金銀花花部發育、小孢子形成與花粉壁發育之研究

Abstract

利用光學與電子顯微鏡觀察金銀花花部早期的發育、花藥組織分化與小孢子形成過程中，小孢子母細胞、營養層、花藥壁層和花粉壁在細胞超微結構上的變化。 由結果得知：金銀花花部各構造的起源，依序為萼片與花瓣始源同時出現、接著雄蕊始源發生，最後出現的是雌蕊始源。 雄蕊始源進行雙子葉型的組織分化，並產生四個藥囊的花藥，每個藥囊都由表皮、花藥內壁、中層、營養層與花粉母細胞構成；其中營養層為雙重起源。 在減數分裂之前時期，花粉母細胞四周有胼胝質壁堆積，並留有原生質通道相通。減數分裂完成後，胼胝質壁堆積完全，原生質通道才消失。 金銀花花粉母細胞的細胞質分裂屬於同時型，並產生四面體形排列的小孢子四分體，被緊密包圍於胼胝質中。待胼胝質瓦解後，小孢子才被釋放到花藥腔中，並行有絲分裂形成一個大的營養細胞與一個小的生殖細胞。 生殖細胞與營養細胞之間的壁瓦解後，生殖細胞周圍的環狀排列的油滴簇擁生殖細胞遊離至營養細胞的中心。接著，營養細胞中開始有大量的澱粉粒堆積。成熟的金銀花花粉為三溝孔粒，主要以儲存油滴與澱粉為主。 營養層細胞在減數分裂之前時期，其細胞壁即開始瓦解，自由小孢子時期才以原生質體的型式侵入小孢子間。在雙細胞時期，入侵的營養層細胞彼此之間界限不明顯，並開始侵入花粉外壁的空腔中。澱粉體時期，營養層的內容物急驟減少，只剩少數殘骸依附在花粉外壁上。最後，這些含有多醣類與脂質的營養層薄層覆蓋於成熟的花粉粒周圍。 小孢子四分體時期，先有臘梅糖堆積在小孢子細胞膜與胼胝質壁之間。原外壁再堆積在臘梅糖上。接著，小孢子分泌外壁物質，並堆積在臘梅糖上。在胼胝質瓦解前，外壁已有刺、頂蓋層、柱狀層與底層的堆積。自由小孢子時期，花粉繼續長大，外壁亦繼續增厚。雙細胞時期，花粉內壁開始形成。澱粉體時期，花粉外壁與內壁完成堆積。 本篇研究提供了金銀花小孢子形成與花粉壁發育的詳細過程，並支持花粉外壁的形成是由營養層與小孢子共同參與的理論，而非單獨由其中任何一者所貢獻。

The early floral development, anther tissue differentiation and the changes in ultrastructures of microsporocytes, tapetum and anther wall layer during the development of Lonicera japonica Thunb. pollen were studied with light and electron microscope. The ontogenic sequence of flower development was initiated by sepal and petal primodia, followed by stamen primodia, and consequently, the pistil primodium. Immediately after initiation of stamen primodium, it differentiated to form a four-microsporangiate anther. The anther wall layers were developed through dicotyledonous type and were composed of epidermis, endothecium, middle layer (one layer), and tapetum. The tapetum was dual origin. On pre-meiotic stage, callose wall was deposited around pollen mother cells with some cytoplasmic channels between pollen mother cells. The cytoplasmic channels retained until pollen mother cells have completed its meiosis. The cytokinesis of pollen mother cells in Lonicera japonica Thunb. was simultaneous. Once meiosis was started, the tetrahedral tetrads enclosed in the callose wall was formed. After callose wall was dissolved, four microspores were released into the anther loculus, where mitosis was taking place, producing a big vegetative cell and a small generative cell. The generative cell wall was then dissloved, and many oil drops accumulated around generative cell which sliped into the center of vegetative cell later. Before pollen grains maturation, a number of starch grains were appeared in them. The mature pollen grains were tri-colporate; oil drops and starch grains were the main storage materials. Tapetal cell wall began to degenerate on pre-meiotic stage, but tapetal cells invaded around microspore after free microspore stage. On bicellular stage, the border of tapetal cells was not evident and then the tapetal materials penetrated into cavity of bacula of pollen wall. At amyloplast stage, tapetal cell inclusions reduced as residues rapidly while lots of starch grains accumulated in pollen grain. At anthesis, the residuous tapetum as a film containing polysaccharides and lipid coated around the mature pollen grain. At the tetrad stage, fibrous glycocalyx was deposited between the callose wall and cell membrane of tetraspores. Primexine was accumulated on glycocalyx, on which exine material secreted by microspore was also accumulated. The accumulation of exine including spines, tectum, bacula and foot layer has been partially finished before callose was dissolved. The thickening of exine proceeded during free microspore stage and finished on amyloplast stage. While the formation of intine was first initiated at bicellular stage and finished at amyloplast stage as exine. The results of this study present a detailed information about the microsporogenesis and pollen wall development of Lonicera japonica Thunb., and ascertained that exine is derived from a combined contribution from tapetum and microspore, rather than from either of them.