Abstract:

In order to study the effects of copper and zinc on polyphenol oxidase (PPO) activity, the PPO activity of 3-year-old Larix principis-rupprechtii seedlings under four treatments (control, zinc, copper, copper + zinc) in different growth periods was analysed. Five organs were leaf, branch, trunk, main root and lateral root. The results showed that the PPO activity patterns of various organs were quite different, the highest could reach 225.2 U·g^-1 in trunk (March) and the lowest was 57.3 U·g^-1 in leaves (May). PPO activity in leaves increased during growth season and reached the maximum in October, PPO activity in branch, trunk, main and lateral root had an orderly change, which was higher in July than in other time. Copper andor zinc affected significantly the PPO activity of various organs, which was closely related to growth periods. Copper could improve the PPO activity in different organs, especially in branch, and copper treatment increased by 95.1% compared with the control in October. Zinc made the PPO activity increase in main root and decrease in other organs, and zinc treatment decreased by 35.5% compared with the control in trunk (October). Copper and zinc were cooperative to improve the PPO activity in trunk and main root. There was significant positive correlation between copper content and PPO activity in L. principis-rupprechtii. Copper and zinc had effects on PPO activity, so as to affect the resistant ability of cold and the growth of seedlings.

Key words: Larix principis-rupprechtii, polyphenol oxidase (PPO), copper, zinc