الفهرس 
Introduction
Plant material and growth conditionsOnly 14 pages are availabe for public view
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Abstract
A pot experiment was conducted to evaluate the beneficial effect of foliar application of trehalose (Tre) (1.5 mM), grain presoaking in salicylic acid (SA) (30 mM) and their interaction on drought tolerance of two wheat (Triticum aestivum L.) cultivars (Gemmieza-7, drought sensitive cultivar and Sahel-1, drought tolerant cultivar). The present study was carried out in a greenhouse at the Faculty of Science, Mansoura University, Egypt, through the two successive seasons (2011/2012) and (2012/2013). Water deficit was imposed by withholding water at the reproductive stage for 30 days. At the end of stress period, re-watering to the field capacity was carried out. Samples were taken for measurements of growth vigor as well as physiological and ultrastructure criteria at the end of stress period before re-watering during grain-filling (21 days post-anthesis) (i.e. 106 days from planting). At harvest (155 days from sowing), yield and yield attributes as well as the biochemical aspects of yielded wheat grains were estimated. 1- In general, the obtained results showed that drought caused general decrease in the growth vigor of root, shoot and flag leaf, pigment content as well as total protein and nucleic acids content in flag leaf of both wheat plants. Exogenous application of SA, Tre or their interaction alleviated the adverse effects of water stress by improving growth vigor of root and shoot, retention of pigment content and increasing the content of total proteins and nucleic acids. Among the cultivars, Sahel-1 showed a better performance and produced more biomass under drought stress when compared with Gemmieza-7. 2- Electron microscopic examination of mesophyll cells of wheat flag leaf revealed that water stress negatively affected the chloroplasts and oleosomes ultrastructure in the two cultivars during grain-filling. Furthermore, water stress caused noticeable decrease in chloroplasts number in mesophyll cells of flag leaf in both cultivars during grain-filling when compared with those of the control plants. 3- Water stress induces marked decrease in transpiration rate; relative water content and water use efficiency but led to significant increase in saturation water deficit in flag leaves of wheat plants. Grain priming with SA and/or Tre counteracted the stress induced by water stress by recovering the turgidity in flag leaf of droughted wheat plants. 4- Water stress reduced bio-membranes stability through inducing its lipid peroxidation resulting in an increment in membrane leakage (ML) with marked decrease in membrane stability index (MSI) in flag leaf of both wheat cultivars during grain-filling. This effect was more conspicuous with Gemmieza-7. Application of SA and/or Tre markedly increased MSI and significantly decreased lipid peroxidation and ML in flag leaf of water stressed wheat plants. 5- It was obvious that drought significantly increased the activity of ascorbic acid oxidase (AAO), peroxidase (POD) and phenylalanine ammonia lyase (PAL) activities and induced a non significant reduction in polyphenol oxidase (PPO) activity in flag leaves of both wheat cultivars during grain-filling comparing with the control plants. Application of SA and/or Tre markedly increased AAO, POD and PAL activities and a non significant decrease in PPO activity in flag leaf of water stressed wheat plants. 6- Water stress caused significant increase in the amount of total phenols and flavonoids in flag leaf of both cultivars during grain-filling where the sensitive plants accumulated more total phenols and flavonoids contents than the tolerant one. Application of SA and/or Tre markedly increased total phenols and flavonoids contents. Water stress resulted in a massive increase (p ≤ 0.05) in the non-photosynthetic pigment content (anthocyanins and lycopene and β-carotene) of the two wheat cultivars particularly drought sensitive one during grain filling. Application SA and/or Tre induced additional increase (p ≤ 0.05) in anthocyanins, lycopene and β-carotene contents. 7- Water stress significantly decreased all yield components and biochemical aspects of yielded grains. Application of SA and/or Tre appeared to alleviate the deleterious effects of water stress on biochemical aspects of yielded grains of wheat plants. For identifying the factors related to the economic yield, the correlation coefficients between the grain yield and all the estimated criteria were determined from the measured mean values.