Abstract: High germination rate at low temperature (low temperature germinability, LTG) is an essential characteristic of rice varieties adapted to direct seeding culture. To determine the difference of LTG among the varieties and its physiological mechanism of seed germination under low temperature, Japonica cultivars USSR5, Hatanishiki and Indica cultivars Miyang23 and N22 were used to study the mechanism of seed germination. The results showed that USSR5 came from the former Soviet Union and Hatanishiki came from Japan had higher seed germinability under low temperature, while Miyang23 and N22 with weakly low temperature germinability. The main reasons were that Miyang23 and N22 were more sensitive to GA3, ABA, and low temperature. Furthermore, it was revealed that low temperature and exogenous hormone might affect the seed germination through regulating the activity of amylase type 3 by electrophoresis. During the seed germinating, the USSR5 seed with high LTG contained higher level of endogenous ABA under low temperature than normal, and the ratio of GA1/ABA was lower than that of N22 under low temperature, this may be one of the main reasons of USSR5 with high LTG.

Key words: Rice, Low temperature germinability, GA, ABA, Amylase