activity, selectivity, and stability. This comprehensive review summarizes recent advancements in electrocatalysts for in‐situ H2O2 production, providing a detailed overview of the field. In particular, the review delves into the design, fabrication, and investigation of catalytic active sites contributing to H2O2 selectivity. Additionally, it highlights a range of electrocatalysts including pure metals and alloys, transition metal compounds, single‐atom catalysts, and carbon‐based catalysts for the 2e‐ORR pathway. Finally, the review addresses significant challenges and opportunities for efficient H2O2 electrosynthesis, as well as potential future research directions. Electrochemical synthesis of hydrogen peroxide (H2O2) through a two‐electron oxygen reduction reaction (2e‐ORR) has emerged as an appealing process for onsite production of this chemically valuable oxidant. This Review studies the experimental efforts in understanding the challenges in catalysis for electrochemical synthesis of H2O2 as well as providing design principles for more efficient catalyst materials.

This study investigated the adsorption behaviour of fluoride ions from fluorine-containing solutions at a defined concentration using Ce 3+ and hydrogen peroxide. The influences of adsorption time, solution pH, adsorbent dosage, initial fluoride ion concentration, and coexisting ions on adsorption efficiency were systematically assessed. The results demonstrated that the adsorbent exhibited high adsorption performance at ambient temperature, achieving a saturated adsorption capacity between 114.47 and 118.43 mg/g. The synergistic action of Ce 3 ⁺ and H₂O₂ provided dual adsorption–precipitation pathways, in which thermodynamically stable CeF₃ formed through ion exchange while surface Ce 4 ⁺–OH sites produced by oxidation further captured fluoride via ligand exchange. The adsorption kinetics conform to the pseudo-second-order model, and the equilibrium data fit both the Langmuir and Freundlich isotherm models. Sulphate ions promoted fluoride removal, whereas chloride and nitrate ions had little effect; however, bicarbonate and carbonate ions strongly inhibited this process. These findings demonstrate that the Ce 3 ⁺/H₂O₂ system offers a robust, cost-effective, and regenerable approach with good tolerance to coexisting anions. Overall, this work not only elucidates the dual mechanism of Ce-based defluoridation but also provides a practical strategy for developing rare-earth-based adsorbents for sustainable and high-efficiency water purification.

Hydrogen peroxide (H₂O₂) is produced, via superoxide and superoxide dismutase, by electron transport in chloroplasts and mitochondria, plasma membrane NADPH oxidases, peroxisomal oxidases, type III peroxidases and other apoplastic oxidases. Intracellular transport is facilitated by aquaporins and H₂O₂ is removed by catalase, peroxiredoxin, glutathione peroxidase-like enzymes and ascorbate peroxidase, all of which have cell compartment-specific isoforms. Apoplastic H₂O₂ influences cell expansion, development and defence by its involvement in type III peroxidase-mediated polymer cross-linking, lignification and, possibly, cell expansion via H₂O₂-derived hydroxyl radicals. Excess H₂O₂ triggers chloroplast and peroxisome autophagy and programmed cell death. The role of H₂O₂ in signalling, for example during acclimation to stress and pathogen defence, has received much attention, but the signal transduction mechanisms are poorly defined. H₂O₂ oxidizes specific cysteine residues of target proteins to the sulfenic acid form and, similar to other organisms, this modification could initiate thiol-based redox relays and modify target enzymes, receptor kinases and transcription factors. Quantification of the sources and sinks of H₂O₂ is being improved by the spatial and temporal resolution of genetically encoded H₂O₂ sensors, such as HyPer and roGFP2-Orp1. These H₂O₂ sensors, combined with the detection of specific proteins modified by H₂O₂, will allow a deeper understanding of its signalling roles.

miRNAs contribute to plant resistance against pathogens. Previously, we found that the function of miR398b in immunity in rice differs from that in Arabidopsis. However, the underlying mechanisms are unclear. In this study, we characterized the mutants of miR398b target genes and demonstrated that multiple superoxide dismutase genes contribute to miR398b-regulated rice immunity against the blast fungus Magnaporthe oryzae. Out of the four target genes of miR398b, mutations in Cu/Zn-Superoxidase Dismutase1 (CSD1), CSD2 and Os11g09780 (Superoxide DismutaseX, SODX) led to enhanced resistance to M. oryzae and increased hydrogen peroxide (H₂O₂) accumulation. By contrast, mutations in Copper Chaperone for Superoxide Dismutase (CCSD) resulted in enhanced susceptibility. Biochemical studies revealed that csd1, csd2 and sodx displayed altered expression of CSDs and other superoxide dismutase (SOD) family members, leading to increased total SOD enzyme activity that positively contributed to higher H₂O₂ production. By contrast, the ccsd mutant showed CSD protein deletion, resulting in decreased CSD and total SOD enzyme activity. Our results demonstrate the roles of different SODs in miR398b-regulated resistance to rice blast disease, and uncover an integrative regulatory network in which miR398b boosts total SOD activity to upregulate H₂O₂ concentration and thereby improve disease resistance.

