title: Cytogenetics of Danish species of Barbarea (Brassicaceae): chromocentres, chromosomes and rDNA sites.
abstract: Seventeen Danish accessions of five taxa of Barbarea, i.e. B. stricta, B. verna, B. intermedia and B. vulgaris ssp. vulgaris and ssp. arcuata including the two morphologically and biochemically differentiated P(pubescent)- and G(glabrous)-types, and 4 P-xG-type hybrids were analysed cytologically using fluorescent in situ hybridization (FISH) and AgNO(3)-staining. The number of chromocentres varied among nuclei of somatic interphases (generally+/-2) centred around 18 in the P-type of B. vulgaris ssp. arcuata, and around 16 in the G-type, and in the other materials. The observations suggest preponderant chromosome numbers of 2n=18 and 2n=16 in root-tip cells. Chromosome numbers of metaphases supported the idea. In situ hybridization demonstrated the presence of a maximum of two rDNA sites in B. intermedia, four sites in B. stricta and B. vulgaris ssp. vulgaris, and six sites in a P-xG-type hybrid of ssp. arcuata and in B. verna. P- and G-types of B. vulgaris ssp. arcuata both had accessions with four and six rDNA sites revealing polymorphism for the character. The sites differed pairwise in size in the taxa except in the P-type. P-type nuclei had peak numbers of four rDNA sites. Nuclei of other taxa had peak numbers of 2. In nuclei with six sites, one very small pair showed no transcriptional activity. Major rDNA sites presented a low frequency of association. The number of stronger rDNA signals agreed with the observation of maximally 2 AgNO(3)-stained nucleoli in B. intermedia and 3 or 4 nucleoli in the other taxa indicating 2 and 4 nucleolus organizing chromosomes in the genomes, respectively.
authors.affiliation: Botanical Group, Department of Ecology, Faculty of Life Sciences, University of Copenhagen, Denmark. moe@life.ku.dk
authors.forename: Marian
authors.initials: M
authors.lastname: Ørgaard
authors.forename: Ib
authors.initials: I
authors.lastname: Linde-Laursen
mesh_terms: D031216:Barbarea / Q000166:cytology* / Q000235:genetics*; D032461:Chromosomes, Plant / Q000235:genetics*; D003582:Cytogenetics; D004275:DNA, Ribosomal / Q000235:genetics*; D003718:Denmark; D014644:Genetic Variation; D017404:In Situ Hybridization, Fluorescence
chemical_list: D004275:DNA, Ribosomal