Effect of salt stress on antioxidant system of plants as related to nitrogen nutrition

In plants of wheat (Triticum aestivum L.) grown in the media with nitrate (NO3- plants), ammonium (NH4+ plants), and without nitrogen (N-deficient plants), the response to oxidative stress induced by the addition of 300 mM NaCl to the nutrient solution was investigated. Three-day-long salinization induced chlorophyll degradation and accumulation of malondialdehyde (MDA) in the leaves. These signs of oxidative stress were clearly expressed in NO3- and N-deficient plants and weakly manifested in NH4+ plants. In none of the treatments, salinization induced the accumulation of MDA in the roots. Depending on the conditions of N nutrition, salt stress was accompanied by diverse changes in the activity of antioxidant enzymes in the leaves and roots. Resistance of leaves of NH4+ plants to oxidative stress correlated with a considerable increase in the activities of ascorbate peroxidase and glutathione reductase. Thus, wheat plants grown on the NH4+-containing medium were more resistant to the development of oxidative stress in the leaves than those supplied with nitrate.