ACCUMULATION OF SECONDARY CAROTENOIDS IN CHLORELLA-ZOFINGIENSIS

We have previously found that in Chlorella emersonii, grown under syne rgistic conditions of high irradiance and low nitrogen, chlorophyll an d primary carotenoids were degraded, whereas secondary carotenoids wer e produced. In this study Chlorella zofingiensis was cultivated under similar conditions. Maximal growth was achieved in a culture growing u nder light irradiance of 150 mu mol quanta m(-2) s(-1) and a nitrogen concentration of 0.5 mg/mL of KNO3. Higher nitrogen concentrations or higher irradiance inhibited cell division. The secondary carotenoids p roduced were identified as canthaxanthin (about 30%) and astaxanthin ( about 70%) in the form of mono- and diesters. Maximal accumulation occ urred in cells starved of nitrogen and grown at a light irradiance of 300 mu mol m(-2) s(-1). Exposure of a thin layer of algal cells to sun light resulted in de-esterification of the astaxanthin esters. It is s uggested that secondary carotenoids have a photo-protective role, that is, under high light conditions they protect chlorophyll and other ph otosynthetic pigments against damage.