Differential bentazon metabolism and retention of bentazon metabolites by plant cell cultures

Abstract

Bentazon [3-(1-methylethyl)-(1 H)-2,1,3-benzothiadiazin-4(3 H)-one 2,2-dioxide] was metabolized to 6-O-β-glucose-bentazon (6-O-G) by suspension-cultured cells of alfalfa ( Medicago sativa L.), carrot ( Daucus carota L.), corn ( Zea mays L.), potato ( Solanum tuberosum L.), rice ( Oryza sativa L.), tobacco ( Nicotiana tabacum L.), and wheat ( Triticum aestivum L.) and T. monococcum L.). Cell cultures of soybean [ Glycine max (L.) Merr.] cultivars which are tolerant to bentazon at the whole plant level metabolized bentazon to the glucose conjugate of 8-OH-bentazon (8-O-G) in addition to 6-O-G. Cell suspension cultures of velvetleaf ( Abutilon theophrasti Medic.) and soybean cultivars which are susceptible to bentazon at the whole plant level did not metabolize bentazon. Bentazon metabolism in rice and in soybean was linear over 2 and 24 hr, respectively. The rate of bentazon metabolism to 6-O-G in rice was about 25 times greater than the rate of bentazon metabolism to 6-O-G plus 8-O-G in soybean. Glucosylated products of bentazon did not readily efflux from soybean cells containing high concentrations of these metabolites. Thus, the metabolites did not readily diffuse across the plasmalemma or the tonoplast but rather were efficiently trapped within the cultured cells. Suspension-cultured cells appear to be a useful system for interspecies comparison and mechanistic studies of bentazon metabolism in plant cells.