Peculiar behavior of the nucleolus and appearance of cytoplasmic nucleolus-like bodies in the roottip meristems ofBrodiaea uniflora Engl. Grown at low temperature

Abstract

Cytoplasmic nucleolus-like bodies, which showed vast variation both in size and in number per cell, were sometimes found in the telophase cells ofBrodiaea uniflora. When the plants were grown at low temperature, the frequency of telophase cells bearing cytoplasmic nucleolus-like bodies increased with the lapse of days. In contrast, growth at moderate temperature reduced this frequency. Prolonged exposure of the plants to low temperature caused peculiar phenomena concerning the behavior of the nucleolus and nucleolar material: 1. retention of nucleolar remnants at high frequency in metaphase, 2. pulverization of the nucleolar remnants into a great number of minute, fluffed fragments during metaphase, 3. appearance of dot-like nucleolar material in anaphase, and 4. appearance of nucleolus-like bodies, sometimes more than 10 Μm in diameter, in telophase. All these structures were strongly impregnated with silver. Electron microscopy revealed that both the nucleolar remnant and the nucleolus-like body consisted primarily of fibrils. Our observations clearly demonstrate that the nucleolus-like bodies are derived from the fibrillar component of the nucleolus and are formed by fusion of dot-like nucleolar material during anaphase.