Ribosomal RNA gene loci and their nucleolar activity in Brassica alboglabra Bailey

Fluorescence in situ hybridization (FISH) and silver staining techniques were used to reveal the number, chromosomal sites and nucleolar activity of ribosomal RNA (rRNA) gene loci in Brassica alboglabra Bailey (genome: CC, 2n = 18). Two major and two minor rRNA gene loci were disclosed using FISH. The two major rRNA gene loci were located on the secondary constrictions of the satellited chromosome pair 9, the two minor 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 chromosome pair 9. Two major nucleoli were recorded in telophase nuclei. In interphase nuclei, two micronucleoli were observed in addition to the two major nuceoli. Thus, it is suggested that the satellited chromosome pair 9 with Ag-NORs contains major active rRNA gene loci leading to 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.