Mode of growth inhibitory activity and metabolism of imazosulfuron in excised roots of plants

Growth inhibition activity of imazosulfuron, 1-(2-chloroimidazo [1, 2-a] pyridin-3-ylsulfonyl)-3-(4, 6-dimethoxypyrimidin-2-yl)urea, against excised pea and soybean roots was investigated. Fifty percents growth inhibition concentrations of imazosulfuron (I50) against pea and soybean roots were 17.6 and 54.2ppb, respectively. When the excised pea roots were incubated in the culture medium containing 25ppb of imazosulfuron and 1mM of either branched-chain amino acids or intermediates of their biosynthetic pathways, the growth inhibition activity of excised roots was alleviated by the combination of isoleucine and valine or α-ketoisovalerate and α-keto-β-methyl-n-valerate. These findings suggest that imazosulfuron exhibits inhibition of acetolactate synthase which catalyses the biosynthetic pathways of branchedchain amino acids. Metabolic fate of imazosulfuron in excised pea roots was studied using the 14C-labeled compounds. imazosulfuron was predominantly demethylated to afford a monodemethyl derivative (HMS) in the roots, and hydrolytically cleaved at the sulfonylurea bond to give a sulfonamide (IPSN) and an aminopyrimidine (ADPM) in the culture medium. Since HMS did not inhibit the growth of excised roots, metabolic fate of imazosulfuron is involved in a selectivity between plants.