title: Tissue culture triggers chromosome alterations, amplification, and transposition of repeat sequences in Allium fistulosum.
abstract: Structural alterations in nuclei and chromosomes of cells derived from callus culture of Allium fistulosum have been studied with fluorescent in situ hybridization (FISH) using 5S ribosomal DNA (rDNA), 45S rDNA, and 375-bp repeat probes. A high frequency of chromosome abnormalities was found to be caused by the loss of telomere-located 375-bp repeats, chromosome fusion, and subsequent breakage-fusion-bridge cycles. Products of chromosome fusions and monocentric and regularly shaped chromosomes showed additional 375-bp repeat and 45S rDNA clusters at unusual sites, suggesting dynamic copy-number changes and transposition of these repeats. Southern hybridization revealed no differences in the 375-bp repeat and 45S rDNA repeat array order or the degree of methylation between DNA isolated from leaves or tissue-culture cells. In addition, protruding, spike-like structures positive for 375-bp repeats were identified on the surface of different-sized nuclei. Transmission electron microscopy analysis revealed the accumulation of densely packed chromatin within spike-like structures. Because root calyptra cells showed similar structures, it is likely that heterochromatic spike-like structures are a feature of nondividing cells at the onset of programmed cell death.
authors.affiliation: Leibniz-Institute of Plant Genetics and Crop Plant Research (IPK), 06466 Gatersleben, Germany.
authors.forename: Dorota
authors.initials: D
authors.lastname: Gernand
authors.forename: Hieronim
authors.initials: H
authors.lastname: Golczyk
authors.forename: Twan
authors.initials: T
authors.lastname: Rutten
authors.forename: Tomasz
authors.initials: T
authors.lastname: Ilnicki
authors.forename: Andreas
authors.initials: A
authors.lastname: Houben
authors.forename: Andrzej J
authors.initials: AJ
authors.lastname: Joachimiak
mesh_terms: D000490:Allium / Q000235:genetics* / Q000254:growth & development* / Q000648:ultrastructure; D002467:Cell Nucleus / Q000648:ultrastructure; D002869:Chromosome Aberrations; D032461:Chromosomes, Plant / Q000235:genetics*; D042622:DNA Repeat Expansion / Q000235:genetics; D004251:DNA Transposable Elements / Q000235:genetics; D018744:DNA, Plant / Q000032:analysis / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics; D017404:In Situ Hybridization, Fluorescence; D018519:Meristem / Q000235:genetics / Q000254:growth & development / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D018517:Plant Roots / Q000235:genetics / Q000254:growth & development / Q000648:ultrastructure; D016615:Telomere / Q000235:genetics; D046509:Tissue Culture Techniques
chemical_list: D004251:DNA Transposable Elements; D018744:DNA, Plant; D004275:DNA, Ribosomal