Abstract:
Optimal nitrogen (N) nutrition has been shown to alleviate the negative effects of drought stress (DS) on plants. The mechanisms of beneficial effect of nitrogen form are not conclusive. In this study, the effects of different ratios of nitrate (NO3 - ) to ammonium (NH4 + ) nutrition on the growth and oxidative damage of two maize cultivar i.e. Zhengdan 958 (ZD958) and Jundan 20 (JD20) were investigated under DS and non-DS in nutrient solution. The activities of superoxide dismutase (SOD) and catalase (CAT) increased, while that of peroxidase (POD) remained unchanged in ZD958 with supplies of NO3 - : NH4 + ratios of either 100:0 or 50:50, while in NO3 - : NH4 + ratio of 0:100 in ZD958 and all NO3 : NH4 + ratios in JD20 all the enzymes showed decreased activities compared to control. Furthermore, DS decreased biomass production, whereas
increased the contents of superoxide radical (O2 •-) and hydrogen peroxide (H2O2), along with an enhanced accumulation of malondialdehyde (MDA) in the leaves of both cultivars. The above effects were greater in JD20 than those in ZD958. An increased ratio of NO3 - : NH4 + in culture solution increased the activities of SOD, POD and CAT while decreased the production of O2 •- and H2O2, thereby diminishing MDA accumulation, and increasing biomass production of drought-stressed plants of both cultivars. The above responses were pronounced in ZD958 than those in JD20. This study demonstrated that increased NO3
- -nutrition played a favored anti-oxidative metabolic role, as compared with NH4 + -nutrition, in the plants thereby increasing tolerance to DS.
