Physiological characteristics of cold stratification on seed dormancy release in rice

Cold stratification is commonly used for breaking seed dormancy in plants. However, the effects of cold stratification on dormancy release and its physiological characteristics are still unclear in rice. Dormancy release by different periods (6, 12, 18 and 24 days) of cold stratification (4 degrees C) was conducted using japonica Jiucaiqing (Oryza sativa L) in this study. Physiological characteristics, including hormones, antioxidant enzyme and a-amylase activities, were further estimated in imbibed seeds after 12 and 24 days cold stratification. Seed dormancy of Jiucaiqing was completely released by cold stratification for 18 and 24 days. The expressions of the hormones, including abscisic acid (ABA), gibberellin (GA) and indole acetic acid (IAA), metabolism related genes OsCYP707A5, OsCYP707A7, OsGA20ox1, OsGA20ox2, OsGH3-2, OsGH3-7 and OsGH3-8 were significantly increased while OsNCED3 and OsZEP significantly decreased in imbibed seeds by cold stratification, which resulted in the rapid decline of ABA and the increases of GA(3) and IAA. The activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), were significantly increased in imbibed seeds by cold stratification, which resulted in a slight increase of H2O2 level. The ratios of GA/ABA, GA/IAA and IAA/ABA and H2O2 level were gradually enhanced in imbibed seeds with cold stratification, which might contribute to the increase of a-amylase activity to promote dormancy release in rice.