Polyhedral bodies (Carboxysomes) of nitrogen-fixing blue-green algae

Blue-green algae possess polyhedral bodies which, under the electron microscope, resemble the carboxysomes containing ribulose-1-5-diphosphate carboxylase (RUDPCase) in the chemoautotrophic bacterium Thiobacillus.2 These bodies are present in vegetative cells but not the heterocysts of 15 strains of Anabaena, Nostoc, Plectonema and Westiellopsis, including material grown photoautotrophically, photoheterotrophically and dark heterotrophically. They are also present in spores (akinetes). Their absence from heterocysts provides morphological evidence in support of the view that heterocysts are deficient in RUDPCase.