The mammoth gene of
Nicotiana tabacum has been transferred to
N. rustica genome through interspecific hybridization followed by repeated backcrossing to
N. rustica. Our previous studies have revealed that the expression and segregation of the mammoth gene was more complex in the
N. rustica genetic background than in
N. tabacum. Plants with abnormal floral expressions such as non flowering (NF) and flower revertants (FR) with altered responses to environmental factors such as photoperiod and thermoperiod frequently appeared in the backcross progeny of
rustica-
tabacum hybrids. The segregation of plants for FR and NF characters among the progeny was highly heterogeneous and chromosome instabilities were found both at mitosis and meiosis.
Characterization of the genomic DNA of
rustica-
tabacum hybrid segregants (FR and NF) and the parental species (
N. tabacum and
N. rustica) was carried out in the present study using thermal denaturation and analytical density gradient analyses. Differences were observed in the DNA composition among the hybrid plants segregating for abnormal flowering expressions, FR and NF, as well as the parental species. Variation was observed in the mole fraction of 5-methyl deoxycytidine in the genomic DNA of the hybrid progenies and the parental species. Variation in the amount of satellite DNA fraction was also found between the hybrid plants, FR and NF and the recurrent parental species
N. rustica. The differences in the buoyant densities, satellite DNA fraction, 5-methyl deoxycytidine contents between FR, NF and
N. rustica suggests reorganization of genomes of the hybrid progenies following interspecific hybridization. The variation could result in part from the abnormal segregation of chromosomes and chromosome aberrations frequently found in the backcross progeny of
rustica-
tabacum hybrids at mitosis and meiosis.
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