Seed pretreatment with hydrogen peroxide (H2O2) can improve stress tolerance due to its biological activity, but the underlying mechanism of its action is largely elusive. This study explored the basis of heat tolerance in maize (Zea mays L.) following seed pretreatment with H 2O2. Seed pretreatment indicated increased H 2O2 content at 1 and 4 h (32 μmol g-1 fresh weight), which declined at 8 h (12 μmol g-1 fresh weight). Pretreatment of seeds with H2O2 for 8 h and incubation in water for 24 h had little effect at 27°C, but at 42°C, seeds showed enhanced α-amylase activity and soluble sugar contents and decreased H2O2 production, solute-leakage and malondialdehyde (MDA). Pretreatment did not affect seed germination at 27°C, but at 42°C seeds showed improved energy of germination and final germination. Furthermore, at 42°C, the seedlings arising from pretreated seeds exhibited improved net photosynthesis and growth and decreased H2O2 and MDA contents and relative membrane permeability (RMP) compared with those at 27°C. Shoots of H2O2-pretreated seedlings grown at 42°C showed the expression of 27 and 63 kDa heat stable (stress) proteins, which were not expressed in the shoot at 27°C or in the root at all H 2O2-concentrations and both temperatures. A possible mechanism of action for H2O2 seed pretreatment, in protecting maize seedlings from oxidative damage is discussed.
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