HaeIII induces position-dependent chromosomal breakage in barley (Hordeum vulgare L.)

The pattern of localized chromosomal breakage induced by the restriction endonuclease HaeIII in reconstructed barley karyotypes T-1586 and T-21 was investigated. It was found that nucleolus organizing regions (NORs) of chromosomes 6 and 7 (segments 46 and 38, respectively), containing actively transcribed ribosomal (r)DNA, as well as segments 39 and 47, both containing condensed rDNA repeats, are the most pronounced aberration hot-spots in T-1586. The number of aberrations observed in these segments was three to five times higher than theoretically expected. The intrachromosomal distribution of chromatid aberrations in karyotype T-21, where the NOR-bearing segments in chromosomes 6 and 7 change their position, revealed a substantial difference in the aberration hot-spot behaviour. A position-specific increase in aberration clustering was observed, most pronounced in segments 38 and 47. On the other hand, segment 46 retained its initial sensitivity, while segment 39 in the new position lost its previous status as a mutation hot-spot. The data are indicative of the expressivity of aberration hot-spots generated after treatment with this restriction endonuclease being influenced by their distinct chromosomal location.