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

Abstract

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 HCOJ has been examined by comparing the rate of photosynthetic 02-evolution with the photosynthetic rate which could be supported solely by C02 arising from the uncatalysed dehydration of HCOJ. No external carbonic anhydrase was detected by potentiometric assay in any of the species used. At pH 8 0, the rates of photosynthetic 02-evolution exceeded the C02 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 02-evolution to the C02 supply rate was even higher (19 to 101:1) at pH 9 0. It is evident from this data that the rate of C02 supply from the spontaneous breakdown of HCOJ 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.