Antioxidative responses of Ocimum basilicum to sodium chloride or sodium sulphate salinization

Soils and ground water in nature are dominated by chloride and sulphate salts. There have been several studies concerning NaCl salinity, however, little is known about the Na2SO4 one. The effects on antioxidative activities of chloride or sodium sulphate in terms of the same Na+ equivalents (25 mM Na2SO4 and 50 mM NaCl) were studied on 30 day-old plants of Ocimum basilicum L., variety Genovese subjected to 15 and 30 days of treatment. Growth, thiobarbituric acid reactive substances (TBARS), relative ion leakage ratio (RLR), hydrogen peroxide (H2O2), ascorbate and glutathione contents as well as the activities of ascorbate peroxidase (APX, EC 1.11.1.11); glutathione reductase (GR, EC 1.6.4.2) and peroxidases (POD, EC 1.11.1.7) were determined. In leaves, growth was more depressed by 25 mM Na2SO4 than 50 mM NaCl. The higher sensitivity of basil to Na2SO4 was associated with an enhanced accumulation of H2O2, an inhibition of APX, GR and POD activities (with the exception of POD under the 30-day-treatment) and a lower regeneration of reduced ascorbate (AsA) and reduced glutathione (GSH). However, the changes in the antioxidant metabolism were enough to limit oxidative damage, explaining the fact that RLR and TBARS levels were unchanged under both Na2SO4 and NaCl treatment. Moreover, for both salts the 30-day-treatment reduced H2O2 accumulation, unchanged RLR and TBARS levels, and enhanced the levels of antioxidants and antioxidative enzymes, thus achieving an adaptation mechanism against reactive oxygen species.