الفهرس 
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Abstract
A greenhouse experiment was conducted on wheat (Triticum aestivum L. cv Sakha 94) to investigate the inhibitory effects of Pb or Ni and to assess the significant concentration of Sonchus oleraceus natural extract in alleviating the toxic effects of Pb or Ni. Initially, fresh Sonchus shoots were collected during the fruiting stage, washed several times, sliced into fine pieces, blended in an electric blender, filtered, and then used to prepare 25%, 50%, and 100% Sonchus stock extract. In two preliminary experiments, the lethal and sub-lethal concentrations of lead and nickel, as well as the effective concentration of Sonchus natural extract and grain priming periods, were determined in wheat seedlings. Based on the results of these preliminary experiments, the sub-lethal concentration of lead acetate or nickel sulphate was estimated to be 100 mM, while the effective concentration of Sonchus extract was 100%. In terms of soaking time, 12 h was determined to be the most effective priming period. The main experiment was carried out during the growing season (December, 2019). Wheat grains of uniform size and shape were divided into two groups. The first group spent 12 h soaking in tap water (water-soaked grains). The second group was primed by soaking in 100 % Sonchus extract for 12 h (Sonchus-soaked grains). Following that, the soaked seeds from each group were sown in plastic pots filled with clay-sandy soil (2:1w/w) and allowed to grow to represent vegetative, flowering, and yield stages. The plants were then left to grow while irrigated with tap water once every two days for the first week (before seedling emergence). The first group (watersoaked) was divided into three subgroups on the 10th day; the first subgroup was the control, which was irrigated with water until the end of the experiment, while the second and third subgroups were irrigated with 100 mM Pb or Ni solutions as single stress treatments until 60 % field capacity. The second group (Sonchus-soaked) was sub-divided into two subgroups, which either irrigated with Pb or Ni, till 60 % field capacity. Following that, water irrigation was performed twice weekly upon all treatments. Meanwhile, the stress treatments were given additional stress dose on days 17, 45, and 90 of growth. Harvesting occurred at three growth stages: vegetative (30 day-old), flowering (66 day- old), and yield stage (125 dayold). The analysis of Sonchus extract revealed that it contained a variety of components as mineral elements (P, Mn, Cu, Zn, Fe, N, K, Ca, and Mg), phytohormones as (gibberellic acid (GA), indole acetic acid (IAA), and abscisic acid (ABA), as well as aromatic cytokinins (ArCKs) and Zeatin), proteins, amino acids, carbohydrates, phenolics, flavonoids, proline, cysteine and glycine betaine, and ascorbic acid. These results demonstrated that Sonchus extract contained a diverse set of beneficial constituents. The main experiment results are summarized as follow: 1. Pb or Ni stress significantly reduced wheat plant growth (root and shoot lengths, fresh and dry masses, and leaf area) compared to the control during the vegetative and flowering stages. The photosynthetic pigments (chl a, chl b, and total pigment content), and photosynthetic activity at the vegetative and flowering stages were significantly reduced by Pb or Ni stress treatment. The carotenoids exhibited a significant increase under Pb or Ni stress. The chl a/b ratio showed a varied response under both stresses that decreased by Pb but increased with Ni relative to the control. However, priming wheat grains with Sonchus extract enhanced the growth parameters and resulted in a significant recovery from the toxic effects of Pb or Ni stress. Moreover, the use of Sonchus extract in grain priming reduced the toxic effects of stress on the photosynthetic apparatus and chloroplast structure. 2. In comparison to the control, the chloroplast ultrastructure in the leaves treated with Pb or Ni revealed a distorted structure, swollen and irregular shape, many dark electron-dense plastoglobuli, reduction in starch grains, disappearance of the intact grana with disruption of the thylakoid membrane and membrane disintegration, and a wide area of chloroplast matrix. The toxicity of Pb or Ni stress was reduced by priming wheat grains with Sonchus extract, which allowed chloroplasts to retain their normal spindle-shaped structure and distribution along the cell wall. 3. The cell wall of Pb or Ni stress treatment exhibited a significant number of deposit ions of Pb or Ni along the cell wall. While, priming of grains with Sonchus extract relieved the adverse effects and deposit ions, and the cell wall regained its natural structure with no dark Pb or Ni deposit ions. 4. TEM images of Pb or Ni stress treatment revealed a blocked intercellular space with black deposit ions of Pb or Ni that accumulated inside them. On the other hand, the intercellular spaces retained their natural structure with no deposit accumulation by grain priming with Sonchus extract. 