In the dissertation research the correlation of radiation-induced transcription response of the main DNA repair genes AtKu70, AtRAD51, AtRad1, AtMsh2 with the efficiency of postradiational recovery of irradiated plants at the level of the whole organism was shown. This correlation manifested itself in the range of sublethal doses of 0.2 Gy - 21.0 Gy, depending on the irradiation mode and was characteristic not only for the irradiated F0 plants, but also for the non-irradiated plants of the generation F1. The highest correlation coefficients (Pearson correlation coefficients r = 0.6 to r = 0.9, p <0.05) for most morphometric indices of irradiated plants with early changes in the expression of AtKu70, AtRAD51 and AtRad1 genes in the tissues of the rosette leaves of Arabidopsis thaliana were observed with repeated irradiation. Correlated with the early transcriptional response parameters included: temporal or terminal growth arrest, the emergence of morphological anomalies, sterility, growth and branching of the stem, accumulation of biomass.
For the first time the nonlinear double-peak dose dependence of the transcriptional activity of AtKu70, AtRAD51, AtRad1 genes in the tissues of rosette leaves of Arabidopsis plants, irradiated at sublethal doses of 3-21 Gy of X-rays, was obtained. These data could be explained by the existence of two subpopulations of plant cells with significantly different radiosensitivity.
The character of expression of the key DNA repair genes of Arabidopsis thaliana plants in the rosette leaves at the margin between the vegetative and generative phases of development is established: expression of the AtRAD51 gene is radiation-inducible, and the AtKu70 and AtRad1 genes are expressed both constitutively and in radiation-inducible manner. It has been shown that irradiation in sublethal doses can not only stimulate, but also suppress transcription of DNA repair genes, as well as lead to the appearance of truncated mRNA. It was found, that both stimulation and inhibition of the growth and development of plants under the influence of radiation in the range of sublethal doses are partly due to activation or repression of the transcriptional activity of the AtKu70, AtRAD51, AtRad1 genes. The inhibitory effect of repeated and chronic, but not single irradiation correlates with increased expression of the AtRad1 gene, and stimulating – with the activation of AtKu70 and AtRAD51 genes. AtKu70 gene positively correlates with plant growth and accumulation of biomass, while the activity of the AtRad1 gene positively correlates with delayed or arrested growth and development, morphological anomalies, sterility of irradiated plants. A negative correlation of transcription of the AtRAD51 gene with morphological anomalies was also established.
Expression of AtRAD51 and AtRad1 genes, increased after irradiation in sublethal doses, might be transmitted to the first-generation progeny, while the induced activity of AtKu70 had not been transmitted. The transgenerational transmission of the increased activity of the AtRad1 gene had been associated with the increased frequency of plants with morphological anomalies in the first postradiational generation as compared to non-irradiated control. Also activity of the AtRAD51 gene has been promoted an increase in the germination and survival of F1 seedlings, the activity of AtRad1 on the contrary.
It has been shown that according to a number of biochemical markers X-ray irradiation at a sublethal dose of 21 Gy leads to accelerated aging of plant leaves. In particular, the ratio of beta-layers and alpha domains of proteins increases and their total content decreases, the content of nucleic acids and lipids decreases, pectin and lignin are replaced by cellulose and hemicellulose, starch is deposited, modification of composition of the fatty acids of cutin is observed, chlorophyll is destroyed and purple pigments are accumulated.
It has been shown for the first time that Atmsh2-/- mutants are more susceptible than Atmsh2+/+ plants to the single-dose, but not repeated or chronic ionizing irradiation in sublethal doses. An independent role of the Atmsh2 gene product in post-radiation DNA repair, as well as its interaction with AtRad1 and AtKu70 genes have been demonstrated.
