The homogenized plant tissues were used immediately or were stored in deep freezer (−70 °C) until used for biochemical analysis. Variation in activity of defense related enzymes, phenylalanine ammonia lyase (PAL; EC 4.3.1.5), peroxidase (POX; EC 1.11.1) and polyphenol oxidase (PPO; EC 1.14.18.1) was determined by enzyme assays according to Ross and Sederoff, 1992 and Hammerschmidt et al., 1982 and Mayer et al. (1965), respectively, and the enzyme activity was expressed as nmoles of cinnamic acid min−1 g protein−1 and change in absorbance min−1 mg−1 of protein, respectively. Each of the enzyme assays were repeated three times.