The role of the root in water supply and plant viability is especially important if plants are subjected to stress at the juvenile stage. This article describes the study of morphophysiological and cytological responses, as well as elements of the anatomical structure of primary roots of three wheat species, Triticum monococcum L., Triticum dicoccum Shuebl., and Triticum aestivum L., to osmotic stress. It was shown that the degree of plasticity of root morphology in water deficit affected the growth and development of aboveground organs. It was found that in conditions of osmotic stress, the anatomical root modulations were species-specific. In control conditions the increase in absolute values of root diameter was reduced with the increase in the ploidy of wheat species. Species-specific cytological responses to water deficit of apical meristem cells were also shown. The development of plasmolysis, interpreted as a symptom of reduced viability apical meristem cells, was revealed. A significant increase in enzymatic activity of superoxide dismutase under osmotic stress was found to be one of the mechanisms that could facilitate root elongation in adverse conditions. The tetraploid species T. dicoccum Shuebl. were confirmed as a source of traits of drought tolerant primary root system for crosses with wheat cultivars.

Chl -chlorophyll; ChlFP -chlorophyll fluorescence parameter; Ek -minimum saturation irradiance; ETRmax -PSII maximum electron transport rate; Fm' -maximum fluorescence yield of the light-adapted leaf; Ft -fluorescence yield just before the saturation pulse; RLC -rapid light curve; Y(II)65,625 -PSII quantum yield of photochemical quenching at PPFD of 65 and 625 µmol m -2 s -1 ; Y(NO)65,625 -nonorganized energy passive dissipation in form of heat and fluorescence at PPFD of 65 and 625 µmol m -2 s -1 ; Y(NPQ)65,625nonphotochemical energy conversion due to downregulation mechanisms at PPFD of 65 and 625 µmol m -2 s -1 ; α -the initial slope of RLC.Acknowledgements: This research was carried out in the framework of the project AP05131734 'Physiological and molecular genetic features of the functioning of the photosynthetic apparatus of alloplasmic lines of wheat, obtained as a result of interspecific crossings, in connection with their drought resistance ' (2018-2020). This grant was funded by the Ministry of Education and Science of the Republic of Kazakhstan. Conflict of interest: The authors declare that they have no conflict of interest. Highlights• PSII quantum yields at early vegetation stages can predict the fertility of wheat • Rapid light curves appeared to be productivity potential indicators • Allolines of T. dicoccum × T. aestivum are perspective for drought tolerance induction

The results of the complex analysis of different wheat species tolerance to drought stress in vivo at different levels of organization as well as in vitro on callus cultures, which was conducted, are presented. The objects of research are as follows: species of wheat-T. monococum L. (A u ), T. dicoccum Shuebl. (A u B), T. polonicum L. (A u B), T. aethiopicum Jakubz. (A u B), T. macha Dek.et.Men. (A u BD), T. compactum Host. (A u BD), and T. aestivum L. (A u BD). The methods of this research are physiological, biotechnological, and cytological. The focus was on nonspecific reactions of cereals to osmotic stress, and species-specific changes according to growth and anatomical and photosynthetic parameters which depend on studied species ploidy were shown. It was shown that results of testing of plant tissues in vivo and in vitro are comparable. It demonstrated the criterions for selection of drought-tolerant forms. Optimal selection criteria were identified, and more drought-resistant wheat species were identified.

Anatomical parameters of the flag leaf as criteria for drought tolerance of two alloplasmic lines (interspecific hybrids) and their parental forms − T. aestivum L. (cultivar of Mironovskaya-808) and T. dicoccum wheat were presented. The parameters studied were the thickness of the abaxial and adaxial epidermis, the thickness of the mesophyll and central vein, and the diameter of the central conducting bundle of the flag leaf. Different degrees of negative impact of sudden drought-stress and permanent water deficit on the anatomical structure of the flag leaf were shown. At the stage of flag leaf formation, anatomical parameters, for example an increase or preservation of the size of the protective and mechanical leaf tissues and the thickness of the mesophyll under stress can serve as criteria for the selection of drought-resistant forms of wheat. It revealed that among the studied genetic lineages the alloline D-d-05 showed the best adaptability and the most stable anatomical parameters of the flag leaf under conditions of moisture deficiency. The different degrees of drought tolerance of the studied lines indicate that the combination of the nucleus and cytoplasm of the parental forms can contribute to both an increase and a decrease in the level of drought tolerance in interspecific hybrids, which indicates the need to continue research with additional molecular genetic analysis.

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