INFLUENCE OF SALT STRESS ON THE GROWTH, ELEMENTS CONTENTS AND ANTIOXIDATIVE ENZYMES ACTIVITIES OF PEA (Pisum sativum L. ) PLANT GROWN IN SAND CULTURE.

Pot experiment was carried out at Faculty of Agriculture, El Bostan, AlexandriaUniversity, in order to evaluate the effect of irrigation with NaCl solutions on the  growth characters, elements contents and antioxidative enzymes activities of pea (Pisum sativum variety Master B) plant grown in sand culture.
                Split plot layout, in randomized completely block design, experiment with six replicates was carried out. The concentrations of NaCl in irrigation water were 00, 25, 50, 75 and 100 mM  prepared in a base nutrient solution. 
                Seeds of pea were sown in a plastic pot containing 2 kg prewashed sand. Two samples of plants (3 for each) were collected at 20 and 27 days after sowing (DAS) for determination of the growth characters, the concentrations of Na⁺, K⁺, Mg²⁺ and Ca²⁺ and the activities of antioxidative enzymes: catalase (CAT), pyroxidase (POD) and ascorbate peroxidase (APX) in leaves and root of the plant.
                The obtained results showed significant decrease in the fresh and dry weights of leaves and root, plant height and leaf area with increasing NaCl concentration treatments. In addition, the concentrations of Na⁺, K⁺ and Mg²⁺ were lower in leaves than in root while those of Ca²⁺ were higher in leaves than in root of both 20 and 27 DAS plants.
                The results showed significant reductions in the activity of CAT enzyme in leaves and root of 20 and 27 DAS plants with increasing salinity. The lowest significant CAT activities were found with 100 mM NaCl treatment which represented values of relative reduction of 20.2 and 10.4% in leaves and 24.3 and 34.2% in root, respectively.
                There were significant increase in the activity of POD in leaves of 20 DAS plants and no significant change in leaves of 27 DAS plants with increasing salinity. The highest significant level of POD activity in leaves of 20 DAS plants (132.3 µM H₂O₂ min^-1. mg^-1 protein) was found with 100 mM NaCl treatment which represented a relative increase of 16.6%. However, for 20 DAS plant, there were no significant variations in POD activity in plant root due to NaCl treatments while for 27 DAS plants, there were significant decreases in POD activity with increasing salinity. The lowest significant level of POD activity in root of 27 DAS plants (1778 µM H₂O₂ min^-1 mg^-1 protein) was found with 100 mM NaCl treatment which represented a relative reduction in POD activity of 35.3%.
                There were significant decreases in the activity of APX enzyme in leaves and root of 20 and 27 DAS plants with increasing salinity. The lowest significant levels were found with 100mM NaCl treatment which represented values of relative reduction in APX activity of 33.9 and 41.5% in leaves and 27.0 and 33.1% in root of 20 and 27 DAS plants, respectively.