5. The Pb or Ni stress treatment induced a change in nucleus structure and nuclear membrane fragmentation, as well as chromatin body disintegration. The priming with Sonchus extract retained the nucleus normal structure. 6. A significant increase in oxidative stress markers as MDA, electrolyte leakage, H2O2 and OH▪ under Pb or Ni stress treatment in comparison to control that was remarkably alleviated by grain priming with Sonchus extract. 7. After Pb or Ni stress treatment, antioxidant enzyme activities such as CAT, POX, and PPO were significantly increased, while ASP and GR were significantly decreased. Concerning the activity of SOD, it was significantly decreased under Pb stress treatment, but increased with Ni stress. Sonchus priming increased the activities of CAT, SOD, ASP, PPO and GR activities, but reduced POX relative to Pb stress. However, priming with Sonchus extract caused an increase in CAT, ASP and GR activities over Ni stress, but decreased POX, PPO, and SOD activity. 8. Compared with control, Pb application increased CAT relative expression and decreased SOD. While, Ni treatment markedly enhanced CAT and SOD genes than the control. Priming with Sonchus extract under both stresses resulted in an increase in CAT gene expression. Moreover, Sonchus priming significantly enhanced SOD gene expression under Pb exposure but decreased its expression under Ni application. 9. There was a considerable rise in ASA content under Pb stress, but a DROP in ASA under Ni stress. Priming with Sonchus extract reversed Pb or Ni effects. The reduced glutathione was lowered by Pb or Ni stress treatments. However, Sonchus extract priming increased the reduced glutathione compared with Pb stress, however, caused a decrease in its content with Ni treatment. 10. The Pb or Ni stress reduced phenolic, flavonoids, TSC and total amino acids in both root and shoot as well as shoot proline and cysteine except shoot flavonoid under Ni. Stress exposure increased the TSP in both root and shoot and shoot glycine betaine. Grain priming with Sonchus extract increase phenolic, TSC and total amino acids in both root and shoot but further decrease shoot proline and reduce shoot glycine betaine compared to single stress treatments. Grain priming with Sonchus extract under Pb stress resulted in a substantial DROP in root flavonoids and a considerable rise in shoot flavonoids relative to Pb stress treatment. On the other hand, grain priming with Sonchus, under Ni stress increased root flavonoid content while decreasing shoot flavonoid content than single Ni treatment. Sonchus priming treatment reduced root TSP with Pb or Ni; while it increased the shoot TSP with Pb stress and its effect was reversed under Ni stress by decreasing TSP content. 11. When compared to the control, Pb or Ni stress reduced shoot N, P, and K macronutrients levels. Furthermore, heavy metal accumulation in root and shoot was induced by Pb or Ni stress treatments. When primed with Sonchus extract, the shoot N, P, and K levels increased significantly under Pb stress while significantly decreased under Ni application. Grain priming with Sonchus extract, on the other hand, reduced the damaging effects of Pb or Ni stress by causing a significant decrease in Pb and Ni uptake and content of root and shoot. 12. Pb increased the flowering phytohormones GA, ABA, and ArCKs while decreasing IAA and zeatin. Ni application significantly increased IAA, GA, ABA, and zeatin while decreasing ArCKs. Surprisingly, these toxic effects were retrieved by using Sonchus extract priming application. 13. Yield parameters including spike length, spike mass, spikelet No, No of grains/spike, mass of grains /spike, mass of 1000 grains and percentage of grain filling negatively reduced under Pb or Ni. On the contrary, Sonchus extract alleviated Pb or Ni effects on wheat and improved the yield criteria. 14. Relative to the control, the grains levels of TSC, total amino acids, glycine betaine, phenolic and flavonoids content greatly increased under Pb or Ni stress, while TSP and proline increased with Pb but decreased under Ni. The cysteine in the grain was declined under Pb but elevated with Ni stress. The Sonchus extract priming alleviate stress toxicity on yield grains phytochemicals. 15. Pb or Ni stress lowered N, P, and K contents of yielded grains relative to control. The irrigation with Pb or Ni dramatically increased the levels of Pb or Ni in the obtained grains. The presoaking with Sonchus extract limited the toxic impacts of both heavy metal stresses and significantly enhanced the N, P, and K content of yielded grains in both Pb+S and Ni+S treatments to match the control levels. Furthermore, presoaking with Sonchus extract significantly lowered the high accumulation of Pb or Ni after stress application compared to single stress treatments.