The Lipoxygenase Activity of Pea Chloroplasts in Relation to Leaf Senescence and Membrane Lipid Peroxidation
WANG Yi-Xing, LIN Zhi-Fang and GUO Jun-Yan(South China Institute of Botany, Academia Sinica, Guangzhou 510650)LI Ming-Qi(Biology Department, South China Agricultural University, Guangzhou 510642)
Chloroplast LOX activity, lipid peroxidation and chlorophyll content in attached pea leaves at different positions and in detached pea leaves treated with ABA were investigated for understanding the relationship between chloroplast LOX activity and leaf-senescence. It was observed that during leaf senescence the MDA content in chloroplasts increased, but the chloroplast LOX activity remained at lower level. The changes of chloroplast LOX activities in senescing detached leaves paralleled with the results obtained from the intact plants except that the transient increased within 2 days after treatment. The results indicated that there was no apparent direct relationship between leaf senescence and the chloroplast LOX activity. The antioxidants α-toco pherol, GSH and propyl gallate inhibited the LOX activity of pea chloroplast. MDA, a product of lipid peroxidation, also inhibited the activity of chloroplast LOX and that of purified soybean LOX-1. Soybean LOX-1 stimulated lipid peroxidation of isolated chloroplasts. MDA and LFP in chloroplasts accumulated with an increase of the concentration of soybean LOX-1. According to these results, a possilble relationship between the LOX activity and lipid peroxidation during leaf senescence was discussed.