Nitric Oxide and Hydrogen Sulfide Crosstalk in Plants: Redox Regulation, Stress Adaptation, and Emerging Applications

Nitric oxide (NO) and hydrogen sulfide (H2S) are key gasotransmitters that regulate multiple aspects of plant growth, development, and stress adaptation. Although their individual signaling pathways have been extensively investigated, the integrated mechanisms underlying NO–H2S crosstalk and its potential agronomic applications remain unclear. This review summarizes current advances in understanding the biochemical interplay between NO and H2S in plants, emphasizing their synergistic roles in redox regulation, antioxidant activation, ion homeostasis, and photosynthetic protection under abiotic and biotic stresses. Special attention has been given to recent progress in nanotechnology-based delivery systems that enable the controlled, localized, and sustained release of gasotransmitters, thereby improving bioavailability and minimizing environmental losses. Studies on foliar, seed, and nutrient-solution applications have demonstrated that combined NO/H2S treatments increase stress tolerance by activating the ascorbate–glutathione (AsA–GSH) cycle, reducing the expression of oxidative markers such as hydrogen peroxide (H2O2) and malondialdehyde (MDA), and improving both short-term (Fv/Fm, antioxidant enzyme activity) and long-term (biomass, SPAD index, yield) physiological outcomes. By integrating molecular insights with applied strategies, this review outlines the emerging potential of NO–H2S signaling as a sustainable tool for crop management in the context of climate change and food security.