Studies On The Mechanisms And Breaking Methods Of Ilex Purpurea Seed Dormancy

The mechanisms of Ilex purpurea seed dormancy were studied in this thesis through the mensuration of the structure and permeability of seed coat, the observation of seed embryo growth, and the bioassay of the solution extracted from different parts of seeds. In order to find out an effective way to overcome dormancy, the seeds were treated by acid scarification, hormones soaking, stratification and combinination pretreatment respectively. The dynamic changes of some physiological indexes during stratification were also measured, so that the mechanisms of seed dormancy could be revealed. The results were shown as follows:The testa of I. purpurea seeds was severely keratinized and the cells were compactly arrayed in this area. Thereby the permeability of seed coat to gas was poor but that to water was not affected. The observation of seed embryo development and the mensuration of the ratio of embryo length to endosperm length showed that the differentiation of seed embryo was not completed at natural maturation. So the physiological after-ripening was needed before the seeds could germinate. The alternative temperature (warm and cold) stratification was beneficial for seed to complete physiological after-ripening. The bioassay of solutions extracted by water or methanol showed that there were germination inhibitors in endosperm (including embryo), and the inhibitory effect could not be completely eliminated by stratification. Among these, the main causes of the dormancy of I. purpurea seed were the after-ripening of embryo and weak permeability of seed coat to gas, while the permeability of seed coat to water and the inhibitors were less important in this respect.The dormancy of I. purpurea seed could not be overcome by warm stratification and natural stratification, while it could be overcome by cold stratification but with low germination percentage. The seed dormancy could effectively overcome by alternative stratification (warm and cold), but the order from warm to cold could not be inversed. Acid scarification could accelerate the germination and promote the germination significantly, but it would make the seed rotten more seriously. Moreover, soaking with GA3 could be beneficial for overcoming dormancy, and this effect would be stronger with increasing concentration. The best treatment obtained in this experiment was that soaking with 98% sulphuric acid for 5 minutes+ 500 mg·L-1GA3 for 48 hours+ warm stratification for 60 days + cold stratification for 160 days, which could raise germination percentage to 51%.During the process of overcoming dormancy, the changes of endogenetic GA3, IAA, ZR, ABA and the ratios of these hormones were synchronistic, but the trends of changes were complicated. Meantime, storage materials were also decomposed, conversed and utilized. And the changes of starch content were most obvious, followed by those of protein and lipid. The activities ofα,β-amylase and ACP were also enhanced, indicating that the metabolism was accelerated in the seeds. And the activities of G-6-PDH and POD were also increased gradually, which were the signs of PPP activation.