Abstract: Pot experiments were conducted in Tonghai(24°07′N,102°45′E,1806.0m altitude) and Dayingjie(24°21′N,102°33′E,1591.0m altitude),two main tobacco-planting areas of Yuxi,Yunnan province.The relationships between tobacco(cultivar K326) leaf SOD,POD and CAT activities and solar UV-B radiation changes were studied under natural conditions and treatment by reducing 25%,50% and 65% of ambient UV-B radiation conditions in field experiment.The results showed that solar UV-B radiation intensity in Dayingjie during tobacco growing period was higher than Tonghai due to local climate characteristics,which was contrary to the normal situation of UV-B radiation with altitude in large scale of Yunnan area.SOD and POD activities of tobacco leaf in Dayingjie were higher than that in Tonghai.SOD and POD activities became weaker with UV-B radiation reducing.However,CAT activities in different treatments kept same.From the time dynamics,three enzymes were negative correlation with UV-B radiation change,SOD and POD showed strong cumulative effect.However,CAT activity affected scarcely by UV-B radiation.It was key period to three kinds of antioxidase activities different among treatments from late July to early August.The results indicated that SOD and POD were sensitive to UV-B radiation change,and tobacco maturity stage was the sensitive period of SOD and POD activities response to UV-B radiation.

Key words: UV-B radiation, UV-B radiation, Tobacco, Antioxidase, Dynamic changes, Cumulative effect