PHYSIOLOGICAL AND PHOTOSYNTHETIC CHANGES DURING THE FORMATION OF RED APLANOSPORES IN THE CHLOROPHYTE HAEMATOCOCCUS-PLUVIALIS

Changes in physiological and photosynthetic parameters were followed i n the freshwater chlorophyte Haematococcus pluvialis Flotow (Volvocale s) during the transformation of green vegetative cells to red aplanosp ores. Formation of aplanospores was induced by exposure to a nitrogen- deficient medium. In spite of an increase in cellular volume (from 6.6 to 41 pL) and a massive accumulation of astaxanthin, chlorophyll cont ent of the mature aplanospore decreased only slightly (from 16 to 14.8 pg. cell-1) as compared to the vegetative cell. Aplanospore formation was characterized by a gradual reduction in the maximal photosyntheti c rate and increases in the photo synthetic quantum requirement and mi nimal turnover time for photosynthetic O2 evolution. Respiration rate increased (4.2 times) and excretion rate decreased (up to 8.8 times) d uring aplanospore formation. Measurements of photosynthetic unit ''siz e'' and estimation of the cellular content of photosystem H reaction c enters suggest that the photosynthetic complex remains relatively stab le during the formation process and in the mature aplanospore. A funct ional relationship between the described changes in the physiology of the cells and their photosynthetic parameters is proposed.