| Abstract: | Summary. The metabolism of monuron in excised leaves of bean (Phaseolus vulgaris L., var. Black Valentine) and corn (Zea mays L., var. Batam Cross) were studied with carbonyl-14C-labelled monuron. The metabolic conversions of monuron in both plant species were exponential and followed first order reaction kinetics. The metabolism of monuron can be divided into two major pathways: demethylation and hydroxylation. At a monuron concentration of 16 ppm the hydroxylation was dominant in the bean leaves. As the concentration of monuron was increased the participation of the hydroxylation pathway became less probably due to the inhibition of enzymes involved by monuron. The demethylation pathway was not affected by higher monuron concentration. In the corn leaf, however, sequential demethylation was always the major pathway of monuron transformation and there was no inhibitory effect observed on either pathways as the concentration of monuron increased. The following radioactive metabolites were found in the alcohol extract of bean and com leaves receiving carbonyl-14C-labelled monuron: N′-(4-chlorophenyl)-N-methylurea, p-chlorophenylurea, two polypeptide complexes of monuron, one polypeptide complex of N′-(4-chlorophenyl)-N-methylurea and β-D-glucosides of N-(2-hydroxy-4-chlorophenyl) urea, N′-(2-hydroxy-4-chlorophenyl) N-methylurea, and N′-(2-hydroxy-4-chlorophenyl)-N,N-dimethylurea. In addition, one minor radioactive peak was found only in the alcohol extract of corn leaves, which yielded four unidentified radioactive metabolites after acid or enzyme hydrolysis with β-glucosidase. Métabolisme du monuron dans des feuilles excisés de maïs et de haricot |
