Studies on centromere, chromomere and nucleolus in pachytene nuclei of rice, oryza sativa, microsporocytes.

Abstract

Pachytene nuclei of rice microsporocytes were examined in regard to centromere constitution, chromomere pattern and nucleolar situation by flame drying method and Giemsa stain. Uridine treatment of intact microsporocytes before preparation distinctly revealed the centromere on late pachytene chromosomes; i.e., 4 equal entities were detected in a centromeric region. Chromosomes treated in KCl solution were stained clearly enough to distinguish their chromomere patterns on 12 bivalents. Mid-pachytene chromosomes were suitable for chromomere analysis and capable of discriminating 12 bivalents with their chromomere patterns, centromere position and length. Supernumerary micronucleoli were frequently observed in a pachytene nucleus in addition to a macronucleolus. They were situated in 3 conditions: free from chromosomes, adhered to the surface of various intervening sites of chromosomes and adhered to the ends of chromosomes. In some nuclei micronucleoli appeared to be excised from macronucleoli, indicating the origin of micronucleoli.