PHYTOHORMONAL MODULATION OF IN-VITRO WHEAT NUCLEAR-DNA METHYLATION BYWHEAT CYTOSINE DNA-METHYLTRANSFERASE

Effects of phytohormones on in vitro DNA methylation by nuclear extrac ts from wheat seedlings were studied. In the presence of some plant gr owth regulators (gibberellic acid, GA(3), 6-benzylaminopurine, fusicoc cin), the incorporation of methyl groups (radioactivity) from [methyl- H-3]S-adenosyl-L-methionine (SAM) into DNA was 30-80% higher than that in control samples without exogenous phytohormones added. The maximal stimulating effect of these phytohormones on DNA methylation by nucle ar extracts was observed at phytohormone concentration 10(-6) M. Under the same conditions the auxins, abscisic acid, zeatin, and epibrassin olide do not show marked effects on DNA methylation. In contrast with the stimulation in nuclear extracts, the phytohormones do not increase DNA methylation by purified wheat DNA-methyltransferase obtained afte r chromatography on DEAE-cellulose and heparin-agarose. Gibberellin an d 6-benzylaminopurine at relatively high concentrations (10(-5)-10(-4) M) inhibit DNA methylation by the purified enzyme. Thus, phytohormone s influence in vitro DNA methylation. The phytohormone effect may be m ediated by nuclear proteins that bind to DNA and control the modulatin g phytohormone effect on DNA methylation in the nucleus. In any case, there is a system of phytohormonal control of DNA methylation in the p lant cell nucleus.