Absorption, Translocation, and Metabolism of 14C-Buthidazole in Alfalfa (Medicago sativa) and Quackgrass (Agropyon repens)

Abstract

The patterns of buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2 imidazolidinone} uptake, translocation, and metabolism, and their potential contribution to crop selectivity, were studied in tolerant alfalfa (Medicago sativa L. ‘Vernal’) and susceptible quackgrass [Agropyron repens (L.) Beauv.]. 14C-Buthidazole was absorbed from a 5-μl droplet by leaves of both alfalfa and quackgrass plants, but did not move basipetally to the roots or nontreated leaves in 14 days. 14C-Buthidazole was absorbed very rapidly from Hoagland's solution by the roots of both species and translocated apoplastically to the leaves. Absorption and translocation of buthidazole did not differ between species, indicating that these processes did not contribute to crop selectivity. The herbicide and five metabolites were present in alfalfa leaf extracts 6 days after treatment. One unidentified metabolite accounted for 40% of the detected radioactivity 6 days after root application. Unmetabolized 14C-buthidazole accounted for 87% of the total radioactivity in quackgrass after 6 days. Metabolites having different chromatographic properties were recovered from the two species. Differential rate and type of metabolism appeared to contribute to buthidazole selectivity between the species.