ULTRASTRUKTUREN IM ZELLKERN DER BÄCKERHEFE

Abstract

Changes in the fine structure of baking yeast which accompany the transition from complete anaerobiosis to aerobiosis have been investigated by the method of freeze-etching. Return to aerobtosis resulted in good synchronization and facilitated a detailed study of the process of nuclear division. Structures corresponding to the fiber, composed of a bundle of cytotubules extending between centriolar plaques, have been seea in addition, another compact straight fiber composed of fibrillar subunits has been discovered. It is close to the nuclear envelope which apparently grows out from a short crystalloid hexagonal prism and becomes long and thin during nuclear division. This dense fiber stretches the dividing nucleus whereas the bundle of tubules between centriolar plaques is passively dragged along. Robinow and Marak do not mention this dense crystalloid fiber, but reasons are given for thinking that the intranuclear bead and rodlet which they stained with acid fuchsin and equated with the fiber apparatus of their electron micrographs correspond in reality to the short crystalloid prism and the stout fiber which are the most conspicuous intranuclear structures in frozenetched specimens from the yeast cultures used in this investigation.