The mechanism of bentazon selectivity

Abstract

Absorption, translocation and metabolism of [ 14C]3-isopropyl-2,1,3-benzothiadiazin-4-one-2,2-dioxide (bentazon) by several plant species were investigated to determine the mechanism of bentazon selectivity. Marked selective phytotoxicities were observed between resistant rice ( Oryza sativa L.) and susceptible Cyperus serotinus Rottb. when treated with bentazon. Absorption and transolcation of bentazon did not differ greatly between highly resistant rice and susceptible C. serotinus. However, a marked difference in bentazon metabolism occurred between the two species. In rice about 80% of the absorbed bentazon was metabolized within 24 h, and after 7 days about 85% was converted to a major water-soluble metabolite and unchanged bentazon was only 5%. In C. serotinus 50–75% of the radioactivity was unchanged bentazon after 7 days. Large amounts of water-soluble metabolites were detected in root-treated resistant plants such as barnyardgrass ( Echinochloa crus-galli Beauv.), soybean ( Glycine max Merr.) and corn ( Zea mays L.), but only small amounts were present in such susceptible plants as Sagittaria pygmaea Miq. and Eleocharis kuroguwai Ohwi. Therefore, the mechanism of bentazon selectivity appears to be a difference between resistant and susceptible species in their ability to metabolize and detoxify bentazon. The major metabolite in rice was identified as 6-(3-isopropyl-2,1,3-benzothiadiazin-4-one-2,2-dioxide)- O-β-glucopyranoside, determined by GC-MS, NMR, IR and gas chromatography after hydrolysis with sulfuric acid or β-glucosidase.