Melatonin alleviates chilling injury and maintains postharvest quality by enhancing antioxidant capacity and inhibiting cell wall degradation in cold-stored eggplant fruit

Melatonin improves the chilling tolerance and quality of postharvest fruit. In this study, we investigated the effect of melatonin on postharvest quality in cold-stored eggplant fruit for 30 d at 5 °C. Melatonin at 100 μmol L−1 was notably effective in decreasing chilling injury (CI) incidence, CI index, weight loss, and in delaying the decrease of lightness, thereby maintaining better postharvest quality of the fruit. Exogenous melatonin inhibited increases in hydrogen peroxide (H2O2), malondialdehyde (MDA), and relative electro-conductivity in the pericarp and pulp, while maintaining higher levels of superoxide dismutase (SOD), catalase (CAT), total polyamines, anthocyanins, and melatonin, as well as the expressions of SOD, CAT1/2, and other genes involved in polyamine biosynthesis (ADC, ODC), melatonin biosynthesis (TDC1, T5H, SNAT1, ASMT, COMT), anthocyanin biosynthesis (PAL, CHS1, CHI, F3H, F3′H, DFR, ANS, 3GT), and cold regulation (COR1, CBF, ZAT2/6/12), thereby conferring the higher chilling tolerance. Melatonin delayed fruit softening and senescence by inhibiting the activities and gene expressions of cell wall degradation enzymes (PME, PG, Cel) and expressions of senescence-associated genes (IAA17, SAG12, SEN4). Overall, these results indicate that melatonin alleviates chilling injury and maintains postharvest quality by enhancing antioxidant capacity and inhibiting cell wall degradation in cold-stored eggplant fruit, which provides a theoretical foundation for extending fruit shelf-life of eggplant during cold storage.