Physiological and Molecular Bases of Drought Tolerance in Wheat (Triticum L.) Genotypes pp. 47-96
Authors: (J.A. Aliyev, Institute of Botany, Azerbaijan National Academy of Sciences, Baku AZ, Azerbaijan)
Abstract: Several thousand wheat (Triticum L.) genotypes were grown in field conditions
under normal water supply and a severe water deficit. Triticum durum L. genotypes
distinguish by higher tolerances to water shortage than those of Triticum aestivum L.
Under severe soil drought conditions during a period of the early spring tillering stage
until the end of grain filling, grain yield and protein losses in numerous genotypes
constitute within 25-65%. Ear photosynthesis plays a crucial role in crop accumulation
and protein synthesis in grain. In tolerant to water stress genotypes, more than 60% of
grain yield and protein synthesis is due to ear photosynthesis. Under dry conditions, the
afternoon depression of leaf photosynthesis increased and the rate of dark respiration
decreased. The rate of photosynthesis of 7- and 8-layered leaves in all genotypes in the
evening, and especially in the morning hours, is higher. Photosynthetic rates of 7- and 8-
layered leaves decreased greatly at the end of the milk ripeness and beginning of wax
ripeness. Under the effect of drought and leaf aging, leaf area and accumulation of dry
biomass shorten by more than half. After two weeks of drought, the intervarietal
differences in photochemical activity, expressed in the higher reduction in extensive
varieties in comparison with the intensive ones, are observed. Activities of Calvin cycle
enzymes (phosphoglycerate kinase, NADP-glyceraldehyde dehydrogenase) decrease with
strengthening of drought, especially in sensitive genotypes. Such a decline occurs more
rapidly in the ear elements at the early stages of development of generative organs.
Activity of enzymes of C4 cycle (PEP-carboxylase, NAD- and NADP-malate
dehydrogenase, aspartate aminotransferase) in C3 plants under soil drought in leaves and
ear elements increases significantly and the pyruvate orthophosphate dikinase is
activated. The correlation between the genetically determined tolerance of wheat
genotypes and level of antioxidant enzymes activity was revealed. Fv/Fm ratio changes
differently in various wheat genotypes during the growing season under drought. Plant
architectonics and various photosynthetic traits are of essential importance in tolerance
together with the root system and stress proteins controlled by certain genes. There is a
correlation between tolerance of genotypes and overexpression of 60, 40.5 and 28-24.5
kDa proteins from the thylakoid membrane of wheat. 920 bp fragment was revealed in
tolerant genotypes using RAPD markers P6 and P7, associated with drought tolerance.
The gliadin and glutenin contents increased under drought conditions compared to a
variant of optimal water supply, and maintenance of albumin and globulin proteins is
reduced in all studied genotypes. Precise screening for drought tolerance of wheat
genotypes using functional markers showed that the transcription factor genes Dreb1, that
cis-regulate drought tolerance, are localized only on the third chromosome of A genome
(3A) in 11 genotypes, whereas in the tolerant genotype Barakatli-95, these genes were
revealed both in A and B genome.
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