Effects of Melatonin on Physiological Characteristics of Trichosanthes kirilowii Seedlings Under Drought Stress

Melatonin (MT), a potent antioxidant, can mitigate abiotic stress. The objective of this study was to determine if foliar spraying of MT can alleviate the stress of Trichosanthes kirilowii seedlings under drought conditions. The results showed that drought stress significantly inhibited the growth of T. kirilowii seedlings, whereas exogenous MT alleviated this inhibition. Compared with the treatment with drought stress alone, the addition of MT significantly increased the stem length, net photosynthetic rate, chlorophyll content, maximum photochemical efficiency, and relative leaf water content of T. kirilowii seedlings after 20 days of drought stress. Under drought stress, the addition of MT significantly reduced the levels of malondialdehyde (MDA) and hydrogen peroxide (H2O2), and reduced electrolyte leakage (EL) in the leaves of T. kirilowii seedlings. Compared with the control group, the antioxidant enzyme activity was significantly enhanced under drought stress, and the contents of soluble sugars (SSs) and proline (Pro) increased significantly. The antioxidant enzyme activity was strongest in the group treated with MT, and the SS and Pro contents were the highest in this group. The results indicate that the addition of MT can maintain the relative water content (RWC) of the leaves of T. kirilowii seedlings under drought stress, significantly enhance antioxidant capacity, reduce drought-induced damage, maintain the stability of the photosynthetic system, and promote the growth of T. kirilowii seedlings.