| This study took SRAP molecular markers to analyze11various kinds of Taraxacum; selecting and identified three kinds of Taraxacum dandelion ploidy and reproductive type by emasculation and bagging, chromosome number for root tip cells and karyotype analysis, flow cytometry; determined pollen viability using the culture medium for pollen germnination; tested the stigma receptivity through benzidine and hydrogen peroxide method, and then observed micromorphological structure of both ripe pollen and stigma in different stages with Scanning Electron Microscope; systematic researched the formation of female gametophyte and embryo development course with paraffin section under the Laster Scanning Confocal Microscope; found and cloned genes related apomixis based on molecular biology techniques. Based on results of the cytology, embryology and genetics, we analysed the apomixis occurrence mechanism of Taraxacum, and evaluated the extent of Taraxacum apomixis, then offered a base studying the genetic rules and molecular mechanism of Taraxacum apomixis.The results are as followed:1. The results of SPAP analysis indicated there exist abundant genetic diversity among species resources of Taraxacum. The Taraxacum in the northest China was divided into three types in molecular level, which was matched with the clustering results of Taraxacum’s morphology. It laid the foundation for the genenic rules and molecular biology of Taraxacum apomixis.2. Through emasculation and bagging, chromosome number and karyotype in root tip cells, flow cytometry of three kinds of Taraxacum, we justified that Taraxacum ohwianum Kitam. is a diploid(2n=2x=16), sexual reproduction; Taraxacum antungense Kitag. is a triploid (2n=2x+x’=24), obligate apomixes; and Taraxacum variegatum Kitag. is a tetraploid (2n=3x+x’=32), facultative apomixis.3. The ripe pollen grains of three kinds of Taraxacum in different reproductive modes could germinate in vitro medium, which showed pollens of three kinds of Taraxacum were to have vitality. The receptivity of flower from bloom to’Y-type’stigmas in full-bloom stage became significantly increased, and it became decreased after stigmas were cornucopia. The micro-structural features showed that the size of pollen grains in sexual reproduction was homogeneous, but the pollen grains of apomixis were bigger variation as well their size were irregular. It was obvious from experiment of pollination biology that the occurrence degree of apomixis was high in Dandong Taraxacum, and the development of both embryo and endosperm in apomixis did not rely on.4. Found unique pattern formation in taraxacum apomixis:dyad through the embryology research; the results of embryology indicated that the megasporogenesis of both gamogenesis and apomixis belonged to single spore type, but the megasporogenesis existed stage of tetrad which is the obvious difference between them. The development of female gamete was same, namely then the uninucleate embryo sac forms7-celled or8-nucleate embryo sac of polygonum type following its three times division successively, and the pictures at different growth stages were provided. The obligate apomixis of Dandong Taraxacum belonged to autonomous type, which was not initiated with the pseudogamy. And both egg cell and central cell developed autonomously, as well the development of embryo was earlier than endosperm.5. In this study, we found and cloned for the first time that MSI1related to the apomixis gene, the whole length of cDNA in Dandong Taraxacum was1424bp. The open reading frame located between1and1272bp, and encoded423amino acids; it has high homology with the homologous amino acids of other species, which was from73.94%to89.44%. The data of Real-time quantitative PCR indicated that MSI1was related to apomixis in Taraxacum and its expression mainly happened in full-bloom stage. However, how MSIl regulated the development of apomixis needed to further research. |
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