Physiological and biochemical characteristics of Japanese yew seedlings as natural temperature falling in autumn and winter.

Japanese yew seedlings of four years old were chosen as experimental materials.Several physiological and biochemical indexes of two groups of Japanese yew seedlings were determined respectively as natural temperature falling in autumn and winter. The first group was growing under natural conditions,while the second group was growing indoor before the experiment. The results showed that: 1)the cell membrane permeability increased as temperature falling.The cell membrane permeability of the first group increased from 44.32% in September to the top point of 52.98% in December. While the second group increased from 47.80% to the top point of 62.12% in December. 2) The semilethal temperature of leaves decreased and the lowest semilethal temperature of two groups were -37.5 and -31.1 ℃.3)The contents of chlorophyll of two groups decreased by 24.7% and 380% respectively from September to January in the coming year.4)The contents of soluble protein and free praline increased firstly, and then decreased, the content of soluble sugar increased gradually, there was no significant difference between two groups. 5)The activities of superoxide dismutase（SOD）and peroxidase（POD）increased as well. The biggest value of SOD and POD of the first group increased by 11.6% and 17.2% respectively compared with that in September. The biggest value of SOD and POD of the second group increased by 19.6% and 5.9% respectively compared with that in September.6) MDA contents of both groups increased gradually from September to January in the coming year by 26.8% and 24.8% respectively. Furthermore, multitude indexes demonstrated that the seedlings in natural conditions had stronger tolerance to low temperature than the other group.