[DNA methylation in wheat seedling and influence of phytohormones].

A labelled DNA is synthesized in the etiolated wheat seedlings 72 hrs after a single addition of [2-14C]orotic acid (1 mCi per 250 seedlings). This DNA does not differ in the methylation degree of cytosine residues and base composition (radioactivity ratios 100.m5C/(C+m5C) and T/(C++m5C) from total seeding DNA. Thus, the radioactivity ratio 100.m5C/(C+m5C) represents in fact the methylation degree of cytosine residues in labelled DNA, and [2-14C]orotic acid can be used for the study of DNA methylation in higher plants. The newly synthesized DNA (21 hr incubation of seedlings with radioactive precursor) is methylated about 2 times less in comparison with fully synthesized radioactive DNA and total seedling DNA. This supports the assumption on a step-wise character of replicative DNA methylation in plants. Phenylacetic acid (30 mg/l) and 6-benzylaminopurine (l mg/l) do not influence the post-replicative DNA methylation, but auxin (FAA) very strongly inhibits the replicative DNA methylation. The phytohormone-induced changes in replicative DNA methylation are considered as a possible mechanism for regulation of DNA replication and, probably, of cell differentiation in higher plants.