Sites of biosynthesis of carotenoids in Capsicum chromoplasts.

Capsicum chromoplasts incubated with isopentenyl diphosphate actively synthesize carotenoids. The enzymes involved in these reactions are compartmentalized: the stroma is the site of phytoene synthesis, the first colourless carotenoid, while desaturation and cyclization of the latter leading to coloured carotenoids, occur in the membrane fraction (chromoplast envelope + achlorophyll lamellae derived in part from the inner envelope membrane). Phytoene synthetase could be used as a marker of chromoplast stroma.