Physiological, Morphological and Ultrastructural to Combination Responses of Cyanobacterium Fischerella sp. FS 18 Effects of Extreme Conditions

Fischerella sp. FS 18 has been characterized physiologically, biochemically and morphologically at the combination of extremely low and relatively high irradiance (2 and 300 ?E.m-2.s-1), different pHs (5, 7, 9) and extremely limited carbon dioxide concentration. Results showed that neutral condition and limited irradiance cause maximum biomass production. The amount of oxygen liberation normalized to dry weight showed higher rate at neutral and then alkaline conditions. Chlorophyll content wassignificantly higher at neutral but the rate of photosynthesis increased at alkaline condition especially at fourth day after inoculation. Both phycobilisome length and PSII/PSI ratio were significantly higher at pH 7. Photosynthetic-irradiance curves showed that although maximum photosynthesis normalized to chlorophyll unit seem higher at neutral conditions, degree of adaptation to limited irradiance and consumed energy need reaching to maximum photosynthesis increase at this condition. Difference in pH, irradiance and DIC concentration could not change photoinhibition resistance pattern even at extremely high light intensities (more than 2000?E.m-2.s-1). Nitrogenase activity pattern were similar to photosynthesis. Biometrical analysis showed that except diameter of the heterocyst at the branches, decline of irradiance cause decrease in cell dimensions regardless of acidity and alkalinity. In low light intensity, there was no hormogonium production at different pHs.. TEM photomicrographs showed relatively linear and parallel configurations of thylakoids at pH 7, extremely limited irradiance and carbon dioxide concentrations. SEM photomicrographs showed holes and ornamentations belong to –especially – vegetative cells of the main axis at both pHs 7 and 9 regardless of light intensity.