Role of superoxide dismutase and peroxidase activities in paraquat-resistant redflower ragleaf (Crassocephalum crepidioides (Benth.) S. Moore)

Abstract

The constituent level of superoxide dismutase (SOD) and peroxidase (POD) activities in susceptible (S) and resistant (R) biotypes of Crassocephalum crepidioides, prior to and following paraquat treatment, was examined at the 6-leaf (6–7 weeks) and 10-leaf (9–10 weeks) stages. Earlier dose response studies had shown survival of resistant plants at the 6- and 10-leaf stages to be 2.9 and 2.6 times that of the susceptible biotype. At the 6-leaf stage, the SOD activity of whole leaf extracts in the untreated R biotype was lower (86%) than that of the S biotype. Paraquat treatment increased SOD activity in the R biotype 2-fold relative to the control (no paraquat) but not in the S biotype. There was also no significant difference (P > 0.05) in the SOD activities of the 2 biotypes after each was treated with paraquat. Furthermore, at the 10-leaf stage, paraquat treatment did not change SOD activity in the S biotype but the activity increased 3-fold (P < 0.05) in the treated R biotype. These observations suggest that SOD could play a part in the mechanism of paraquat resistance and that this is more evident at the more mature stage. The ratio of POD activity (R/S) was relatively constant at 6- and 10-leaf stages after paraquat treatment. POD therefore did not appear to be important in the mechanism of paraquat resistance in C. crepidioides.