Abstract: Japonica rice (Xingshi) and Indica rice(Guizao 2) seeds were used to investigate the germination rate，vigor index and heat-stable proteins after stored at room temperature for 8 years. Results showed that the optimum moisture contents of Indica rice seeds stored in Beijing were 5.5% and 6.0%, but for Japonica rice seeds they were 6.5% and 7.0%. The optimum moisture contents were 4.5% for Indica rice seeds and 5.5%and6.0% for Japonica rice seeds stored in Nanchang. .It indicated that the level of the optimum moisture content of Japonica rice seeds was higher than Indica rice seeds stored at room temperature in the same area. But the level of the optimum moisture content will decrease with the increase of average temperature and above zero accumulate temperature in the storage. The result of SDS-PAGE electrophoresis showed that 39.4kD heat-stable protein appeared only in seeds of Indica rice that was tolerant of ultra-drying, but did not appear in seeds of Japonica rice that was untolerant of ultra-drying . The heat-stable protein disappeared when the germination percentage of Indica rice seeds was zero. The SDS-PAGE electrophoresis of 41.6kD heat-stable protein was also different between the two cultivars. The spectrum disappeared when the germination percentage of Japonica rice seeds was zero. These results suggested that the two kinds of heat-stable proteins might be related to dehydration tolerance and vigor lost of seeds.

Key words: Rice, Optimum moisture content, Dehydration tolerance, Heat-stable protein, Germplasm conservation