Wheat, an important food crop in the world, accounting for one-fifth of the total calories and protein, is a sensitive culture to the lack of soil moisture. Drought impairs plant growth and development, affects physiological and biochemical processes and reduces plant productivity. Photosynthetic assimilation of CO2 is considered to be one of the physiological processes most sensitive to drought. This review is devoted to the analysis of literature data and the results of own works on the effect of drought on the wheat photosynthetic apparatus traits at different levels of its organization — from morphological to molecular. The relevance of research on traits associated with drought resistance is due to a significant, compared to other abiotic factors, yield reduction due a drought, the frequency of dry conditions during the wheat growing season, the complex nature response of this culture’s to drought, and the need to accelerate the breeding process. The analysis of the morphological traits of the photosynthetic apparatus proves that, in addition to the direct effect of this stress on the plant assimilation surface area, it also affects the absorption and efficiency of the conversion of light energy into biomass, and also depends on the remobilization of photosynthetically assimilated carbon from the non-leafy organs of wheat. While the integral indicator — a photosynthesis rate — reduced under drought stress (the magnitude of this decrease depends on the genotype, the stage of plant development and the stress severity), individual components of photosynthetic activity can be differently. In particular, the non-photochemical quenching of chlorophyll a fluorescence in diverse wheat lines under drought conditions had a multidirectional nature. The promising features of wheat drought tolerance discovered in recent years are considered, in particular, long-term rearrangements of the photosynthetic apparatus, including changes in the structure of PSII-LHCII phosphorylation along with protein stoichiometry. The review also considered the role of antioxidant enzymes of chloroplasts, which prevent drought-induced accumulation of reactive oxygen species and thus prevent functional and structural changes in chloroplasts, chlorophyll degradation, and disruption of the integrity of thylakoid membranes. According to the literature, the role of organic and inorganic substances in maintaining the osmoregulation of plants in the water deficit was considered and the probable mechanisms of their action were analyzed. Quantitative trait loci associated with wheat drought tolerance DNA markers as mechanisms of drought tolerance in wheat are also described. Therefore, the analysis of literature and own data showed that tolerance of the photosynthetic apparatus to drought in different genotypes of wheat may be associated with different mechanisms. It is hypothesized that the combination of several/some mechanisms in one genotype offers a promising strategy for increasing crop resistance.
Keywords: wheat, drought, specific mass of leaves, photosynthesis, photosynthetic activity, antioxidant protection, osmoregulation
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