SATELLITED CHROMOSOMES, NUCLEOLUS ORGANIZER REGIONS AND NUCLEOLI OF BRASSICA-CAMPESTRIS L, BRASSICA-NIGRA (L) KOCH, AND SINAPIS-ARVENSIS L

Giemsa staining was used to characterize the satellited chromosomes, a nd silver staining, to detect nucleolus organizer regions and nucleoli in Brassica campestris (genome: AA, 2n = 20), B. nigra (BB, 2n = 16) and Sinapis arvensis (SS, 2n = 18). B. campestris had one pair of sate llited chromosomes, while B. nigra had three pairs. S. arvensis had fi ve distinct satellited chromosomes and a sixth chromosome with a faint satellite. Silver-stained nucleolus organizer regions (Ag-NORs) were localized at the secondary constrictions of the satellited chromosomes . Two Ag-NORs and a maximum number of two nucleoli were revealed in B. campestris. Heteromorphism for size of Ag-NORs and nucleoli was obser ved in one accession of B. campestris. In B. nigra, six Ag-NORs and si x nucleoli were observed at early and late telophase, respectively. In S. arvensis, six Ag-NORs and six nucleoli were revealed. Size differe nces were noticed within and between pairs of Ag-NORs. The presence of three pairs of active NORs in B. nigra and S. arvensis is an addition al support for the hypothesis of a basic number of x = 3 in the Brassi ceae.