Studies On Seed Dormancy Mechanism Of Taxus Chinensis Var. Mairei

Taxus chinensis var.maire(iLemee et I'ev1.)Cheng et L.K.Fu is a precious and endangered tree species only distributed in China, and belongs to the 1st-class protection of national protected plants. It can be used as medicine, timber and ornamental plant. The seed of T. chinensis var. mairei, however, has strong dormancy and only germinates after two winters and one summer under natural conditions, which has aroused difficulties to use seed as propagation material. The dissertation systematically studies the mechanisms of T. chinensis var.mairei seed dormancy. The main results show that:1. The dormancy of T. chinensis var . mairei seed belongs to combinational dormancy. The matured seed of T. chinensis var . mairei has integrated configuration, but is small in volume and after-riping is needed, which is the main cause of dormancy. The seed coat is very hard and dense; there is cutin in the surface of seed coat, which hinders the permeability of air, but this is not the cause of dormancy; and there are also germination inhibitors in the mesocoat, endopleura and endosperm. These factors are the main causes of seed dormancy. The extraction solutions of the mesocoat, endopleura and endosperm all inhibit the germination of cabbage seeds and growth of cabbage seedlings. The inhibitory effects become stronger as the contents of extraction solutions increase.2. All extraction phases are gained in seed coat and endosperm by using systematical solvent separation method. The inhibitory effects of endosperm extraction phases to the growth of cabbage seedling height can be taxised as, in turn from strong to weak, the extraction phase of methanol, of ethyl acetate, of aether, of petroleum ether and of water; those to the growth of cabbage seedling root can be taxised as, of methanol, of aether, of ethyl acetate, of water and of petroleum ether. The inhibitory effects of seed coat extraction solutions to the growth of cabbage seedling height and root can be taxised as, of methanol, of petroleum ether, of ethyl acetate, of aether and of water.3. The GC-MS analysis indicates that there exist manifold organic compounds in the seed coat and endosperm of T. chinensis var.mairei seed, mainly organic acids, benzenes and esters etc. The mensurations of the activities of organic compounds such as heptanoic acid,nonanoic acid,octanoic acid,ethyl phthalate,octadecanoic acid,benzoic acid and acetic acid, which have larger peak areas and resembility more than 85%, indicate that the inhibitory effects of these organic compounds become gradually stonger as the contents increase.4. The contents of endogenetic ABA in the endosperm gradually descend as the time of stratification prolongs; but the contents of GA increase, the contents of IAA and ZR increase at the beginning of stratification then descend as the time prolongs, the same as the ratios of GA /ABA, IAA/ABA and ZR/ABA, as a result, the dormancy is gradually overcome. The contents of endogenetic ABA, GA, IAA and ZR all gradually descend in the course of stratification.5. The activity of amylase and the contents of soluble sugar and soluble protein rise at the beginning of stratification then descend as the time prolongs, but the contents of lipid and starch gradually descend. In the course of stratification, the activity of POD rises at the beginning of stratification then descends as the time prolongs, but the change of combined activities of G-6-PDH and 6-P-GDH, phosphoesterase does not reveal obvious discipline, but in general has two peak values.6. Embryonic cell and apical meristems continue to divide as the time of stratification prolongs, so the embryo increases in volume and turns from ivory-white to viridescence, which are the signs of gradually maturing seed. In the course of stratification, the lipids in the embryonic cell gradually degrade; nucleolus appears and increases in volume. Meanwhile, the number of mitochondria increases, and the golgiosome appears; the embryo can germinate by this time.7. The treatment of soaking with 200 mg?L-1 GA and washing by gliding water for 1 weeks followed by stratification of wet sand (1:3) in warm and cold stratification (day at 23℃/night at 10℃) for 4 months then 5℃for 4 months can significantly arouse the germination percentage and is effective methods to overcome dormancy of T. chinensis var.mairei seeds.