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Abstract Physiological Studies on the Effect of some Antioxidants on Germination, Growth and some Metabolic Activities of Cowpea (Vigna unguiculata) Plant Eman Zakaria Ahmed (Botany& Microbiology Dept., Faculty of Science, HelwanUniversity) Abstract The present work aimed to study the effect of four antioxidants on growth and some metabolic activities of cowpea (Vigna unguiculata L.) plant under normal and salinity stress conditions. This included chemical synthesis and characterization of selenium nanoparticles (SeNPs ≡ 33.4 nm) using sodium selenate and ascorbic acid. Seeds soking for 2h in different concentrations of four antioxidants (Ascorbic acid (AsA) and gallic acid (GA), sodium selenate (NaSeO4) and nanoselenium (SeNPs), or NaCl for assessing the suitable treatments that might improve cowpea growth and yield under normal and salinity stress conditions in pot experiment. Soaking cowpea seeds in AsA and GA up to 150 ppm, NaSeO4 and SeNPs up to 25 μM significantly increased seedling length (plumule and radicle lengths) accompanied with increase in activity of hydrolytic (α, ß amylase and protease) enzymes, soluble sugars and proteins, whereas a reverse situation was observed with salinity, where increasing salinity from 50 to 250 mM, decreased germination percent, seedling length, activity of hydrolytic enzymes, soluble sugars and proteins compared to control seedling. [Abstract] During the first season: Foliar spray of cowpea plant with four antioxidant compounds (AsA and GA at 50, 100, 150, 200, ppm, NaSeO4 and SeNPs at 6.25, 12.5 and 25 μM) significantly increased almost all growth criteria (i.e. length of roots and stem, fresh and dry weights of root, stem and leaves, No. of leaves and total leaves area cm2/plant), as well as weight of 100 seed and quality of seed. During the second season a revese situation was obtained with salinity, where NaCl at 100 mM decreased growth criteria, weight and quality of seed as compared with untreated control plants, while foliar spray with four antioxidants compounds at low concetrations alleviated the adverse effect of salinity stress on growth of cowpea plants. Furthermore, GA was more effective than AsA at 100 ppm and SeNPs was more effective than Na2SeO4 at 6.25 μM in enhancing nodule formation, increasing nitrogenase activity, the levels of the growth hormones indole acetic acid (IAA), gibberellic acid (GA3) and cytokinins (CKs) of cowpea leaves, with a relatively lower abscisic acid (ABA) content and higher GA3/ ABA ratios, which explains the increase in growth parameters and seed weight in treated plants compared to control, but salinity decreased the level of growth promoters hormones and increased ABA content of cowpea leaves. Application of AsA, GA, NaSeO4 and SeNPs at low concentration alleviated the adverse the effect of salinity on cowpea plants by increasing the level of growth promoters hormones as compared to control and salinity stress plants.In addition, application of AsA, GA, Na2SeO4 and SeNPs, especially at low concentration increased the total photosynthetic pigments (TPP), total carbohydrate (TC), total [Abstract] soluble proteins (TSP), DNA, RNA, different minerals, non enzymatic antioxidants (i.e. ascorbic acid, total antioxidant capacity, total phenols and flavonoids), activities of antioxidant enzymes (catalase, peroxidase, ascorbic peroxidase, ascorbic oxidase, superoxide dismutase, glutathione peroxidase and glutathione reductase) and oxidative enzyme (polyphenol oxidase) accompanied by decrease in total soluble sugars (TSS) in leaves, stress markers (lipid peroxidation, the percentage of electrolyte leakage (EL) and H2O2 content) and activity of IAAoxidase enzyme compared to control plants. A revese situation was obtained with salinity, where NaCl at 100 mM decreased photosynthetic pigments and activity, TC, TSP, DNA, RNA, different minerals, while increased TSS, non enzymatic antioxidants, stress markers and activities of antioxidants enzymes, PPO, and IAA oxidase as compared with untreated control plants. Application of four antioxidants compounds at low concentration alleviated the adverse effect of salinity on the previous measured activities. Transmission electron microscopy showed small, dark deposits in leaf and seed of plants treated with SeNPs at 6.25 and 50 μM, which probably originated from the nanoparticles absorbed on to the leaves and deposits in seeds. In conclusion, application of AsA and GA at 100 ppm, SeNPs and Na2SeO4 at 6.25 μM improved vegetative growth, yield of seed, nutritional value and quality of cowpea plants under normal and salinity stress conditions. Key Words: Cowpea; Vigna unguiculata; Antioxidants; Ascorbic acid; Gallic acid; Selenium; NanoSelenium. |