Clomazone Selectivity: Absence of Differential Uptake, Translocation, or Detoxication

Concentrations of clomazone in nutrient solution causing 50% reduction in shoot fresh weights were 325 and 2 μM for soybean and velvetleaf, respectively. Root uptake of 14C–clomazone from nutrient solution and translocation to shoots were similar for the two species. Soybean and velvetleaf contained similar amounts of 14C per plant; however, because velvetleaf had lower tissue weights, concentration of 14C was higher in velvetleaf. Clomazone did not accumulate in roots but was rapidly translocated to shoots of both species. No more than 30% of absorbed clomazone remained in roots at any time in the experiment. Soybean and velvetleaf leaves contained 4.2 and 1.7 nmol clomazone g−1 fresh weight, respectively, and 3.7 and 6.1 nmol clomazone metabolites g−1 fresh weight, respectively. Thus, velvetleaf metabolized clomazone more rapidly than soybean did. Treatment of clomazone metabolites with β-glucosidase demonstrated that metabolism occurred by oxidative cleavage and conjugation of the benzyl moiety in both plant species. One aglycone cochromatographed with 2–chlorobenzylalcohol. The results suggest that reduced absorption or translocation or increased detoxication of clomazone by soybean seedlings is probably not responsible for their tolerance to this herbicide.