Photosynthetic 14CO2 Fixation in Differently Pigmented Anabaena cylindrica

Abstract

Growth of Anabaena cylindrica at different intensities of white and red light (> 650 nm) was associated with changes in the content and composition of the pigments. The ratio of chlorophyll a to phycocyanin and carotenoids varied from 1:8.1:0.7 in low white light grown cells to 1:6.3:1.3 in cells grown at strong white light and to 1:18.4:0.8 in cultures exposed to red light. The chlorophyll a content was identical in cultures grown in low white and red light and decreased about 50% in those grown in strong white light. The phycocyanin content was enhanced (100%) in Anabaena cells grown in red light and diminished (65%) in those grown in strong white light. Total amino acid content and the values of aspartate, glutamate, glutamine, glycine and arginine studied by high performance liquid chromatography were lower in cells grown in strong white light and red light than in low white light. A markedly enhanced amount of alanine was estimated in strong white light Anabaena extracts. In cells grown in red light, so far not identified primary amines were also detected. Short term kinetics experiments on photosynthetic 14 CO 2 fixation (percentage proportion of soluble products) of these cyanobacteria cultures showed that the Calvin cycle is the main CO 2 assimilation pathway. The percentage proportion of radioactivity of total amino acids arises from low white light to strong white light cells; the main part of the 14 C-label could be detected in aspartate, alanine and glycine/serine. A decrease of the 14 C-label of sugar monophosphates was found in strong white light cultures in comparison to low white light and red light Anabaena cylindrica . The enzyme activities of ribulose-1,5-bisphosphate carboxylase, aspartate-α-ketoglutarate and aspartate aminotransferase decreased in strong white light grown cells. On the other hand, an increase of activities of malate dehydrogenase (NADPH 2 and NADH 2 ), alanine and serine-pyruvate aminotransferases could be observed. Phosphoenolpyruvate carboxylase activity showed practically no change. Our findings indicate that the phosphoenolpyruvate carboxylation reaction must be enhanced in strong white light grown cells.