Giemsa C-Banding and the Evolution of Wheat

Abstract

The somatic chromosomes of common wheat, Tri-ticum aestivum L. (2n = 6x = 42), and those of two of its diploid progenitors and T. speltoides, have been individually identified by a Giemsa staining technique. In wheat, telocentric chromosomes were used to aid the recognition of individual chromosomes, and an ideogram has been constructed depicting the C-band positions. There is no similarity in the C-banding of chromosomes within a homoeologous group, with the possible exception of group 5. Comparisons of the C-banding of the diploid species T. monococcum, T. speltoides, and T. tauschii with that of the A, B, and D genomes, respectively, in hexaploid wheat corroborate that T. speltoides could not be the donor of the B genome to wheat and that T. monococcum and T. tauschii are the probable donors of the A and D genomes, respectively.The Giemsa staining technique for the detection of constitutive heterochromatin in cereal chromosomes has been described by Gill and Kimber (1). The C-bands in cereal chromosomes are usually present in the centromeric area and, additionally, may-or may not be present in interstitial or terminal regions or both. There is a characteristic C-banding pattern for the individual chromosomes in somatic metaphases and, thus, also for the species. These features enabled the identification of all of the somatic metaphase chromosomes of rye and also allowed the recognition of rye chromosomes in wheat-rye addition lines (2). Other species for which C-banded somatic karyotypes have been described are Scilla sibirica (3), AUium flavum (4), and some species of Anemone (5). Quinacrine mustard and other compounds can be used to produce differential fluorescence (Q-banding), and Q-banded somatic karyotypes have also been described in a few plant species (3,4,6,7).A unique situation exists in wheat (Triticum aestivum L. The technique for C-banding is that previously described by Gill and Kimber (1, 2). The dehydration of the slides was usually limited to 1 hr, and the roots were not left in the glacial acetic acid for more than 1 day. Solutions were generally less than 2 weeks old.Photomicrographs, all at the same magnification, were made of somatic cells containing the telocentric chromosomes. The telocentrics were cut out of the prints and mounted to produce a karyotype arranged according to the homoeologous classification (Fig. 1). Since the prefixation treatment used leads to different degrees of contraction from root to root and even from cell to cell, the amount of contraction was not uniform.-Thus, the arm ratios seen in Fig. 1 are not necessarily those of the complete chromosomes. However, the relative positions of the bands within a chromosome arm are assumed to be -constant.An ideogram of the wheat karyotype was produced by drawing the bands at their correct positions within an arm on a chart in which the correct arm ratio and relative size is represented to scale (Fig. 3). The relative sizes and arm ratios used are those determined by Sears (19) for telophase II of cultivar Chinese Sp...

Influence of chromosome structure on the degree of meiotic pairing of intercultivar wheat hybrids (Triticum aestivum L.)

“…The C-banding pattern for these chromosomes was consistent with the one described by Gill and Kimber (1974), Seal (1982), Van Nieckerk and Pienaar (1983), and Endo and Gill (1984).…”

High molecular weight glutenin subunit variation in the Sitopsis section of Aegilops. Implications for the origin of the B genome of wheat

“…Many workers have arrived at this conclusion studying morphological characteristics (Sarkar and Stebbins, 1956), satellite chromosomes (Riley et al 1958) cytoplasmic proteins (Barhman et al 1988) chromosome banding (Chen and Gill, 1983), and amount of nuclear DNA (Rees, 1963;Rees and Walters, 1965) whereas many others have excluded it using the same type of analysis (Waines and Kimber, 1973;Natarajan and Sarma, 1974;Gill and Kimber, 1974;Hadlaczky and Belea, 1975;Iodansky et a!., 1978;Kerby and Kuspira, 1988).…”

Heterochromatin, aberrant endosperm nuclei and grain shrivelling in wheat-rye genotypes

“…Diploid rye (4C nuclear DNA amount = 33l4 pg) contains about 33 per cent more DNA than the largest of the diploid genomes found in tetraploid and hexaploid wheat (4C = c. 249 pg). Moreover, rye chromosomes characteristically possess large C-bands at one or both telomeres, as well as some intercalary bands (Verma and Rees, 1974), while wheat chromosomes possess only minor C-bands at, or near, some of their telomeres, although they do possess small intercalary C-bands (Gill and Kimber, 1974). Telomeric heterochromatin in rye is late replicating at S (Lima-de-Faria and Jaworska, 1972;Ayonoadu and Rees, 1973).…”