Effect of Melatonin on Chilling Injury and Ripening of Postharvest Mango Fruits during Shelf Life after Refrigeration and Underlying Physiological Mechanism

We investigated the effect and underlying mechanism of postharvest treatment with 0.5 mmol/L melatonin (MT) treatment 1 h on chilling injury (CI) and ripening of ‘Guifei’ mango fruits during 4 days of shelf life at 25 ℃ after refrigeration at 4 ℃ for 28 days. The results showed that MT treatment markedly decreased CI and enhanced soluble solids content (SSC), respiration rate and ethylene production, while accelerating the decline in hue value and firmness of chilled mango fruits. Compared with the control group, MT treatment promoted the increase in the contents of water-soluble pectin (WSP) and chelate-soluble pectin (CSP) and the activities of polygalacturonase, β-galactosidase and endo-1,4-β-D-glucanase and accelerated the decrease in pectin methylesterase activity, thereby leading to cell wall degradation and fruit softening. Compared with the control group, higher activities of 1-aminocyclopropane-1-carboxylic acid synthase (ACS) and 1-aminocyclopropane-1-carboxylic acid oxidase (ACO) and the expressions of their encoding genes (MiACS and MiACO) were observed in MT-treated fruits. Moreover, MT up-regulated the expression of MiETR1, MiERS1, MiERF1, MiEIN2, MiCBF1 and MiICE1 while down-regulating the expression of MiCTR1. These results indicated that MT treatment could promote the restoration of ripening and reduce CI in mango fruits during shelf life after storage at low temperature.