Differential Absorption, Translocation and Metabolism of Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] by Soybean Cultivars

Soybean (Glycine max (L.) Merr.) cultivars have been reported to range in tolerance to injury by 4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one (metribuzin), from tolerant (e.g.‘Bragg’) to susceptible (e.g.‘Coker 102’ and ‘Semmes’). ‘Bragg,’‘Coker 102’, and ‘Semmes’ soybeans were grown in sand subirrigated with nutrient solution containing labelled (¹⁴C-carbonyl metribuzin) and nonlabelled metribuzin to determine cultivar variability in absorption, translocation, and metabolism of metribuzin. Plants were periodically harvested, autoradiographed, and radioactivity in tissue extracts quantified. Data indicated that all 3 cultivars readily absorbed and translocated metribuzin. However, ‘Bragg’ tissues accumulated greater quantities of metribuzin metabolites than the other two cultivars. The major ¹⁴C-containing metabolite in ‘Semmes’ and ‘Coker’ roots and stems was 6-tert-butyl-as-triazine-3-5-(2H,4H)-dione, whereas the major ¹⁴C-metabolite isolated from‘Bragg’ roots and stems was a glucose conjugate. Results indicated that differential-intraspecific responses to metribuzin may result from differential capacities for herbicide detoxification by conjugation.