**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**) -- 2H^i^; I-44 (**B**) -- 5H^i^; I-39 (**C**) -- 6H^i^. 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.

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References:

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.