Abstract
The most abundant unicellular calcifying alga, Emiliania huxleyi (Coccolithophrales, Haptophycea), is known to form a huge bloom in the ocean. Therefore, the alga plays a significant role in the global carbon cycle. To know physiological factors for bloom formation, it is essential to reveal the initial metabolism of photosynthesis. Using a 14C-radiotracer technique, we analyzed primary metabolites in photosynthesis. The labelling pattern was typical for C3 photosynthesis but the operation of beta-carboxylation was also active to produce significant amount of amino acids such as Ala, Asp and Glu. By the homology search of β-carboxylation enzymes in the Emiliania EST library, partial sequences highly homologous to phosphoenolpyruvate carboxykinase (PEPCK) and pyruvate carboxylase (PYC) were found. Northern blotting analysis revealed that the PYC transcript increased under illumination whereas the PEPCK transcript was suppressed. These results indicated that PYC is a responsible enzyme for active anaplerosis during photosynthesis in this alga.
