The study of ultrastructural transformations of the nuclear domains of cells of actively dividing tissues of the meristem under the influence of abiotic environmental factors such as cold, salinity, changes in the magnetic field parameters accompanying the change in the level of gene expression and chromatin modification allow visualizing these processes. We present the details of the process of structural organization, formation and disassembly of the nucleolus, chromatin condensation during the progression of the cell cycle studied by the method of classical TEM in the cells of the meristematic zone of the wheat root. The transformations of peripheral chromosomal material (PCM) in telophase, nucleolonema of nucleoli in interphase and prophase, chromatin transformation (condensation and decondensation) under conditions of the geomagnetic field, weakened magnetic field and static magnetic field at low positive temperatures and salinity were investigated and analyzed. Using an analysis of the dynamics of structural modifications of proliferating nuclei, there was a disturbance in the formation of the chromonema and condensed chromatin in the middle interphase, a change in the structural organization of the nucleolus during the transition from late interphase to prophase, as well as a change in the structure of PCM, pre-nucleolus and chromatin in telophase. A scheme has been proposed for the formation of a specific nucleolonemal and chromonemal structure and its influence on the structural organization of chromosomes in anaphase and telophase. The nature of this structure identified earlier in normal and stressful conditions in rye and barley [1,2] and wheat in the acidic and alkaline reaction of the environment and cold [3,4] is discussed. The studied effects associated with the transformation of the structural organization of the nuclei caused a change in the expression level of the genes of some DNA methyltransferases, probably related to the epigenetic regulation of the genome. The proposed mechanisms of action of low positive temperatures, salinization, magnetic field on the nuclear compartment and its domains, regulation of chromatin decondensation, export of pro-ribosomal particles under stress, and the fine structure of the nucleolonema are discussed. This work was supported by the Russian Science Foundation (grant 18-016-00150) and by the state assignment АААА-А18-118051890089-0. Referenses: 1.Baranova EN, Baranova GB, Kharchenko PN (2011) Effect of weak magnetic field and low positive temperature on chromatin and nucleolus ultrastructure of rye and barley. Russ Agric Sci 37: 453-461. 2. Wang J, Zhang F (2015) Nucleolus disassembly and distribution of segregated nucleolar material in prophase of root-tip meristematic cells in Triticum aestivum L. Arch Biol Sci 67: 405-410. 3. Avetisova LV, Kadykov VA (1985) Ultrastructure of Wheat Apical Meristem Cells at Low Positive Temperatures, 1: Nuclear Structure. Tsitologiya, 27: 28–32. 4. Baranova EN, Gulevich AA (2009) Structural organization of nuclei and nucleoli of wheat shoot and root meristem during germination under alkaline pH conditions . Russ Agri Sci 35: 11-14.