| Germplasm resources is the most fundamental and strategic resources for human survival and social progress. Since the 20th century, the diversity of crop genetic resources has been continuously lost because of increaseing of population, deterioration of environment and promotion of new varieties. More effective preservation of crop germplasm resources has become increasingly urgent. At present, preservation of germplasm in genebank at low temperature is the most important ways. Because of its expensive cost, a cost-effective technique for germplasm conservation is needed urgently.To this aid, rice seeds of Xingshi (Orysa sativa, L. japonica) and Guichao 2 (Orysa sativa L. indica) were dried to different moisture contents ranging from 3.0% to 10.6%. Seeds were stored at different climatic zones, Sanya, Nanchang, Beijing, Xining, Urumchi and Harbin in room temperature, and continuously tested seed vigor and viability every year for 11 years. The results were used to analyze the relationship among the storage temperature, the range of optimum moisture contents and seed longevity. The seed viability and the affecting factors were also discussed. Through the testing of seed leachant conductivity, MDA content, activity of antioxidant enzymes, isoenzymic zymogram of antioxidant enzymes and isoenzymic genes expression, the range of optimal moisture content and the physiological and biochemical mechanism of extending dried seed longevity were studied. The main results were summarized as follows:1. When rice seeds dried to 3.0% moisture content, over-drying injure occurred and seed germination rate and germination index declined. The over-drying injure did not increased during storage at -18℃. After appropriate humidification treatment, the over-drying injure could be alleviated to some extent. The capacity of resistant for drying of Guichao 2 was stronger than that of Xingshi.2. After 11 years storage, all the germination rate of rice seeds were less than 50% in Nanchang and Sanya. While in Beijing, Xining, Urumqi, Harbin, and other places, seed germination rate with moisture content of 10.6%-4.5% was still higher than 50%. It was negatively correlated between the upper limit and range of seed moisture content and mean annual temperature, annual accumulated temperature above 0℃, while the lower limit of moisture content was positively and significantly correlated. Moisture content of 6.5%-5.0% was widely adaptable to all climatic zones for rice seeds. Longevity of rice seed with appropriate moisture content could be greatly extended.3. The survival curves of rice seeds stored at room temperature showed anti-S-shape and the loss of seed viability was not declined constantly over time. Dried seeds with appropriate moisture content delayed the phase of viability rapid declining compared with non-dried seeds of moisture content of 10.6% and over-dried seeds of moisture content of 3.0%. Though average annual temperature are 5.7℃in Urumchi and Xining, the seed viability in Xining maintained higher than in Urumchi . 4. Seed leachant conductivity and malondialdehyde (MDA) content in embryo were not significantly correlated with seed moisture content and viability when stored in Nanchang at room temperature 9 years. APX, CAT, GR and SOD activities were maintained well in embryo when seed moisture content was optimal while CAT activity was significantly higher than embryo of over-dried seeds. There were significant correlation between APX, CAT activity and germination rate in germinated seeds stored in Nanchang at room temperature. APX, CAT and GR activity in seed endosperm was significantly lower than that of embryo and SOD activity in seed endosperm was close to or slightly higher than that of embryo.5. Isoenzymic zymogram of APX, GR and SOD was not different in embryo and endosperm of dry seeds and germinated seeds with high and no viability. Isoenzymic zymogram of CAT in embryo was different between seeds of high and no viability. This showed that CAT isoenzyme activity was consistent with the loss of seed viability.6. The results showed that APX, GR and SOD isoenzymes genes in seeds with high and no viability expressed differently. CAT isozyme gene CAT A (D29966) showed reduced expression, it might be the base of CAT activity decrease, and the reason of loss of seed viability.
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