The study is devoted to the problem of the genetic basis of plant adaptation. The important adaptive traits of the model species of Arabidopsis thaliana were studied: vernalization requirement, flowering time and the time of seed germination in plants of northern natural populations (Karelia). Specific expression patterns of the gene FLC and VIN3 , which control these traits, have been revealed. A low level of FLC mRNA transcripts in non-vernalized plants at the rosette stage was established, with followed by increased expression on the 10-30th day of vernalization, which differs from the data of other researchers. The initially low level of VIN3 mRNA transcripts in non-vernalized plants unexpectedly increases in some populations during vernalization on the 20th day, in contrast to literature data. It has been shown that a longer vernalization (9 week) is required for a mass transition to flowering of plants from populations of the northern periphery of the species range in the Onega Lake basin compared to vernalization (6 weeks) of plants from the milder climate of Lake Ladoga islands. A study of the degree of dormancy of seeds, which affects the time of germination, showed that in cold climates A. thaliana seeds have a stronger dormancy at a high summer temperature (22 ºС) compared to a cool autumn temperature (10 ºС). This ensures their germination in the autumn and flowering in the spring, after the end of vernalization. It is suggested that in Karelian Arabidopsis thaliana populations located on the northern periphery of the species range, one of the mechanisms of plant adaptation to a cold climate is adaptive pleiotropy, exhibited in the peculiarities of the expression of the FLC and VIN3 genes, which control the timing of seed germination in autumn and flowering plants in spring, after vernalization, which ensures both seedling survival and maximum reproductive success.

The study is focused on the extent of the genetic diversity of marginal populations. The level of genetic variability in natural populations of Arabidopsis thaliana (L.) Heynh. occupying the northern part of the species’ range was evaluated (microsatellite markers were used). The high population polymorphism of A. thaliana in the northern part of its range is most likely connected with adverse environmental conditions. The findings amplify existing ideas about marginal populations’ genetic polymorphism.

The role of the genetic and epigenetic component in the formation of the natural genetic load and fitness of M 5-mutant posterities of perennial cross-pollinated grass Festuca pratensis Huds. is shown. M 5-mutant generations were created at different levels (high, moderate and low) of soil fertility nutrition available to maternal plants. The size of the seedling pool with a suppressed chlorophyll deficiency, survival and fertility of plants, influence of stabilizing natural selection as applied to the above components of fitness were estimated.

We investigated the formation patterns of the components of fitness (survival and fecundity) in meadow fescue plants with suppressed chlorophyll deficiency, which are associated both with the mechanisms of phenotypic changes in the color of seedlings at the juvenile stage of their development under resuppression (repopulation, reversion) and with their rate (fast, slow).

Birch species introduced in Karelia Betula ermanii Cham. and Betula japonica Sieb., as well as native species Betula pendula Roth and Betula pubescens Ehrh. were compared in terms of microgametophyte fertility and vitality, pollen grain and pollen tube size. It is demonstrated that each of the species has developed its own strategy in male gametophyte formation and behaviour under certain ambient conditions. Compared to introduced species, native ones showed higher stability in formation and manifestation of pollen morphophysiological parameters, except for vitality. In introduced species, male gametophyte was more sensitive to changes in the weather and climatic conditions under which pollen formed (B. japonica) and had lower pollen fertility compensated by high vitality (B. ermanii).