MICROMORPHOGENESIS DURING DIATOM WALL FORMATION PRODUCES SILICEOUS NANOSTRUCTURES WITH DIFFERENT PROPERTIES(1).

Micromorphogenesis within the silica deposition vesicle (SDV) of the diatom Pinnularia viridis (Nitzsh) Ehrenb. resulted in distinct silica nanostructures and layers within forming valves and girdle bands. These siliceous components were similarly disclosed following alkaline etching of mature valves/girdle bands, where their different susceptibilities to dissolution over time resulted from apparent differences in silica density and/or chemistry. The bulk of silica appeared to be deposited at the interface of the forming valve or girdle band with the silicalemma and occurred by the outward expansion of microfibrils of silica that aligned perpendicularly to the silicalemma. Microfibrils originated from both sides of the "silica lamella," the first nanostructure formed within the SDV, and several silica species of distinct nanostructure and density resulted, including distinctive inner and outermost silica "coverings" of mature valves/girdle bands and the central and terminal nodules. Not all silica deposition and micromorphogenesis occurred in contact with the expanding silicalemma, but was somehow directed within the SDV cavity, and resulted in the distinct silica layers that lined the raphe fissures and poroids. Following alkaline etching, the inner surfaces of valves/girdle bands, as well as the silica layers lining the raphes, poroids, and slits, were determined to be significantly more resistant to alkaline etching than the exterior surfaces, while the outer silica coating and the nodules were quickly dissolved. The processes of micromorphogenesis must have exerted precise control over the chemical nature of the silica formed at different positions within the SDV and affected the overall structure and function of the diatom wall.