Studies On Mechanism Of Dormancy And Germination Of Cornus Japonica Seed

The seeds of Cornus japonica possess the biological character of deep dormancy, andbegin to geminate2years later after they are collected. On this paper, the causes of seeddormancy of C. japonica were investigated by permeability test of seeds, in vitro culture ofembryo excision test, and the bioassay of extracts from different parts of seeds. The methods ofbreaking dormancy were studied by treating seeds several days （2d、3d and4d）with differentcontents of GA3((400mg.L^-1、500mg.L^-1、600mg.L^-1)combined with cold stratification. In orderto reveal the mechanism of seed dormancy and germination, the hormone contents andnutriments content of treated seeds sampled at the process of cold stratification were measured.The conclusions drown from all experiments are as follows:1. According to the test of water absorption, we know the testa had some difficulty inpermeability, which was one of reasons of seed dormancy. Culture of excised seeds revealed thatthe embryo of C. japonica was not dormant. The growth of cabbage seedlings treated withextracts from the testa of C. japonica was significantly inhibited, that shows there exists somesubstances inhabiting seed germination in the testa.2. The dormancy óf seeds were completely broken when the seeds treated with500mg.L^-1GA3for3d combined with cold stratification. The seed germination percentage was67%at theperiod of30d stratification, and the result was up to98%at50d,3. In the process of breaking seed dormancy, the dynamic changes of souble sugar andstarch showed increasing trend at the beginning and decreasing trend at the end of ofstratification. However, the contents of souble protein and crude fat declined with the period ofstratification. The nutriments content in the seeds treated with500mg.L^-1GA3for3d showed themost quickly rate of deceasing. The results was consistent with its highest germination.4. The tendency of hormons revealed different character. The contents of GA3increasedwith the longer period of cold stratification.At the same time, the contents of IAA and ABAdeclined, ZR increased at the beginning of stratification then declined. The ratios of GA/ABAand ZR/ABA gradually increased, and the ratios of IAA/ABA gradually declined..5. In conclusion, the type of dormancy in Cornus japonica seeds is complicated dormancy,including physical dormancy and physiological dormancy.