Effect of ammonium nitrate on the heterocyst differentiation and nitrogen fixing activity of Anabaena HA 101

Heterocysts were able to be induced while the blue-green alga Anabaena HA 101 were grown in a medium free from ammonium nitrate, but the heterocyst formation was inhibited while the Anabaena were grown in medium containing 5 mM ammonium nitrate. Heterocysts which had already formed were enhanced to senescence by the ammonium nitrate. Heterocyst transformation from certain vegetative cells into adult heterocysts accompanied with protein synthesis. A maximal level of protein synthesis as well as the high activity of nitrogenase was detected while the late proheterocysts transformed to mature heterocysts. Heterocyst is the site of nitrogenase synthesis and of the nitrogen fixation.