Mutations in rDNA. 1. Dependence of chromosome mutation induction on positions and activity of nucleolus organizer regions.

Studies on chromatid aberration induction in NORs of standard and reconstructed karyotypes, as well as in the single translocation lines of barley, indicate a correlation between synthetic activity (transcription) of rDNA and frequency of chromosome mutations induced by HU. Experimental evidence in favour of this inference arises from analyzing karyotypes with NORs located at their original sites and karyotypes with NORs translocated from their original sites. The close correlation between the different rate of synthetic activity (transcription) in nucleolus formation and the comparable range of variation in aberration involvement of NORs observed in translocation lines are discussed.