Does astaxanthin protect Haematococcus against light damage?

ABSTRACT

The photoprotective function of the ketocarotenoid astaxanthin in Haematococcus was questioned. When exposed to high irradiance and/or nutritional stress, green Haematococcus cells turned red due to accumulation of an immense quantity of the red pigment astaxanthin. Our results demonstrate that 1) The addition of diphenylamine, an inhibitor of astaxanthin biosynthesis, causes cell death under high light intensity; 2) Red cells are susceptible to high light stress to the same extent or even higher then green ones upon exposure to a very high light intensity (4000 mumol photon m(-2)s(-1)); 3) Addition of 1O2 generators (methylene blue, rose bengal) under noninductive conditions (low light of 100 mumol photon m(-2)s(-1) induced astaxanthin accumulation. This can be reversed by an exogenous 1O2 quencher (histidine); 4) Histidine can prevent the accumulation of astaxanthin induced by phosphate starvation. We suggest that 1) Astaxanthin is the result of the photoprotection process rather than the protective; 2) 1O2 is involved indirectly in astaxanthin accumulation process.