Studies on the biochemistry and fine structure of silica-shell formation in diatoms : Chemical Changes in the wall of Navicula pelliculosa during its formation.

Wall formation in Navicula pelliculosa was studied in Si-starvation synchrony. Electron microscopy of walls, prepared by mechanical shaking, indicated that they were free, of cytoplasmic contamination. Removal of the frustule, using HF, indicated that a higher ratio of organic material to silica occurred in the girdle bands below the punctae and in the raphe region. The organic material was investigated following incorporation of (14)C. Material added to newly formed walls prior to and during Si-deposition contained more radioactivity in amino acids than in other constituents. Once Si-uptake ceased, material with increased fucose and xylose content became labelled. Secondary material, the main labelled constituents of which were mannose and glucoronic acid, was added to old walls at all times. Si-uptake was investigated using (31)Si. The rate of assimilation increased during the first hour following addition, remained constant over the next three hours, and then decreased markedly during the separation of daughter cells. Varying amounts of (31)Si could be extracted from intact cells, using hot or cold solvents. These results are discussed in relation to the sequence in which proteinaceous material and polysaccharides are formed during morphogenesis of the diatom wall.