Global climate change and associated adverse abiotic stress conditions, such as drought, salinity, heavy metals, waterlogging, extreme temperatures, oxygen deprivation, etc., greatly influence plant growth and development, ultimately affecting crop yield and quality, as well as agricultural sustainability in general. Plant cells produce oxygen radicals and their derivatives, so-called reactive oxygen species (ROS), during various processes associated with abiotic stress. Moreover, the generation of ROS is a fundamental process in higher plants and employs to transmit cellular signaling information in response to the changing environmental conditions. One of the most crucial consequences of abiotic stress is the disturbance of the equilibrium between the generation of ROS and antioxidant defense systems triggering the excessive accumulation of ROS and inducing oxidative stress in plants. Notably, the equilibrium between the detoxification and generation of ROS is maintained by both enzymatic and nonenzymatic antioxidant defense systems under harsh environmental stresses. Although this field of research has attracted massive interest, it largely remains unexplored, and our understanding of ROS signaling remains poorly understood. In this review, we have documented the recent advancement illustrating the harmful effects of ROS, antioxidant defense system involved in ROS detoxification under different abiotic stresses, and molecular cross-talk with other important signal molecules such as reactive nitrogen, sulfur, and carbonyl species. In addition, state-of-the-art molecular approaches of ROS-mediated improvement in plant antioxidant defense during the acclimation process against abiotic stresses have also been discussed.

• Drought is one of the primary abiotic stresses, seriously implicating plant growth and productivity. Stomata play a crucial role in regulating drought tolerance. However, the molecular mechanism on stomatal movement-mediated drought tolerance remains unclear. • Using genetic, molecular and biochemical techniques, we identified that the PdGNC directly activating the promoter of PdHXK1 by binding the GATC element, a hexokinase (HXK) synthesis key gene. • Here, PdGNC, a member of the GATA transcription factor family, was greatly induced by abscisic acid and dehydration. Overexpressing PdGNC in poplar (Populus clone 717) resulted in reduced stomatal aperture with greater water-use efficiency and increased water deficit tolerance. By contrast, CRISPR/Cas9-mediated poplar mutant gnc exhibited increased stomatal aperture and water loss with reducing drought resistance. PdGNC activates PdHXK1 (a hexokinase synthesis key gene), resulting in a remarkable increase in hexokinase activity in poplars subjected to water deficit. Furthermore, hexokinase promoted nitric oxide (NO) and hydrogen peroxide (H₂O₂) production in guard cells, which ultimately reduced stomatal aperture and increased drought resistance. • Together, PdGNC confers drought stress tolerance by reducing stomatal aperture caused by NO and H₂O₂ production via the direct regulation of PdHXK1 expression in poplars.

Guard cells can integrate and process multiple complex signals from the environment and respond by opening and closing stomata in order to adapt to the environmental signal. Over the past several years, considerable research progress has been made in our understanding of the role of reactive oxygen species (ROS) as essential signal molecules that mediate abscisic acid (ABA)-induced stomatal closure. In this review, we discuss hydrogen peroxide (H₂O₂) generation and signalling, H₂O₂-induced gene expression, crosstalk and the specificity between ABA and H₂O₂ signalling, and the cellular mechanism for ROS sensing in guard cells. This review focuses especially on the points of connection between ABA and H₂O₂ signalling in guard cells. The fundamental progress in understanding the role of ABA and ROS in guard cells will continue to provide a rational basis for biotechnological improvements in the development of drought-tolerant crop plants with improved water-use efficiency.

Hydrogen peroxide (H₂O₂) is reported to inhibit biotrophic but benefit necrotrophic pathogens. Infection by necrotrophs can result in a massive accumulation of H₂O₂ in hosts. Little is known of how pathogens with both growth types are affected (hemibiotrophs). The hemibiotroph, Septoria tritici, infecting wheat (Triticum aestivum) is inhibited by H₂O₂ during the biotrophic phase, but a large H₂O₂ accumulation occurs in the host during reproduction. Here, we infiltrated catalase, H₂O₂ or water into wheat during the biotrophic or the necrotrophic phase of S. tritici and studied the effect of infection on host physiology to get an understanding of the survival strategy of the pathogen. H₂O₂ removal by catalase at both early and late stages made plants more susceptible, whereas H₂O₂ made them more resistant. H₂O₂ is harmful to S. tritici throughout its life cycle, but it can be tolerated. The late accumulation of H₂O₂ is unlikely to result from down-regulation of photosynthesis, but probably originates from damage to the peroxisomes during the general tissue collapse, which is accompanied by release of soluble sugars in a susceptible cultivar.