Silica transport in the demosponge Suberites domuncula: fluorescence emission analysis using the PDMPO probe and cloning of a potential transporter

Abstract

Silicon is, besides oxygen, the most abundant element on earth. Only two taxa use this element as a major constituent of their skeleton, namely sponges (phylum Porifera) and unicellular diatoms. Results from combined cytobiological and molecularbiological techniques suggest that, in the demosponge Suberites domuncula, silicic acid is taken up by a transporter. Incubation of cells with the fluorescent silica tracer PDMPO [2-(4-pyridyl)-5-[[4-(2-dimethylaminoethylaminocarbamoyl)methoxy]phenyl]-oxazole] showed a response to silicic acid by an increase in fluorescence; this process is temperature-dependent and can be blocked by DIDS (4,4-di-isothiocyanatostilbene-2,2-disulphonic acid). The putative NBC (Na+/HCO3-) transporter was identified, cloned and analysed. The deduced protein comprises all signatures characteristic of those molecules, and phylogenetic analysis also classifies it to the NBC transporter family. This cDNA was used to demonstrate that the expression of the gene is strongly up-regulated after treatment of cells with silicic acid. In situ hybridization demonstrated that the expression of the sponge transporter occurs in those cells that are located adjacent to the spicules (the skeletal element of the animal) or in areas in which spicule formation occurs. We conclude that this transporter is involved in silica uptake and have therefore termed it the NBCSA [Na+/HCO3-[Si(OH)4]] co-transporter.

Experimental silicon demand by the sponge Hymeniacidon perlevis reveals chronic limitation in field populations

“…Likewise, it remains unclear how dissolved silicon is internalized by the sponges. Suggestions have been made that a sodium-bicarbonate co-transporting system could somehow be involved in taking up silicic acid from seawater (Schröder et al, 2004), which would rather be consistent with a transport enzymatic kinetic. Our results reveal that, despite H. perlevis being a species evolved to growth at the intertidal zone, its uptake system appears to have been designed to consume daily much higher amounts of Si than are allowed by the natural DSi concentrations in the sublittoral zone.…”

Identification of a silicatein(-related) protease in the giant spicules of the deep-sea hexactinellidMonorhaphis chuni

“…Therefore, it is very surprising that in this habitat these two hexactinellid sponges synthesize the largest bio-silica structures existing on earth (see Introduction). From studies with the demosponge S. domuncula it is known that sponges have the potential to actively accumulate silicate, through a silica-bicarbonate {Na + /HCO 3 -[Si(OH) 4 ]} cotransporter (Schröder et al, 2004). We have recently postulated that all siliceous sponges, including Monorhaphis, are provided with enzymatic machinery to polymerize/condense bio-silica through the enzyme silicatein Wang et al, 2007) to construct/synthesize their spicules, which may be up to 3·m long and 10·mm thick in the case of Monorhaphis.…”

Plants and Light Manipulation: The Integrated Mineral System in Okra Leaves

“…PDMPO is a fluorophore that electrostatically interacts with the silica surface 36. PDMPO was used to investigate silica deposition in diatoms and radiolaria,37, 38, 39, 40, 41 and in plants to visualize extracted silica bodies 42. By superimposing the microCT and confocal images, we create a 3D map of the whole leaf showing the distributions of calcium oxalates, silica, and the naturally fluorescing chlorophyll.…”