Melatonin Extends the Edible Window Period of Kiwifruit by Modulating Energy Metabolism and Respiration: A Comparison with 1-Methylcyclopropene and Acetylsalicylic Acid

The narrow edible window period of kiwifruit poses significant challenges for the high-value fresh fruit industry. This study comparatively evaluated the effects of 1-methylcyclopropene (1-MCP), melatonin (MT), and acetylsalicylic acid (ASA) on “Guichang” kiwifruit by analyzing their physiology, energy metabolism, and transcriptomic profiles. The results indicated that 0.5 μL/L 1-MCP, 1.0 mmol/L MT, and 2.0 mmol/L ASA were the optimal concentrations, all of which significantly inhibited ethylene production and respiration intensity. These treatments effectively maintained fruit firmness, vitamin C content, and high energy status by preserving ATP levels and the activities of H+-ATPase and Ca2+-ATPase while suppressing the activities of CCO, SDH, 6-PGDH, and G-6-PDH. Transcriptomic analysis and RT-qPCR verification revealed that these preservatives re-programmed key respiratory pathways, including glycolysis, the TCA cycle, the pentose phosphate pathway, and oxidative phosphorylation. MT exhibited transcriptomic responses highly similar to 1-MCP (sharing 13 KEGG pathways) and resulted in the lowest decay rate among treatments, whereas 1-MCP showed the strongest maintenance of core firmness. Our findings suggested that MT exhibited promising performance across multiple quality- and energy-related parameters and may serve as a potential alternative treatment for maintaining kiwifruit quality during the edible window period. Future studies should functionally validate the identified candidate genes and evaluate the effects of MT on sensory and flavor attributes under commercial storage and distribution conditions.