Numerous publications report the existence of intracellular "Si" storage pools in diatoms representing intracellular concentrations of ca. 19-340 mM depending on the species. "Si" storage pools in diatom cells, if present, are supposed to accumulate "Si" for the production of new valves. The accumulated "Si" is then transported into the Silicon Deposition Vesicle (SDV) where the new cell wall is synthesized. Interestingly, the reported concentrations of intracellular "Si" within the storage pool sometimes strongly exceed the solubility of monosilicic acid (ca. 2 mM pH < 9). Various types of "Si" storage pools are discussed in the literature. It is usually assumed that "Si" species are stabilized by the association with some kind of organic material such as special proteins, thus forming a soluble silicic acid pools inside the cells.
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