Effects of external Ca~(2+) on membrane lipid peroxidation of cucumber seedling roots under cinnamic acid stress

In order to explore the physiological mechanisms of external Ca2+ involved in improving cucumber(Cucumis sativus L.) adaptation to cinnamic acid(CA) stress,the effects of Ca2+ on the growth and active oxygen metabolism were investigated through hydroponic experiment.The results showed that CA decreased root fresh weight,length of taproot,number of laterals and the activity of catalase(CAT),whereas increased the activities of superoxide dismutase(SOD),peroxidase(POD) and superoxide anion(O-·2) producing rate,contents of H2O2 and malondialdehyde(MDA) as well as electrolyte leakage,suggesting that oxidative damage and membrane peroxidation occurred in CA-treated root tissues.External Ca2+ promoted the activities of SOD and CAT,but reduced the activity of POD,O-·2 producing rate,the contents of H2O2 and MDA,and permeability of cell membrane under CA stress.These results indicated that the elimination of active oxygen species and maintenance of membrane stability may be one of the mechanisms of external Ca2+ inhancing CA tolerance of cucumber to CA stress.