الفهرس 
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Abstract
Summary
The objective of the present work is to study the effect of various levels of salinity (100, 150 and 200 mM) NaCl on growth, some related metabolic activities of Zea mays L. (TWC.321) white plant. Also, the present investigation was focused on the effect of seed soaking in 0.5 µM sodium selenate, 200 ppm α-tocopherol and 250 ppm ascorbic acid alone or alternate combination, to alleviate or at least modify the pattern of changes induced by the salinization treatment.
The main experimental results can be briefly summarized in the following points:
I. Preliminary test is two experiments; the first experiment is laboratory experiment that was applied to study the effect of different concentrations of NaCl (100, 150, 200, 250 and 300 mM) on germination of Zea mays grains up to 7-days-old. The obtained results showed that the measured germination criteria (coleoptile length (cm), coleorhiza length (cm), fresh and dry weight (gm/plant) of coleoptile and coleorhiza) inhibited by increasing salinity stress on Zea mays L. grains. In which maximum inhibition observed in both 250 and 300 mM of NaCl. On the other hand, these concs nearly lethal to maize grain so, both of concentrations ignored in greenhouse experiments and complete next step with three concs only (100, 150 and 200 mM) NaCl. The second experiment is greenhouse experiment was that applied to study the effect of soaking maize grains in different concentrations from selenium as sodium selenate (0.00, 0.25, 0.5, 1, 5, 10, 15, 20 and 25 µM), α-tocopherol (0.00, 50, 100, 150, 200, 250 and 300 ppm) and ascorbic acid (0.00, 50, 100, 150, 200, 250 and 300 ppm) on growth characteristics of 15-day-old maize plants. According to the results of these experiments both greenhouse bag experiments were conducted.
The obtained results revealed that all growth criteria (shoot and root length, leaf area, number of leaves per plant, fresh and dry weights of both shoot and root system) were markedly increased at 0.5 µM sodium selenate, 200 ppm α-tocopherol and 250 ppm ascorbic acid.
II. According to the results from preliminary experiment, principal greenhouse experiments were carried out after 40-day-old maize plant. The first greenhouse experiment taken place by sterilization maize grains then presoaking in 0.5 µM sodium selenate, 200 ppm α-tocopherol and 250 ppm ascorbic acid each one alone for 12 hr after 20 day from sowing the plants were irrigated with different concentrations of NaCl (100, 150 and 200 mM) till reached to 40-day-old maize plants. The second greenhouse experiment has the same steps of the first greenhouse experiment but presoaking of maize grains in alternate combination between (0.5 µM sodium selenate or 200 ppm α-tocopherol or 250 ppm ascorbic acid) to alleviation salinity effect.
1. The obtained results revealed that all growth criteria (shoot and root length, leaf area, number of leaves per plant, fresh and dry weights of both shoot and root system) were markedly reduced with increasing salinity levels, and the inhibitory effect of salt stress was more pronounced at the highest level of salinity in maize as a compared with control plants. Applications of Se or α and AsA individual or in alternate combination by grain soaking led to a significant increase in the above growth characteristics of salt stressed maize plants, as compared with those of the corresponding salt stressed plants.
2. Increasing the salinity levels caused a marked decrease in membrane stability and a marked increase in membrane leakage of maize plant. Application of Se or α and AsA alone or/and their alternate combination resulted in a significant increase in membrane stability and a significant decrease in membrane leakage maize plant as compared with those of the reference controls.
3. The contents of photosynthetic pigments (chlorophyll a, chlorophyll b, carotenoids and total pigments) were significantly reduced with increasing the salinity levels in maize plant when compared with those of the non-salinized plants. Application of Se or α and AsA alone or/and interactively combined of them can alleviate the damage effects of salt stress on pigments content as compared with those of the reference controls.
4. It has been found in the present work that total soluble sugars of shoots were sharply increased by increasing salinity levels on maize plant; whereas insoluble sugars and total carbohydrates were decreased by increasing salinity levels as a compared with the controls at the vegetative growth stages. Application of Se or α and AsA individual or/and interactively integration of treatments led to marked increase in insoluble sugars and total carbohydrates with decreasing in total soluble sugars fractions in tested plant.
5. Salt stress induced highly stimulatory effect on the production of soluble protein with inhibitory effect in proline, insoluble and total protein consistently with rising of salinity level in tested plant during vegetative stage. Application of Se or α and AsA alone or/and interactively integration chosen treatments by grain soaking led to a significant increase in insoluble protein ,total protein and proline content with decreasing in soluble protein content of salt stressed maize plants as compared with those of the reference controls.
6. The obtained results showed two prominent types of modification were observed. These types are (i) the de novo synthesis of a new set of proteins was induced and (ii) the disappearance of some other proteins these responses were observed under the effect of sodium selenate, α-tocopherol, ascorbic acid or their alternate combination alone or with salt stress.
7. Salt stress induced a significant increase in phenolic aglycones content with a significant decrease in flavonoids, phenolic glycosides and total phenol contents in tested plant with rising salinity levels especially at the highest level of NaCl. On the other hand, treatments with individual or/and interactively mixed of chosen concentrations by grain soaking under salinity levels were associated with either a significant increase in flavonoid or phenolic glycosides or total phenolic contents with decreasing phenolic aglycones content as compared with those of the reference controls.
8. Activity levels of some hydrolytic enzymes like amylases and protease enzymes showed a progressive significant increase with the increase in the concentration of NaCl. Application of Se or α and AsA alone or/and interactively combined treatments, showed a decreasing in both enzymes activity as a compared with reference control plants.
9. Activity levels of polyphenol oxidase and peroxidase enzymes showed a progressive significant increase with the increase in the concentration of NaCl, while the behavior of phenylalanine ammonialyase, catalase enzyme showed an opposite response which might lead to an accumulation of H2O2 as compared with those of the non-salinized plants. It has been also observed that the activity of peroxidase polyphenol oxidase enzymes of salt stressed maize plant was mostly significantly decreased as a result of Se or α and AsA alone or/and interactively combined treatments, while phenylalanine ammonialyase and catalase enzymes showed significant increase as compared with those of the reference controls plants.
10. The shoot contents of sodium ion Na+ contents were significantly increased with increasing the salinity level, while K+, Ca+2, K+/Na+, Ca+2/Na+ and Mg+2 contents were decreased as compared with the non-salinized plants (control plants). Application of Se or α and AsA alone or/and interactively combined treatments, induced a beneficial effect, since it led to a reduction of Na+ accumulation concomitantly with increases in K+, Ca+2, K+/Na+, Ca+2/Na+ and Mg+2 contents in maize plants as compared with those of the reference controls.
11. The accumulation of elemental selenium, total tocopherols and ascorbic acid contents in tested plants were significantly increased with rise of salinity levels especially at the highest level of NaCl. On the other hand, treatments with individual or/and interactively mixed of chosen concentrations by grain
soaking under different concentration of NaCl were associated with a significant increase in elemental selenium, total tocopherols and ascorbic acid contents as compared to reference controls.
It is worthy to mention that, nearly all the estimated parameters in this work (morphological or metabolic), showed the best response in principal greenhouse experiments under the alternate combination treatments, which showed that, these treatments especially; sodium selenate + α-tocopherols + ascorbic acid are the best way to partially or completely alleviate the harmful effect of salt stress.
The obtained results were discussed in the light of those recorded by other investigators.