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Pretreatment of lower H_2O_2 doses (0.05, 0.5 and 5 mM) for 24 h was able to dose-dependently attenuate lipid peroxidation In wheat seedling leaves mediated by further oxidative damage elicited by higher dose of H_2O_2 (150 mM) for 6 h, with 0.5 mM H_2O_2 being the most effective concentrations. Further results lllustrated that 0.5 mM H_2O_2 pretreatment triggered the biphasic production of H_2O_2 during a 24 h period. We also noticed that only peak Ⅰ (0.25 h) rather than peak Ⅱ (4 h) was approxlmately consistent with the enhancement of heme oxygenase (HO) activity, HO-1 gene expression. Meanwhile, enhanced superoxide dismutase (SOD) activity, Mn-SOD and Cu, Zn-SOD transcripts might be a potential source of peak I of endogenous H_2O_2. Further results confirmed that 0.5 mM H_2O_2 treatment for 0.5 h was able to upregulate HO gene expression, which was detected by enzyme activity determination, semi-quantitative reverse transcription-polymerase chain reaction and western blottlng. Meanwhile, the application of N,N'-dimethylthiourea, a trap for endogenous H_2O_2, not only blocked the upregulation of HO, but also reversed the corresponding oxidation attenuation. Together, the above results suggest that endogenous H_2O_2 production (peak I) plays a positive role in the induction of HO by enhancing its mRNA level and protein expression, thus leading to the acclimation to oxidative stress.