We have studied in intact radish seedlings the effects of mevinolin (at concentrations of 0.25 to 5 μᴍ), a specific inhibitor of HMG-CoA reductase, and, therefore, of mevalonate biosynthesis, on the production of various isopentenoids and prenyllipids. Whereas the content of free desmethyl sterols was decreased steadily, only depending on the concentration of inhibitor present in the parts of seedlings investigated separately (e.g. roots, hypocotyls. and cotyledons), the effect on ubiquinone accumulation was different. Irrespective of the part of seedlings being analyzed, the maximal inhibition reached was 50%. Plastidic pigment accumulation, however, as well as that of chloroplast quinones (plastoquinone and phylloquinone), appeared even to be enhanced at low inhibitor concentrations and was not significantly lowered by application of 5 μᴍ mevinolin. α-Tocopherol showed a similar profile in the dose response to compounds known to be exclusively synthesized in the plastid. The results indicate a differential accessibility of the mevalonate synthesizing enzymes presumably present in the cytoplasm, mitochondria and plastids in respect to the inhibitory action of mevinolin. If prenyllipid formation in the different cell compartments solely depended on cytoplasmic mevalonate biosynthesis, all prenyllipids should be affected to the same extent as the sterols, which are exclusively synthesized by cytoplasmic enzymes.
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Schindler et al. (1985) studied this question.