Clomazone Does Not Inhibit the Conversion of Isopentenyl Pyrophosphate to Geranyl, Farnesyl, or Geranylgeranyl Pyrophosphate in Vitro

Clomazone, an herbicide that reduces the levels of leaf carotenoids and chlorophylls, is thought to act by inhibiting isopentenyl pyrophosphate isomerase or the prenyltransferases responsible for the synthesis of geranylgeranyl pyrophosphate. Cell-free extracts prepared from the oil glands of common sage (Salvia officinalis) are capable of converting isopentenyl pyrophosphate to geranylgeranyl pyrophosphate. Clomazone at 250 micromolar (a level that produced leaf bleaching) had no detectable effect on the activity of the relevant enzymes (isopentenyl pyrophosphate isomerase and the three prenyltransferases, geranyl, farnesyl, and geranylgeranyl pyrophosphate synthases). Thus, inhibition of geranylgeranyl pyrophosphate biosynthesis does not appear to be the mode of action of this herbicide.