Influence of composition of nutrient medium on the metabolism of chlortoluron in plant‐cell suspension cultures

Abstract

AbstractThe herbicide chlortoluron readily underwent oxidative metabolism in suspension cultures of cotton and maize. Major attack in cotton cells was by stepwise N‐demethylation followed by relatively slow ring‐methyl hydroxylation. The most prominent single metabolites seen after 1 day and 7 days were 3‐(3‐chloro‐p‐tolyl)urea and its benzyl alcohol analogue, respectively. In maize cells, ring‐methyl hydroxylation was apparently the preferred mode of metabolism. Only low amounts of the demethylated derivatives of chlortoluron were evident, and the major residues present at both 2 days and 7 days were the benzyl alcohol derivative of chlortoluron and 3‐(3‐chloro‐4‐hydroxymethylphenyl)‐1‐methylurea. In both species, a substantial proportion of the free ‘phase 1’ metabolites was initially expelled to the medium, but at later times, these were found largely within the cell as polar conjugates.Two approaches were used to examine the influence of the composition of the medium on metabolism. Firstly, cells of both species were grown in four different nutrient media, which were selected to give variation in the organic nutrient and growth factor fraction; secondly, cells were grown in one medium, varying the level of 2, 4‐D. In cotton, the rate of metabolism of chlortoluron correlated with the extent to which the four media supported cell growth, Variations were also seen for maize but no correlation with growth rate could be made. For both species, metabolism was retarded when cells were sub‐cultured from a medium lacking coconut water to one containing 10% of this supplement. A fifty‐fold range in concentration of 2, 4‐D had little effect on metabolism in cotton, although a fall‐off in rate occurred at the highest level. However, in maize a marked trend towards accelerated metabolism with increasing content of 2, 4‐D up to 20 mg litre−1 was seen, which was independent of effects on growth.The qualitative nature of chlortoluron metabolism in both species was unperturbed by substantial variations in the composition of the medium.