Summary: Synchronized akinete differentiation occurred following the transition from exponential to non-exponential (linear) growth, the major trigger being energy limitation. Young akinetes first accumulated cyanophycin, then developed a multilayered extracellular envelope and a thickened wall. The dry weight, chlorophyll , glycogen and carbon contents of mature akinetes were greater than those of vegetative cells, while their contents of DNA, RNA, protein, phycocyanin and nitrogen were similar to those of vegetative cells. Akinetes were resistant to desiccation and low temperatures, but not to temperatures above the maximum for vegetative cell growth.

In N-grown cultures heterocyst differentiation ceased at the end of exponential growth, while cell division continued, and akinetes first appeared in a regular pattern at a fixed distance (9 cells) from the nearest heterocyst. Exogenous NH inhibited the differentiation of heterocysts and, in their absence, akinetes developed in irregular positions. The regular spatial pattern imposed on akinete differentiation by heterocysts was, like the heterocyst spatial pattern itself, independent of N fixation. Similar changes in both patterns induced by 7-azatryptophan suggested that they share a common mechanism of control.


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