2.9. Defense enzyme properties
Defense enzyme properties of pot plant in fresh leaf, root and stem were tested after eight weeks growth, which included polyphenol oxidase (PPO, EC 1.10.3.1), peroxidase (POD, EC 1.11.1.7) and superoxide dismutase (SOD, EC 1.15.1.1). Peroxidase (POD) activity was measured according to Manoranjan and Dinabandhu (1976). The reaction product was measured spectrophotometrically at 470 nm and one unit
of POD activity was defined as an increase of 0.01 in readings for 1 g fresh material per minute under these assay conditions. Superoxide dismutase (SOD) activity was determined according to Rao et al. (1996). All reactions started by adding riboflavin under 4000 lux of fluorescent light at room temperature for 25 min, and product was measured at 560 nm. One unit of SOD activity was defined as the amount of enzyme that inhibits the rate of nitro blue tetrazolium (NBT) reduction by 50% under these assay conditions. Polyphenol oxidase (PPO) activity was assayed according to the method of González et al. (1999). The increase in absorbance of reaction product was measured at 420 nm for 5 min. One unit of PPO activity was defined as the amount of enzyme that caused an increase of 0.01 at 420 nm per minute.