ANTIOXIDANT ROLE OF ASTAXANTHIN IN THE GREEN-ALGA HAEMATOCOCCUS-PLUVIALIS

The green unicellular alga, Haematococcus pluvialis has two antioxidat ive mechanisms against environmental oxidative stress: antioxidative e nzymes in vegetative cells and the antioxidative ketocarotenoid, astax anthin, in cyst cells. We added a reagent that generates superoxide an ion radicals (O-2(-)), methyl viologen, to mature and immature cysts o f H. pluvialis. Tolerance to methyl viologen was higher in mature than in immature cysts. Mature (astaxanthin-rich) cysts showed high antiox idant activity against O-2(-) in permeabilized cells, but not in astax anthin-free cell extracts, while immature (astaxanthin-poor) cysts had very low antioxidant activities against O-2(-) in both. The results s uggested that astaxanthin accumulated in the cyst cells functions as a n antioxidant against excessive oxidative stress. The same levels of a ntioxidant activities against O-2(-) in both permeabilized cells and c ell extracts from vegetative cells suggested the presence of antioxida tive enzymes (superoxide dismutase).