Genotypic control of centromere positions of parental genomes in hordeum x secale hybrid metaphases

Schwarzacher Robinson, T.; Finch, R.A.; Smith, J.B.; Bennett, M.D.

Journal of Cell Science 87(2): 291-304


ISSN/ISBN: 0021-9533
Accession: 005520497

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The spatial disposition at metaphase of centromeres from Hordeum and Secale in root tips cells of H. chilense .times. S. africanum is described and compared with corresponding results for H. vulgare .times. S. africanum obtained previously. In both of these F1 sexual hybrids (2n = 2x = 14) each of the seven chromosome types from Secale was easily distinguished by its large size from any of the seven from Hordeum. In H. chilense .times. S. africanum, centromeres of Secale chromosomes tended to be nearer the centre of the metaphase plate than did centromeres of Hordeum chromosomes in both squash preparations seen by light microscopy and unsquashed cells examined using electron microscope three-dimensional serial thin section reconstructions. This difference was significant in some individual cells, and highly significant for pooled data for reconstructed cells and separately for squashed metaphases. In no cell were Hordeum centromeres on average significantly nearer the centre of the metaphase plate than Secale centromeres. These results agreed with those previously obtained for H. vulgare .times. S. africanum in that: (1) centromeres of the two parental haploid sets tended to be spatially separate; and (2) centromeres from one particular parent usually tended to be in the peripheral region of the metaphase plate that surrounded the central region containing the centromeres from the other parent. However, these results contrasted completely with those obtained previously in that Secale centromeres tended to be more central than Hordeum centromeres in H. chilense .times. S. africanum, but more peripheral than Hordeum centromeres in H. vulgare .times. S. africanum. As centromeres of the parental set with the larger chromosomes (i.e. Secale) can be either inside, or outside, centromeres from the parental genome with the smaller chromosomes (i.e. Hordeum), then clearly, a tendency for a concentric separation of parental genomes is not a packing phenomenon determined by chromosome size per se, but this is presumably under genotypic control.