الفهرس 
Salinity stress
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Abstract
This study aims to evaluate the biochemical and molecular responses of salt-stressed soybean (cv. Giza111) under different ZnONPs (25, 50, 100 and 200 mg/L). The preliminary experiments revealed that lethal dose of NaCl was 300 mM and the sub-lethal dose was 250 mM as well as 50 mg/L (ZnONP-T2) treatment was the most effective treatment which enhanced the plant and alleviated the harmful effect induced by salinity stress. The results revealed that salinity stress (250 mM NaCl) caused a high reduction in the germination percentage by 65% compared to control. Moreover, data indicated that 25 mg/L (ZnONP-T1) decreased the germination percentage by 30 % compared to control. In addition, 100 and 200 mg/L (ZnONP-T3 and ZnONP-T4) reduced the percentage by 43.4 % and 48.4 % respectively, compared to control. In contrast, 50 mg/L (ZnONP-T2) significantly increased germination percentage of the presoaked seeds by 20 % compared to control. Under salinity stress (250 mM NaCl), 25 mg/L and 50 mg/L ZnONPs increased germination percentage of the presoaked seeds compared to saltstressed seeds. The maximum increase was found in seeds presoaked with 50 mg/L (ZnONP-T2+S) where a significant increase the germination percentage by 37 % was recorded compared to saltstressed seeds (250 mM NaCl). However, a reduction in germination percentage was recorded with 100 and 200 mg/L (ZnONP-T3+S and ZnONP-T4+S) by 18 % and 36.3 %, respectively. At 21-day old seedlings growth parameters as (root length, shoot height, leaf area and fresh and dry weights of roots and shoots) were studied and our results showed that high NaCl (250 mM) produced a highly significant reduction in all studied growth parameters by 19%, 42% and 28% of the length of the shoot and root as well as leaf area respectively, compared to control. On the other hand, seed-soaking with ZnONPs caused increase in lengths of shoot and root as well as leaf area, by 27.2 %, 21.6 % and 21.9 %, respectively compared to control. This result indicates that ZnONPT2 (50 mg/L) is very likely the most successful zinc oxide nanoparticles concentration that improve soybean plant growth. In addition to that, our results showed that high concentration of NaCl (250 mM) induced a significant reduction in photosynthetic efficiency and photosynthetic pigments (chl. a, chl. b and carotenoids) of (21day-old) soybean seedlings by 46.4%, 47% and 46%, respectively compared to control. Meanwhile, carotenoids were significant increase by 1.17-fold compared to control. In contrast, soaking soybean seeds with only ZnONPs or together with high NaCl (250 mM) primarily increased photosynthetic pigments in unstressed as well as stressed seedlings. Interestingly, seed presoaking with 50 mg/L of ZnONPs (ZnONP-T2) significantly increased photosynthetic activity and photosynthetic pigments (Chl. a and Chl. b) and decreased carotenoids under salinity stress (250 mM NaCl) by a percentage 41.5%, 53%, 42% and 26% compared with salt-stressed seedlings alone. This result indicates that 50 mg/L of ZnONPs enhanced the photosynthetic performance of unstressed and saltstressed soybean seedlings. Furthermore, when soybean seedlings were exposed to 250 mM NaCl, malondialdehyde (MDA) content greatly accumulated by 1.19-fold compared to control plants. In contrast, soaking of soybean seeds with ZnONPs reduced MDA content. The maximum reduction (30.2%) was observed in ZnONP-2+S seedlings compared to salinized seedlings alone. Similarly, our results indicated that high salt concentration (250 mM NaCl) caused a high significant increase in proline content by 1.75-fold compared to control but soaking soybean seeds with different ZnONPs concentrations generally decreased proline content in ZnONP-T1, ZnONP-T2, ZnONP-T3 and ZnONPT4. However, the least reduction was observed in ZnONP-T2 seedlings by 5 % compared to control (unstressed) seedlings. On the other hand, the maximum reduction (36.6%) in proline content recorded in ZnONP-T2+S seedlings compared to salinized seedlings alone. On the other hand, the activities of antioxidant enzymes (peroxidase POX, catalase CAT and superoxide dismutase SOD) were highly increased at 250 mM of NaCl by 54%, 37% and 64%, respectively compared to control. Whereas, Seed-soaking with ZnONPs in combination with reduced the activity of all tested antioxidant enzymes under high salinity stress (250 mM NaCl). The most reduction was more obvious in treatment ZnONPs (50 mg/L) with salinity level (250 mM NaCl) by 43%, 18% and 32%, respectively. Additionally, these results showed stress-dependent changes in isozyme patterns for peroxidase (POX), catalase (CAT) and superoxide dismutase (SOD) where; CAT isozymes pattern showed only one locus of two allelic bands while, POX and SOD isozymes pattern exhibited two loci with multi-allelic bands (locus 1 and locus 2). Interestingly, in ZnONP-T2+S seedlings some of this above-mentioned isozyme allelic bands disappeared compared to salinized seedlings alone. In addition, high salt concentration (250 mM NaCl) induced increase the content of compatible osmolytes such as total soluble proteins and total soluble carbohydrates content of 21-day old soybean seedlings by 76% and 75%, respectively compared to control. On the contrary, the total soluble proteins and carbohydrates decreased with treatment using concentrations of ZnONPs (25, 50, 100 and 200 mg/L). The ZnONPs treatment of 50 mg/L reduced the values 43% and 36%, respectively compared with salinity stressed plants. Moreover, results indicated that salinity stress severely reduced potassium and zinc content in response to salinity stress by 81% and 68%, respectively counter to Na+ ion content which was increased in salt-stressed seedlings by 2.16-fold compared to control. In contrast, ZnONPs treatments alleviated the harmful effect caused by salinity stress where zinc and potassium content was elevated in all ZnONPs treated soybean seedlings and the most significant increase was 50 mg/L ZnONPs by 2.7-fold and 1.67-fold, respectively compared to salt-stressed seedlings.