Akinetes of the Cyanobacterium Nostoc PCC 7524: Macromolecular and Biochemical Changes during Synchronous Germination

Abstract

Summary: Akinetes of Nostoc PCC 7524 germinated synchronously when diluted into fresh medium in the light in the absence of a source of combined nitrogen. The akinetes and their daughter cells were unable to fix N2 until the first heterocysts differentiated in the young three-celled filaments after 19 h. The large glycogen reserves of the mature akinetes were not necessary for germination, since fixation of CO2 commenced immediately and 70% of the fixed carbon accumulated as glycogen. Although cyanophycin was degraded after 6 h, this reserve material was subsequently resynthesized with concomitant breakdown of phycocyanin. These nitrogen reserves were not required for protein synthesis, which was initiated immediately after the induction of germination, apparently at the expense of another, non-proteinaceous, reserve material. Although RNA synthesis occurred without lag, DNA synthesis commenced only after 80 min. Quantitatively similar changes were observed during germination in the presence of combined nitrogen except that neither cyanophycin nor phycocyanin were degraded and balanced growth was achieved more rapidly.