title: Structural changes of Ag-stained nucleolus organizing regions and nucleoli during meiosis in Allium flavum.
abstract: Microsporogenesis of Allium flavum was investigated by light microscopy using a silver impregnation technique. Ag-positive structures were present at the nucleolus organizing regions (NORs) in all stages of the meiotic cycle. During prophase I the nucleoli were found to be composed of a strongly impregnated central and a weakly impregnated peripheral component, probably corresponding to the pars fibrosa and pars granulosa, respectively. A heteromorphism with regard to the presence of a NOR allowed the determination of the crossing-over frequency in the chromosome arm concerned.
mesh_terms: D002466:Cell Nucleolus / Q000648:ultrastructure*; D003434:Crossing Over, Genetic; D008540:Meiosis; D009697:Nucleolus Organizer Region / Q000648:ultrastructure*; D010944:Plants; D012834:Silver
chemical_list: D012834:Silver