Silica-containing inclusions in the cytoplasm of diatom Synedra acus.

Cells of the araphid pennate diatom Synedra acus subsp. radians contain large inclusion (1-15 μm) storing silica, as revealed by transmission electron microscopy and EDX-analysis. The size of the inclusions increases with the time of cultivation of diatoms. Approximate concentration of SiO2 in the inclusions is 1-4%. It is assumed that silica in the inclusions is present as gelatinized silica-gel. These results explain the possible mechanism of transport of silicic acid into the cell against the concentration gradient.