Abstract
Light-dependent carotenoid formation has been investigated in the cyanobacterium Synechocystis PCC 6803. Upon transfer of cultures from low- (35 μmol m −2 s −1) to high-intensity illumination (500 μmol m −2 s −1), a decrease of the endogenous carotenoids to 85% of the initial value is observed. Treatment with norflurazon, an inhibitor that blocks the synthesis of coloured carotenoids, demonstrates a much stronger degradation of the existing carotenoids, which was more pronounced at high light intensities. However, the amounts of the accumulating precursor phytoene reveal that de novo biosynthesis is enhanced under high-light conditions. Nevertheless, this upregulated synthesis cannot fully compensate for carotenoid loss by photodegradation. The potential of the carotenoids from Synechocystis to protect against photosensitized and radical peroxidation reactions has been evaluated. It is found that myxoxanthophyll, which is preferentially synthesized in high light, exhibits the strongest protection and that echinenone is the most stable carotenoid under photo-oxidative conditions.
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