Metabolism of N-hydroxymethyl dimethoate and N-desmethyl dimethoate in bean plants

N-Hydroxymethyl carbonyl-¹⁴C] dimethoate (0.43 ppm) and N-desmethyl carbonyl-¹⁴C] dimethoate (0.50 ppm) were stem-injected into bean plants (Phaseolus vulgaris) in two separate experiments. Plants were harvested periodically, extracted, fractionated, and analyzed for metabolites. The resulting pattern of metabolites formed from the administration of these two compounds was different. Radioactivity was not detected in the organic fraction 2 days after N-desmethyl dimethoate administration. N-Desmethyl dimethoate was rapidly broken down to dimethoate carboxylic acid and other polar metabolites, then further degraded into materials which became part of the plant constituents. N-Hydroxymethyl dimethoate was quite stable in the plant. Most of the material not remaining as parent became rapidly conjugated and constant levels of conjugate were maintained. Very little radioactivity was bound in the plant marc. The metabolic pathway of these compounds is as follows: N-hydroxymethyl to the glucoside or N-desmethyl derivative; the N-desmethyl metabolite degrades primarily to the carboxylic acid but also to N-desmethyl dimethoxon, either of which in turn may be degraded to dimethoxon carboxylic acid. The conversion of -NHCH₂OH to -NH₂ is a slow reaction so that conjugation becomes the route of choice when the plant is treated with N-hydroxymethyl dimethoate.