الفهرس 
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Abstract
Vegetation composition and soil attributes in the lower tributaries were studied from 36 geo-refereced stands (20 × 20m) in the deltaic part and along the main trunks of studied wadis from north to south of Eastern Desert along the Red Sea coast (near to Hurghada Province). The aim of the present study was to investigate the present status of the floristic composition of wadis distributed in the study area, the plant communities inhabiting different habitats and the environmental factors affecting species diversity in the study area.
The studied stands were randomly chosen at locations where considerable vegetation cover and/or sensible changes in floristic composition were encountered. In each stand, presence percentage (P%), life forms and chorological affinities for each species were calculated. Soil physico-chemical analyses were carried out, and 16 parameters were used in the multivariate analyses where TWINSPAN (classification) and CCA (ordination) were applied.
Significant differences between TWINSPAN vegetation groups were tested by ANOVA. Sixty-three species (40 perennials and 23 annuals) were recorded in this area, belonging to 58 genera from 28 different families. 42% of the recorded flora was belonging to five families arranged descending as: Fabaceae > Brassicaceae > Asteraceae > Chenopodiaceae > Zygophyllaceae. Therophytes and Chamaeophytes constituted 66 % of the main bulk of life form the spectrum of the recorded flora. Also, Saharo-Arabian species consisted 65% followed by the Mediterranean (□29%).
TWINSPAN yielded 5 vegetation groups; group E were located in the proximity of Wadi El-Mallaha and Wadi Beli. Groups A, C and D appeared to be closer to Wadi Dib and W. Abu Had, while stands of group (B) were in Wadi Beli. These groups were clearly separated along the first two axes of
DCA. Both diversity indices showed positive significant correlations with phosphates and chlorides, and negative significant correlations with sodium, magnesium, total soluble salts and fine sand. Canonical Correspondence Analysis (CCA) revealed the importance of Na, K, Ca, PO4, gravels, coarse sand, silt and clay in species distribution patterns.
Salinity stress hinders plant growth of several crop plants and induces changes in diverse processes in vascular plants. Sodium nitroprusside and lipoic acid are thought to play an important role in plant adaptation to salinity. Therefore, the present study was conducted to verify the effect of exogenously applied priming agent treatments (sodium nitroprusside and lipoic acid) to counteract the inhibition in growth and yield of white radish Raphanus sativus
L. plant under salinity stress.
In the current study, three experiments were conducted.
• The first experiment was carried out using different levels of the two priming agents; Sodium nitroprusside (0.1, 0.2 and 0.5 mM) and lipoic acid (1, 2 and 3 mM), to evaluate the effective concentrations of them that alleviated the adverse effect of salinity (for one week) in the framework of a Petri dish- experiment.
• In the second experiment test plant was grown in soil cultures under different NaCl levels were (0, 30, 60, 90,120, 150 mM) for two months. External application of priming treatments sodium nitroprusside (0.2 and 0.5 mM) and lipoic acid (1 and 3 mM), to clarify whether priming treatment can alleviate the inhibitory effects of salinity on the studied growth criteria and biochemical analysis or not. In order to clarify some detailed physiological basis how sodium nitroprusside and lipoic acid regulate a number of biochemical and physiological processes that increase plant salinity tolerance. Indeed, to verify the individual differences between the studied priming treatments in their protective potentiality to salt stress resistance of white radish plant.
• The last part of this study was conducted for three months to verify if priming treatments could alleviate NaCl-induced reduction in tuberous root fresh weight of white radish plant or not.
The conclusions that were reached out of the results obtained from this study are summarized in the following main points:
1. A gradual reduction in some growth criteria (shoot and root length) and germination attributes in radish plant was observed by increasing sodium chloride supply in the culture media. Application of priming agents counteracted this inhibitory effect. Depending on the results of this experiment, effective concentrations of sodium
nitroprusside (0.2 and 0.5 mM) and lipoic acid (1 and 3 mM) have been chosen to be applied in the next experiment.
2. Symptomatic variation in older leaves showed leaf area reduction, root length and plant height shortening- visual symptoms for salinity were more sever in non–primed plants than primed ones.
3. Salinity reduced fresh and dry biomass production in shoots and roots of test plant. However, external application of priming agent treatments ameliorated this inhibitory effect by stimulating both shoots and roots fresh and dry biomass yield in white radish plant.
4. Salinity reduced leaf dry weight, and leaf relative water content of test plant. However, external application of priming agent treatments alleviated this inhibitory effect.
5. Salinity stress in leaves of white radish plants did not show reduction in photosynthetic pigments contents (Chl. a, Chl. b and carot.). The external application of SNP as priming agent triggered significantly photosynthetic pigments biosynthesis particularly at the highest salinity levels. While, LP failed to show the same response.
6. Salt stress increase the concentration of Na+ and Cl- particularly at the shoot system of white radish plant. The application of SNP and LP reduced the concentration of Na+ and Cl- significantly in shoot and root systems.
7. High concentration of sodium chloride reduced the content of potassium significantly. External application of LP and SNP increased K+ content in root and shoot tissues.
8. Sodium chloride in the growth medium imposed non-significant increase or no change in soluble carbohydrates content in the leaves and roots of non-primed white radish plants, respectively. External application of priming agent treatments significantly enhanced soluble carbohydrates content than that of stressed plants under salinity stress conditions.
9. A significant increase in free amino acids and soluble proteins content was observed in leaves of white radish plants as a result of salt stress. Meanwhile, this stimulatory effect was even increased upon external application of priming agents.
10. In order to clarify some detailed physiological bases, how salinity could induce oxidative stress, and if sodium nitroprusside and lipoic acid regulate a number of biochemical and physiological processes that increase plant salinity tolerance through reducing oxidative damage? in situ localization of superoxide in white radish leaves as reactive oxygen species (ROS), in addition to MDA, as biomarker for lipid