Putative silicon transport vesicles in the cytoplasm of the diatom Synedra acus during surge uptake of silicon

Abstract

We studied the growth of the araphid pennate diatom Synedra acus subsp. radians (Kützing) Skabichevskii using a fluorescent dye N(1),N(3)-dimethyl-N(1)-(7-nitro-2,1,3-benzoxadiazol-4-yl)propane-1,3-diamine (NBD-N2), which stains growing siliceous frustules but does not stain other subcellular organelles. We used a clonal culture of S. acus that was synchronized by silicon starvation. Epifluorescence microscopy was performed in two different ways with cells stained by the addition of silicic acid and the dye. Individual cells immobilized on glass were observed during the first 15-20 min following the replenishment of silicic acid after silicon starvation. Alternatively, we examined cells of a batch culture at time intervals during 36 h after the replenishment of silicic acid using fluorescence and confocal microscopy. The addition of silicic acid and NBD-N2 resulted in the rapid (1-2 min) formation of several dozen green fluorescent submicrometer particles (GFSPs) in the cytoplasm, which was accompanied by the accumulation of fluorescent silica inside silica deposition vesicles (SDVs) along their full length. In 5-15 min, GFSPs disappeared from the cytoplasm. Mature siliceous valves were formed within the SDVs during the subsequent 14-16 h. In the next 8-10 h, GFSPs appeared again in the cytoplasm of daughter cells. The data obtained confirm observations about the two-stage mechanism of silicon assimilation, which includes rapid silicon uptake (surge uptake) followed by slow silica deposition. It is likely that the observed GFSPs are silicon transport vesicles, which were first proposed by Schmid and Schulz in (Protoplasma 100:267-288, 1979).

Titanium uptake and incorporation into silica nanostructures by the diatom Pinnularia sp. (Bacillariophyceae)

“…When diatoms grow exponentially (i.e. resource-unlimited growth), silicic acid (SiOH 4 ) is actively transported via silica transporters (SITs) into the cytoplasm and then via transport vesicles into silica deposition vesicles (SDVs) (Annenkov et al 2013 ). This process involves active transport against a concentration gradient from cytosol into the SDV and a pH gradient because the inside of the SDV has a lower pH.…”

The Probable Mechanism for Silicon Capture by Diatom Algae: Assimilation of Polycarbonic Acids with Diatoms—Is Endocytosis a Key Stage in Building of Siliceous Frustules?

“…PVA-NBD was prepared by PVA modification with 4-chloro-7-nitro-2,1,3-benzoxadiazole (NBD-Cl), tagged PVI and PVP were synthesized from the corresponding copolymers which contained 2%-3% of vinyl amine units. PAA-NBD was obtained by the reaction of poly(acryloil chloride) with NBD-N2H amine (Annenkov et al 2013). The labeled polymers were purified from low-molecular weight fluorescent compounds by multiple precipitation and dialysis.…”

“…PAA‐NBD was obtained by the reaction of poly(acryloil chloride) with NBD‐N2H amine (Annenkov et al. 2013). The labeled polymers were purified from low‐molecular weight fluorescent compounds by multiple precipitation and dialysis.…”

Silica-containing inclusions in the cytoplasm of diatom Synedra acus

“…Skabitsch. In one of the studies performed at the Institute of Limnology [4] using epifluorescence light microscopy, large inclusions stained with silicaspecific intravital dye were found in the cytoplasm of S. acus, but the direct method did not show the presence of silica in these inclusions.…”