Intragenome distribution of 5-methylcytosine in DNA of healthy and wilt-infected cotton plants (Gossypium hirsutum L.).

Fractionation of DNA of healthy and wilt-infected cotton plants has been carried out according to the reassociation kinetics and the content of GC and 5-methylcytosine in the resulting fractions has been studied. The genome of cotton plant was found to be methylated quite unevenly. The GC rich (GC equals 64.7 mole%) fraction of highly reiterated sequences (Cot equals 0-3.7 times 10- minus 2) has a high content of 5-methylcytosine (5.8 mole%), whereas the methylation degree of the fraction of unique sequences (Cot larger than or equal to 487) is very low (the 5-methylcytosine content is about 0.5 mole%). In plants being infected with wilt, the 5-methylcytosine content in DNA or cotton leaves decreases two-fold; no changes in the structure and molecular population of DNA has been found. The sharp change in the 5-methylcytosine content in DNA of infected plants takes place at the expense of the decrease in the 5-methylcytosine content in fractions of highly reiterated sequences. The methylation degree of unique sequences (structural genes) remains unchanged.