Comparative Effects of Paraquat on Antioxidant Components and Scavenging Enzymes in Kwangkyo and Hood Soybean

The effect o f paraq u a t on hydroxyl radical production , glutathione and ascorbate content, and glutathione reductase and superoxide dism utase activities was assayed in the to lerant “K w angkyo” and the susceptible “ H o o d ” cultivars o f soybean [Glycine max (L.) Merr.]. Seed­ lings o f both cultivars a t the fully expanded first trifoliate leaf stage were treated with paraquat at 0, 1, 10, 100, 500, and 1000 |im. The in vivo generation o f hydroxyl radicals was estim ated by m easuring m ethanesulfonic acid (M SA) produced in soybean leaves treated with dim ethylsulfoxide (D M SO ) and paraquat. The levels o f paraquat-induced production o f hydroxyl radicals were similar in K w angkyo and H ood soybean. A scorbate levels in the two cultivars were com ­ parable and were reduced by paraq u a t treatm ent. T o ta l glutathione levels were similar in both cultivars, but K w angkyo had m ore glu tath ione in the reduced form than H ood. T reatm ent with low concentrations o f paraqua t enhanced oxidized glutathione levels in H ood. A t high concentrations, paraq u a t decreased the levels o f to tal and reduced glutathione in both culti­ vars. The endogenous activities o f glu tath ione reductase and superoxide dism utase were simi­ lar in Kwangkyo and H ood soybean. T reatm ent w ith selected concentrations o f paraquat enhanced the activity o f these enzymes in trifoliates o f the to lerant Kwangkyo. Overall, the results o f this study do no t suggest a strong involvem ent o f com ponents o f the ascorbate-glutathione cycle in the observed tolerance o f K w angkyo soybean to the herbicide paraquat.