Photosynthetic metabolism in the cyanophytaOscillatoria rubescens D.C.

Short term¹⁴C labelling experiments and enzymatic activities related to primary pathways of photosynthesis have been studied in the cyanophytaOscillatoria rubescens D.C. from axenic cyclostat cultures. Responses of samples from cultures with different amounts of nitrogen are presented and compared. Variations in photosynthetic pigments are used to quantify the degree of nitrogen starvation at different levels.PEPcarboxylase activity remains low and is not affected by nitrogen starvation. RuBPcarboxylase activity is lowered to nearly two thirds of its normal metabolic rate by starvation but PEPcarboxykinase and aspartate aminotransferase activities are significantly higher in this case. Malate dehydrogenase is slightly altered and malic enzyme is never active. Starved algae replaced in fresh complete media fix rapidly¹⁴C in nitrogen compounds such as amino acids. Results are discussed in regard to both physiological and ecological characteristics ofO. rubescens. PEPcarboxykinase can play a role in making efficient use of HCO ₃ ^- .Abbreviations AAT aspartate aminotransferase - APC allophycocyanin - ASM 1 algal synthetic medium, 1st modification - DW dry weight - GAPDH glyceraldehyde 3-phosphate dehydrogenase - MDH malate dehydrogenase - PC phycocyanin - PE phycoerythrin - PEP phophoenolpyruvate - PEPC phosphoenolpyruvate carboxylase - PEPCK phophoenolpyruvate carboxykinase - PGA 3-phosphoglyceric acid - RuBPC ribulose bisphosphate carboxylase