The activity of antioxidant enzymes in maize and sunflower seedlings as affected by salinity and different nitrogen sources

The effect of salinity (100 mM NaCl) and different nitrogen sources (NaNO₃/(NH₄)₂SO₄) on the activity and spatial distribution of antioxidative enzymes (glutathione reductase, GR; superoxide dismutase, SOD; guaiacol peroxidase, POD; and catalase, CAT) and glutathione-S-transferase (GST) was investigated in maize and sunflower seedlings. Leaves and roots were collected after 2 weeks of treatment. Roots of maize were cut into segments and the cortex and stele were also separated. Salinity caused a clear reduction in plant biomass. The biomass production of ammonium-fed plants was lower than that of nitrate-fed plants. The antioxidant enzymes exhibited higher activities in salinity-treated plants. Changes in antioxidant enzyme activities caused by different N sources differed in the two species. Ammonium-fed plants showed higher CAT activity in both plant species and higher GR activity in maize and sunflower leaves, with the highest GST activity in maize. POD and SOD activities were lower in both maize and sunflower seedlings and lower GR activity was observed in maize roots. SOD and POD activities were higher in the mature sections of the root than in the tips. GR activity was higher in the younger parts of the nitrate-fed plant roots. The antioxidant enzyme activities were higher in the cortex than in the stele of the nodal roots.