EVIDENCE FOR A PHOTOPROTECTIVE FUNCTION FOR SECONDARY CAROTENOIDS OF SNOW ALGAE

Snow algae occupy a unique habitat in high altitude and polar environm ents. These algae are often subject to extremes in nutrient availabili ty, acidity, solar irradiance, desiccation, and ambient temperature. T his report documents the accumulation of secondary carotenoids by snow algae in response to the availability of nitrogenous nutrients. Unusu ally large accumulations of astaxanthin esters in extra-chloroplastic lipid globules produce the characteristic red pigmentation typical of some snow algae (e.g. Chlamydomonas nivalis (Bauer) Wille). Consequent ly, these compounds greatly reduce the amount of light available for a bsorption by the light-harvesting pigment-protein complexes, thus pote ntially limiting photoinhibition and photodamage caused by intense sol ar radiation. The esterification of astaxanthin with fatty acids repre sents a possible mechanism by which this chromophore can be concentrat ed within cytoplasmic globules to maximize its photoprotective efficie ncy.