Aspects of silicification in wall morphogenesis of diatoms

The siliceous cell wall of diatoms is formed in a silica deposition vesicle that is delimited by a membrane, the silicalemma. Once the siliceous wall matures, it is expelled and a new plasmalemma is formed underneath. Underlying wall formation is a multitude of events and processes, some of which are now known. A comparative study on wall morphogenesis in seven centric diatoms leads to the following conclusions: (1) the silica deposition vesicle is formed by the coalescence of small vesicles; (2) the silicalemma becomes part of the organic casing of the mature siliceous wall; (3) at least four morphological forms of deposited silica can be seen during the development of wall components; (4) microtubules, serving as cytoskeletons, are associated with the formation of certain wall components initiated from a cytoplasmic protrusion. These events are discussed in detail.