To evaluate the responses of canola seedlings to different levels of drought stress and nitrogen at different growth stages, a factorial experiment was conducted in a completely randomized design with three replications at the experimental greenhouse of Mohaghegh Ardabili University in 2013. | Turkish Journal of Agriculture and Forestry Research Article Turk J Agric For (2015) 39: 601-612 © TÜBİTAK doi: Changes in enzymatic and nonenzymatic antioxidant defense mechanisms of canola seedlings at different drought stress and nitrogen levels 1, 1 1 Seyed Ahmad KALANTAR AHMADI *, Ali EBADI , Sodabeh JAHANBAKHSH , 2 3 Jahanfar DANESHIAN , Seyed Ataolah SIADAT 1 Department of Agronomy and Plant Breeding, Faculty of Agriculture, University of Mohaghegh Ardabili, Iran 2 Seed and Plant Improvement Institute, Iran 3 Department of Agronomy and Plant Breeding, Ramin Agriculture and Natural Resources University, Khuzestan, Iran Received: Accepted/Published Online: Printed: Abstract: To evaluate the responses of canola seedlings to different levels of drought stress and nitrogen at different growth stages, a factorial experiment was conducted in a completely randomized design with three replications at the experimental greenhouse of Mohaghegh Ardabili University in 2013. Treatments included three levels of drought stress (30%, 50%, and 70% of FC) and five levels of nitrogen (control, based on soil test results; 25% less than the recommended level; 50% less than the recommended level; 25% more than the recommended level; and 50% more than the recommended level). The recommended level of nitrogen, based on soil test results, was g of nitrogen per kilogram of soil. Results showed that drought stress, nitrogen, and their interaction significantly affected the enzymatic activity of antioxidant catalase (CAT), polyphenol oxidase (PPO), and peroxidase (PO) at various stages of growth. Proline was also affected by drought stress and nitrogen. Maximum CAT activity ( OD mg protein min–1) was observed at the 4–6 leaf stage under mild drought stress conditions (50% of FC) and a nitrogen application rate 50% less than the recommended level. Increased rates of .
