Dicotyledons Sensitive to Herbicides that Inhibit Acetylcoenzymea Carboxylase

Abstract

The key regulatory enzyme in fatty acid biosynthesis, acetyl-coenzymeA carboxylase (ACCase), is known to occur in two structural forms. In prokaryotes three types of subunit make up ACCase while in eukaryotes a single multifunctional peptide carries out all three functions (1). In most plants both forms of ACCase occur. A multisubunit “prokaryotic” form occurs in the chloroplasts of dicots and most monocot species (2, 3). A multifunctional ^-eukaryotic“ form of ACCase occurs in the plant cytosol and has recently been reported to occur in the chloroplasts of Brassica napus (4). The prokaryotic form of ACCase is relatively insensitive to inhibition by ACCase-inhibiting herbicides compared to the eukaryotic form (2) rendering most plants insensitive to these herbicides. In contrast, the Gramineae have only the eukaryotic form of ACCase but not the prokaryotic (2, 3) and are susceptible to ACCase-inhibiting herbicides which have become known as ”graminicides“. Until recently, sensitivity to ACCase-inhibiting herbicides was only known from the Gramineae suggesting that the phenomenon had evolved only once. However, the ACCase-inhibiting herbicide haloxyfop has recently been registered for the control of two dicots Erodium botrys and E. moschatum in Australia.