Transcriptional Activity of Translocated NORs in Barley (Hordeum Vulgare L.)

The standard barley cultivar "Freya" and structural mutant forms ab, s, q, T21 and T627 were used to investigate the transcriptional activity of homologous rDNA loci (NORs) based on the positive reactions of NORs of metaphase chromosome with AgNO 3 and the number and size of silver stained nucleoli in somatic interphase cells and meiocytes. Fluorescent in situ hybridization (FISH) was also used. The chromosomal rearrangement enables testing of intrachromosomal suppression of NORs and provides insight into the mechanisms of intraspecific nucleolar dominance. Considerable difference in gene expression (nucleolar dominance) after AgNO 3 and FISH was established only in line ab, when both NORs (5H and 6H rDNA loci) are co-localized on the same or opposite arms of the chromosome. Translocation-induced intraspecific nucleolar dominance is probably the result of interaction of NOR6H and NOR5H or other genetic factors (like up-elements) located on the NOR-bearing chromosomes. The significance of such an unusual phenomenon is discussed.