Iron superoxide dismutase (Fe-SOD) localization in Chroococcidiopsis sp (Chroococcales, Cyanobacteria)

One-month-old and 1-year-old cultures of Chroococcidiopsis sp. were examined for the presence and distribution of iron superoxide dismutase (Fe-SOD) by immunogold labelling. In 1-month-old cultures, comprising cell aggregates, Fe-SOD was localized mainly in the. nucleoplasm and in the cell envelope. In I-year-old cultures, where the cells were mainly single, Fe-SOD was present in the peripheral cytoplasm. However, in isolated cells, Fe-SOD was abundant also in the envelope but absent in the nucleoplasmic areas. Its occurrence in the aggregates and in the envelope of isolated cells suggests that it could function as a barrier against oxygen radicals both in the cytoplasm and in the extracytoplasmic area. The presence of Fe-SOD supports the notion that Chroococcidiopsis is a primitive cyanobacterium and that this enzyme. originated very early in the history of Earth when oxygenic photosynthesis arose.