الفهرس 
Lead accumulation and transport in plantsOnly 14 pages are availabe for public view
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Abstract
The present work aimed at studying the inhibitory effect of Pb and F. graminearum stress applied on wheat (Triticum aestivum L., cv. Masr 1), and to evaluate the ameliorating effects of natural weed extracts as purslane or chard as well as, chemical solutions like calcium or salicylic acid in alleviating the damaging effects imposed by Pb or F. graminearum on wheat plant. The sub-lethal concentration of Pb and the effective concentrations of Ca and SA that can alleviate the deleterious effect of Pb on wheat were determined according to preliminary experiments in which different concentrations of Pb (50, 75, 100, 150 and 200 mM) and Ca supplied as CaCl2 solution (1, 5 and 10 mM) and the conc. of SA (0.02, 0.05 and 0.1 mM) were used. Moreover, the weed extracts were prepared with two different concentrations each (25 and 50%). Depending on the results of these preliminary experiments, the sub-lethal concentration of Pb was 100 mM, while the dose used of Ca and SA were 5 and 0.05 mM, respectively and the most effective weed extract con, was 25% for both extracts used. The inoculation of F. graminearum on wheat was made according to the review. The main experiment was done during the growing season of wheat from November to April. The grains of Triticum aestivum were selected carefully for apparent uniformity of size and shape, sterilized as described above. The sterilized grains were divided into five main groups; the first group was soaked in distilled water and considered as a control. The second group was primed in 25% aqueous purslane extract and the third group was primed in 25% aqueous chard extract, as a natural weed extract. However, the fourth group was primed in calcium chloride solution (5 mM CaCl2) and the fifth group was primed in salicylic acid solution (0.05 mM), as chemical stimulants. All grains were left in the soaking solutions for 12 hours, then the soaking solutions were drained out and the grains were washed again with distilled water to get rid of any solution remnants. Each group in the five main groups was divided into three sub-groups:- Subgroup A: grains were sown in soil perceived distilled water and considered as a control for the previously mentioned soaking solutions. Subgroup B: grains were sown in soil perceived 100 mM lead acetate solution and considered as abiotic stress treatment. Sub-group C: grains were sown in soil preinoculated with Fusarium graminearum mycelial growth. The treatment with F. graminearum was carried out according to Porter and Merriman (1983). After the complete seedling establishment, all pots were irrigated with distilled water and left to grow under controlled conditions (12:12 day/night, 25/15°C ± 2 and 70% relative humidity) till the end of the growth season. All treatments were represented in triplicates and the experimental design was completely randomized. The obtained results in the present study could be summarized as follows: 1- Pb and F. graminearum treatments highly reduced some of the growth parameters (shoot length, root length, and leaf area) at the seedling stage. The priming treatments in purslane, chard, Ca and SA treatments significantly ameliorated the deleterious effects of Pb and F. graminearum by increasing shoot length, root length, and leaf area compared with both stressors treatment, but remained lower than that of the control. 2- Regarding the photosynthesis, it was highly diminished with Pb and F. graminearum treatment which was manifested in the low photosynthetic activity and the great reduction in Chl a, Chl b, total chlorophylls content and Chl a+b/carotenoids ratio as well as, there was a significant increase in the carotenoid content and Chl a/b ratio. Remarkable enhancement in the photosynthetic activity and in the content of Chl a, Chl b, total chlorophyll content, and Chl a+b/carotenoids ratio were recorded with the priming treatments of purslane, chard, Ca and SA treatments. Furthermore, the priming treatments decreased carotenoids content and Chl a/b ratio to a value near the untreated control. 3- The results clearly showed that Pb and F. graminearum treatments resulted in an increase in the MDA content (lipid peroxidation product), C=O content (protein oxidation product) and electrolyte leakage in the seedling stage, which was considered as signs of the highly destructive oxidative stress induced by Pb and F. graminearum treatments. However, the purslane, chard, Ca and SA priming treatments led to a highly significant recovery to the harmful effect imposed by both stressors which were reflected as lower production of MDA, C=O contents and electrolyte leakage of wheat seedlings. 4- Concerning the antioxidant activity, Pb and F. graminearum treatments resulted in a highly significant increase in peroxidase, catalase, superoxide dismutase, and polyphenol oxidase activities. Moreover, not only the antioxidant enzymes but also compounds like ascorbic acid and flavonoid contents were increased with Pb and F. graminearum treatments. On the contrary, purslane, chard, Ca and SA priming treatments led to a remarkable recovery from the effects imposed by Pb and F. graminearum treatments on the activities of POX, CAT, SOD and PPO as well as, the ascorbic acid, phenolic, and flavonoid contents. 5- Pb and F. graminearum treatments resulted in highly significant increases in proline, glycine betaine and total amino acids content of wheat seedlings. On the other hand, the priming treatments of purslane, chard, Ca or SA have recovered the harmful effects of Pb and F. graminearum and decreased the aforementioned induced osmolytes concentrations. 6- Regarding antioxidant activity, Pb and F. graminearum treatments resulted in a highly significant increase in the activities of DPPH and PMA of wheat seedlings, whereas the priming treatments of purslane, chard, Ca or SA resulted in a significant reduction in DPPH and PMA activities of wheat seedlings compared to both stress treatments. 7- Pb and F. graminearum treatments resulted in an observed increase in free radical contents represented by H2O2 and OH radical of wheat seedlings. Alternatively, the priming treatments of purslane, chard, Ca or SA resulted in an alleviating effect by decreasing the prementioned free radicals content relative to Pb and F. graminearum treatments. 8- The mineral contents (N, P, K and Ca) of the wheat shoot, root, and grains were remarkably decreased under Pb and F. graminearum treatments. Opposite to the effect of Pb and F. graminearum, priming treatments of purslane, chard, Ca or SA give rise to an ameliorating effect by increasing the mineral contents of shoot, root, and grains of wheat close to the content of the untreated control. 9- The treatment of Pb led to a remarkable increase in Pb ion content of shoot, root, and grains of the wheat plant whereas, the priming treatments of purslane, chard, Ca or SA resulted in a significant reduction in Pb ion content of all plant parts. 10- All the yield parameters including the percentage of mature grains per spike, the number of grains per spike, the weight of grains per spike and weight of 1000 grains were highly decreased with Pb and F. graminearum treatments. Nonetheless, the priming treatments of purslane, chard, Ca or SA treatment led to a significant recovery from the harmful effects induced by Pb and F. graminearum treatments, where the recorded yield parameters were distinctly increased, compared with those in the stress treatments. 11- At the seedling stage, Pb treatment led to a highly significant increase in the expression of some genes level (CAT, GR, MT, and PC), and the F. graminearum treatment also led to a remarkable induction of (CAT, GR, MT and PC). Furthermore, the priming treatments in purslane, chard, Ca or SA resulted in retaining the values of the aforementioned gene expressions under Pb stress close to the control value, while the level of CAT and GR genes was decreased to values close to that of the untreated control under F. graminearum inoculation. Although, the change in MT and PC were not significant under all priming treatments except MT under chard priming treatment compared to F. graminearum treatment. 12- The expression of PR2 gene had no evident change under different stress conditions, while PR4 expression showed a remarkable increase under F. graminearum inoculation and a significant reduction in PR4 by using purslane, chard, Ca or SA priming treatments was achieved compared to F. graminearum inoculation. Therefore, it might be concluded that the use of natural weed extracts (25% purslane or chard) and chemical solutions (Ca and SA with the concentration of 5 and 0.05 mM, respectively) were powerful and cheap tools for alleviating HMs stress imposed by Pb and F. graminearum inoculation on the wheat plant.