Plastidic Isoprenoid Synthesis Changes from an Autonomous to a Division-of-Labor Stage During Chloroplast Maturation

Carotenoids, plastoquinone, tocopherols and the phytyl moiety of Chlorophyll are generally known as isoprenoids synthesized in the chloroplast. The origin of IPP to form these plastidic compounds is, however, still under debate. We are able to demonstrate that the basal region of leaves from 10-d old barley seedlings containing developing chloroplasts forms plastidic isoprenoids predominantly from photosyn-thetically fixed CO2 and only to a lesser extent from added mevalonate (Mev). The conditions totally changes during chloroplast maturation. The ability to form these compounds from CO2 disappears at the apical region of the leaves containing mature chloroplasts. In this region IPP, formed from added Mev, is effectively used for isoprenoid synthesis. Developing and mature chloroplasts isolated from leaf protoplasts conform in behavior with the corresponding leaf regions.