DIFFERENTIAL AMPLIFICATION OF RDNA REPEATS IN BARLEY TRANSLOCATION AND DUPLICATION LINES - ROLE OF A SPECIFIC SEGMENT

Variation in restriction pattern, relative amounts of the two ribosoma l DNA (rDNA) repeats, and the overall content of rDNA were compared am ong twelve segmental duplications and eleven parental translocations i nvolving NOR6 and NOR7 of cultivated barley. Southern blot hybridizati on revealed two rDNA repeats of 9.9 kb and 9.0 kb. While all duplicati ons showed dimers for these rDNA repeats, the duplication lines D29 an d D47 displayed trimers in addition to a higher proportion of rDNA rep eats as dimers. The rDNA of D1, D29 and D47 showed resistance to Bam H I and Taq I digestion, indicating possible methylation of cytosine and adenine. Densitometric scans of autoradiographs revealed variations i n the relative amounts of the 9.0 kb and 9.9 kb rDNA repeats among dif ferent karyotypes. Dot blot hybridizations indicated variation in the overall rDNA content. Comparison of the 9.0/9.9 kb ratios and the perc entage of genomic DNA hybridizing to an rDNA clone of barley illustrat es differential amplification for the two rDNA repeats. When the segme ntal composition of these deviating lines were compared, it was eviden t that the relative position of the segment 12-16 of chromosome 6 dete rmines differential amplification while duplication of the same segmen t controls the overall rDNA content.