title: Connection between rod bivalents and incomplete meiotic association at NORs in Hordeum marinum Huds.
abstract: The hypothesis of a connection between rod bivalent formation and incomplete meiotic association at NORs of SAT-chromosomes of H. marinum is supported. PMCs of H. marinum ssp. gussoneanum (2x), two diploid ssp. marinum × ssp. gussoneanum (2x) hybrids and two ssp. gussoneanum (4x) × Secale cereale hybrids at metaphase I (M-I) were analyzed by in situ hybridization. The probe pTa71 labelled rDNA sites at NORs of a single pair of homologous or near-homologous SAT-chromosomes of H. marinum in each material. In the three diploids, M-I was regular with ring bivalents and one or a few rods (av.13.52 bound arms cell(-1)). More rod bivalents than the expected one out of seven, i.e. 30, 67 and 89% included rDNA-carrying chromosomes. Corresponding bound short arm frequencies were 0.89, 0.72 and 0.52, while long arms and arms of other chromosomes presented complete or near- complete association. The two heterogenomic hybrids had a less regular M-I (av. 8.04 bound arms cell(-1)) including 20% rDNA-carrying rods with bound arm frequencies of 0.29 in short and 0.87 in long arms. Positions of chromosome associations were established in all 150 rDNA-carrying bivalents. In 77 bivalents with short arm associations, 4% of these occurred proximally to, none at, and 96% distally to rDNA sites, i.e. in satellites. In 143 bivalents with long arm associations, 83% occurred at interstitial and 17% at terminal positions. The observations combine increased frequency of rDNA-carrying rods with decreased frequency of association at NOR regions of SAT-chromosomes. The basis for the relationship is discussed.
authors.affiliation: Botany Group, Department of Agriculture and Ecology, Faculty of Life Sciences, University of Copenhagen, Denmark. ill@life.ku.dk
authors.forename: Ib
authors.initials: I
authors.lastname: Linde-Laursen
authors.forename: Roland
authors.initials: R
authors.lastname: Von Bothmer
mesh_terms: D032461:Chromosomes, Plant / Q000235:genetics*; D018744:DNA, Plant / Q000737:chemistry; D004275:DNA, Ribosomal / Q000737:chemistry; D018745:Genome, Plant; D001467:Hordeum / Q000235:genetics*; D008540:Meiosis / Q000235:genetics*
chemical_list: D018744:DNA, Plant; D004275:DNA, Ribosomal