Metabolism of metalaxyl in cell suspension cultures of Lactuca sativa L. and Vitis vinifera L

The metabolic fate of metalaxyl in suspension cultures of Lactuca sativa has been investigated as a function of explant source, culture age, and nutrient medium quality. In all cases, the fungicide was the subject of diverse metabolic attack yielding products which arose from O- and N-dealkylation, alkyl and aryl hydroxylation, and ester hydrolysis. Substantial amounts of metabolites were found in the culture filtrates although products arising from aryl hydroxylation and combined O-/N-dealkylation accumulated exclusively as cellular conjugates. Cultures newly isolated from the cotyledon, hypocotyl, and root of seedlings displayed very little variation in the rate and qualitative nature of breakdown and in the relative distribution of metabolites among the polar conjugate fraction, unconjugated cellular fraction, and culture filtrate. Similarly, metabolism proceeded independently of changes in nutrient medium composition. A suspension culture initiated from 4-year-old hypocotyl callus produced less identifiable metabolites and had an impaired ability to perform alkyl hydroxylation, O-dealkylation, and ester hydrolysis. A greater proportion of metabolites occurred as polar conjugates in the 4-year-old hypocotyl cells than that in the newly isolated hypocotyl line. The metabolic profile seen in Vitis vinifera was similar to that in L. sativa and a time-course study indicated some interconversion of metabolites and a change in the ratio of two atropisomers formed by alkyl hydroxylation.