Differential antioxidative response in barley leaves subjected to the interactive effects of salinity and potassium deprivation

Salinity and low potassium availability are important environmental factors restricting plant growth and productivity throughout the world because these two stresses frequently coexist. Our objective in this work was to determine the influence of salinity and potassium deprivation in the cultivated barley species Hordeum vulgare L. (var. Manel) grown in hydroponics during two weeks either on a potassium-sufficient nutrient solution (3 mM K+) without (+K/-NaCl) or with 100 mM NaCl (+K/+NaCl), or on a potassium-free medium minus NaCl (-K/-NaCl) or containing 100 mM NaCl (-K/+NaCl). Growth, parameters of oxidative stress (malondialdehyde content (MDA), carbonyl groups content (C = O), hydrogen peroxide concentration (H2O2), antioxidant enzymes activities [superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), guaiacol peroxidase (GPX, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), dehydroascorbate reductase (DHAR, EC, 1.8.5.1), and glutathione reductase (GR, EC 1.6.4.2)], and antioxidant molecules (ascorbate and glutathione) were determined. Results showed that growth of vegetative organs was more affected by the interactive effects of salinity and potassium deficiency than by their individual effects indicating an additive effect of these two constraints. Contrary to carbonyl groups, MDA content increased in all treatments and the highest accumulation was observed in plants subjected to the interactive effects of the two stresses, indicating the importance of potassium nutrition in mitigating the peroxidation of lipids caused by salinity. H2O2 concentration was negatively correlated with the activities of antioxidative enzymes and the accumulation of non-enzymatic antioxidants implicated in its detoxification. Results suggest that a cooperative antioxidant defense system plays an important role for the tolerance of H. vulgare to salinity and potassium deprivation.