Melatonin-mediated redox regulation in fruits: modulating oxidative signaling for quality preservation

Melatonin is a key regulator of postharvest redox homeostasis, enhancing antioxidant defenses and coordinating ROS signaling. Its application effectively delays senescence, preserves fruit quality, and offers a sustainable strategy for improving postharvest storability. Postharvest deterioration of fruits and vegetables represents a major challenge to quality retention, shelf life, and commercial profitability, largely due to oxidative stress and disruption of reactive oxygen species (ROS) homeostasis. During ripening, cold storage, mechanical injury, and pathogen infection, excessive ROS accumulation including superoxide radicals and hydrogen peroxide leads to lipid peroxidation, membrane destabilization, tissue softening, enzymatic browning, and degradation of nutritional and sensory attributes. Maintaining redox balance is therefore essential for preserving postharvest quality. Melatonin has recently emerged as a pivotal regulator of postharvest redox homeostasis. Beyond its role as a potent free radical scavenger, melatonin functions as a signaling molecule that modulates antioxidant defense systems and integrates multiple stress-response pathways. It enhances the activities of key antioxidant enzymes, including superoxide dismutase, catalase, and ascorbate peroxidase, thereby limiting oxidative damage and sustaining membrane integrity. In addition, melatonin interacts with nitric oxide, hydrogen sulfide, and respiratory burst oxidase homolog (RBOH)-dependent signaling networks, coordinating ROS production and scavenging to maintain cellular equilibrium. Exogenous melatonin applications have been shown to delay senescence, preserve firmness and color, maintain bioactive compounds, and improve stress tolerance in numerous horticultural crops such as strawberry, mango, grape, and banana. Combined treatments with salicylic acid, hydrogen sulfide, resveratrol, or ozone further refine redox regulation and enhance postharvest resilience. Although variability among species and incomplete mechanistic insights remain limitations, advances in omics technologies, molecular breeding, smart packaging systems, and AI-assisted monitoring offer promising tools for precision redox management. Overall, manipulating melatonin-ROS interactions represent a sustainable strategy to extend storability and reduce postharvest losses.