Effects of Paraquat on Lipid Peroxidation and Antioxidant Enzymes in Aquatic Fern Azolla microphylla

Paraquat is most extensively used methyl viologen herbicide to control weeds in the rice-Azolla ecosystem. The effects of different paraquat (PQ) dosages on growth, lipid peroxidation, and activity of antioxidant enzymes of Azolla microphylla Kaul. were investigated. The results indicated that Azolla fronds survived only at the concentrations of 2-6 mu M PQ. Frond fragmentation and browning occurred after 24 h at 8 mu M PQ. At 24 h, the amount of proteins decreased by 48.7 % in Azolla fronds exposed to 10 mu M PQ than that in control fronds. The supplementation of 10 mu M PQ increased the activities of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), and ascorbate peroxidase (APX) by 2,4-, 1,8-, 3,0-, and 2,2-fold, respectively, as compared with control. The content of PQ and activities of SOD, CAT, GPX, and APX were found to be positively correlated. Our study showed that PQ (2- 6 mu M) caused ROS overproduction in Azolla fronds, which were scavenged by induced activities of antioxidant enzymes.