II.10 Meiosis in 8 chromosome barley haploids.
George Fedak. Research Branch, Agriculture Canada, Ottawa, Ontario, K1A OC6, Canada.
Since no synapsis between normal and extra chromosomes was observed in 8 chromosome paired barley, the 8 chromosome haploid was produced to determine if the extra chromosome fragment would pair with homologous segments of normal chromosomes when its true homologue was absent. Production of four haploid plants was achieved by pollination of the 8 chromosome paired barley with diploid H. bulbosum according to established methods (Fedak, 1972).
In somatic cells the extra chromosome is one-third of the length of a normal chromosome as previously described (Wiebe et al. 1974) and could readily be distinguished in meiotic preparations (Fig. 1 & 2). The chromosome configuration observed most frequently at metaphase I in the haploid was one bivalent of normal chromosomes plus six univalents including the extra fragment (Table I). Other configurations observed, in order of decreasing frequencies were: eight univalents, two bivalents plus four univalents including the fragment, one trivalent including the fragment plus five univalents and other combinations in lower frequencies. In addition to normal chromosome synapsis, low frequencies of secondary associations such as end to end, side by side and end to side arrangements were observed at metaphase I in the 8 chromosome haploid. For example in Figure 2 the extra chromosome was associated with a normal in an end to side association while three normal chromosomes formed a ring-rod type of trivalent. In Figure 3 a type of trivalent was formed from a combination of end to end and to side associations of normal chromosomes.
Table 1 Metaphase I and Secondary Associations in 8 Chromosome Barley Haploids
The frequency of cells containing a single bivalent in an 8 chromosome haploid derived from Wiebe's 16 chromosome plants was approximately 50% (Table 1) compared to 13% bivalent formation in 7 chromosome barley haploids obtained from other sources (unpublished). Since the 8 chromosome haploid was derived from lines that carried a translocation, the high bivalent frequency is probably caused by the presence of the translocation in the haploid.
The low frequency of pairing the extra fragment with its homologous sections of normal chromosomes in the haploid reflects the lack of pairing of the fragment with normal chromosomes at the diploid level in agreement with earlier reports that chromosome synapsis in barley is initiated at or near the end and removal of these structures will eliminate chromosome pairing.
References:
Fedak, G. 1972. Production of haploids in barley. Barley Newsletter 16:36-37.
Wiebe, G.A., Ramage, R.T. and Eslick, R.F. 1974. Eight-paired barley lines. BGN. 4:93-95
