Methylation of DNA in NaCl-adapted cells of potato.

Salt-adapted and control cells of the cultivated potato, Solanum tuberosum cultivar Russet Burbank, untreated or treated with 5-azacytidine (an inhibitor of DNA methylation), were compared with respect to: a) % of cytosine methylation in total nuclear DNA, as determined by HPLC; b) fresh and dry weight. Adapted and control cells were compared also with respect to % of cytosine methylation in DNA, which was purified from DNaseI-partially-digested chromatin and size fractionated by electrophoresis in agarose gels. The growth (represented by dry weight) of the NaCl-adapted cells in saline medium lacking 5-azacytidine was similar to that of control cells in standard medium. The adaptation of the cells was correlated with some increase (+16%) of methylation in total DNA and with a much greater increase in the lower molecular weight DNA fractions which were obtained from the presumably more active chromatin. As expected, the treatment of the cells with the methylation inhibitor induced a decrease in the level of methylation. The decrease of methylation, however, was much greater in the adapted cells, whose dry weight, unlike in the control, was not affected by this treatment.