FUNCTIONAL ASPECTS OF SECONDARY CAROTENOIDS IN HAEMATOCOCCUS LACUSTRIS (VOLVOCALES). III. ACTION AS A “SUNSHADE”1

We investigated the protection from photoinhibition by different developmental stages of Haematococcus lacustris Girod] Rostafinski using chlorophyll fluorescence measurements of single cells and suspensions. An overall correlation between higher cellular content of secondary carotenoids and the capacity to withstand excessive irradiation was observed in flagellated cells and aplanospores of H. lacustris. Low-light-reversible spreading of extra-chloroplastic secondary carotenoids occurred in the periphery of the cell during strong irradiation. This process resulted in increased shading of the cup-shaped chloroplast as demonstrated by a decrease in chlorophyll fluorescence. Extrachloroplastic accumulation of secondary carotenoids in H. lacustris can be interpreted as a specific adaptation to habitats that exhibit strong insolation.