Barley Genetics Newsletter (2008) 38:1-3
Gamma-induced pericentric inversion in barley (Hordeum vulgare L.)
K. I. Gecheff, Institute of Genetics, Acad. D. Kostoff
Bulgarian Academy of Sciences
1113 Sofia, Bulgaria.
The karyotype of barley has been subjected to an extensive experimental reconstruction with respect of both fundamental and applied aspects (for review see Taketa et al. 2003). Reciprocal translocations have been the basic type of structural rearrangements used in this species along these lines. To my knowledge, there are very few attempts to use pericentric inversions as morphological markers for identification of barley chromosomes. For a long time our efforts were aimed at induction by gamma-irradiation of pericentric inversions which affect asymmetrically the morphology of barley chromosomes. Three homozygous lines, namely, I-11, I-44 and I-39, containing such pericentric inversions in chromosomes 2H, 5H and 6H, respectively, were produced so far. The morphology of reconstructed chromosomes is described in this paper.
Dry seeds of both standard two-rowed spring barley variety “Freya” and translocation line T-1586, originating from the same variety were used as experimental material. Doses between 100 and 200 Gy of gamma-rays were applied in order to produce chromosomal rearrangements. Data concerning cytological and selection techniques are given in our previous papers (Gecheff 1989; 1996). The idiograms of chromosomes were constructed following the proposals of Marthe and Künzel (1994).
Since pachytene analysis that might reveal a specific loop formation in plant heterozygous for inversions is practically inapplicable in barley, the examination of the morphology and Giemsa N-banding patterns of somatic metaphase chromosomes were the main approach for selection of plants of interest and identification of inversion breakpoints. Later on, the nature of the induced structural rearrangements were confirmed by examination of meiotic metaphase I of F1 hybrid plants in crosses of mutant forms with their parent lines.
Pericentric inversion 2H
The karyogram analysis of somatic metaphases of mutant line I-11 revealed an alteration in the morphology of chromosome 2H (an apparent increase in the long/short arm ratio) without any change in the morphology of the rest of chromosomes of the karyotype. A comparative analysis of Giemsa N-banded metaphase chromosomes showed an intrachromosomal transfer of the most distal band of the short arm to the long arm of this chromosome, that has evidently resulted from a pericentric inversion embracing a large segment with total length of 65 mGNs. The putative sites of the inversion breakpoints were found to be located within the segments that do not exceed 9 mGNs, as indicated by arrowheads in Fig. 1A.
Pericentric inversion 5H
This inversion was easily identified because it affects dramatically the standard morphology of chromosome 5H. The evident increase of the size of the satellite up to 36 mGNs was accompanied by corresponding reduction in the size of the long arm of this chromosome. Using the approach mentioned above, the inversion breakpoints are supposed to be localized within the segments that have the same length as the satellite (Fig. 1B).
Pericentric inversion 6H
Due to the transfer of the proximal band in the short (satellite) arm of chromosome 6H, it became possible to map the inversion breakpoints (indicated by arrowheads in Fig. 1C) with great precision. The size of the inverted segment which involves the centromere was found to run up to 58 mGNs in length.
Fig. 1. Idiograms of Giemsa N-banded chromosomes in inversion lines: I-11 (A) – 2Hi; I-44 (B) – 5Hi; I-39 (C) – 6Hi. On the left side of each reconstructed chromosome, the constitution of the respective standard type (2H, 5H and 6H) is shown. The putative position of the inversion breakpoints are shown by arrowheads. The figures at the end of chromosome arms display their size in milliGeNomes (mGN), i. e., one thousandth of the genome length. NOR – nucleolus organizing region.
Gecheff, K. I. 1989. Multiple reconstruction of barley karyotype resulting in complete cytological marking of the chromosome complement. Theor. Appl. Genet. 78:683-688.
Gecheff, K. I. 1996. Production and identification of new structural chromosome mutations in barley (Hordeum vulgare L.). Theor. Appl. Genet. 92:777-781.
Marthe, F. and G. Künzel. 1994. Localization of translocation breakpoints in somatic methaphase chromosomes of barley. Theor. Appl. Genet. 89:240-248.
Taketa, S., I. Linde-Laursen, and G. Künzel. 2003. Cytogenetic diversity. In: R. von Bothmer, T. Hintum, H. Knüpff and K. Sato (eds) Diversity in barley (Hordeum vulgare L.), Elsevier, pp. 97-119.