Abstract
Low temperature is the most common abiotic stress factors during the eggplant cultivation in solar greenhouses. Melatonin plays important roles in plant resistance to low temperature. However, the role of melatonin in regulating chilling tolerance and extending the preharvest shelf life of eggplant fruits is still unknown. In this study, we investigated the effects of exogenous melatonin on eggplant plants and fruits in response to low temperature. Under simulated low-temperature conditions, exogenous melatonin significantly relieved the chilling symptoms of seedlings by reducing reactive oxygen species (ROS) and malondialdehyde (MDA) levels and relative leakage rates. These reductions were caused by higher superoxide dismutase (SOD) and catalase (CAT) activities and increased endogenous polyamine and melatonin levels compared with those in untreated seedlings. Notably, the expression levels of SOD, CAT1/2, and polyamine synthesis genes (ADC and ODC) were also increased by 100 μmol · L−1 melatonin, as well as those of genes involved in melatonin synthesis (TDC, T5H, SNAT, ASMT, and COMT) and cold regulation (COR1, CBFa/b, and ZAT2/6/12). To further investigate the effects of melatonin on eggplant leaves and fruits under natural low temperature conditions, 100 μmol · L−1 melatonin was sprayed on the functional leaves at three days before commodity maturation. Melatonin significantly alleviated chilling injury in the leaves and pericarp and extended the preharvest shelf life of the fruit by increasing the expression of COR1, CBF, ZAT2/6/12, and API5 and decreasing the expression of senescence-related genes (NCED1/2 and SAG12). Therefore, 100 μmol · L−1 melatonin improved chilling tolerance and fruit shelf life by upregulating ZAT2/6/12 to affect ROS- and senescence-related processes, which provides a reference for alleviating cold stress and extending the preharvest fruit shelf life in eggplant.
