Hydrogen peroxide concentration was estimated using the method of Velikova et al. (2000). 0.5g of the leaf was crushed with pestle mortar and plant material was homogenized in 10ml of 0.1% trichloroacetic acid on an ice bath. The extract was centrifuged at 12,000rpm for 10 minutes. The reaction mixture was added with 0.5ml supernatant, 0.5 ml potassium phosphate buffer, and 1 ml of potassium iodide (1 M). The absorbance was considered at 390 nm and 0.1% trichloroacetic acid (TCA) was used as blank. The H2O2 contents were determined from a standard curve, and the values were expressed as l mol/g fresh weight.