Fluorescence microscopic evidence for intracellular silicon storage pools in diatoms and their partial separation

Fluorescence microscopy in Cyclotella nana under silicon starvation shows SSP-derived silica can reach intracellular concentrations up to ca. 540 mM, far above 2 mM saturation.

• Why it matters: The work addresses how intracellular silicon storage pools (SSPs) are chemically state and localized, and how SSP silicon is mobilized into the silicon deposition vesicle (SDV).
• What they did: Cells were labeled with PDMPO to visualize SSP-only silica formation during silicon starvation, then subcellular fractionation by density gradient centrifugation quantified cytoplasmic silicon at 3–10% (ca. 50–160 mM).
• The result: 29Si NMR indicates the cytoplasmic silicon is condensed silica, but its lower concentration than the ca. 540 mM fluorescence estimate suggests missing SSP silicon is in large aggregates/compartments or bound to cell wall biosilica.

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