Fig. 4. A colchicine-treated meristematic root-tip metaphase cell of a double monotelosomic line of rye showing both the co-localization of the rDNA sites detected by in situ hybridization (red) and the silver stained Ag-NORs (dark brown). On condensed NORs (arrows), the silver signal reveals the previous expression of rRNA genes, whereas the two hybridization sites of identical size demonstrate that the two rDNA loci have equivalent numbers of ribosomal cistrons. Bar, 5 µm.