The heterocyst, regularly spread among more numerous vegetative cells (ratio 1:15), receives carbon compounds fixed by the neighboring vege­tative cells in exchange of the nitrogenous compounds fixed by them. Nitrogenase, like hydrogenase, needs an anaerobic environment to func­tion and can produce hydrogen only under certain conditions (absence of molecular nitrogen). The ratio of evolution of hydrogen and oxygen roughly corresponds to the ratio of the heterocysts and vegetative cells and also with the ratio of nitrogen and carbon for nutritive requirements.

If the algal culture is exposed to argon for about 24 hours, due to nitro­gen starvation, differentiation of the heterocysts increases from 6% up to 20%. In addition, a yellowish color appears due to the loss of the light­trapping pigment phytocyanin, resulting in less carbon dioxide fixation, i. e., oxygen evolution and an increase in light conversion efficiency by almost 0.5%. Induction of reversible hydrogenase in the heterocysts, as its theoretically higher turnover principle, is less affected by N2 and O2, and independent of ATP, it becomes more desirable and needs heterocysts to be genetically improved.