Pretreatment of seed with H2O2 improves salt tolerance of wheat seedlings by alleviation of oxidative damage and expression of stress proteins

Increased salinity is a stringent problem to crop production while seed pretreatment can effectively induce salt tolerance in plants. Hydrogen peroxide (H2O2), a stress signal molecule, was evaluated as seed treatment to produce the metabolic changes, which could lead to improved salt tolerance in wheat. Soaking in 1, 40, 80 and 120 mu M H2O2 revealed a low penetration, reaching maximum at 5h (2.58 +/- 0.23 mu molg(-1) fresh seeds at 120 mu M) and declining thereafter to the level of water control by 8h. This revealed the activation of antioxidants and H2O2 scavenging in seed after 5h. Seeds treated with 1-120 mu M H2O2 for 8h and germinated in saline (150 mM NaCl medium curtailed the mean germination time (MGT) being even less than water controls. Level of H2O2 in seedlings arising from H2O2-treated seeds grown under salinity was markedly tower than salinized controls, suggesting the operation of antioxidant system in them. These seedlings exhibited better photosynthetic capacity, particularly the stomatal conductance (gs), thus improving the leaf gas exchange due to stomatal component of photosynthesis. Moreover, H2O2 treatment improved leaf water relations and maintained turgor. Although Na+ and Cl- content increased due to salinity, H2O2-treated seedlings displayed greater tissue K+, Ca2+, NO3- PO43- levels and improved K+:Na+ ratio. H2O2 treatment enhanced the membrane properties, as revealed from greatly reduced relative membrane permeability (RMP) and less altered ion leakage pattern (comparable to water controls). Seedlings exhibited the expression of two heat-stable (stress) proteins with apparent molecular masses of 32 and 52 kDa. Results suggest that H2O2 signals the activation of antioxidants in seed, which persists in the seedlings to offset the ion-induced oxidative damage. These changes led to the expression of stress proteins and improved physiological attributes, which supported the seedling growth under salinity. (c) 2006 Elsevier GmbH. All rights reserved.