Influence of Oxime Ether Safeners on Glutathione Content and Glutathione-Related Enzyme Activity in Seeds and Seedlings of Grain Sorghum*’**

The influence o f the oxim e ether safeners, oxabetrinil and C G A -133205, on glutathione co n ­ tent, glutathione reductase (EC 1.6.4.2), and glutathione-S-transferase (EC 2.5.1.18) activity in seeds and seedlings o f grain sorghum (Sorghum bicolor (L.) M oench. var. Funk G -522-D R ) was investigated. Plant material for these experim ents was derived from seed that was either untreated, or treated with 1.25 or 0.4 g ai/kg seed o f oxabetrinil or C G A -133205, respectively. M easurem ents were conducted at 0, 1, 2, 4, 8 , 12, 24, 36, and 72 h after the initiation o f germ i­ nation. In safener-treated sorghum seeds, the levels o f total and reduced glutathione decreased gradually after the initiation o f germ ination reaching a low at 8 to 1 2 h and then increased continuously reaching a m axim um at 48 h. The greatest increases in glutathione levels were observed in oxabetrinil-treated sorghum seedlings. G lutathione reductase activity was consist­ ently higher in untreated seeds o f grain sorghum for the first 24 h o f im bibition , but at 36 to 72 h g lutathione reductase activity increased in the safener-treated tissues. C G A -133205 ap­ peared to have a greater stim ulatory influence on the activity o f glutathione reductase than did oxabetrinil. For the first 8 h after germ ination was initiated, glutathione-S-transferase activity in oxabetriniland C G A -133205-treated seeds rem ained enhanced com pared to that o f un­ treated seeds, but was at or below the levels o f the activity o f glutathione-S-transferase extract­ ed from untreated seeds for the remainder o f the experim ent. N on-en zym atic conjugation o f m etolachlor with reduced glutathione increased as the pH o f the reaction solution increased from 6.0 to 8.0. Oxabetrinil at 1 to 40 and C G A -133205 at 1 to 160 |im enhanced nonenzym atic conjugation o f m etolachlor with glutathione. At 80 and 160 |j.m , oxabetrinil reduced the am ount o f non-enzym atic conjugation o f m etolachlor. O xabetrinil conjugated with re­ duced glutathione at low rates either enzym atically or non-enzym atically at pH 8.0 while C G A -133205 did not at any pH . In the presence o f m etolachlor, the am ount o f non-enzym atic conjugation o f oxabetrinil was decreased, indicating that m etolachlor is m ore reactive towards glutathione than is oxabetrinil. Overall, these data suggest that during the early stages o f seed germ ination and seedling developm ent o f grain sorghum , oxim e ether safeners can enhance the detoxication o f the herbicide, m etolachlor, through enzym atic or non-enzym atic conjugation to reduced glutathione by enhancing either the level o f reduced glutathione and /or the activity o f glutathione-related enzym es.