PHOTOSYNTHETIC CHARACTERISTICS OF DUNALIELLA-SALINA (CHLOROPHYCEAE, DUNALIELLALES) IN RELATION TO BETA-CAROTENE CONTENT

Photosynthetic characteristics of Dunaliella salina with high (red form) and low beta-carotene (green form) concentrations were studied. D. salina growing in brine saltworks exhibited a high level of beta-carotene (15 pg cell-1). The rate of oxygen evolution as a function of irradiance was higher in the red than in the green form (on chlorophyll basis). Photosynthetic inhibition of the green form was observed above 500-mu-mol m-2 s-1. The red form appeared more resistant to high irradiance and no inhibition in O2 evolution was observed up 2000-mu-mol m-2 s-1. However, when these results are expressed on a cell number basis the rate of oxygen evolution was significantly higher in the green form. Carbonic anhydrase (CA) activity (total, soluble, membrane bound) was found in red and green forms. CA was higher in the red form on a chlorophyll basis, but lower if expressed on a protein basis. The light dependent rate of oxygen evolution and photoinhibition depends on the concentration of beta-carotene in D. salina cells.