Application of Melatonin-Enhanced Tolerance to High-Temperature Stress in Cherry Radish (Raphanus sativus L. var. radculus pers)

The growth and development of cold-season plants are susceptible to high temperature. Melatonin is a plant growth regulator with potential to improve plant tolerance to biological and abiotic stresses. In our study, cherry radish ( Raphanus sativus L. var. radculus pers ) was cultured at a high temperature (35 °C/30 °C day/night) and different concentrations (0, 11.6, 17.4, 29.0, 34.8 and 67.0 mg L −1 ) of melatonin were applied to these high-temperature stressed plants to its effects on biomass, quality, antioxidant enzyme activity, chlorophyll and endogenous hormone contents. The plants were grown under normal temperature (25 °C/20 °C) as control and high-temperature condition as HT-stress treatment. The results revealed that under high temperature with 29.0 mg L −1 melatonin treatment, cherry radish biomass was significantly increased by 12.9%, and the soluble protein and soluble solid were increased by 18.7 and 9.2%, respectively. The activity of antioxidant enzyme, ascorbate peroxidase and peroxidase were increased by 43.7 and 45.5%, respectively. The chlorophyll a and carotenoid contents were increased by 7.4 and 20.0% compared with the control at 27 days. The auxin and abscisic acid contents were significantly increased by 28.5 and 6.7% compared with HT at 9 days. Thus, application of optimal rate of melatonin had a positive effect on cherry radish growth under high-temperature stress.