الفهرس 
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Abstract
This study was conducted to investigate the effect of temperature stress on growth , biochemical constituents as well as anatomy , ultrastructure and DNA finger print of leaves of three tomato cultivars Fayrouz, Azize & N23-48 and to find out if priming 10-3, 10-5& 10-7 molar β-sitosterol or 100ppm gibberellic acid can counteract the harmful effect of temperature stress on plant during vegetative growth . It is evident from the obtained results that, exposure the three tomato cultivars to temperature stress caused a decrease in the determined some growth parameters and relative water content. Photosynthetic pigments, different carbohydrate fractions, different nitrogen fractions and some antioxidant enzymes. In addition some changes in protein patterns and DNA finger print as well as alterations in structure of leave were detected such as decrease in leaf thickness, swelling of palisade layer at 10o C , appearance of trichomes on cell epidermis at 45o C of N23-48 cultivar. The negative effect of temperature stress was more acute at 10o C more than 45o C. Regarding the treatments of the three cultivars tomato with gibberellic acid or β-sitosterol either alone or with temperature stress, a general significant increase in all of the estimated growth parameters, relative water content and biochemical aspects was observed , especially in case of Fayrouz and N23-48 cultivars with 100ppm gibberellic acid or 10-5 molar β-sitosterol. Concerning the anatomical changes, these treatments led to a general significant increase in leaf and epidermis cell wall thickness. In addition, protein banding of the three tomato cultivars leaves showed expression of new bands and disappearance of another in comparing with the control. Moreover ultrastructure of leave of N23-48 cultivar ( that showed the best response ) cleared distinct differences in the volume of the cells, cytoplasm, vacuole, cell wall thickness as well as in the examined organelles such as chloroplast, mitochondria, nucleus and nucleolus.