Daucus carota cells contain specific DNA methyltransferase inhibitors that interfere with somatic embryogenesis

Results reported in this paper show that carrot cells contain a thermostable inhibiting activity of cytosine-5-DNA methyltransferase that upon filtration chromatography can be resolved in three major peaks. An inhibiting activity was found in all plant species tested, though at a concentration lower than in carrot. These inhibiting activities differ in size, sensitivity to various hydrolytic treatments, specificity for DNA METases of eukaryotic and bacterial origin and kinetic of inhibition. Results of chemical analyses indicate that the inhibitors are different from lipidic inhibitors described in Escherichia coli and Streptomyces sp. and, for their sensitivity to proteinase K, appear to have a proteinaceous nature. The addition of these inhibitors (Sephadex G 25 peak II and peak III) to actively growing suspension rice cells reduced the rate of in vivo DNA methylation without interfering with DNA synthesis. Peak II also induced a general demethylation effect in carrot cell suspension even if weaker than that caused by 5-azacytidine. Interestingly, inhibitors suppressed carrot embryogenesis but did not prevent undifferentiated cell proliferation of suspension cultures.