ELECTRON MICROSCOPY OF ULTRATHIN SECTIONS OF SCHIZOSACCHAROMYCES OCTOSPORUS I

Abstract

Karyokinesis occurs well in advance of cytokinesis in this yeast. The nucleus, surrounded by a limiting membrane which remains intact during all observed stages of division, divides by a process of elongation and constriction. Intranuclear structures were not observed. Cytokinesis involves formation of a transverse cell wall by annular centripetal growth of an inner lateral portion of the cell wall. The cytoplasmic membrane is closely associated with the developing transverse wall which, after initial formation, increases in thickness and eventually splits to separate completely the daughter cells. Prior to splitting, the transverse wall is partitioned by the formation of electron dense transverse membranes. These membranes serve initially as the outer portion of the cell wall of newly separated cells.