AL-SAHEAL, Y. A., and A. S. LARIK. 1985. Genetic parameters of tlax genotrophs. V . Behaviour of nuclear DNA in parental and FI generations. Can. J . Genet. Cytol. 27: 6-1 I. The nuclear DNA difference between large (L) and small (S) genotrophs, induced in the tlax variety 'Stormont Cirrus' (PL), was investigated using Feulgen photometry. L and S genotrophs were crossed, respectively, to the PL genotype and the parental, and Fl generations were grown in greenhouse ( T I ) and field (T?) temperatures. Results demonstrate that (i) the DNA values show increased reversion in the crosses, compared with the parents at T I and less reversion in the crosses, than in the parents, at T2; (ii) more reversion occurs in the PL maternal crosses than in the PL paternal crosses; and (iii) the PL genotroph possess a nuclear and a cytoplasmic factor which plays a direct part in determining nuclear DNA changes in the chromosomes of the stable genotype.
Changes in the amount of nuclear DNA can be induced in 'Stormont Cirrus', a plastic variety (PL) of flax, by different environments, but not in the linseed variety 'Royal' (R) which is not plastic. PL is thought to contain nuclear and cytoplasmic factors, not possessed by R, which are necessary for the plastic characters to appear. Further crosses have shown that the PL nuclear factor plays a direct part in the determination of plasticity and that the cytoplasmic factor is maintained in the presence of both PL and R nuclei. Insofar as the genetic analysis has been taken, the distribution of genetic factors determining plasticity (+) or nonplasticity (−) in PL and R are as follows: nuclear factor (PL, +; R, −); cytoplasmic factor (PL, +; R, −); nuclear factor for synthesizing de nouveau cytoplasmic factor (PL, −; R, −); nuclear factor for maintaining the cytoplasmic factor (PL, +; R, +); site at which DNA changes occur (PL, +; R, +). It is suggested that the nuclear factor is activated by the cytoplasmic factor, and must come directly from a cytoplasm containing the cytoplasmic factor to be operative.Key words: flax, genotype plasticity, plasticity, genotrophs.
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