Transcriptional activity of an inversion split NOR in barley (Hordeum vulgare L.).

The transcriptional activity of NORs in a new structural mutant of barley (PK-88-4) was studied based on the positive reaction of NORs of metaphase chromosomes with AgNO3 and the number and size of silver-stained nucleoli in somatic interphase cells and meiocytes. PK-88-4 proved to contain a pericentric inversion that split NOR 7 into two unequal parts residing in the opposite arms of the reconstructed chromosome 7(5). This chromosomal rearrangement enables testing of intrachromosomal suppression of NORs and provides insight into the mechanisms of intraspecific nucleolar dominance. Both parts of the split NOR proved to be transcriptionally active, and are not subject to intrachromosomal nucleolar dominance. Thus, translocation-induced intraspecific nucleolar dominance is probably the result of interaction of NOR6 and NOR7 or other genetic factors located on the NOR-bearing chromosomes 6(6H) and 7(5H).