絲瓜的雄花發育和花粉發育之研究

Abstract

本實驗主要利用光學顯微鏡、掃描式電子顯微鏡和穿透式電子顯微鏡研究絲瓜（Luffa cylindrica）雄花在不同發育時期的各種變化，茲分成七部分描述和討論：1．田間觀察與外部形態、2．早期花部發育、3．花藥組織分化、4．小孢子形成與花粉的發育、5．花粉壁的發育、6．營養層的發育與花粉鞘的形成、7．組織化學染色。 由結果得知，花始原以逆時針方向螺旋狀的順序自總狀花序始原冒出，萼片始原也以逆時針方向螺旋狀的順序冒出，花瓣與雄蕊則5個同時冒出，雄蕊由最初的圓形隆起發展成迂迴捲曲狀的藥囊。 花藥組織分化屬於雙子葉型。花藥內的初級造孢組織來自皮下層的平周分裂而來的內層細胞的發育，經過多次細胞分裂形成造孢細胞，細胞膜外堆積胼胝質後成為小孢子母細胞。花藥壁由外而內依序為表皮層、花藥內壁、中間層（2?3層）、營養層。 小孢子母細胞在行減數分裂之前，細胞膜與細胞壁之間首先有胼胝質的堆積。減數分裂後細胞質的分裂屬於同時型，胼胝質向心性的堆積在四個小孢子之間，產生四面體排列的四分體，在四分體期間小孢子的花粉外壁開始發育。之後，胼胝質瓦解，釋出小孢子，此時營養層的細胞壁瓦解，且細胞內開始累積大量脂肪球。小孢子漸漸液胞化，並開始有脂肪球的累積。小孢子進行一次細胞不等分裂，產生生殖細胞與營養細胞，前者包含在後者之內，此時花粉內壁也發育完成。成熟花粉粒的儲存物有脂肪球與澱粉粒兩種；前者在細胞溶質內形成，後者則在澱粉體內累積。營養層最後徹底瓦解，細胞內累積的大量脂肪球往花粉粒的方向移動，變成花粉鞘，附在花粉粒的表面，經化學染色結果為脂質成分。營養層為分泌型，在四分體晚期至小孢子早期時最活化，細胞質內有兩種胞器製造脂肪球，一為平滑內質網，一為油質體。 絲瓜花粉外壁的發育始於四分體早期，首先有纖維狀物質堆積在細胞膜與胼胝質之間，然後有原始外壁物質堆積在纖維狀物質上。接著，小孢子分泌花粉外壁物質（似孢粉質顆粒），而不再有原始外壁物質的堆積，花粉外壁的基本形態便已成形，有頂蓋層、柱狀層和底層。花粉外壁內層形成於四分體晚期，與底層之間有白線狀構造。外壁內層有兩層，第二層出現於小孢子早期，其功能可能與花粉壁高度的彈性和延展性有關。在小孢子晚期時，花粉內壁首度出現於孔區外壁內層下方。花粉內壁在雙細胞時期發育完成，孔區的內壁可分成三層。 由組織化學染色的結果得知，花粉外壁柱狀層之間的纖維狀物質和花粉內壁含有多醣類，而孔區的花粉內壁除了多醣類之外，尚含有蛋白質。 本文推測花粉外壁形式的控制可能早在花粉母細胞時期就已決定，屬於孢子體（2N）的控制，但其發育所需的物質則由小孢子和營養層共同提供。

The changes of staminate flower and pollen during different developmental stages of Luffa cylindrica (L.) Roem were studied with light microscope, scanning and transmission electron microscope. Floral primodium initiated from infloresence primodium in a spiral order. Five sepal primodia intiated from the edge of a floral primodium in a spiral order, too. Then five petal primodia arised simultaneously in a whorl arrangement, followed by five stamen primodia. Consequently, the stamen grew up and developed a curved anther. The anther wall layers occurred as dicotyledonous type and were composed of epidermis, endothecium, middle layers (2 ? 3 layers) and tapetum. Sporogenous tissue was derived from the inner layer, which was resulted from periclinal division of the hypodermal layer. Callose wall was deposited between the plasma membrane and cell wall of microspore mother cells before meiosis. The cytokinesis after meiosis occurred simultaneously by the centripetal invasion of callose wall, then a tetrahedral tetrad enclosed in the callose wall was produced. After callose wall was dissolved, four microspores were released into anther loculus. At the same time, tapetal cell wall was disintegrated, and deposition of lipid droplets started in tapetal cytoplasm. Deposition of lipid droplets also occurred in the cytosol of microspores during the middle and late microspore stage. Haploidal mitosis of microspore took place, which resulted in a big vegetative cell and a small generative cell. Mature pollen grains contained two kinds of reserves, lipid droplet and starch grain; the former was produced in the cytosol and the latter was deposited inside the amyloplasts. The secretory tapetum reached its optimal activity from the late tetrad to early microspore stage. Two organelles involved in production of lipid droplets were smooth endoplasmic reticulum (SER) and elaioplast. As tapetal cytoplasm degenerated, clusters of lipid droplets that were deposited within the cytosol and elaioplast moved towards the pollen grain. At anthesis, pollenkitt derived from tapetum were coated on the surface of the mature pollen grain. Development of pollen wall started during the early tetrad stage. At the beginning, a fibrillar material was deposited between the callose wall and plasma membrane of microspores. The primexine was then accumulated on the position where fibrillar material possessed. Subsequently, exine material secreted by microspore itself was accumulated on the same position to replace primexine. The tectum and bacule had been formed before the discontinuous foot layer was visible. There were two distinguishable layers in endexine. The outer one seemed to be formed after the appearance of white lines which was just beneath the foot layer at the late tetrad stage, and the inner one was formed after dissolution of callose wall and composed of a number of sporopollenin-like granules. At the late microspore stage that was just before the haploidal mitosis of microspore, the intine was formed under the endexine at aperatural zone. After mitosis, the formation of intine finished around the pollen grain beneath the inner endexine. There were three layers in the intine of aperatural zone. Fibrillar material between the bacules and intine showed PAS positive reaction. Besides PAS, the intine of aperatural zone also showed Coomassie blue positive reaction. The results of this study present a detailed information about the microsporogenesis and pollen wall development of Luffa cylindrica (L.) Roem, and ascertained that exine was derived from a combined contribution from tapetum and microspore, rather than from either of them. We presumed that the control of exine pattern has been determined in the microspore mother cell.