CARBONIC ANHYDRASE ACTIVITY IN THE BLOOM‐FORMING DINOFLAGELLATE PERIDINIUM GATUNENSE

The response of carbonic anhydrase (CA) activity in Peridinium gatunense Nygaard, the natural bloom‐forming dinoflagellate in Lake Kinneret, to diel and seasonal variations in environmental conditions was characterized under controlled laboratory experiments. Simulated diel cycles demonstrated large changes in the ambient concentration of dissolved CO₂ and parallel changes in CA activity. The CA activity depended on the total concentrations of inorganic carbon (C₁) and in particular on the dissolved CO₂. Lowering the C₁concentrations resulted in a large increase in CA activity within several hours. Light and photosynthesis were both required for the induction of CA activity. Under CO₂ ‐limited conditions, the dependence of the photosynthetic rate on CA (estimated from the ratio of photosynthetic rates in the presence or absence of CA inhibitors) was greater in P. gatunense than in other eukaryotic microalgae. This points to the ecological significance of CA in photosynthetic carbon uptake mechanisms of a large, dominant alga in a natural ecosystem.