Nitric Oxide Biology in Horticultural Commodities: Integrative Roles in Ripening, Senescence, and Storage Longevity

Postharvest senescence is a highly coordinated physiological process that drives the progressive decline in fruit quality, ultimately limiting shelf life, marketability, and commercial value. It is characterized by extensive metabolic reprogramming, redox imbalance, membrane deterioration, cell wall remodeling, and hormonal regulation that collectively accelerate ripening and tissue senescence. Among the signaling molecules involved in these processes, nitric oxide (NO) has emerged as a pivotal gaseous signaling molecule that coordinates multiple regulatory networks governing postharvest fruit physiology. This review provides a comprehensive and critical synthesis of recent advances in NO biology, highlighting the roles of endogenous NO biosynthesis, homeostasis, and signaling, together with exogenous NO application through gaseous NO and NO donors, including sodium nitroprusside and S-nitrosoglutathione. Accumulating evidence demonstrates that NO effectively delays fruit senescence by modulating ethylene biosynthesis and signaling, strengthening antioxidant and defense systems, preserving membrane integrity, maintaining cellular redox homeostasis, and enhancing tolerance to chilling injury and pathogen infection. Particular emphasis is placed on the intricate crosstalk between NO and phytohormones, including ethylene, abscisic acid, salicylic acid, melatonin, auxin, cytokinins, and gibberellins, highlighting its central role in coordinating ripening, stress adaptation, and quality maintenance. Furthermore, the molecular mechanisms underlying NO-mediated regulation of energy metabolism, cell wall remodeling, and post-translational protein modifications, particularly S‑nitrosylation, are discussed. Finally, current challenges associated with NO-based postharvest technologies, including application strategies, dosage optimization, safety considerations, and commercial scalability, are critically evaluated, and future research priorities are proposed to facilitate the sustainable implementation of NO for postharvest management of horticultural commodities.