Mother Cell Wall Cleavage during Filament Formation in Stichococcus bacillaris (Trebouxiophyceae, Chlorophyta)

Stichococcus Nägeli is a unicellular green algal species that belongs to the Trebouxiophyceae. Stichococcus bacillaris Nägeli NIES-3639 propagates by binary fission, but can form a filament without separating into two daughter cells. Transmission electron microscopy showed that cytokinesis starts according to invagination of the plasma membrane at the plane of division. Synthesis of the daughter cell wall occurs on the surface of invaginating plasma membrane during the protoplast division phase. The mother cell wall may cleave after protoplast division in either the single-cell or filament state. Field emission scanning electron microscopy revealed scars of cleaved mother cell walls from the single-cell state, two-cell state after cell division, and four-cell state during filament formation. Because the mother cell wall was cleaved, the delay of the daughter cell separation may have caused filament formation. Since this cell division cycle repeats rapidly, it may begin before the separation of the daughter cells yielded by the former cell cycle.