Boron Enhances Antioxidative Defense in the Leaves of Salt-affected Pistacia vera Seedlings

Boron (B) toxicity and salt stress are widely observed in arid and semi-arid regions. Nonetheless, little is known about the interactions between B and salt stress with respect to plant defense systems. In this study, seedlings of Pistacia vera 'Badami'-a valuable crop of arid lands in central Persia-were treated with different B concentrations in soil (0, 2.5, 5, 10, and 20 mg.kg-(1)) to investigate oxidative injuries and antioxidative defense responses of the plants to salt stress (0, 800, 1600, and 2400 mg NaCl.kg(-1) of soil). Salt stress and application of 20 mg B.kg(-1) of soil intensified electrolyte leakage, lipid peroxidation, and lipoxygenase activity in pistachio leaves. Additional supplementation of B up to 5 mg.kg(-1) soil significantly decreased malondialdehyde (MDA) and H2O2 under salt stress. The alleviating effects of B on oxidative stress parameters were related to the improvement in antioxidant enzymes activity (ascorbate peroxidase and catalase), and the non-enzymatic antioxidant compounds (ascorbic acid and phenolic compounds), compared with those treated with either salt stress or a high concentration of B. However, application of 20 mg B.kg(-1) of soil exacerbated the oxidative damage induced by salt stress. On the contrary, applying mild salt stress mitigated the toxic effects of B on the plant, since oxidative stress due to B toxicity was significantly reduced by application of 800 mg NaCl.kg(-1) of soil. In conclusion, the optimization of B supply in the soil was suggested to alleviate the oxidative damage due to salt stress.