heterocyst

Once a heterocyst has formed it cannot revert to a vegetative cell.

Nitrogenase is inactivated by oxygen, so the heterocyst must create a microanaerobic environment.

The senescent heterocyst undergoes vacuolation and finally breaks off from the filament causing fragmentation.

For the proper functioning of nitrogenase, the intracellular environment of the heterocyst must be anaerobic, a task achieved by the oxygen-impermeable structure of the heterocyst wall.

Filamentous cyanobacteria (such as Anabaena and Nostoc ) subscribe to a developmental program of heterocyst formation that is widely considered the primitive state and that correlates with their exceedingly large genomes.