Abstract: The effects of 24epibrassinolide (EBR) on the growth and ascorbateglutathione (AsA-GSH) cycle in cucumber (‘Jinchun 2’) seedling roots under suboptimal temperature, light and salt environment were studied. The results showed that under the suboptimal environment, the superoxide anion (O₂^-_·) production rate, hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) contents were increased, and lipid peroxidation was aggravated in cucumber seedling roots, which significantly inhibited the growth of seedling roots. EBR improved the activities of antioxidant enzymes such as ascorbate peroxidase (APX), glutathione reductase (GR) and dehydroascorbate reductase (DHAR), increased the contents of ascorbic acid (AsA) and glutathione (GSH) and the ratios of AsA/DHA and GSH/GSSG in roots of cucumber seedlings under the suboptimal environment. Moreover, EBR effectively promoted the metabolism of AsAGSH cycle in cucumber seedling roots, and maintained a strong antioxidant ability, which significantly reduced the H₂O₂ and MDA contents and the superoxide anion production rate, reduced the membrane lipid peroxide level, consequently promoting the root growth of cucumber seedlings under the suboptimal temperature, light and salt environment.

Key words: gas exchange., drought, Camellia japonica (Naidong), shading