THE EFFECT OF HIGH IRRADIANCES ON GROWTH, BIOSYNTHETIC ACTIVITIES ANDTHE ULTRASTRUCTURE OF THE GREEN-ALGA BOTRYOCOCCUS-BRAUNII STRAIN DROOP 1950 807-1/

The green alga Botryococcus braunii strain DROOP 1950/807-1 was grown in a batch culture supplemented with 3 % of CO2 at 25-degrees-C and at a wide range of irradiances. The biomass doubling times in the expone ntial phase were 5, 3.7, 3.4 and 2.5 days for 15, 40, 90, and 180 W . m-2, respectively. The transmission electron microscopy revealed that the ultrastructure of cells growing for 14 days under 90 and 180 W . m -2 differs from those growing under 15 and 40 W . M-2 by the presence of large ''structured vacuoles''. In addition, under low irradiance (1 5 W . m-2) the cells were surrounded with a low amount of small hydroc arbon droplets and were full of starch grains. Under medium irradiance s (40 and 90 W . m-2) the cells were surrounded with several layers of huge hydrocarbons droplets. Under high irradiance (180 W . m-2) a lar ge amount of exopolysaccharides was released into the medium. The resu lts indicate that the metabolic pathways of the strain can be easily c ontrolled by different irradiations, i. e. from starch to hydrocarbons and polysaccharides. In addition, the alga is able to use biocarbonat e as a source of carbon at a wide range of irradiances (35, 75, and 15 0 W . m-2) because the final pH of the medium in enclosures reached H = 11 at all irradiances.