USE OF SOYBEAN (GLYCINE-MAX) AND VELVETLEAF (ABUTILON-THEOPHRASTI) SUSPENSION-CULTURED CELLS TO STUDY BENTAZON METABOLISM

Metabolism and phytotoxicity of bentazon by suspension-cultured cells of soybean and velvetleaf were compared. Growth of suspension cells of both species was reduced when the cells were exposed to increasing concentrations of bentazon. However, soybean plants were tolerant and velvetleaf plants were susceptible to postemergence applications of bentazon. After incubation with 1 .mu.M 14C-bentazon for 6 h, soybean and velvetleaf cells in the log phase of the culture growth cycle contained similar levels of 14C (6 nmol/g fresh weight). Of the total 14C in the soybean cells 57 to 92% was present as the glucosyl conjugates of 6-OH- and 8-OH-bentazon with the remainder present as bentazon; the percentage depended on the phase of the culture growth cycle. Bentazon metabolism was greatest in the stationary phase of growth. Thin, transverse sections of soybean hypocotyl metabolized bentazon to the same two metabolites as soybean suspension cells did. The ratio of 6-O-glucosyl-bentazon to 8-o-glucosyl-bentazon was always greater than 1:1 for both the hypocotyl sections and the suspension cells. Bentazon metabolites were not detected in the velvetleaf cells, the velvetleaf hypocotyl sections, or the media of either species. Soybean suspension-cultured cells appear to be a valid and advantageous system for studying the hydroxylation and glucosylation of bentazon, the primary reactions believed to be responsible for detoxication of the herbicide in tolerant plants.