Studies on the biochemistry and fine structure of silicia shell formation in diatoms VII. Sequential cell wall development in the pennateNavicula pelliculosa

Summary The development of the wall of synchronized culture ofN. pelliculosa is described. The first step, modification of the 3-2 configuration of the girdle bands of the wall during interphase, occurs immediately before mitotic division by the addition of a third girdl band to the hypotheca. Following cytokenesis, the new valve is initiated when a primary central band is formed within a silica deposition vesicle. This band extends the length of the cell and contains a central nodule. Secondary arms extend from the central nodule, join with extensions of the primary central band, and constitute the raphe rib. Mounds or knolls are formed on the central nodule and disappear as the valve matures. Transapical ribs appear on both the primary central band and secondary arms, and cross extensions join to form the sieve plate areas. The wall appears to be released by a joining of the inner silicalemma and the plasmalemma. An organic coat covers the newly released wall. Two girdle bands are formed and released sequentially.