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

Abstract

The influence of the oxime ether safeners, oxabetrinil and CGA-133205, on glutathione content, glutathione reductase (EC 1.6.4.2), and glutathione-S-transferase (EC 2.5.1.18) activity in seeds and seedlings of grain sorghum (Sorghum bicolor (L.) Moench. var. Funk G-522-DR) was investigated. Plant material for these experiments was derived from seed that was either untreated, or treated with 1.25 or 0.4g ai/kg seed of oxabetrinil or CGA-133205, respectively. Measurements were conducted at 0, 1, 2, 4, 8 , 12, 24, 36, and 72 h after the initiation of germination. In safener-treated sorghum seeds, the levels of total and reduced glutathione decreased gradually after the initiation of germination reaching a low at 8 to 12 h and then increased continuously reaching a maximum at 48 h. The greatest increases in glutathione levels were observed in oxabetrinil-treated sorghum seedlings. Glutathione reductase activity was consistently higher in untreated seeds of grain sorghum for the first 24 h of imbibition, but at 36 to 72 h glutathione reductase activity increased in the safener-treated tissues. CGA-133205 appeared to have a greater stimulatory influence on the activity of glutathione reductase than did oxabetrinil. For the first 8 h after germination was initiated, glutathione-S-transferase activity in oxabetrinil- and CGA-133205-treated seeds remained enhanced compared to that of untreated seeds, but was at or below the levels of the activity of glutathione-S-transferase extracted from untreated seeds for the remainder of the experiment. Non-enzymatic conjugation of metolachlor with reduced glutathione increased as the pH of the reaction solution increased from 6.0 to 8.0. Oxabetrinil at 1 to 40 μM and CGA-133205 at 1 to 160 μm enhanced nonenzymatic conjugation of m etolachlor with glutathione. At 80 and 160 |j.m , oxabetrinil reduced the am oun t of non-enzym atic conjugation of metolachlor. Oxabetrinil conjugated with reduced glutathione at low rates either enzymatically or non-enzymatically at pH 8.0 while CGA-133205 did not at any pH. In the presence of metolachlor, the amount of non-enzymatic conjugation of oxabetrinil was decreased, indicating that metolachlor is more reactive towards glutathione than is oxabetrinil. Overall, these data suggest that during the early stages of seed germination and seedling development of grain sorghum , oxim e ether safeners can enhance the detoxication of the herbicide, metolachlor, through enzymatic or non-enzymatic conjugation to reduced glutathione by enhancing either the level of reduced glutathione and/or the activity of glutathione-related enzymes.