[Content of 5-methylcytosine in various families of repeating sequences of DNA in some higher plants].

Three families of repeating DNA sequences from 6 higher plants species are isolated. It is found that DNAs of plants examined at the same developmental stages differ considerably in the content of fractions with different repetition frequency of nucleotide sequences. The content of non-repeating sequences in the genome of the plants varies from 23.8 to 41.4%, the differences in the content of highly repeating fractions are less expressed (from 20.3 to 29.4% of the genome). The ratio of fractions changes considerably during ontogenesis: DNA of seeds contains more highly repeating sequences than DNA of seedlings. Fractions of nucleotide sequences with different repetition frequency, isolated from the same DNA, are little distinguished in the GC-pair content, and are characterized by a relatively high content of 5-methylcytosine: the methylation degree of cytosine is at least 17%. However, the degree of cytosine methylation is increased in fractions with high content of copies per genome in seedlings and leaves DNA of all the plants studied. The content of 5-methylcytosine in highly repeating fractions is 12% higher than in non-repeating sequences. Seed DNAs have some other distribution of 5-methylcytosine in different fractions: the degree of cytosine methylation in non-repeating and highly repeating sequences is practically the same.