Novel class of rDNA repeat units in somatic hybrids between Nicotiana and Atropa.

Behavior of ribosomal RNA genes in the process of somatic hybridization was analyzed using hybrids Nicotiana tabacum + Atropa belladonna. Blothybridization of parental species DNAs to (32)P-rDNA specific probes revealed two classes of ribosomal repeats in both tobacco and nightshade; their length was 11.2 kb, 10.4 kb (tobacco) and 9.4 kb, 10.2 kb (night-shade). For analysis of hybrids, labelled (32)P rDNA specific probes were hybridized to DNA of parental species and somatic hybrids digested with restriction endonucleases EcoR1, EcoRV and BamH1. A new class of ribosomal DNA repeat, absent in parental species, was found in hybrid line NtAb-1. Possible mechanisms of appearence of a new rDNA class in the process of somatic cell fusion are discussed.