Antioxidative system in maize roots as affected by osmotic stress and different nitrogen sources

The activities of antioxidative enzymes and contents of proline and total phenolics were assayed in roots of two maize (Zea mays L.) genotypes grown in a medium containing nitrate (NO3 (-)) or both nitrogen forms, nitrate and ammonium (NH4 (+)/NO3 (-)). An increase in the activities of class III peroxidases (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX), ascorbate oxidase (AO) and proline content, and decrease in phenolic content were observed in NH4 (+)/NO3 (-) in comparison with NO3 (-) grown plants. When polyethylene glycol (PEG) was added to both nitrogen treatments, the content of total phenolics and proline was increased, especially in NH4 (+)/NO3 (-) treatment. The PEG treatment decreased enzyme activities in NH4 (+)/NO3 (-) grown plants, but in NO3 (-) grown plants activities of POD and SOD were increased, opposite to decreased APX and AO. Isoelectric focusing demonstrated increased activities of acidic POD isoforms in PEG treated NO3 (-) grown plants, and lower activities of both, acidic and basic isoforms in NH4 (+)/NO3 (-)grown plants.