Evidence for the Interaction of an Imidazolinone Herbicide with Leucine, Valine, and Isoleucine Metabolism

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Abstract
Effects of the imidazolinone herbicide AC243 997 [2-(5-isopropyl)-5-methyl-4-oxo-2-imidazolin-2-yl) nicotinic acid] on the growth of corn (Zea mays L. ‘Black Mexican Sweet’) cell suspension cultures were characterized. The herbicide caused half maximal growth inhibition at concentrations in the range of 10 nM to 30 nM. Significant reductions in protein synthesis were observed following treatment of cells with 10 μM herbicide. Analysis of free amino acid pool sizes indicated that levels of the biosyn-thetically related amino acids leucine and valine were substantially decreased in cells exposed to 10 μM herbicide. Supplementation of suspension culture growth media with leucine and valine plus isoleucine (1 mM each) reversed growth inhibitory effects of AC243 997 at levels ranging from 10 nM to 1 mM. The results suggest a specific interaction of this imidazolinone herbicide with leucine, valine, and isoleucine metabolism.