Exogenous potassium nitrate alleviates salt-induced oxidative stress in maize

The effects of the exogenous potassium nitrate application on major antioxidant enzymes, photosynthetic pigment content, malondialdehyde, hydrogen peroxide and free proline were investigated in salt-stressed (75 mM NaCl) maize genotype (ADA 9510). Plants were grown in growth chamber for ten days. After five days of applications (control, 0 mM NaCl), S75 (75 mM NaCl), potassium nitrate (3 mM KNO3) and S75 + potassium nitrate (75 mM NaCl + 3 mM KNO3), plants were harvested. The results showed that salt stress significantly decreased chlorophyll a, chlorophyll b and total chlorophyll contents and increased the activities of superoxide dismutase, ascorbate peroxidase and glutathione reductase. Malondialdehyde, hydrogen peroxide and free proline contents were increased by salt stress. These results showed that salinity led to the oxidative stress and destruction of photosynthetic pigments in maize leaves. The exogenous potassium nitrate application, on the other hand, caused to the increased chlorophyll a, chlorophyll b, total chlorophyll and total carotenoid, elevated level of ascorbate peroxidase and glutathione reductase, and decreased malondialdehyde, hydrogen peroxide and free proline content. This kind of changes may indicate that the exogenous potassium nitrate application activates the antioxidant defence system and counteract the oxidative stress. Thus, it may be concluded that the exogenous potassium nitrate application improves salt tolerance and encourage the growth of maize plants under salt stress at early seedling stage