GrainGenes
A Database for Triticeae and Avena
Wheatley and Kasha, pp. 72-74
II. 26. Effects of cycloheximide treatments on prophase and metaphase cells of a (2X) Hordeum vulgare X (2X) H. bulbosum hybrid.
W. G. Wheatley and K. J. Kasha, Crop Science Department, University of Guelph, Guelph, Ontario, Canada, N1G 2W1. "R"
Finch, Smith and Bennett (1981) and Finch and Bennett (1981) recently described the spatial separation of the two haploid parental genomes in intergeneric hybrids of Hordeum vulgare X Secale africanum. From their observations, they concluded that the chromosomes of the Hordeum and Secale genomes occupy distinctly different positions within mitotic cells of those hybrids. Our observations of prophase and metaphase cells in root meristems of a diploid interspecific hybrid between (2X) H. vulgare and (2X) H. bulbosum suggest that the two parental genomes are also separated in mitotic cells. These observations were made on cells obtained from roots treated with 10 ug/ml cycloheximide, an inhibitor of protein synthesis. Treated roots were fixed in acetic acid: alcohol (1:3) and later prepared for cytological examination by staining the nuclei with Feulgen and counterstaining the cytoplasm with Fast Green. Cells were not squashed during slide preparation so that the relative positions of the chromosomes in the mitotic cells were not disturbed by this step.
In some prophase cells, from roots treated with cycloheximide for 2 to 3 hours, a distinct separation of groups of chromosomes was observed. As shown in Figure 1, two groups of chromosomes could be distinguished. One group was associated with the nucleolus while the other group was not. In Figure 1 the group of chromosomes associated with the nucleolus was located at one pole of the prophase nucleus and in Figure 2 this group appeared to be centrally located. The other seven chromosomes of the prophase cells appeared to be located either at the opposite pole of the prophase nucleus (Figure 1) or peripherally (Figure 2) to the group of chromosomes associated with the nucleolus. Since the nucleolus organizer of the bulbosum genome is suppressed in these hybrids it seems likely that the latter group represents the chromosomes of the vulgare genome. In roots treated for 1 h with cycloheximide and allowed to recover for 2 hours in water metaphase cells were observed with varying numbers of non-congressed chromosomes. As shown in Figure 3, as many as seven chromosomes could be observed to be non-congressed. Since none of these chromosomes was a satellite chromosome and one chromosome had a karyotype similar to that of chromosome #7 of bulbosum we suggest that the non-congressed chromosomes were those of the bulbosum genome. In the metaphase cell shown in Figure 4 satellite chromosomes were observed in the center of the cell while other chromosomes, some having undergone centromere separation, were displaced to the periphery of the cell. We suggest, as described previously in the Hordeum X Secale hybrids, that the vulgare chromosomes appear to occupy the center of the metaphase plate during mitosis in these cycloheximide treated roots.
These observations suggest that treatment with cycloheximide disturbs the congression of the bulbosum chromosomes onto the metaphase plate and that this may eventually result in the elimination of these chromosomes (Wheatley, Noda and Kasha, unpublished observations). Secondly, the vulgare chromosomes in these hybrid cells appear to congress at metaphase fairly normally following the 1 h treatment. The reason for this is not known. It would appear that the nucleolus may confer some added stability to the vulgare chromosomes prior to and perhaps during the initial movement of the chromosomes to the metaphase plate.
References:
Finch, R. A., J. B. Smith and M. D. Bennett. 1981. Hordeum and Secale mitotic genomes lie apart in a hybrid. J. Cell Sci. (in press).
Finch, R. A. and M. D. Bennett. 1981. Spatial separation of mitotic parental genomes in Hordeum X Secale hybrids. Barley Genetics IV.