Exact Location of rRNA Genes in Vicia faba Chromosomes

Abstract

Ribosomal RNA (rRNA) genes were visualized in chromosomes of Vicia faba by high resolution in situ hybridization. The interphase nucleus showed two large and two small signals of rRNA genes associating nucleoli. At prophase and metaphase the signals with differences in sizes appeared at both adjacent sides of the secondary constriction of the large metacentric chromosomes. Two large signals were located at the proximal region of the satellite. The metaphase chromosome with the connecting thread at the secondary constriction was hybridized with rDNA. Chromomycin A₃-bands appeared on the chromosomes which showed the signals of the hybridized rDNA. By silver nitrate staining, the nucleoli at interphase and the secondary constriction of the chromosome at mitotic prophase and metaphase were darkly stained. As Ag-NOR stained actively transcripting NOR, the large portion of rRNA genes condensed and located both chromosomal sides of the secondary constrictions was inactive during the cell cycle in the meristematic tissue of the root.