Effects of calcium infiltration treatment on enzymatic browning of red Fuji apples Variation of Polyphenol Oxidase Activity and Isozyme in Transgenic Homozygous Tetraploid Potato (Solanum tuberosum L.) EFFECTS OF Se, Zn AND THEIR INTERACTION ON POLYPHENOL OXIDASE ACTIVITY OF TEA LEAVES IN DIFFERENT SEASONS Comparative Study of Isozymes of Peroxidease and Polyphenol Oxidase in the Cultivars of Pumpkin