EFFECT OF DROUGHT STRESS ON ANTIOXIDANT MECHANISMS OF WEEDY RICE

The effect of varying levels of water stress simulated by polyethylene glycol (PEG) on oxidative parameters (malondialdehyde, MDA) and superoxide anion (O-2(-)), the activities of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), glutathione reductase (GR). dehydroascorbate reductase (DHAR), as well as the content of non-enzymatic antioxidants ascorbate acid (ASA) and glutathione (GSH) were studied in the leaves and roots of weedy rice (Oryza saliva f. spontanea) heb07-2 and wr04-6, cultivated rice (Oryza saliva L.) variety yuefu and upland rice iapar9. Drought stress significantly increased MDA and O-2(-) production. The MDA and O-2(-) of heb07-2 increased significantly slower than other oxidants under drought indicating that heb07-2 accumulated lower ROS (reactive oxygen species) with intact cell membrane and lower level of lipid peroxidation. Under normal conditions, the activities of antioxidant enzymes in heb07-2. wr04-6, iapar9, and yuefu were similar. However, under stress, the activities of SOD, POD, CAT, APX, GR, and DHAR were significantly enhanced in heb07-2 than in iapar9 and wr04-6, whereas they were decreased in yuefu after 72 hrs of drought. The mechanism of drought tolerance in weedy rice involves enhanced antioxidant defense mechanisms.