Novel applications of exogenous melatonin on cold stress mitigation in postharvest cucumbers

This study aims to investigate the effect of exogenous melatonin (EMT) on cold injury (CI) and the physiological indicators of cucumbers under refrigerated conditions (2 °C). After being treated with different concentrations (0, 50, 100, and 500 μmol L −1 ) of EMT, the postharvest cucumbers were stored at 2 °C. During storage, cucumbers were collected at designed intervals (0, 3, 6, 9, and 12 d) and rewarmed for 2 days at room temperature (20–22 °C). The impacts of EMT were evaluated by periodically monitoring the changes in chilling injury index and physiological properties including weight loss rate, respiratory intensity, tissue electrolyte leakage, malondialdehyde (MDA) content, vitamin C, soluble protein content, free proline, and reactive oxygen species. Compared with the control, the treatment of EMT at the concentration of 100 μmol L −1 could significantly improve the contents of soluble protein, vitamin C, and free proline content and inhibit the rise of chilling injure index, weight loss rate, respiration intensity, tissue electrolyte leakage, MDA content, and reactive oxygen species. In addition, the results indicated that EMT treatment at a specific level (100 μmol L −1 ) had an effective impact on alleviating the CI of cucumbers during storage at low temperatures.