Physiological response of herbicide-resistant cell variants of Datura innoxia to branched-chain amino acids

Abstract

The growth of wild-type Datura innoxia cells was inhibited by the branched-chain amino acids valine, leucine and isoleucine when they were supplied exogenously. Acetolactate synthase (ALS), the first enzyme in the biosynthesis of the branched-chain amino acids, is the target of several structurally diverse herbicides such as sulfonylureas, imidazolinones and triazolopyrimidines. Cell variants resistant to these herbicides were also tested for their response to exogenously supplied branched-chain amino acids; some of the variants were resistant while others were as sensitive as, or more sensitive than, wild-type cells. Free amino acids from wild-type (Px4) and a chlorsulfuron-resistant variant (CSR6) were analysed with and without a 48-h exposure of cells to combinations of valine, leucine and isoleucine. CSR6 cells had smaller pools of branched-chain amino acids than did those of Px4 but accumulated the amino acids in larger quantities than did Px4 cells when branched-chain amino acids were supplied exogenously, except when valine and isoleucine were fed together or in combination with leucine. These alterations in branched-chain amino acid metabolism in sulfonylurea-resistant variants highlight the importance of screening herbicide resistant mutants for potentially undesirable side effects.