The study of male gametogenesis of Taiwania cryptomerioides Hayata

台灣杉（Taiwania cryptomerioides Hayata ）， 又名亞杉， 屬杉科 （Taxodiaceae）為台灣原產之針葉樹 種。採集台大實驗林溪頭營林區和有 水坑營林區之雄毬果之各個發育階 段，並於小孢子減數分裂時期分別以 醋酸洋紅檢測染色體，發現不孕性的 植株在花粉行減數分裂時，開始有不 正常的現象出現，應該是造成有水坑 花粉不孕的首要因素。正常的細胞具 有正常的染色體配對，但不正常的細 胞的部份染色體排列於中央，一些未 配對的染色體則散落在角落，這些未 配對的染色體，會形成一個個較小的 細胞核，當減數分裂結束後，這些減 數分裂不正常的細胞，多半無法完成 細胞質分裂，造成一個細胞中有多個 細胞核出現。 在經由Aniline blue 染色中，正常 的四分體有明顯且螢光強烈的胼胝質 堆積;不正常的四分體，明顯地表現 出胼胝質累積量不足的現象或幾乎沒 有胼胝質累積，且細胞質分裂亦未完 全，造成其中一個小孢子中有二個細 胞核或數個細胞核，且花粉外壁發育 不完全，在孢子囊開裂前這些不孕的 小孢子會急劇的崩解。由此研究得知 有水坑花粉不孕的原因可能為染色體 分離不全和胼胝質堆積不全所造成。The study of male gametogenesis on a conifer species endemic to Taiwan, Taiwania cryptomerioides Hayata (Taxodiaceae) was done in this article. With the aids of fluorescent and electron microscopic observations, the ontogenic processes in the fertile and sterile microsporangia are compared, using the samples collected from Chitou Experimental Forest and Yeou-Shoei-Keng Clonal Orchard of National Taiwan University, Nantou, Taiwan. Before meiosis, there was no significant difference in ultrastructure between the fertile and sterile microsporangia. Asynchronous pollen development with various tetrad forms may occur in the same microsporangium either of fertile or sterile strobili. As the meiotic steps proceeded, the irregular chromosomal and nuclear behavior was observed in the sterile microsporangia. This included: abnormal chromosome segregation and cytokiness, and nuclear fusion of the meiotic products. Moreover, a callose wall was observable in the fertile dyad and 2 tetrad, but not in the sterile one. After dissolution of the callose wall, the fertile microspores were released into the locule, while some sterile microspores still retained as tetrads or dyads with intertwining of exine walls in the proximal faces. As a result, there was no well-developed lamellated endexine, granulate ectexine, or intine in the sterile microspores. Eventually, the intracellular structures in sterile microspores were dramatically collapsed before anthesis. The present study shows that the abortion in pollen development and male gametogenesis is possibly attributed to the abnormal chromosome and the absence of the callose wall