GrainGenes

II. 24. Reconstructed barley karyotypes with six satellite chromosomes.

H. Nicoloff (1) M. Anastassova-Kristeva (2), G. Kunzel (3), and R. Rieger (3). (1) Institute of Genetics, Academy of Sciences, Sofia, Bulgaria. (2) Institute of Morphology, Academy of Sciences, Sofia, Bulgaria. (3) Zentralinstitut fur Genetik und Kulturpflanzenforschung der Akademie der Wissenschaften der DDR, 4325 Gatersleben, German Democratic Republic.

The standard karyotype of barley consists of 7 pairs of chromosomes, two pairs of which are satellite chromosomes (chromosome pair 6 and chromosome pair 7) (Nilan 1964). Due to transcription of rRNA cistrons located in the nucleolar organizers of the four barley satellite chromosomes, four nucleoli (primary nucleoli) are being formed at late telophase of mitosis (Nicoloff et al. 1977a, b, Anastassova-Kristeva et al. 1977).

Analyzing a collection of lines homozygous for reciprocal translocations by a method described by Nicoloff et al. (1977a), two barley lines (T 21 and T 627) have been found which contain six instead of the four primary nucleoli per cell characteristic of the barley standard karyotype. This finding prompted us to study these two translocation lines in somewhat more detail with respect to the chromosome structural changes involved in karyotype reconstruction.

It was found that the karyotypes of the two translocation lines (T 21 and T 627) differ from the standard karyotype of Hordeum vulgare by the presence of two structurally changed chromosome pairs in each of them. (Fig. 1).

Figure 1. Karyotypes of T 21 and T 627 translocation lines.

Translocation line T 21

The structurally changed chromosomes in the karyotype of this translocation line (Fig. 1) resulted from a reciprocal translocation involving chromosome 5 and 7 as confirmed by use of a translocation tester set kindly provided by A. Hagberg, Svalof (Sweden).

One of the translocation points is localized in the short arm of chromosome 5, the other within the secondary constriction of chromosome 7 close to the satellite. SAT-chromosome 6 is of the same structure as in the standard karyotype. Due to the reciprocal translocation, the reconstructed karyotype T 21 contains three chromosome pairs with nucleolus organizing activity, i.e., chromosome 5⁷, 6 and 7⁵. The nucleolus organizing activity of chromosome 5⁷ results from the exchange of the distal part of its short arm for a small part of the secondary constriction together with the satellite of chromosome 7. The larger part of the secondary constriction of chromosome 7 remained in its original position and became joined with the distal part of the short arm of chromosome 5.

Translocation line T 627

This line differs from the standard karyotype of barley by involvement of chromosomes 3 and 6 in a reciprocal translocation as verified by the translocation tester set. In this case, one of the translocation points is localized in the long arm of chromosome 3, the second within the secondary constriction of chromosome 6 of the standard karyotype (Fig. 1). Chromosome 7 remained a structurally unchanged SAT chromosome and corresponds to the same chromosome in the standard complement. Translocation line T 627 is, similar to line T 21, characterized by the presence of three chromosome pairs with nucleolus organizing activity: chromosomes 3⁶,  6³, and 7. In T 627, the satellite and a small part of the secondary constriction of standard chromosome 6 had been exchanged for the distal part of the long arm of chromosome 3 and chromosome 6 was left with the larger part of its secondary constriction now joined with the distal part of the long arm of chromosome 3.

The nucleolus organizing activities in the reconstructed karyotypes of the two translocation lines were confirmed by means of scoring the number of primary nucleoli being formed at late telophase.

Detailed results of the analysis of these two translocation lines will be published elsewhere (Nicoloff et al. 1977b; Anastassova-Kristeva et al. 1977).

References:

Anastassova-Kristeva, M., Nicoloff, H., Kunzel, G. and R, Rieger. 1977. Nucleolus formation in structurally reconstructed barley karyotypes with six satellite chromosomes (in preparation).

Nicoloff, H., Anastassova-Kristeva, M. and G. Kunzel. 1977a. Changes in nucleolar organizer activity due to segmental interchanges between satellite chronosomes in barley. Biol. Zentralblatt (in press).

Nicoloff, H., Anastassova-Kristeva, M., Kunzel, G. and R. Rieger. 1977b. The behavior of nucleolus organizers in structurally changed karyotypes of barley. Chromosoma (Berl.) (in press),

Nilan, R. A. 1964. The cytology and genetics of barley. Monographic suppl. Nr. 3 Research studies. Washington State Univ. Pullman.

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