Boron Protection for O2 Diffusion in Heterocysts of Anabaena sp. PCC 7119

The effect of boron on nitrogenase activity has been studied. When cells were dependent on N(2) fixation, the lack of boron inhibited nitrogenase activity. However, under anaerobic conditions or in the presence of Na-dithionite this effect was not observed. Nitrogenase synthesis was not affected by boron deficiency. Similarly, the heterocyst number was not altered. Examination of boron-deficient cultures showed, however, some dramatic changes in heterocyst morphology. The increased activity of those enzymes related to the maintaining of the low intracellular level of toxic oxygen species (superoxide dismutase, catalase, and peroxidase) support our hypothesis of the role of boron in heterocyst envelope stabilization.