X-ray irradiation promoted asymmetric somatic hybridisation and molecular analysis of the products.

Complementation of two metabolic deficiences - nitrate reductase and tryptophan synthase - was used to select for somatic fusion hybrids between tobacco (Nicotiana tabacum) and henbane (Hyoscyamus muticus) with prior X-irradiation of one partner. Using species specific, radioactively labelled DNA probes it could be shown that a) irradiation significantly reduced the amount of chromosomal DNA of the irradiated fusion partner in the somatic hybrid, b) irradiation with doses which completely inhibit protoplast division did not pevent transfer of substantial amounts of chromosomal DNA into the fusion hybrids (so called 'cybrids') and c) this method transfers functional nuclear genes together with the partial genome from the irradiated partner.