Variations in carboxylase activity in marine phytoplankton cultures, ß-carbolxylation in carbon flux studies

Abstract

Here carboxylase activity measurements for marine phytoplankton are described. Two indices measuring carboxylase activity in marine phytoplankton were used. The first measures Rubisco activity per unit chlorophyll (R/Chl; nmol CO sub(2) ( mu g chl a+b+c) super(-1)/h) while the second is the ratio of beta -carboxylase activity to Rubisco activity, expressed as %( beta C/R), which reflects the proportion of inorganic carbon fixed by these 2 groups of carboxylases. These ratios were studied in (1) different algal species in culture, (2) during the different growth phases of a culture, and (3) after a light-dark transition to measure the time response of carboxylase activities. These indices were different from one species to another at the same stage of growth. In autotrophic cells, beta -carboxylation remained low ( beta C/R < 40). The beta C/R ratio increased significantly when R/Chl began to decrease at the end of the growth phase of a culture of Skeletonema costatum . The heterotrophic dinoflagellate Crypthecodinium cohnii , grown on an organic medium, incorporated inorganic carbon in the dark through PEPCK activity.