Pigment mutant C‐6D of the green alga Scenedesmus obliquus exhibits a light‐dependent chloroplast differentiation. The changes were analyzed by high performance liquid chromatography (HPLC). Dark‐grown cells of mutant C‐6D contain only precursors of carotenoids (carotene, neurosporene, lycopene and β‐zeacarotene). The lycopene and two neurosporenes were identified to be cw‐isomers. After transfer to light lycopene decreases rapidly. Simultaneously the other precursors increase for a short period and then decrease, too. Using a specific HPLC‐system the changes in carotene‐ and xanthophyll‐content were analyzed. During the first 30 min of illumination the amount of β‐carotene increases very fast and then levels off. The kinetics of xanthophyll‐formation differ remarkably. Whereas lutein is synthesized immediately after onset of illumination, all other xanthophylls are formed with high rates only after a lag‐phase of about 30 min. After illumination in the presence of nicotine no cyclic carotenes and xanthophylls could be detected. Instead of the cw‐lycopene these cells contain high amounts of the all ‐trans lycopene. The light‐regulation of the biosynthetic pathway leading to carotenes and xanthophylls in mutant C‐6D is discussed.
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Klaus Humbeck (1990) studied this question.
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