A study of bentazon uptake and metabolism in the presence and the absence of cytochrome P-450 and acetyl-coenzyme A carboxylase inhibitors

The metabolism of bentazon in a resistant variety of soybean [ Glycine max (L.) Harcor] was investigated. Soybean leaves produced two major metabolites under both light and dark conditions, metabolism being enhanced in the dark. No metabolism of bentazon could be demonstrated in the identically treated susceptible species, shepherd's pure [ Capsella bursa-pastoris (L.) Medicus], and leaf necrosis was evident after 2 days. Bentazon metabolites were separated by TLC and identified as 6-hydroxybentazon and a glycosyl conjugate, determined by comigration and β-glucosidase treatment, respectively. Pretreatment of leaves with the norbornanodiazetine tetcyclacis, the triazoles BAS 110 and BAS 111, and the pyridine metyrapone had no significant effect upon bentazon uptake but inhibited its metabolism in soybean, causing leaf necrosis, in each case, 2 days after bentazon treatment. Pretreatment of leaves with the acetyl-coenzyme A carboxylase inhibitors sethoxydim and diclofop-methyl had no significant effect upon bentazon uptake or metabolism at the concentrations used. These findings are discussed in relation to bentazon selectivity in soybean.