Ultrastructure of mitosis and cytokinesis during spermatogenesis inPorphyra yezoensis(Bangiales, Rhodophyta)

Abstract

AbstractWe studied mitosis and cytokinesis during spermatogenesis in the red algaPorphyra yezoensisUeda using electron microscopy with the cryofixation-freeze-substitution technique and by fluorescence microscopy using tubulin immunofluorescence and SYBR Gold staining. Spermatogenesis occurred along the blade margin with a series of cell divisions. During interphase, two nucleus-associated organelles (NAOs) were located close to the nuclear envelope and had a ring-on-ring morphology. In prophase, the NAOs migrated to the future mitotic poles. The nuclear envelope of prometaphase nuclei became deeply depressed below each NAO, and the two rings of the NAOs appeared to separate until early telophase. The chromosomes became aligned at the equator in metaphase, although individual chromosomes and their kinetochores were not clearly defined. The two rings of the NAO moved next to each other on the nuclear envelope during mid-telophase, and then NAO replication occurred. In late telophase, the pair of NAOs repositioned on the nuclear envelope. Cytokinesis started with furrowing of the plasma membrane.