Uptake and Accumulation of Inorganic Carbon by a Freshwater Diatom

Abstract

Colman, B. and Rotatore, C. 1988. Uptake and accumulation of inorganic carbon by a freshwater diatom.—J. exp Bot 39: 1025–1032. The mechanism of uptake of inorganic carbon and its accumulation has been studied in the freshwater diatom Navicula pelliculosa. No external carbonic anhydrase could be detected, although it was detected in cell extracts. The rate of photosynthetic O₂ evolution, in media in the range pH 7.5–8.5, exceeded the calculated rate of CO₂ supply 2- to 5-fold, indicating that HCO⁻₃ was taken up by the cells. At an external pH of 7.5, the internal pH, measured by ¹⁴C-dimethyloxazolidine-2, 4-dione distribution between the cells and the medium, was pH 7.6 in the light and pH 7.4 in the dark. Accumulation of inorganic carbon was determined by the silicone oil centrifugation method and inorganic carbon pools of 23.5 mol m⁻³ were found, a concentration 21.6-fold that in the external medium. The results indicate an active accumulation of inorganic carbon against pH and concentration gradients in this diatom, probably by active HCO⁻₃ uptake.