Nitrogenase in free-living and symbiotic cyanobacteria: Immunoelectron microscopic localization

Abstract Nitrogenase (Fe-protein) was localized in the free-living cyanobacterium Anabaena cylindrica and in the cyanobionts of Cycas revoluta and Peltigera aphthosa , using colloidal gold as an immunocytochemical marker. The Fe-protein was found to be evenly distributed throughout the heterocyst cytoplasma in A. cylindrica and in both the cyanobionts, including multiple heterocysts of the C. revoluta cyanobiont. No label was observed in the vegetative cells of free-living A. cylindrica or of the cyanobionts, although the cyanobionts apparently live under microaerobic conditions.