SILICON DEPOSITION DURING THE CELL-CYCLE OF THALASSIOSIRA-WEISSFLOGII(BACILLARIOPHYCEAE) DETERMINED USING DUAL RHODAMINE-123 AND PROPIDIUMIODIDE STAINING

The relatively non-toxic dye, rhodamine 123 (R123), was incorporated i nto the frustule of Thalassiosira weissflogii Grun. clone ACTIN in dir ect proportion to biogenic silica (BSi). R123 was used together with t he DNA stain propidium iodide to track and quantify Si deposition duri ng the cell cycle of T. weissflogii using flow cytometry. Silicon depo sition was not continuous through the cell cycle. Deposition of the va lves occurred during M phase. The hypocingulum was largely deposited d uring G1 with some suggestion of minor girdle band deposition during G 2. Silicon deposition did not occur during S phase. Assuming that a co mplete frustule consists of an epivalve, epicingulum, hypocingulum, an d hypovalve, then 40% of cellular BSi was contained within the cingulu m of T. weissflogii with 60% present in the valves. These percentages correspond to 0.38 pmol Si in the two cingula and 0.57 pmol Si in the valves. Temporal differences in the timing of silicic acid uptake and deposition during the cell cycle of T. weissflogii suggested that depo sition of both the new valves and the cingulum is supported by an inte rnal pool of dissolved Si acquired during G2.