Ultrastructure of cell division in the unicellular red algaFlintiella sanguinaria

摘要

Cell division was examined with the electron microscope in the unicellular red algaFlintiella sanguinaria.Flintiellamorphologically resemblesPorphyridium purpureum, the only other red algal unicell that has been examined for ultra-structural details of cell division. Both genera are in the order Porphyridiales (Bangiophyceae), an unnatural assemblage of reduced forms in great need of taxonomic revision. Before mitosis, the nucleus migrates to the cell periphery. As in all red algae examined, exceptPorphyridium, the nucleus-associated organelle is a polar ring. At prometaphase, one or two microtubule-containing cytoplasmic invaginations penetrate the nucleus at each pole. By metaphase an intranuclear spindle is found in association with a typical metaphase chromosomal plate. The nuclear envelope is intact except for a single, large gap at each pole. Perinuclear endoplasmic reticulum is absent. An elongated anaphase interzonal midpiece is formed which breaks down at telophase. The daughter nuclei are widely separated by the chloroplast, which is constricted at the same time as daughter cell formation occurs by a cleavage furrow associated with a finely filamentous region similar to the contractile ring found in many animal cells. Because of pronounced differences in several mitotic features, it is concluded thatFlintiellais not closely related toPorphyridiumand instead shows closer phylogenetic ties with other macroscopic genera.