Chromosome Banding and Heterochromatin in Vicia Faba

This study documents the distribution of bands in Vicia faba root-tip chromosomes as shown by acid treatment, quinacrine mustard fluorescence, various forms of Giemsa banding and orcein banding methods, and demonstrates the coincidence of these bands with the position of heterochromatin as shown by cold treatment and late replication. Heterochromatin in the large metacentric M chromosome is located in two areas: (a) around the centromere and (b) adjacent to the secondary constriction. The latter is not late-replicating but is judged to represent classical nucleolus-associated heterochromatin. Heterochromatin in the smaller sub-telocentric S chromosomes is located in the intercalary and proximal areas of their long arms and in the short arm of two chromosomes. The variable expression of particular chromosome segments with different banding techniques testifies to certain differences between heterochromatic regions and emphasizes the existence of several classes of heterochromatin. In situ molecular hybridization of labelled complementary RNA to chromosomal DNA indicates the presence of repetitive DNA in both euchromatin and heterochromatin of the V. faba genome.