Interconversion of Prenyl Pyrophosphates and Subsequent Reactions in the Presence of FMC 57020

In vitro studies of the influence of FMC 57020 on terpenoid biosynthesis have shown that this herbicide acts at an early stage. It affects the conversion of isopentenyl pyrophosphate to geranylgeranyl pyrophosphate catalyzed by isopentenyl pyrophosphate isomerase and prenyl transferase. An inhibition of the carotenogenic enzymes phytoene desaturase, ζ-carotene desaturase, and lycopene cyclase could be excluded. Comparison of I50 values for in vivo chlorophyll, carotenoid, ergosterol and gibberellin biosyn- thesis as well as in vitro formation of phytoene. phytol and kaurene in various autotrophic and heterotrophic organisms have shown that terpenoid biosynthesis in the chloroplast is much stronger affected than extraplastidic terpenoid formation.