Abstract: [Objective] We compared the effects of different dehydration conditions on germination of dormancy-released seeds of Fraxinus mandshurica and explored the intrinsic physiological changes of seeds under different conditions to provide theoretical and technical basis for redrying and storage of dormancy-released seeds of F. mandshurica.[Method] Using single factor design, the dormancy released seeds of F. mandshurica were used to investigate seed germination ability after dehydration at different temperatures(5, 10, 15, 20, 25, 30, 35℃). Then, the effects of dehydration temperature(normal temperature 20℃ and low temperature 5℃), dehydration speed(slow and fast), and their interaction on seed germination after dehydration were investigated using two factor design. In order to determine the response of seed cell membrane permeability, antioxidant system enzyme activity and storage material metabolism to different dehydration treatments, the activities of antioxidant enzymes (SOD, POD and CAT), malondialdehyde (MDA) content, soluble sugar, soluble protein and starch contents in seeds under different conditions were measured.[Result] The seed germination rate and germination index showed the trend of increasing at the beginning and then decreasing with the rising of the dehydration temperature, and the germination time of seeds showed the opposite trend. The germination ability of seeds dehydrated at normal temperature (20℃) was the best, and the germination ability of seeds dehydrated at high temperature(35℃) or low temperature(5℃) was weak. Compared with the normal temperature dehydration, the relative electrical conductivity and MDA content of seeds dehydrated at low temperature increased significantly, the POD and CAT enzyme activity in embryos was significantly decreased, no significant changes in the contents of soluble sugar and starch in the seeds, but soluble protein content decreased significantly. Compared with the slow speed dehydration, the relative electrical conductivity and MDA content of seeds dehydrated at fast speed increased significantly, the SOD and POD enzyme activity in embryos was significantly decreased, no significant changes in the contents of soluble sugar and starch in seed, but soluble protein content decreased significantly.[Conclusion] The optimum dehydration temperature for dormancy-released seeds of F. mandshurica is 20℃, high (35℃) or low (5℃) temperature dehydration can lead to the declined seed germination rate and germination index, and the prolonged germination time. After dehydration at low temperature or fast dehydration, the relative electrical conductivity and MDA content of the seeds were increased significantly, the activity of antioxidant enzymes in seed embryos and the soluble protein content of the seeds decreased significantly. These changes should be the causes for the decrease of seed germination ability. The activity of antioxidant enzymes in seed embryos had different responses to dehydration with low temperature and fast dehydration. POD and CAT were more sensitive to dehydration at low temperature, but SOD was more sensitive to fast dehydration. SOD, POD and CAT must be coordinated, so that the active oxygen free radicals can be maintained at a low level and harmless to the cells. The decline of the protective function during dehydration at low temperature or fast dehydration is mainly related to the changes of protein, but not the changes of soluble sugar or starch.

Key words: Fraxinus mandshurica, dehydration tolerance, seed germination ability, cell membrane permeability, antioxidant enzyme activity, soluble protein