Abstract
Nucleolar activity was analyzed in two samples of plants of the wild onion speciesAllium cernuum, one from Canada (2n=14) and one from the United States of America (2n=14+3B), using phase contrast analysis and C- and Ag-NOR-banding. Three chromosome pairs of the standard A-chromosome complement show small telomeric satellites, which corresponds to the maximum number of Ag-NOR-bands at metaphase and to the telomeric C-heterochromatin. However, the maximum number of nucleoli observed at interphase was eight, indicating that another chromosome pair possesses nucleolar activity. Corresponding results were obtained for the A-chromosome complement of plants from the United States of America, however, these plants further possess three small metacentric supernumerary chromosomes, which show telomeric satellites on both arms, corresponding to two telomeric Ag-NOR-bands observed after silver staining. The presented data clearly indicate that the B-chromosomes ofAllium cernuum possess rDNA gene clusters which show strong nucleolar activity.
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