蒺藜草無融合生殖特性的研究

The characterization of apomictic reproduction in Cenchrus echinatus

王世英(Shi-Ying Wang)

指導教授 ： 張松彬

國立臺灣大學/生物資源暨農學院/農藝學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.02091

摘要

無融合生殖是一種透過種子進行無性繁殖的生殖方式，依發育上的差異又可分為無孢子生殖、二倍孢子生殖和不定胚生殖等三種類型。
在台灣，前人對無融合生殖的研究，主要集中在黍族的物種。此篇論文中將透過胚囊發育的觀察、流式細胞儀推測種子胚與胚乳的倍體數、根尖細胞染色體數觀察，此三種方式建立起蒺藜草無融合生殖模式的基本特性。
無融合生殖型蒺藜草的成熟胚囊與有性生殖型者一樣同屬於八核型胚囊，又稱蓼型胚囊，具有一個卵細胞、兩個助細胞、兩個極核和三個反足細胞，在胚囊發育過程中，反足細胞會增生成多核的反足細胞團。不論是無融合生殖型或是有性生殖型的蒺藜草，都會形成合點端朝上、珠孔端朝下的倒生型胚囊，在胚囊的發育型態上，兩種生殖類型的差別不明顯。在無融合生殖型蒺藜草中，具有同一胚珠內產生多胚囊的現象，這是無孢子生殖的胚囊發育特色之一。另外也觀察到異位型胚囊，此特殊胚囊的發育方向垂直於合點端與珠孔端的軸線，且與珠孔不相通。透過多胚囊現象與異位型胚囊的觀察，可推測蒺藜草的無融合生殖類型是屬於無孢子生殖。
在蒺藜草根尖細胞染色體數目的實驗中，經觀察多個細胞染色體數後，推測所採集的材料無論是有性生殖或是無融合生殖的種子皆為同一倍體數，染色體數目為六十八條 (2n = 4x = 68)，為四倍體植株。
流式細胞種子篩選法為一種利用流式細胞儀來偵測種子中胚與胚乳細胞倍體數的方法。在本論文中，是以單顆種子為一偵測單位與多顆種子為一偵測單位等兩種分類來進行流式細胞儀的操作。在單顆種子流式細胞種子篩選法中，可以觀察到此顆種子中胚與胚乳細胞的倍體數，無融合生殖型的種子由四倍體的胚與八倍體的胚乳組成，跟經雙重受精後形成四倍體胚與六倍體胚乳的有性生殖型種子不同。無融合生殖型種子的四倍體胚，來自未減數分裂的卵細胞自發性發育而來，八倍體的胚乳源自兩個未減數分裂的極核自發性產生，兩者皆不需要受精即可形成種子。多顆種子流式細胞種子篩選法用以判斷專性或非專性無融合生殖，結果顯示同一植株中同時具無融合生殖與有性生殖型種子，因此推測蒺藜草是屬於非專性的無融合生殖。

關鍵字

蒺藜草 ； 無融合生殖 ； 胚囊發育 ； 流式細胞種子篩選法

並列摘要

Apomixis is an asexual reproductive mode through seeds, and it is classified in three types based on the developmental differences: apospory, diplospory and adventitious embryony.
Previous apomixis studies in Taiwan are focus on Paniceae species. In this thesis, we established the basic characteristics of apomictic mode in Cenchrus echinatus through the observations of embryo sacs, flow cytometric seed screening (FCSS), and chromosome counts.
Both apomictic and sexual C. echinatus plants showed similar embryo sacs of Polygonum type, which the 8-nucleated embryo sac composes of one egg cell、two synergid cells、one central cell of two polar nuclei and three antipodals. Both apomictic and sexual plants have anatropous ovules. Multiple embryo sacs, however, were observed in one ovule in apomictic individuals. This observation is a typical character of apospory. In addition, an alternative oriented embryo sac was found in our studies. This embryo sac developed perpendicularly to the axis of chalazal and micropylar ends, and there is no passage between this embryo sac and the micropyle. Depending on the observations of multiple embryo sacs and the different oriented embryo sac, we speculate the apomictic type of C. echinatus is apospory.
While counting the chromosome numbers of somatic cells from root tips, both apomictic and sexual C. echinatus cells are plants tetraploid which possess 68 chromosomes (2n = 4x = 68).
The results from single-seed FCSS and bulk-seed FCSS revealed the apomictic seeds built of a tetraploid embryo and an octoploid endosperm autonomously without fertilization. Facultative apomictic plants produce both apomictic and sexual seeds in same maternal individuals.

並列關鍵字

Apomixis ； Cenchrus echinatus ； embryo sac ； flow cytometric seed screening ； FCSS

參考文獻

方莞婷 (2003) 黍族 (禾本科)植物無融合生殖之篩選方法. 國立成功大學生物學研究所碩士論文. 台南

Albertini E, Porceddu A, Ferranti F, Reale L, Barcaccia G, Romano B, Falcinelli M (2001) Apospory and parthenogenesis may be uncoupled in Poa pratensis: a cytological investigation. Sexual Plant Reproduction 14.

Asker S (1980) Gametophytic apomixis: elements and genetic regulation. Hereditas 93:277-293.

Barcaccia G, Mazzucato A, Albertini E, Zethof J, Gerats A, Pezzoti M, Falcinelli M (1998) Inheritance of parthenogenesis in Poa pratensis L.: auxin test and AFLP linkage analysis support monogenic control. Theoretical and Applied Genetics 97:74-82.

Bicknell RA (1997) Isolation of a diploid apomictic plant of Hieracium aurantiacum. Sexual Plant Reproduction 10:168-172.