Ultrastructure of the centric diatom, Cyclotella meneghiniana: vegetative cell and auxospore development

Publisher Website
Google Scholar
Abstract
In Cyelotella meneghiniana the location of the nucleus in the vegetative cell changes as the cell diameter is decreased by successive cell divisions. Other features of the vegetative cell are ultrastructurally similar to other diatoms: chloroplasts are enveloped by chloroplast endoplasmic reticulum; pyrenoids are traversed by a single thylakoid; mitochondria contain tubular cristae; and dictyosomes are located near the nucleus. The auxospore has one or more large vacuoles that restrict the organelles to a narrow, peripheral band of cytoplasm. The organelles of the auxospore are morphologically similar to those found in the vegetative cells. Peripheral endoplasmic reticulum is present in the auxospore but not in the vegetative cell. The wall of the immature auxospore is composed of an organic component that is supplemented with siliceous scales as the auxospore matures. A metagamic mitosis precedes formation of each of the valves of the initial cell. Both valves of the initial cell are formed inside the silicalemma from the centre outward, following a localized plasmolysis in the auxospore. Valves of the initial cell are rounded ratber than undulating as in the vegetative cell and marginal spines are absent on the initial cell. Cell division results in formation of valves with normal morphology.