Study On Phenotypic Variation Of Seed And The Changes Of Active Substances During Seed Germination Of Cercidiphyllum-Japonicum Sieb.et Zucc.(Cercidiphyllaceae)

Based on the distribution of Cercidiphyllum japonicum in China,the phenotypic traits of 11 C.japonicum populations were investigated,and phenotypic traits variation rule and its correlation with environmental factors were studied.In addition,aiming at the problem of low seed germination rate,the dynamic changes of enzyme activities,hormones and phenols during seed germination were investigated,and the internal factors affecting the germination of C.japonicum were discussed.Finally,the endangered mechanism and related protection measures of C.japonicum were also discussed to provide a theoretical basis for the research and development of efficient germination accelerating technology of C.japonicum.Through the test results can be known:1.Phenotypic variation of fruit and seed phenotypes of C.japonicum.The reflect the real measurement indicators of phenotypic traits incense tree species in the group or the group there were significant differences between（P<0.01）,but in the group of the phenotypic differentiation coefficient and variance component（20.95%）were significantly greater than the group of the phenotypic differentiation between the coefficient and variance component（6.09%）.The variation range of seed phenotypic traits in 11 different populations of C.japonicum ranged from 3.5%to20.6%,and the mean variation coefficient was 10.9%.The coefficient of variation of pod length was the largest（CV=20.6%）.Second variation amplitude of the larger grains and legumes such as wide phenotypic traits（CV=14.0%,12.3%）,and the seeds and wings wide variability in minimum（CV=8.2%,8.5%,3.5%）the biggest difference are nearly three times the left and right sides,pods,and kernels per phenotypic traits in different provenance of discrete degree is bigger,genetic stability is low.The mean phenotypic variation coefficient（CV=15.9%）of the Hupingshan population was significantly higher than that of the other populations,indicating that the phenotypic diversity of the Hupingshan population was relatively rich.However,the Fengtongzhai population（CV=7.7%）had the lowest degree of variation and genetic diversity.The variation of phenotypic traits of C.japonicum was related to environmental factors such as longitude,altitude,annual precipitation and annual sunshine.Its phenotypic characteristics are similar to that of most plants.In some areas,the population of C.japonicum is distributed in patches or islands,showing a random variation pattern.Combined with the low phenotypic genetic diversity among populations of C.japonicum,it could be inferred that there were barriers in gene exchange among populations of C.japonicum,which led to the low level of genetic diversity of the species.In addition,the fragmentation of its distribution due to human logging intensifies the scattered distribution of individual plants,which further leads to genetic drift.It can not adapt to the external environment well,which may be one of the reasons for its extinction.Conservation strategies:1)Yipingshan in Hunan was selected as the key conservation area in situ;2)To increase the genetic diversity,we should introduce the species from the adjacent populations that belong to the same group as the wasp and barb villages.3)Qinling in Shaanxi Province were taken as the germplasm source of genetic breeding.2.The change of enzymatic activity in the process of seed germination（1）During the germination stage,the activities of POD,SOD,APX andα-amylase all showed a trend of"increasing first and then decreasing",and the activities reached the peak value（93.26 U/g min-1,295.59 U/g,4.56U/g,0.10 mg/g）when the radula length was 0-1 cm.β-amylase activity fluctuated（0.31～0.69 mg/g）,while CAT showed an increasing trend（8.84～14.42 U/gmin-1）.This is because during germination,with the increase of activities of SOD,POD,CAT and APX,on the one hand,reactive oxygen species and free radicals can be eliminated to avoid damage;on the other hand,by controlling the range of H₂O₂,PPP pathway can be enhanced to promote seed germination.In addition,during seed germination,starch needs nutrients and energy generated by amylase degradation to promote seed germination,and amylase degradation is mainly accomplished byα-amylase andβ-amylase synergism.Therefore,PEG,ASA and GA can be used to improve seed vigor,and then increase enzyme activity to promote seed germination.（2）At the germination stage of C.japonicum seeds,the contents of IAA,ZT and other hormones showed a trend of"rising first and then decreasing",the former reached the peak value（26.83 ng/GFW）when the young root length was 2～3cm,and the latter reached the peak value（9.97 ng/g FW）when the radicle length was 0～1cm.The content of ABA decreased gradually with germination,which was 37.58 ng/g FW at the beginning of sowing and 16.73 ng/g FW when the length of young root was larger than3 cm.The content of GA₃ remained stable during seed germination（3.80～4.12 ng/g FW）.This is because the seed germination process will be affected by ABA,IAA,ZT and other hormones.（3）The content of total phenols,as the inhibitory agents of seed germination,showed a trend of"increasing first and then decreasing"during seed germination.When the seeds did not germinate 10 days after sowing,the total phenol content reached the maximum value（323.46 mg GAE/100g）.When the length of young roots was greater than 3cm,the total phenol content decreased to the lowest（187.64 mg GAE/100g）.This is because with the germination of seeds,the increase of enzyme activity leads to the acceleration of enzymatic hydrolysis and the generation of phenolic substances.In addition,phenolic substances affect the germination of seeds by affecting the changes of endogenous hormones.Therefore,seed germination can be promoted by reducing the content and concentration of total phenols.