FUNCTIONAL-ASPECTS OF SECONDARY CAROTENOIDS IN HAEMATOCOCCUS-LACUSTRIS [GIROD] ROSTAFINSKI (VOLVOCALES) .4. PROTECTION FROM PHOTODYNAMIC DAMAGE

The function as an antioxidant seems to represent the central principl e of chemopreventive activity of carotenoids against cancer initiation and promotion. The aim of this study was to clarify whether or not ex trachloroplastic-accumulated secondary carotenoids (astaxanthin, canth axanthin and echinenone) of Haematococcus lacustris [Girod] Rostafinsk i exhibit a similar antioxidative activity in protecting the cell of t his green alga from photo-oxidative damage. In vivo experiments were p erformed, investigating the effect of UV radiation, artificial photose nsitizers (rose bengal, toluidine blue) and copper-mediated lipid pero xidation on suspensions of flagellates which contained different amoun ts of secondary carotenoids. The results revealed a higher resistance of red flagellates to photo-oxidative stress. The findings are discuss ed with respect to the shading function of secondary carotenoids and k nown protective mechanisms involving quenching of reactive oxygen spec ies and radical reactions in plant cells. A hypothesis for this functi onal aspect of secondary carotenoids in H. lacustris preventing injury by excessive insolation is suggested: ketocarotenoids, first accumula ted in lipid vacuoles around the nucleus, might act as a physico chemi cal barrier, protecting particularly the genome from free radical-medi ated damage.