ELECTRON MICROSCOPY OF ULTRATHIN SECTIONS OFSCHIZOSACCHAROMYCES OCTOSPORUSII

Abstract

Electron micrographs illustrate the cytological changes occurring during plasmogamy, karyogamy, and subsequent nuclear division in Schizosaccharomyces octosporus. The conjugation process appears to be initiated by the attachment of the cells in pairs by a portion of the cell wall. Fusion of cells by means of projection tubes was not observed. The central portion of the connecting cell then disintegrates, thereby forming a short, narrow conjugation canal which subsequently increases both in length and width. At this stage, the nuclei migrate toward one another, and fuse within the canal. The limiting membranes remain intact except in the region of nuclear fusion. Subsequent nuclear division appears to occur by a process of constriction. Intranuclear structures were not observed. The structure and behavior of other components of the yeast cell during the conjugation process were also studied. Observations on the vacuole lend further support to the view that the vacuole is not an integral part of the nucleus.