FUNCTIONAL-ASPECTS OF SECONDARY CAROTENOIDS IN HAEMATOCOCCUS-LACUSTRIS (VOLVOCALES) .3. ACTION AS A SUNSHADE

We investigated the protection from photoinhibition by different devel opmental stages of Haematococcus lacustris [Girod] Rostafinski using c hlorophyll fluorescence measurements of single cells and suspensions. An overall correlation between higher cellular content of secondary ca rotenoids and the capacity to withstand excessive irradiation was obse rved in flagellated cells and aplanospores of H. lacustris. Low-light- reversible spreading of extrachloroplastic secondary carotenoids occur red in the periphery of the cell during strong irradiation. This proce ss resulted in increased shading of the cup-shaped chloroplast as demo nstrated by a decrease in chlorophyll fluorescence. Extrachloroplastic accumulation of secondary carotenoids in H. lacustris can be interpre ted as a specific adaptation to habitats that exhibit strong insolatio n.