Functional aspects of secondary carotenoids in Haematococcus lacustris [Girod] Rostafinski (Volvocales) IV. Protection from photodynamic damage

The function as an antioxidant seems to represent the central principle of chemopreventive activity of carotenoids against cancer initiation and promotion. The aim of this study was to clarify whether or not extrachloroplastic-accumulated secondary carotenoids (astaxanthin, canthaxanthin and echinenone) of Haematococcus lacustris Girod] Rostafinski exhibit a similar antioxidative activity in protecting the cell of this green alga from photo-oxidative damage. In vivo experiments were performed, investigating the effect of UV radiation, artificial photosensitizers (rose bengal, toluidine blue) and copper-mediated lipid peroxidation on suspensions of flagellates which contained different amounts of secondary carotenoids. The results revealed a higher resistance of red flagellates to photo-oxidative stress. The findings are discussed with respect to the shading function of secondary carotenoids and known protective mechanisms involving quenching of reactive oxygen species and radical reactions in plant cells. A hypothesis for this functional aspect of secondary carotenoids in H. lacustris preventing injury by excessive insolation is suggested: ketocarotenoids, first accumulated in lipid vacuoles around the nucleus, might act as a physico chemical barrier, protecting particularly the genome from free radical-mediated damage.