INFLUENCE OF SALINITY AND AMMONIUM: NITRATE RATIO ON GROWTH, PHOTOSYNTHESIS, FATTY ACID AND THE ACTIVITY OF ANTIOXIDATIVE ENZYMES IN CANOLA

The effects of sodium chloride (NaCl) salinity (0 and 200 mM) and ammonium (NH4): nitrate (NO3) ratios (100:0, 25:75, 50:50, and 75:25) on growth, photosynthesis, fatty acids and the activity of antioxidative enzymes were investigated in canola plants. Leaf area and fresh and dry weights of leaves were significantly reduced by the salinity. The reduction in vegetative characteristics varied in both salinized and unsalinized plants according to the NH4:NO3 ratios so that the lowest reduction was observed with the 50:50 (NH4:NO3) ratio. Increased NH4 up to 50 percent (50:50) of total N, promotes the yield at both salinized and unsalinized plants. In both salinized and unsalinized plants, the increased NH4 and NO3 ratio in the nutrient solution reduced the photosynthetic (Pn) rate and stomatal conductance; however, the reduction in Pn rate was severely impaired at a higher ratio of NH4 in the nutrient solution. In both salinized and unsalinized plants, the 75:25 ratio had the lowest potassium (K) and sodium (Na) content; however, the K/Na ratio was the highest in 50:50 ratio. An increase of NH4 in the solution led to a significant increase in NH4 content in both salinized and unsalinized plants. Salinity increased NH4 content so that the salinized plant had nearly twice as high NH4 content in the leaves. The activity of nitrate reductase was increased by increasing NH4 from 0 to 50% and then reduced at a higher ratio of NH4 in the solution. The activities of antioxidative enzymes increased in salinized plants regardless of the NH4:NO3 ratios. In salinized plants, the activities of superoxide dismutase and catalase enzymes were increased by 44.4 % and 97.5%, respectively. Within salinized and unsalinized treatments, the highest activities of all antioxidant were observed in 75:25 ratio, while they remained unchanged for all NH4:NO3 ratios. The increased NH4 content in the solution increased the oil content and the maximum oil content in both salinized and unsalinized plant was obtained in both 50:50 and 75:25 ratios. The percentage of oleic acid was affected by both salinity and NH4:NO3 ratios. The ratios of NH4:NO3 had no effect on the protein content; however, salinity reduced the protein content by 20%.