Cell division inHymenomonas carterae(Braarud et Fagerland) Braarud (Prymnesiophyceae)

Abstract

The cell division cycle of Hymenomonas carterae (Braarud et Fagerland) Braarud was investigated at the ultrastructural level. DNA synthesis and cytokinesis occurred during the 8-hour dark period. All organelles, including the flagellar bases were replicated prior to nuclear division. Prophase consisted of a clustering of the chromosomes into distinct groups and the disappearance of the nucleolus. During metaphase there was complete dissociation of the nuclear envelope resulting in the formation of an open spindle containing no major organelles. The metaphase plate formed at right angles to an imaginary line joining the two pairs of flagellar bases. Elongation of the cell and separation of the chromosomes occurred at anaphase. During early telophase the nuclear envelope veformed and was closely associated with the chromosome masses, resulting in the nuclear possessing convoluted profiles. Telophase was characterized by complete break down of spindle fibres, rounding off of the nuclear profiles, reappearance of the nucleolus, emergence of the flagella and the final separation of the two daughter cells.