The Kinetics of Amiben Absorption and Metabolism as Related to Species Sensitivity

The rates of absorption and metabolism of 3-amino-2,5-dichlorobenzoic acid (amiben) were investigated in 3-day-old roots of amiben-sensitive velvetleaf (Abutilon theophrasti Medic.) and amiben-tolerant morningglory [Ipomoea hederacea (L.) Jacq.].The initial rates of amiben absorption and binding were identically concentration dependent for both species for external concentrations from 0.02 to 500 mg/liter.THE RATES AT WHICH THE ABSORBED AMIBEN WAS: 1) bound; 2) incorporated into an unidentified amiben complex (amiben-X) and N-(3-carboxy-2,5-dichlorophenyl)-glucosylamine (N-glucosyl amiben); and 3) accumulated in these tissues during a 24-hr period was investigated at widely different concentrations for both species. There were no salient differences between the species in their amiben absorption rate at 5 mg/liter, but the absorbed amiben was complexed as N-glucosyl amiben more rapidly and to a greater extent in morningglory; maximum rate of glucosylation was attained earlier after exposure to amiben in morningglory than in velvetleaf. At nearly equitoxic concentrations (100 and 1 mg/l, 5 and 0.05 mg/l for morningglory and velvetleaf, respectively), the rates at which the absorbed amiben was distributed among N-glucosyl amiben, amiben-X and amiben were very similar for both species, although morningglory absorbed amiben at the faster rate. At amiben concentrations required for equal expression of the herbicidal effect, morningglory conjugates amiben at a faster rate and tolerates higher levels of free amiben than velvetleaf. Amiben toxicity in a species is expressed at that concentration which saturates the glucosylation process, and results in amiben accumulation at sufficiently high levels to exert its toxic effect. A scheme for amiben metabolism in plants is presented.