| Taxus yunnanensis(Taxus wallichiana var. wallichiana) is an endangered species on China’s national protection list. This plant is located mainly in Yunnan, Sichuan, Chongqing, and Tibet. Taxus yunnanensis is one kind of significant pharmacological plant resources, and it is rich in taxol, it has a broad development prospects. In nature,the seeds of T. yunnanensis need about 2 years to eliminate dormant factors for germination. To shorten the time of seed germination and improve the germination rate, many studies of seeds on biology, physiological ecology, and cultivation have been conducted.However, there are no consistent views and conclusions about how to improve germination rates. Thus, clarification of the embryonal germination characteristics 、the water permeabilityendogenous hormonesand other studies of seed coats form the basis for understanding causes of seed dormancy. In order to explore the mechanisms of T. yunnanensis seed dormancy and germination, T. yunnanensis seeds were used for morphological observation, water permeability tests, and tests on the effects of different seed sizes and endosperm quantities on the germination rate for in vitro embryos. The main results of this thesis are as follows:1. With the increase of maturity of T. yunnanensis,seeds gradually increased, and the kernel,which gradually filled with seedshad also increased gradually with the seed.The amount of seed dry matter reduced.Seed moisture content decreased.Seed germination rate gradually increased. Immature seeds(Aril greenish or pinkish, coated seed length 1/2 to not fully coated) and mature seeds(Aril red)in size and shape of seed, seed kernel,embryo, seed weight, seed moisture content, seed coat structure were very close.Besides,both were bottle-shaped embryo, and the embryo was differentiated into cotyledons, radicle and hypocotyl.In the physiological indexes, the germination rate is very similar.Therefore, immature seeds(Aril greenish or pinkish, coated seed length 1/2 to not fully coated seeds) have reached the morphological and embryo physiological mature stage.2. Fresh seeds of T. yunnanensis were used in the tests, The volume range for embryos and seeds was 0.156–1.012 and 51.658–109.649 mm3. The volume ratio of an embryo versus a seed(E:S) was 7.4%. respectively. Seed and embryo volume size were likely to be one of the factors that made in vitro embryo culture germination rate different..3. When in vitro embryo culture with a new harvest of T. yunnanensis seed,inoculation time had a greater impact on the seed embryo germination. The germination rates of embryo without endosperm, with 1/2 of the endosperm and with full endospermwere all highest, followed by 3 d seeds after harvest. However from the beginning of harvest 14 d, the germination rate of embryos with 1/2 endosperm decreased gradually, while with full endosperm was 0.4. At the beginning of the storage,The water absorption rate of intact seeds was lower than that of cut seedsand acid-corrodedseeds. However, the differences of water absorption rates for seeds corroded by cut seedsand acids for 40 min were reduced with the extension of soaking time. When the moisture content of a seed was saturated, there was no significant difference of water absorption rate among intact, cut, and acid-corrodedseeds. At the same time, the water absorption test showed that with the extension of storage time, water absorption rate was faster, sTab. time was shorten, permeability was also increased.The water permeability of seed and the seed coat structure had a close relationship.5. The extractsof seed, seed coat, kernel, endosperm and embryo inhibited the seed germination and seedling growth rate of Brassica campestris. In various parts of T. yunnanensis seed extraction and testing of inhibitors, inhibitory effects of extracts from kernel on the germination rate, root length, shoot length, simple vigor index of Brassica campestriswere higher than the extracts of seed coat.6. With the extension of storage time, the changes of GA and ZR content in the embryo, endosperm, seed coat, kernel and seed and variation in seed were relatively sTab., and the content was low. IAA and ABA contents fluctuated. What’s more, ABA and IAA played an important role in the dormancy and germination of seeds. In the middle of the seed storage(6 m), IAA/ABA in seed coat, IAA/ABA in kernel, IAA/ABA, GA/ABA, ZR/ABA in seedwere rising. When the seed was about to germinate, IAA/ABA, GA/ABA, ZR/ABA ratio were at a higher level.7. The results showed that, compared with the germination rate of in vitro embryo with and without endosperm, the endosperm was an important factor in vitro embryo germination. It could be concluded that the seed dormancy of T. yunnanensis was moderate and caused by physiological dormancy.Many factors can contribute to physiological dormancy; this study confirmed that the physical characteristics of seed coat also has a centain effect on seed dormancy of T. yunnanensis.8. With the extension of storage time, ABA content was decreased, but IAA and IAA/ABA ratio were increased of all the the seeds parts.Morever, combined with the p hysical characteristics of seed coat, the biological detection of the extrats of seed and the phenomenon of seed germination in 15 months. It can be concluded that seeds hav e physiological after ripening phenomenon. |
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