EFFECT OF MONOOXYGENASE INHIBITORS ON BENTAZON UPTAKE AND METABOLISM IN MAIZE CELL-SUSPENSION CULTURES

Maize "black Mexican sweet" (BMS) cell suspension cultures were used to study the effects of various cytochrome P450 monooxygenase inhibitors on the uptake and metabolism of the herbicide bentazon. Maize cells rapidly absorbed bentazon and metabolized it via aryl hydroxylation and glycosylation to a glycosyl conjugate of 6-hydroxybentazon. BMS cells accumulated bentazon to levels approximately 20-fold greater than those in the external medium. When BMS cells were incubated in an external medium containing 25 μM bentazon, the formation of the glycosyl conjugate (ca. 2 nmol/min/g fresh wt) was rate-limited by aryl hydroxylation. Tetcyclacis, a plant growth retardant, phenylhydrazine, a mechanism-based cytochrome P450 inhibitor, and piperonyl butoxide, an insecticide synergist, inhibited bentazon metabolism with I50 values of approximately 0.1, 1.0, and 1.0 μM, respectively. Other mechanism-based cytochrome P450 inhibitors, 3(2,4-dichlorophenoxy)-1-propyne and aminobenzotriazole, also inhibited bentazon metabolism but were less effective. The results obtained with selected inhibitors are consistent with the hypothesis that aryl hydroxylation of bentazon is catalyzed by a cytochrome P450 monooxygenase. © 1991.