Photosynthetic carbon assimilation in the blue‐green alga Coccochloris peniocystis
Abstract. Cells of the blue-green alga Coccochloris peniocystis, grown at air levels of CO2, were exposed to [l4C]bicarbonate in the light for periods of 0.5 to 2.0 s followed by exposure to unlabelled bicarbonate for longer periods of time in the light. The kinetics of tracer movement during these pulse-chase experiments demonstrate that the principal mechanism of CO2 fixation in this alga is the C3-pathway although an appreciable amount of the C4 acid aspartate is found as one of the initial products of photosynthesis. Degradation of the labelled aspartate revealed that after 20 s of illumination, over 95% of the radioactivity was located in the β-carboxyl of this C4 acid. This alga possesses little, if any, capacity for either the enzymatic decarboxylation of C4 acids or the regeneration of phosphoenolpyruvate (PEP) from pyruvate mediated by the enzyme pyruvate, Pi dikinase. These data further demonstrate the lack of a functional C4-pathway in this alga.