Role of hydrogen peroxide pre-treatment on the acclimation of pistachio seedlings to salt stress

Oxidative stress, provided that a mild level is imposed, can benefit the plants latterly subject to stress. In the present work, acclimation of pistachio seedlings, which had previously been sprayed with different concentrations of hydrogen peroxide (H2O2) as an oxidative stressor, to salt stress was investigated. The plants, formerly treated with 0, 1, 5, or 10 mM H2O2, were subsequently imposed to NaCl stress (120 or 240 mM) for 7 days. The results revealed that the levels of ionic leakage, proline and reducing sugar in the leaves as well as the sodium and chlorine concentrations in the roots and the shoots were increased under salt stresses, while the chlorophyll and relative water content (RWC) were reduced. The exposure of the H2O2-pretreated seedlings to salt stress led to higher proline and reducing sugar contents, and greater RWC and chlorophyll compared with the seedlings only treated with salt. Pre-treating with H2O2 made the potassium uptake by the roots enhance. Conversely, the sodium content decreased, leading to a correspondingly lower Na+/K+ ratio. Thus, acclimation to salinity with a mild H2O2 stress seems to operate through an enhanced osmotic adjustment activity and improved ionic balance (Na+/K+ ratio) of pistachio seedlings. However, more studies need to be done, particularly at the molecular level, to boost our understanding of the mechanisms involved in H2O2-mediated, induced resistance to salt stress.