Cyanobacteria life history

Cyanobacteria are an extremely ancient group which have never developed the controlled division of cells by mitosis or meiosis. Sexual reproduction is therefore unknown, and multiplication is entirely vegetative (asexual), usually brought about by fragmentation, binary fission, or the formation of endospores,

Endospore Cyanobacteria

Fig. 8.3 Order Chroococcales. (a) Recent Synechocystis. (b) Precambrian Archaeosphaeroides. (c) Precambrian Huroniospora. (d) Precambrian Myxococcoides. (e) Recent Anacystis. (f) Fossil Renalcis. (g) Recent Eucapsis colony. (h) Precambrian Eucapsis-like colony. (i) Recent Entophysalis. Scale bar = 10 |m. ((b) Based on Schopf & Barghoorn 1967; (c) based on Barghoorn & Tyler 1965; (d) and (h) based on Cloud 1976; (g) based on Fogg et al. 1973; (i) from Chapman & Chapman 1973.)

Fig. 8.3 Order Chroococcales. (a) Recent Synechocystis. (b) Precambrian Archaeosphaeroides. (c) Precambrian Huroniospora. (d) Precambrian Myxococcoides. (e) Recent Anacystis. (f) Fossil Renalcis. (g) Recent Eucapsis colony. (h) Precambrian Eucapsis-like colony. (i) Recent Entophysalis. Scale bar = 10 |m. ((b) Based on Schopf & Barghoorn 1967; (c) based on Barghoorn & Tyler 1965; (d) and (h) based on Cloud 1976; (g) based on Fogg et al. 1973; (i) from Chapman & Chapman 1973.)

akinetes or hormogonia. Cell division involves the splitting of a cell into two daughter cells by inward growth of the wall (i.e. binary fission, Fig. 8.3a). The cell contents are randomly distributed between new cells, unlike the orderly mitotic divisions of eukary-otes. Fragmentation simply involves the breaking up of a colony into smaller ones. Endospores form by the internal subdivision of cells into two or more spores that are subsequently released to grow into new colonies (Fig. 8.3i). Akinetes are also spore cells, but these develop singly from vegetative cells by enlargement and the formation of a thick, often sculptured wall (Fig. 8.4c). After conditions of desiccation or chilling, new filaments germinate from the akinete. Hormogonia are characteristic of filamentous forms. These are short detached pieces of the trichome which glide out of their sheath and develop separately (Fig. 8.4a).

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