Abstract:Eucalyptus grandis×Eucalyptus urophylla seedlings were used as materials to study the effects of boron on membrane lipid peroxidation and endogenous protective systems in leaves under low temperature. The results showed that relative conductivity rate, O2-. production rate, malondialdehyde (MDA) content and polyphenol oxidase (PPO) activity in leaves were increased at 5℃ with boron-deficiency (≤10 μmol/L). On the contrary, the contents of ascorbate (ASA) and soluble protein, the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) were decreased. However, addition of 15 μmol/L boron in the culture medium could alleviate chilling injury and enhance the tolerance to low temperture in the seedlings.