Effects of the Herbicide Pretilachlor and the Safener Fenclorim on Glutathione Content and Glutathione-Dependent Enzyme Activity of Rice

The influence of individual or combined treatments of the chloroacetanilide herbicide preti­lachlor and the safener fenclorim on glutathione content and the activity of glutathione reduc­tase (GR, EC 1.6.4.2) and glutathione-S-transferase (GST, EC 2.5.1.18) of rice (Oryza sativa L., var. Lamont) was investigated in a time-course study including 0, 12, 24, 48, and 72 h peri­ods after treatment. Pretilachlor applied alone at 2 μM did not influence the levels of total or reduced glutathione of germinating rice seedlings. Fenclorim applied alone at 20 μM increased significantly the levels of total and reduced glutathione of rice seedlings at 12, 24, and 72 h after treatment. The combination of pretilachlor and fenclorim increased the levels of total and reduced glutathione of rice at all time periods. GR activity extracted from pretilachlor-treated rice seedlings was significantly lower than that extracted from untreated rice seedlings. Pretreatment of rice seedlings with the safener fenclorim increased GR activity at 12 and 24 h, but not at 48 and 72 h after treatment. GR activity extracted from rice seedlings treated with the combination of pretilachlor and fenclorim was significantly higher than that of untreated controls at 12, 24, and 48 h after treatment. Pretreatment of rice seedlings with pretilachlor reduced the activity of GST which catalyzes the conjugation of this herbicide with reduced glutathione at time intervals greater than 24 h. Pretreatment with fenclorim did not have any effect on GST activity of rice seedlings. Pretreatment with the combination of pretilachlor and fenclorim increased GST activity of rice seedlings at the 48 and 72 h periods. These results suggest that a simultaneous application of pretilachlor and fenclorim is critical for the enhance­ment of glutathione and glutathione-related enzyme activity and the protection of rice from pretilachlor injury.