Sokolova D. Epigenetic component of radioadaptation under chronic and acute radiartion exposure of plants

The thesis is devoted to identifying the role of DNA methylation in radiation exposure and plant adaptation to irradiation. The investigation was carried out on two hybrids of corn and was focused on studying the connection between adaptive changes in whole organism and rearrangements of satellite and transcribed DNA methylation patterns under different exposure modes. As independent marker of changing radioresistance the chromosome aberration yield was used. The thesis consists of four experimental series. The fist one is devoted to determine time interval between irradiation fractions and passage from maintenance methylation to de novo one and effect of time between fractions on DNA methylation pattern rearrangements and adaptation rate. The rearrangements of satellite and transcribed DNA methylation patterns in adaptive reaction's formation were shown. Such changes mostly were due to demethylation of existed and methylation of new sites, that meant pass from maintenance methylation to de novo one under increasing 1 hour time between fractions of acute exposure. Such result pointed to connection between inducible and constitutive reactions while adaptation was formed. That indicated connection between the effects and different characteristic terms implementation of epigenetic mechanisms that underlied adaptation. Increasing of time between fractions led to changes in DNA methylation patterns and chromosome aberration yield that indicated to realization of different adaptation mechanisms by their raising time. Statistic analysis of connection between mitotic index and chromosome aberration yield under various doses and intervals between irradiation pointed to existence of two types of repopulation meristematic repair. The one was connected with passage of sleeping meristematic cells to active proliferation, thus was dedicated to changing of ontogenetic cell program. With aim of next investigation of connection between adaptive changes and DNA methylation the studying was carried out in the second experimental series under different exposure modes: "adaptive - challenge irradiation", chronic gamma-irradiation and combined irradiation. Shown that under chronic and combined radiation exposure the range of changed restriction fragments was wider than under acute one. This indicated to great role of de novo DNA methylation in formation of radiobiological reactions. The investigation of effect of original methylation pattern of two DNA types to plant radioresistance and formation of adaptation was carried out by choosing from corn seeds subpopulations with different germination rate and their irradiation under various exposure modes: acute UV-C irradiation and "adaptive - challenge exposure". In the third and fourth experimental series was indicated connection between various seeds' germination rate and polymorphism of functionally different DNA methylation patterns of seedlings and their radioresistance. The data allowed considering the DNA methylation pattern as the factor of organism's individual radioresistance, and polymorphism of methylation pattern as the factor of population radioresistance. It was found that the plant organism's adaptive capacity was tightly connected to the activity of growth processes and the original DNA methylation pattern of functionally different sequences. And adaptive capacity of plant population was associated with polymorphism of DNA methylation pattern. Great changes of DNA methylation pattern not only transcribed but also satellite DNA shown while adaptation formation under all exposure modes pointed to importance of this factor in plant radioresistance and role in epigenetic regulation of adaptation by chromatin remodeling .