RIBOSOMAL-RNA GENE LOCI AND THEIR NUCLEOLAR ACTIVITY IN BRASSICA-ALBOGLABRA BAILEY

Fluorescence in situ hybridization (FISH) and silver staining techniqu es were used to reveal the number, chromosomal sites and nucleolar act ivity of ribosomal RNA (rRNA) gene loci in Brassica alboglabra Bailey (genome: CC, 2n = 18). Two major and two minor rRNA gene loci were dis closed using FISH. The two major rRNA gene loci were located on the se condary constrictions of the satellited chromosome pair 9, the two min or rRNA gene loci, on the terminal region of the short arms of the non -satellited chromosome pair 8. Two silver-stained nucleolus organizer regions (Ag-NORs) were detected on the secondary constrictions of chro mosome pair 9. Two major nucleoli were recorded in telophase nuclei. I n interphase nuclei, two micronucleoli were observed in addition to th e two major nuceoli. Thus, it is suggested that the satellited chromos ome pair 9 with Ag-NORs contains major active rRNA gene loci leading t o the formation of major nucleoli, while the non-satellited chromosome pair 8 without detectable Ag-NORs carries minor active rRNA gene loci responsible for the formation of micronucleoli.