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Landsmann and Uhrlg (1985) using a random potato 25s rDNA probe, found a 70% reduction
In 25s rRNA genes in 2 of 12 Solanum tuberosum plants regenerated from protoplarts. They
were regarded as mutants deficient In riborornol RNA-genes.
The TdHcum aesh'vumnuclear rDNA repeat unit has been shown to be heterogeneous In length,
due to the non-transcribed spacer region (Gerlach and Bedbrook, 1979 and Appels and
Dvorak, 1982). Rode et al., (19871, also 0bSe~ed the rDNA containing the non-transcribed
spacer region to display a length polymorphlm In gametoclones of wheat. Davies et al.
(1986) observed 17 of 551 regenerated wheat plank to have altered ADHl zymogram.
Progeny with altered zymogram in 13 01 the regenerants were aneuploid. The remaining 4
regenerants gave rise to euplold progeny with altered ADHl zymograms. lhey interprded
three of the somaclonal mutants lo possess a 4Aa isochromaome, a 3BS/4Au translocation
and a 7BS/4Aa translocation respectively. Brelman et 01. (19870) analyzed progenies of plank
regenerated from scutellar callus of bread wheat (Triticum aestivum 1.) for the organization d
the intergenic spacer of rRNA genes located at the sites of nucleolar organizer regions (Nor
loci). When the DNA was digested with the restrlction endonucleare Toql and probed wiM a
specllc rDNA fragment by southem Mot-hybridiuation, three progeny plclnk of cultivar 'ND7532'
showed reducfion in the number of rDNA space*. The diversiiy was expressed In qualitative
and/or quantitative changes In Toql fragmented spacer lengths. The regenerated plank had
a missing or reduced amounts of the 1.9 kbp Taql fragment. Another plant showed ratio d 2.7
and 3.0 kbp Taql fragments different from that of control. One plant showed the loss of the 2.7
kbp Taql fragment. The variation In the length of Me rDNA repeats is prchbly due to a
reduction in the number of 135 bp repeak because the Idtw repeats occupy mod of the DNA
sequences between these sties (Appsb and Dovacak, 1982). On. other phi digested wHh
EcoRI-BamHI showed a lou of the 4.4 kbp EcoRI-BamHI fragment. On screening Me progeny
01 149 plank regenerated from lmmduro whud wnbryor. Ryan and Scowcmtl(1987) found