Studies On Seed Dormancy Mechanism Of Daphne Giraldii Nitsche

Daphne giraldii Nitsche.belonging to Daphne linn.of Thymelaeaceae,commonly called Zushima in Chinese folk medicines,has been used to treat injuries,aches and rheumatism.Pharmacological investigations showed that Zushima had anti-inflammation,anti-fertility,analgesia,anti-thrombotic,anti-tumor,anti-malarial,hypnotic and sedative activities.Because the seed of D.Giraldii has strong dormancy,so it could be the main difficulties for its artificial propagation.In order to study the dormancy mechanism of D.Giraldii seeds,the testa structure and water permeability,the bioassay of extracts from testa and seed embryo,the embryo excision test,seed embryonic development and endogenous inhibitors were examined;The seeds also treated by soaking with different concentration and kinds of hormone solutions and different temperature and stratification method in order to find out the useful method for breaking seed dormancy;the nutriments content,endogenous hormone content,and enzymes activities were also determined to further reveal the mechanisim of seed dormancy.The major results are as follows:1.The dormancy of D.Giraldii seed belongs to combinational dormancy.After natural maturation period,the seed embryo uncompleted differentiation and uncompleted development were the main reasons for D.giraldii seed dormancy;The testa morphology structure and imbibitional characteristics of D.Giraldii seed was not the reason of seed dormancy,some germination inhibitors in the testa and embryo of D.Giraldii seed were also the main causes of the seed dormancy.2.The various extraction solutions of different part of D.giraldii seed are all have a serious impact on the seed germination and seedlings growth of cabbage.With the increase of the concentration of the extraction solutions,the inhibition effect was gradually increased.3.All extraction phases are gained from the seed testa and embryo of D.giraldii,by use the method of systematical solvent separation.The inhibitory effects of testa extraction phases had similar degrees on the growth of cabbage seedling height and root,the inhibitory effect from strong to weak can be roughly taxised as,the extraction phase of methanol>ethyl acetate>water>petroleum and aether;The influence degree of D.Giraldii seed embryo extraction solutions on the seedling height of cabbage can be taxised as,methanol>aether>petroleum and ethyl acetate>water,and for the seedling root can be taxised as,methanol>water>petroleum and aether>ethyl acetate.4.By GC-MS analysis,the seed spermoderm and embryo of D.giraldii Nitsche.contained manifold organic compounds,mainly organic acids,esters,hydrocarbon,ketones etc.There were 9,12-Octadecadienoic acid(Z,Z)-;Octadecanoic acid;Acetic acid;Dibutyl phthalate;Octane;Cyclooctasiloxane;hexadecamethyl-;Hexadecanoic acid;methyl ester;Butyl citrate;Tributylacetylcitrate;Cycloheptasiloxane;tetradecamethyl;4H-Pyran-4-one;2,3-dihydro-3,5-dih ydroxy-6-methyl;9-Octadecenamide,etc.which have larger resembility.5.With the extension of the time of outdoor stratification,the contents of endogenetic ABA in the embryo of D.Giraldii seeds decreased,but the contents of GA3 increase in the late stratification period,the contents of IAA increased at first and then decreased with the stratification time prolongs,the contents of ZR changed little,the ratios of GA3/ABA gradually increase as the time of stratification prolongs,IAA/ABA increase in post stratification period,ZR/ABA increase at ending stratification period.As a result,the dormancy is gradually overcome.6.Some important physiology indices correlated with seed dormancy and germimation physiology were measured.The result suggested that the relieving degree of dormancy was close with the metabolism of the storage substances in embryos.During the release of dormancy,the contents of soluble sugar increased at first and then decreased with the stratification time prolongs,the soluble protein gradually descend during this time and at the same time the main storage substances fat and amylum were successively degraded,and the activity of some interrelated enzymes such as Peroxidase,Acid phosphatase,G-6-PDH and 6-PGDH become stronger,and the ratios of promoting germination hormones and inhibitory hormones increased accordingly.7.With the time of natural stratification,Each part of D.Giraldii's seed embryo developed into maturation gradually,characterized by an increased cotyledon cell size(from closing to cracking),rounded germ,visible vascular in hypocotyl and in radicle.In later period of stratification,with the ability to sprout,each part of D.Giraldii's seed embryo has developed completely.On the other hand,under indoor stratification condition,a dysplasia was found in its hypocotyl at the end of stratification,of which,the radicle was shorter.8.In summary,it is suggested that,under indoor stratification condition,GA3(150 mg·L-1)and 6-BA(30 mg·L-1)were both conductive to D.Giraldii germination,but showed imperfect to the development of its hypocotyl and in radicle.Thus accordingly,the natural stratification by ditching outdoor in late October was more simple and convenient,more economical,as well as more secure.