Some New Aspects of Isoprenoid Biosynthesis in Plants

Abstract

A myriad of natural compounds are derivatives of a common C-5 isoprene unit and are thus classified as isoprenoids. It is impossible to cover all aspects of plant isoprenoid biosynthesis, which would go far beyond the scope of this contribution. I will rather try to focus the reader’s attention on some recent aspects, which, at first sight, are not compatible or are even in conflict to each other. Other aspects, partially discussed a long time ago, might be looked at under a new aspect. Of course, with these limitations, not only set by the space available, the selection of literature and subjects must remain quite personal and will also include some aspects of our own studies. The problem of intracellular localization of enzymes, especially for those standing at the entry of the multi-branched isoprenoid pathway, is still a matter of debate and will be discussed in view of new findings. At recent meetings research groups from Japan and Switzerland have presented evidence of alternative pathways of mevalonate and/or isopentenyl pyrophosphate formation in plants, the latter one being reminiscent of the so-called Rohmer pathway occurring in certain bacteria. The possible existence of two independent and strictly compartmentalized biosynthetic pathways for the formation of a single intermediate would explain contradictory results as to the partial or complete independence of organelles from cytoplasmic enzymes, deduced from incorporation and inhibition studies as well as by determination of enzyme activities in subcellular fractions.