AMPLIFICATION OF REPETITIVE DNA FROM NICOTIANA-PLUMBAGINIFOLIA IN ASYMMETRIC SOMATIC HYBRIDS BETWEEN NICOTIANA-SYLVESTRIS AND NICOTIANA-PLUMBAGINIFOLIA

Asymmetric somatic hybrids were obtained between a chlorophyll-deficie nt mutant of Nicoliana sylvestris (V42) and a nitrate-reductase (NR)-d eficient line of N. plumbaginifolia (cnx20 or Nia26), using each of th e parents alternately as the irradiated donor. Irradiation doses appli ed ranged from 10 to 1,000 Gy of gamma-rays. Hybrid selection was base d on complementation of NR deficiency with wild-type NR genes. To aid in the analysis of somatic hybrids, species-specific repetitive DNA se quences from N. plumbaginifolia (NPR9 and NPR18) were cloned. NPR18 is a dispersed repetitive sequence occupying about 0.4% of the N. plumba ginifolia genome. In turn, NPR9, which is part of a highly repetitive DNA sequence, occupies approximately 3% of the genome. The species-spe cific plant DNA repeats, together with cytological analysis data, were used to assess the relative amount of the N. Plumbaginifolia genome i n the somatic hybrids. In fusion experiments using irradiated N. plumb aginifolia, an increase in irradiation dose prior to fusion led to a d ecrease in N. plumbaginifolia nuclear DNA content per hybrid genome. F or some hybrid lines, an increase in the quantity of repetitive sequen ces was detected. Thus, hybrid lines 1NV/21, 100NV/7, 100NV/9, and 100 NV/10 (where N. plumbaginifolia was the irradiated donor) were charact erized by amplification of NPR9. In the reverse combination (where N. sylvestris was the irradiated donor), an increase in the copy number o f NPR18 was determined for hybrid clones 1VC/2, 1VC/3, 100VC/2 and oct 100/7. Possible reasons for the amplification of the repeated sequence s are discussed.