Abstract
The green unicellular alga, Haematococcus pluvialis has two antioxidative mechanisms against environmental oxidative stress: antioxidative enzymes in vegetative cells and the antioxidative ketocarotenoid, astaxanthin, in cyst cells. We added a reagent that generates superoxide anion radicals (O2 −), methyl viologen, to mature and immature cysts of H. pluvialis. Tolerance to methyl viologen was higher in mature than in immature cysts. Mature (astaxanthin-rich) cysts showed high antioxidant activity against O2 − in permeabilized cells, but not in astaxanthin-free cell extracts, while immature (astaxanthin-poor) cysts had very low antioxidant activities against O2 − in both. The results suggested that astaxanthin accumulated in the cyst cells functions as an antioxidant against excessive oxidative stress. The same levels of antioxidant activities against O2 − in both permeabilized cells and cell extracts from vegetative cells suggested the presence of antioxidative enzymes (superoxide dismutase).
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