Ecological Adaptive Strategy On Spread And Germination Of Dimorphic Fruits Of Fraxinus Velutina

Seed polymorphism is adaptation in morphological and physiological for plant species to growing environment around plant which has bet-hedging strategy in dispersal and germination,ensure reproduction of population and potential expand the population.The research on Seed polymorphism has important significance to the relationship between phenotypic characteristics and ecological evolution.This study compared the fruit traits of morphological and structural,dispersal characteristics,germination characteristics and transcriptomics of early seed budding between two different fruits.The main results of this experiment are as follows.(1)The fruit phenotypic characteristics were campared.The fruit weight of the three-winged type was significantly higher than that of the two-winged type,but wing length and width were lower.Fruit width and fruit length were significantly influenced by year,but the weight of fruit and seed were less affected by year.Correlation between phenotypic traits existed,especially traits associated with wing type.Abnormal seeds were produced in two kinds of fruit,such as rot seeds,empty seeds or much seeds in a fruit.The fruit phenotypic characteristics were an adaptation mechanism,and phenotypic diversity is the basis of the differences between dispersal and germination in order to avoid the sibling competition.(2)Anatomy of fruit and seed structure provided some results.The difference was mainly in the pericarp structure near the end of micropyle between three-winged and two-winged fruit.Two-winged pericarp had two sets of vascular bundles,but three-winged pericarp had three sets of that.Beyond that,both two kinds of fruits and seeds had the following characteristics.The structure of pericarp and endosperm were compact.Embryo had matured.The central vascular bundle crossed through the cotyledon,hypocotyl and growing point of the germ.The mesocarp cell in the fruit wing were cavity.There were many spaces in the seed,such as between endosperm and embryo,between cotyledon,between radicle and endosperm.The structural characteristics of fruit contribute to spread seed,protect the seeds from bad environment and inhibit germination.(3)The analysis of spread distance and diffusion time between three-winged and two-winged fruit gave us some some conclusions.The wing shape of fruit affected the dispersal characteristics.The three-winged fruits spread farther than two-winged fruits and is easy to spread under the action of gusts,but the two-winged fruits had longer diffusion time than that of three-winged fruits and easily secondlyspread.The combination of two dispersal mechanisms between two-winged and three-winged fruits helped to avoid sibling competition among species and promote the proliferation and reproduction of Fraxinus velutina.(4)Two kinds of seeds had their own adaptive range to photoperiod,light intensity and temperature during germination,and could regulate their germination behavior to successfully germinate according to their different environmen.The germination difference between two kinds of seeds in the same conditions was mainly due to the two-bets strategy of seed polymorphism.The optimum photoperiod for seed germination were 12h/12 h.Germination percentage of two-winged seeds was higher than that of three-winged seeds under 24 h and 8h illumination,but the results were opposite when the seeds were exposed to 12 h and 10 h illumination.The germination rate of two kinds of seeds in the dark was lowest.The results which two-winged seeds could germinate under the light intensity of1000,2000,3000 and 4000Lx showed that two-winged seeds had wide range of light intensity for germination than three-winged seeds.Three-winged seeds germinated better under low light intensity.Two-winged seeds need high temperature than three-winged seeds for germination,but three-winged seeds had broad temperature than two-winged seeds.Three-winged seeds could germinate well in the constant temperature(20 to 30℃)and variable temperature(35/20).This results indicated that three-winged seed had potential to germinate in different temperatures.The germination rate of two kinds of seeds increased significantly with the increase of temperature,and variable temperature could significantly promote seed germination and the seedling emergence rapidly.(5)The effects of storage time and pericarp on seed germination were compared.The results showed that ripeness could promote seed germination regardless seed or fruit.The pericarp inhibited seed germination which due to the pericarp reduced light arrived to the seeds,and the light intensity felt by seeds decreased so that pericarp limits seed germination.(6)We obtained approximately 4350 differences unigenes and 3875 annotated functional genes by transcriptome analysis to the early stage seed germination which were incubation(25℃1700Lx24hlight).Up genes had 1936,but down genes had 2414.There were significant differences in the gene expression between two kinds of seeds in the early stage of germination.2077 genes were annotated in the GO enrichment terms and assigned to 41 GO secondary functional categories.1263 genes were annotated by KEGG Pathway analysis and assigned to 108 signaling pathways.20 pathways weresignificant among all of signaling pathways.(7)The analysis of photosynthetic antenna proteins and photosynthetic pathways showed that three-winged seeds which were in the early stage of germination reduced light energy captured by LHCA and LHCB for avoiding light damage.The results indicated that three-winged seeds which were in the early stage of germination were more adapted to low illumination than two-winged seeds(8)The GO enrichment terms which were important to the seed germination were identified,they were germination of seeds(GO:0009845),positive regulation of seed germination(GO:0010030)and seed dormancy process(GO:0010162).Gene expression of three-winged seeds was all down-regulated in these biological processes.The gene expression of β-1,3-glucannase,methionine synthase and s-adenosine methionine synthase were down-regulated in three-winged seeds。This indicated that the germination of three-winged seeds was weaker than that of two-winged seeds,and the gene regulation reason for difference of germination rate between two kinds of seeds was proved.To sum up,three-winged fruit was an adaptaion for mother tree to the growing environment.Seeds spread further and expanded the range of the population by three-winged fruits dispersal.The survival of species was assured by the spread of two-winged fruits.Two kinds of fruits could cope with different environments during germination,which added a germination mechanism adapted to environmental changes.The combination of the two types of fruit is the adaptation of the species to the ecological environment.The bet-hedging strategy existed in fruit dispersal and seed germination,which not only were phenotypic evolution,but also adaptive variation in gene regulation.An evolutionary mechanism had produced from phenotype to gene.