ACETYL-COA CARBOXYLASE - A GRAMINICIDE TARGET SITE

Acetyl-CoA carboxylase catalyses the first committed step in fatty aci d (and acyl lipid) formation. The enzyme has been shown to exert a hig h degree of flux control for lipid biosynthesis in leaves and, therefo re, it is not surprising that chemicals which can inhibit it effective ly are successful herbicides. These chemicals belong mainly to the cyc lohexanedione and aryloxyphenoxypropionate classes and are graminicide s. The reason for the selectivity of these herbicides towards grasses lies in the nature of the target site, acetyl-CoA carboxylase. Recent advances in our knowledge of acetyl-CoA carboxylases from sensitive an d resistant plants has revealed some important facts. Dicotyledons, wh ich are resistant, have a multi-enzyme complex type of carboxylase in their chloroplasts while grasses have a multifunctional protein. Both divisions of plants have two isoforms of the enzyme, the second being in the cytosol. Detailed study of multifunctional forms of acetyl-CoA carboxylases, which have different sensitivities to herbicides, sugges ts that herbicide resistance is correlated with cooperativity of herbi cide binding to the native dimeric form of the carboxylase.