Nitric oxide and phytohormones molecular crosstalk regulating fruit quality and postharvest management.

Nitric oxide (NO) has emerged as a pivotal signaling molecule regulating postharvest fruit physiology, functioning far beyond its early recognition as a simple reactive nitrogen species. Increasing evidence highlights NO as a central signaling hub that integrates redox homeostasis, hormone signaling, transcriptional control, and post-translational regulation to modulate fruit ripening, senescence, and stress responses, and enhance disease resistance during postharvest storage. At the molecular level, NO participates in complex crosstalk with reactive oxygen species, reactive sulfur species, and plant growth regulators, including ethylene, abscisic acid, jasmonates, salicylic acid, melatonin, and hydrogen sulfide. These interactions fine-tune cellular signaling networks that govern antioxidant defense, energy metabolism, cell wall remodeling, and pathogen resistance. Recent advances have expanded the NO signaling landscape through mechanisms such as S-nitrosylation and the formation of N-nitrosomelatonin, revealing additional layers of post-translational and metabolic regulation relevant to postharvest quality maintenance. Moreover, NO-mediated transcriptional reprogramming and redox-based modifications of key regulatory proteins provide mechanistic insights into how NO delays senescence, alleviates chilling injury, and preserves sensory and nutritional attributes of harvested fruits. Exogenous NO applications, delivered as gas, donors, or emerging nano-formulations, further demonstrate practical potential for extending shelf life and enhancing stress tolerance, although challenges related to dosage optimization, delivery systems, and safety remain. This review integrates current knowledge on NO biosynthesis, signaling pathways, and molecular crosstalk in postharvest fruit biology, with an emphasis on systems-level integration of NO-driven regulatory networks. By bridging fundamental mechanisms with applied postharvest strategies, future research directions aimed at translating NO signaling insights into reliable and sustainable technologies for postharvest quality management.