Chromosome pairing and chiasma formation in wheat plants triisosomic for the long arm of chromosome 5B

Abstract

Chromosome pairing and chiasma formation have been analyzed at the light and electron microscopic levels in wheat plants triisosomic for the long arm of chromosome 5B. Complete reconstruction of the chromosome complement from one zygotene nucleus, as well as analyses of several hundred spread and silver stained nuclei, showed that pairing was arrested at the beginning of zygotene, the mean degree of pairing in five nuclei being 25 percent (range 8-37). At this stage, multiple associations of chromosomes were present, signifying pairing beth between partly-homologous and nonhomologous chromosome segments. A few multivalents were present at metaphase I together with bivalents and univalents. The chiasma frequency (a mean of 18 per cell) was only half of that seen in normal wheat. In spread nuclei at late diplotene, a mean of 41 segments ofsynaptonemal complex was counted, 20 of which had thickened lateral components. The results are discussed in relation to the possible dosage effect of the Ph gene located on the long arm of chromosome 5B.

The effect of chromosome 5B on synapsis and chiasma formation in wheat, triticum aestivum cv. Chinese Spring

“…early diplotene, where the conditions for crossing over are suboptimal as degradation of the synaptonemal complex has started. Ultrastructural investigations of wheat triisosomic for 5BL have on the contrary shown that the reduction in chiasma frequency to half of that seen in euploid wheat correlates with pairing arrest at an early stage of zygotene (84). Secondly, there is as originally described by FELDMAN some chiasma formation between homoeologues in this genotype.…”

“…The materials, the growth conditions and the procedures for light and electron microscopy are described in the individual reports in this series (18,20,21,22,23,30,79,80,84).…”

“…The ultrastructural investigations now comprises studies of chromosome pairing in trihaploid wheat with and without chromosome 5B (79), wheat-rye hybrids nullisomic for 5B, euploid hybrids and hybrids where chomosome 5B has been replaced by an isochromosome for the long arm of chromosome 5B (monoisosomic 5BL) (80), hexaploid wheat nullisomic for 5B (22), monosomic for 5B (21), euploid wheat (18,20,31), and wheat monoisosomic and diisosomic for 5BL (23) and triisosomic for 5BL (84). These studies were all performed on the cultivar Chinese Spring.…”

Chromosome pairing and synaptonemal complex formation in hexaploid wheat, nullisomic for chromosome 5B

“…The present paper is a part of a series, attempting at the ultrastructural level to investigate the effect of different dosages of chromosome 5B on synapsis and chiasma formation (1,2,3,9,10,11). In this study the results of the analysis of plants nullisomic for chromosome 5B are reported.…”

“…That these multivalents had arisen by crossing over between homoeologous chromosomes was subsequently shown by RILEY and KEMPANA (7), who, by crossing plants nullisomic for 5 B with euhexaploid wheat, obtained plants that were heterozygous for translocations. The chromosomes involved in the translocations were identified by test crosses to lines in which one specific chromosome was monosomic and it was shown that the translocations had formed between homoeologous chromosomes, indicating crossing over between homoeologues in the nullisomic 5B wheat.The present paper is a part of a series, attempting at the ultrastructural level to investigate the effect of different dosages of chromosome 5B on synapsis and chiasma formation (1,2,3, 9,10,11). In this study the results of the analysis of plants nullisomic for chromosome 5B are reported.…”