The status of ribosomal RNA genes during nuclear DNA reversion in flax

Heritable changes in plant weight and nuclear DNA content may be induced in certain varieties of flax by different fertilizer environments. The large stable form (L) has 16% more nuclear DNA that the small stable form (S). In subsequent generations in particular environments the nuclear DNA difference disappears, although the plant weight differences remain, while in other environments both DNA and plant weight differences are maintained. The large stable form has 56-70% more rRNA genes than the small stable form. The majority of this difference in rDNA is maintained in types where the nuclear difference has reverted. It is suggested that the expression of the flax genome may be susceptible to a reduction in the multiplicity of rRNA genes which limits the availability of protein synthetic machinery needed for growth.