Effects of Paraquat on Ascorbic Acid and Malondialdehyde Contents, and Superoxide Dismutase Activity in Spinach Chloroplasts under Light and Dark

The amounts of ascorbic acid in chloroplasts treated with light and light+paraquat (PQ) were reduced by 81 and 82% of initial level, respectively at 24 hr at incubation. And those treated with dark and dark+PQ were decreased by W and 55% of the original level, respectively. Malondialdehyde (MDA) contents at 24 hr of dark and dark+PQ treatment were increased by 6 and 31% of the initial level, respectively. When chloroplasts were treated with light and light+PQ, MDA contents after 24 hr were increased by 88 and 146% of the initial level, respectively. SOD activities treated with light and light+PQ were increased by 10 and 20% of the initial level, respectively for 3 hr and thereafter reduced by 46 and 49% of the original level, respectively at 24 hr. However, the SOD activities treated with dark and dark+PQ were decreased by 37 and 30% of the initial level, respectively. It is considered that PQ triggers the oxidation of ascorbic acid, the induction of lipid peroxidation and the inactivation of SOD under light so that PQ has inhibitors effect on the pathway of plant metabolism. Key word: ascorbic acid, malondialdehyde, superoxide dismutase, paraquat, lipid peroxidation.