الفهرس 
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Abstract
A pot experiment was conducted to evaluate the beneficial effect of foliar application of glycine betaine (10mM), grain presoaking in salicylic acid (0.05 M) and their interaction on drought tolerance of two wheat (Triticum aestivum L.) cultivars (sensitive, Sakha 94 and resistant, Sakha 93). The obtained results showed that water stress caused noticeable increases in root length, number of adventitious roots, soluble sugars and nitrogen. On the other hand, water stress caused a massive reduction in fresh and dry masses of root, growth vigor of shoot, leaf area, pigments content, polysaccharides, protein- N and total nitrogen in both wheat cultivars. Exogenous application of GB, SA or their interaction could counteract the adverse effects of drought by improvement of growth vigor of root and shoot, leaf area, retention of pigments content, increasing the concentration of organic solutes (soluble sugars and soluble nitrogen) as osmoprotectants, keeping out the polysaccharides concentration and/or stabilization of essential proteins in both wheat cultivars. The application of GB, SA or their interaction induced some modifications in the anatomical features of the flag leaf and peduncle of main shoot which appeared to be an adaptive response to drought stress. Drought induced marked decreases in diurnal and mean daily values of transpiration rate, stomatal pore areas (on upper and lower sides), relative water content, water use efficiency, indole-3-acetic acid (IAA), gibberellic acid (GA3) and cytokinins (CKs) but led to a significant increase in the abscisic acid (ABA) concentration in flag leaves of the two wheat cultivars. Grain presoaking in salicylic acid (SA) or foliar application with Glycine betaine (GB) alleviated the stress induced by drought by keeping water within leaves and consequently recover the turgidity of stressed plants by restricting the transpiration rate, stomatal closure, decreasing the ABA level and enhancing the growth promoters (IAA, GA3 & CKs) particularly with the sensitive cultivar. Furthermore, the effect was more pronounced with GB+SA treatment. Water stress caused an increase in osmotic pressure, proline, total soluble nitrogen, total soluble sugars, organic acids, ions (Na+, K+,Ca+2, Mg+2 and Cl-) content as well as Na+/K+ ratio in cell sap of flag leaves in both wheat cultivars. The resistant variety had higher values of osmotic pressure, proline, organic acids and ions content than the sensitive one. On the other hand, the applied chemicals mitigated the effect of water stress, the effect was more pronounced with GB+SA treatment, on the used wheat cultivars. The used chemicals increased the osmotic pressure and the osmolytes concentrations. The osmotic pressure appeared to depend on proline, TSN, TSS, organic acids and the ions content. The applied chemicals appeared to alleviate the effect of water stress on wheat yield (particularly the sensitive one) and the biochemical aspects of yielded grains. The effect was more pronounced with GB+SA treatment.