Avoidance strategy of high light in Haematococcus

Abstract

Carotenoids in plants and algae are known for their role as photosynthetic antenna pigments or antioxidant effect. A unicellular green alga Hematococcus produces a red carotenoid, astaxanthin, from β-carotene as a precursor and accumulates in the cell. Recent studies have revealed that astaxanthin is contained in lipid droplets and localized outside the chloroplast. It is suggested that astaxanthin has the other functions essentially different from β-carotene and lutein localized in the chloroplast. When time-lapse imaging analysis was performed, astaxanthin contained lipid droplets actively in the cell. In the Hematococcus cell, it was observed that the strong light was avoided by shielding the light directly. As a result of hyperspectral and freeze-fracture replica imaging, it became clear that Haematococcus developed a successful adaptive strategy for light intensity using astaxanthin-containing oil droplets to avoid strong light.