CYTOLOGICAL CONSEQUENCES OF DNA AMPLIFICATION IN AN ANTHER CULTURE-DERIVED DOUBLED HAPLOID LINE OF NICOTIANA TABACUM

An increase in nuclear DNA, without an increase in chromosome number, has been found to occur as a result of anther culture in Nicotiana tabacum L. The objective of this study was to determine the cytological consequences of this DNA amplification in F₁ hybrids between a doubled haploid that had undergone a substantial increase in DNA and the cultivar from which that doubled haploid was derived. Mitotic and meiotic analyses were performed on plants obtained from reciprocal crosses of N. tabacum cv. NC95 and NC95 SCDHL 12, a doubled haploid line that has 41% more DNA than the parental cultivar. While no cytological abnormalities were observed in either parental line, numerous abnormalities were seen in both somatic and meiotic tissues of the F₁ hybrid. Chromosome losses, which appeared to result from spindle errors, were observed in these tissues. It is speculated that the spindle errors may be the result of a genetic unbalance caused by combining genomes with widely differing amounts of DNA. In addition to the spindle errors, a quadrivalent with an atypical morphology was observed in meiotic diplotene and metaphase I cells of the hybrid. The quadrivalent configuration was interpreted to represent pairing between amplified homologous regions in homeologous chromosomes. Further investigations of additional doubled haploid × cultivar lines is required before the significance of these findings to the anther culture process in N. tabacum can be fully assessed.