昆欄樹花部發育及小孢子形成之研究

昆欄樹是一種過去被認為缺乏導管的植物，其分類地位也在木蘭目、毛茛目、金縷梅目或昆欄樹目等原始被子植物之間，不斷地被討論與挪動。近年的被子植物分類系統 (angiosperm phylogeny group, APG) 建議昆欄樹應歸屬於真雙子葉植物基群，掃描式電子顯微鏡的觀察也確認其木材中具有原始導管。然而，詳細的花部發育與小孢子形成的研究仍相對缺乏。本論文係針對昆欄樹的花部發育及小孢子形成為研究重點，作為昆欄樹與相關支序植物的發育與形態比較基礎。昆欄樹的花部發育需要約九個月，為兩年型的生殖週期，也是很多溫帶樹木常見的類型。昆欄樹花序早期發育中，側花接續著花苞片出現，兩兩一組由下往上螺旋發生。頂花則是隨著數片中間苞片而出現，頂花比起下方的數朵側花更早發育，因此昆欄樹的花序屬於有限花序中的葡萄狀花序。側花有近軸面延後發育的現象，二片先出苞片先於花器官出現，著生於早期非輻射對稱的花托基部，隨後雄蕊以螺旋排列方式發育。數片鱗片狀的構造在雄蕊之前出現，這些小鱗片 (退化花被) 在頂花較側花更為明顯。頂花的中間苞片、小鱗片和雄蕊依序由下而上以螺旋排列的方式出現。最後，心皮在最內圈雄蕊之內排成輪狀，折合心皮具有延長而向外彎曲的柱頭，柱頭成熟時具有兩列稜脊狀的瓶狀乳突細胞。昆欄樹雄蕊的花藥壁為基本型，有一層內壁層、三層中間層及一層營養層。營養層為單層細胞的分泌型。小孢子母細胞先有胼胝質堆積而獨立分離，隨後進行減數分裂和同時型質裂，產生四面體排列的四個小孢子，它們一同被包覆在胼胝層中。初生外壁首先堆積於胼胝層與小孢子細胞膜之間。隨後細胞膜開始波浪狀內陷，原頂蓋層在細胞膜突起處堆積，而後原柱狀體則由細胞膜起始向上延長至原頂蓋層下。接著，胼胝層漸漸瓦解，小孢子游離並分開，花粉外壁底層進行堆積，隨著自由小孢子進入液胞期，外壁內層及花粉內壁也接續形成。花粉外壁底層厚而外壁內層薄，且兩者於非孔區都為連續。自由小孢子時期花藥壁的營養層內側同時可見的中空烏氏體；最後，小孢子開始進行細胞不等分裂，產生了一個較大型的營養細胞，包圍住另一個較小型的生殖細胞。昆欄樹的成熟花粉粒為兩個細胞的三溝花粉，並具有網狀紋飾的花粉外壁。以昆欄樹的花部發育及小孢子形成過程結果為基礎，與鄰近真雙子葉植物基群的相關特徵比較。昆欄樹花部構造中的基部合生折合心皮、長而向下延伸的柱頭與瓶狀的單細胞柱頭乳突細胞等特徵，是與黃楊目植物的共同特徵，為此姊妹支序之穩定特徵，也支持其間的親緣關係。

關鍵字

真雙子葉植物基群；花部苞片；花器官排序；花粉發育

並列摘要

Trochodendron aralioides Sieb. & Zucc. (Trochodendraceae), a tree long considered to lack vessel elements in its wood, was discussed and moved among Magnoliales, Ranunculales, Hamamelidales or Trochodendrales of the basal angiosperms. Recent studies (angiosperm phylogeny group, APG) suggest that T. aralioides should belong to the basal eudicots, and it contains primitive vessels based on scanning electron microscope study. To date, the details of floral development and microsporogenesis of T. aralioides are lack. In the dissertation, the floral development in different stages and the microsporogenesis of T. aralioides are explored to discuss the relationship between T. aralioides and the close clusters in the basal eudicots. For floral development of T. aralioides, it takes about 9 months to develop and the 2-year reproductive cycle of T. aralioides is typical of many temperature trees. In the early development of T. aralioides inflorescences lateral flowers are initiated spirally after the appearance of the floral pherophylls (subtending bracts). The terminal flower is preceded by metaxyphylls and is initiated earlier than the uppermost lateral flowers of the botryoid inflorescence. Small scales seemed as rudimentary perianth organs precede the stamens. These scales are more conspicuous in the terminal flower than in the lateral flowers. In the radially symmetrical terminal flower, the metaxyphylls, the small scales and the stamens are initiated in a spiral acropetally during early development. At anthesis, stamen phyllotaxis appears irregular or approximately whorled as a result of the rapid elongation and irregular slight curvature of the stamen filaments which distorts the originally regular pattern. Finally, the numerous carpels arise simultaneously in a single whorl within stamens. In the stamens, the anther wall is the basic type with an epidermis, an endothecium, three middle layers, and a tapetum. The anther tapetum is glandular and cells are uniseriate. In microsporogenesis of T. aralioides, microspore mother cells undergo meiosis with simultaneous cytokinesis to produce tetrahedral tetrads enclosed within a callose wall. Before development of the protectum, primexine is inserted against the callose, and the plasma membrane is invaginated. Then, the probacula are elongated under the protectum and arise basally from the plasma membrane. The foot layer formation is concomitant with callose wall dissolution. The endexine and intine is initially formed in the vacuolated microspore stage. The foot layer is thick, and the endexine is thin. The foot layer and the endexine are both continuous. Hollow Ubisch bodies are observed on the inner surface of the tapetum in free microspore stage. Consequently, microspores undergo mitosis to produce two unequal cells, a large vegetative cell and a small generative cell. Pollen grains are tricolporate, reticulate and 2-celled at the time of shedding. Base on the floral development and microsporogenesis of T. aralioides, we compared those with the other basal eudicots. The bottle-shaped, the unicellular stigmatic papillae and the long, decurrent stigma of basal united carpels of T. aralioides are similar to those of the Buxales. Therefore, the persisting floral characteristics of T. aralioides support the phylogenetic relationship with the cluster of basal eudicots in APG IV.

並列關鍵字

Basal eudicots ； Floral bracts ； Floral phyllotaxis ； Pollen development

參考文獻

Albert VA, Gustafsson MHG, Laurenzio LD (1998) Ontogenetic systematics, molecular developmental genetics, and the angiospermpetal. In: Soltis DE, Soltis PS, Doyle JJ (eds) Molecular Systematics of Plants II: DNA Sequencing. Kluwer, Boston, pp 349–374

Angiosperm Phylogeny Group (1998) An ordinal classification for the families of flowering plants. Ann Mo Bot Gard 85:531–553

APG II (2003) An update of the angiosperm phylogeny group classification for the orders and families of flowering plants: APG II. Bot J Linn Soc 141:399–436

APG III (2009) An update of the angiosperm phylogeny group classification for the orders and families of flowering plants: APG III. Bot J Linn Soc 161:105–121

APG IV (2016) An update of the angiosperm phylogeny group classification for the orders and families of flowering plants: APG IV. Bot J Linn Soc 181:1–20

國際替代計量

昆欄樹花部發育及小孢子形成之研究

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