Evidence for Bicarbonate Transport in Species of Red and Brown Macrophytic Marine Algae

Cook, C. M., Lanaras, T. and Colman, B. 1986. Evidence for bicarbonate transport in species of red and brown macrophytic marine algae.—J. exp. Bot. 37: 977–984. The capacity of 17 species of marine macrophytes to take up $HCO3-$ has been examined by comparing the rate of photosynthetic O₂-evolution with the photosynthetic rate which could be supported solely by CO₂ arising from the uncatalysed dehydration of $HCO3-$. No external carbonic anhydrase was detected by potentiometric assay in any of the species used. At pH 8·0, the rates of photosynthetic O₂-evalution exceeded the CO₂ supply rate 6 to 24-fold in 15 species of red algae, and 7 to 11-fold in 2 species of brown algae. The ratio of photosynthetic O₂-evalution to the CO₂ supply rate was even higher (19 to 101: 1) at pH 9·0. It is evident from this data that the rate of CO₂ supply from the spontaneous breakdown of $HCO3-$ cannot support the observed rates of photosynthesis in these algae. Thus, the data provide substantive evidence that $HCO3-$ is taken up by these marine macrophytes as a source of substrate for photosynthesis.