Basis of selectivity of the herbicide flupyrsulfuron-methyl in wheat
1997
Koeppe, M.K. | Barefoot, A.C. | Cotterman, C.D. | Zimmerman, W.T. | Leep, D.C.
Flupyrsulfuron-methyl, methyl 2-[[[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl] amino]sulfonyl]-6-(trifluoromethyl)-3-pyridinecarboxylate monosodium salt, formerly DPX-KE459, is a new postemergence sulfonylurea herbicide for the control of grass and broadleaf weeds in wheat. Similar to other sulfonylureas, the site of action of flupyrsulfuron-methyl is acetolactate synthase (ALS), an enzyme in branched-chain amino acid biosynthesis. Studies of in vitro inhibition of ALS across sensitive and tolerant species-discount differential active site sensitivity as the basis for wheat tolerance to this herbicide. However, wheat and the tolerant weeds Avena fatua and Phalaris minor metabolized flupyrsulfuron-methyl very rapidly with half-lives of < or = 2 h. Metabolism in the moderately tolerant species Setaria viridis was intermediate (half-life of 10 h), and slow in Alopecurus myosuroides (half-life of 20 h), a sensitive species. The initial metabolic pathway of flupyrsulfuron-methyl in wheat primarily involves glutathione conjugation; whereas in an equally tolerant species. P minor, this herbicide is not metabolized by glutathione conjugation but apparently by O-demethylation. Flupyrsulfuron-methyl is metabolized via both pathways (glutathione conjugation and O-demethylation) in A. fatua, also a tolerant species. Differential rates of metabolism in sensitive and tolerant plant species are responsible for the selectivity of flupyrsulfuron-methyl.
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