Abstract: Taking the seedlings of cucumber cultivar ‘Jinchun 4’ as test material, this paper studied the effects of foliar application of exogenous melatonin (MT) on the active oxygen metabolism of the seedlings under high temperature stress. Under the stress, the exogenous MT could significantly decrease the leaf superoxide radical (O₂^-.) production rate, hydrogen peroxide (H₂O₂) content, cell membrane permeability (electrolyte leakage), and malonaldehyde (MDA) content, but increase the activities of superoxide radical (SOD), peroxidase (POD), and catalase (CAT), and the contents of ascorbic acid (AsA), glutathione (GSH), and soluble proteins, illustrating that pretreatment with MT could inhibit the reactive oxygen species (ROS) production, raise the anti-oxidative enzyme activities and antioxidant contents, and decrease the membrane lipid peroxidation and electrolyte leakage to protect the integrity of lipid membranes, being able to alleviate the damage of high temperature stress to the seedlings.

Key words: melatonin, cucumber (Cucumis sativus), high temperature stress, active oxygen metabolism, Tibetan Plateau, The Lhasa River basin, farmland, soil moisture, influence factors, ecological redundancy analysis (RDA).