Study On The Dormancy Characteristic Of Rice(Oryza Sativa L.) Seeds

The dormancy of rice seed is an important agronomic trait as it directly relates with rice grain and seed quality, especially with the pre-harvest sprouting resistance of seeds. Pre-harvest sprouting of rice seeds can occur easily in higher temperature and rainy weather of rice harvest season in South China and significantly reduce rice seed quality. On the other hand, In rice breeding and seed production, if rice seeds remain deep dormancy at the time of sowing, they will have difficulty to germinate or the germination rate will be very low, this status is not conducive to seed vigor test in time and seed purity indentification. Therefore, investigating the dormancy of rice seed and its physiological mechanism will be able to provide theoretical basis for the breeding of rice varieties with different dormancy intensity and take appropriate measures to solve the problem of rice seed pre-harvest sprouting and ensure the yield and quality for rice seed production.In this study, the fresh mature seeds of different types of rice varieties or strain lines were used as experiment material, seed germination percentage and the water absorption rate, respiration rate, the change of the activity of α-amylase and acid phosphatase, content of soluble sugars and soluble proteins of seeds duing germination process were measured to evaluate the dormancy characteristic and its physiological mechanism. In addition, we preliminarily identified seed dormancy-related genes OsVP1,Sdr-4and TRAB1in various types of rice seeds with dormancy difference, and assayed their expression differences with fluorescence quantitative PCR method. The results were as follows:1. Seeds of Chaling wild rice have deep dormancy, its dormant period is more than3months, the freshly harvested seeds can not germinate under suitable conditions, after storage for3months, its germination rate reached46%.2.28dual-purpose genic male sterile rice varieties or strains exhibited remarkable differences in seed dormancy degree.5varieties or lines showed extremely strong dormancy (seed germination percentage≦5%);8varieties or lines have strong dormancy (seed germination percentage between6%and40%);7varieties or lines have moderate dormancy (seed germination percentage between41%and70%); S318has shallow dormancy (seed germination percentage is71%); and zhu1S has no dormancy (seed germination percentage is93%);6lines have dormancy with special behavior.3.699different rice lines (including143cold resistant lines,383overwintering lines) exhibit remarkable differences in seed dormancy. Among them,20lines showed extremely strong dormancy (seed germination percentage was≦5%);73lines have strong dormancy (seed germination percentage between6%and40%),;140lines have moderate dormancy (seed germination percentage between41%and70%);290lines have shallow dormancy (seed germination percentage between71%and90%); and146lines have no dormancy (seed germination percentage was above90%);30lines have dormancy with special behavior.4. Peeling (hull) has a significant role on rice seed dormancy, the changes of water absorption rate and respiration rate have a direct relation with rice seed dormancy. After de-hull processing, the seed germination rate significantly increased, water absorption rate and respiration rate obviously rose, but there were significant differences between different varieties with dormancy, the effect of de-hull was greater on the varieties with strong dormancy and less on the non-dormant varieties. It was suggested that the inhibition of hull on rice seed germination may be caused by its mechanical stress or the role of inhibitory substances in it.5. In dried fresh and3d germination treated seeds, the activity of α-amylase and the content of soluble proteins showed a negative relationship with seed dormancy intensity, which might be as important physiological indicators to evaluate rice seed dormancy. The activity of acid phosphatase was positively correlated with seed vigor, but out of proportion to the intensity of its dormancy. The content of soluble sugar was not appropriate with seed dormancy intensity also. 6. The reported dormancy-related genes OsVP1, Sdr-4and TRAB1showed remarkable difference in expression in different rice seeds but did not exhibit linear relationship with dormancy intensity.