Embryology of Cycas taitungensis

• Main Authors: Yi-Ming Lee, 李宜明
• Other Authors: Hann-Chung Lo
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/77115801432336727645

碩士 === 國立臺灣大學 === 森林環境暨資源學研究所 === 94 === Summary Cycas taitungensis is dioecism. Whole grows stage spending about one year. The male cone is conic shape. It mostly grows on the top of the plant lonely. It includes of several hundreds microsporophylls， arranging in twist shape. Several hundreds microsporangiums are gained on the dorsal site of microsporophyll. Each stipe grow up two to four microsporangiuns. Developing to mature form of male cone needs three months. Since early February, microsprophyte initial appear . In early March, microsporangium initial could be found on the dorsal site of microsporophyte. In early April, several times of mitosis of sporogenous cell in the microsporangium occur and several hundreds microspore mother-cells are bred. Microspore mother-cell goes on meiosis to develop tetrad. In middle April, microspore tetrads disparts to single nucleus microspore, than growth to two-nucleus pollen grain. From middle April to middle May, each mature pollen grain has three cells insite. There are tube cell, generative cell and prothallial cell. After middle May, mature microsporangium breaks down and pollens spread. In middle June, pollens on nucellus are budding. In late July, a body cell, a tube cell,a stalk cell and a prothallial cell are developed in thepollen tube on the top of nucellus. In middle August, the tip of pollen tube breaks. It releases materials consisting of sperm to archigonium chamber. The spermatozoids conjugate with ovum inside of archigonium to create zygote to complete impregnation. The mature female cone consists of several hundreds megasporophyte. The bottom of each megasporophyll comprises 2-6 ovules. Mature ovule has a sheet of integument. The space between integument is called micropyle. Integument covers nucellus. Space within nucellus is pollen-chamber. Female gametophyte locates at the centre of ovule. Micropylar end of female gametophyte has two to four archigoniums. Each archigonium contents of one ovum. Impregnation and development happen to them independently. Finally, only one mature embryo is formed. Female cone appears in middle February. Female cone initial comes from the top of plant. In early March, ovule initial appears under the epidermis of lateral basal site of megasporophyll. Ovule initial begins to protrusion in late March. Integument initial and nucellus initial are developed. The spaces between protruding integument build up micropyle spontaneously. In early April, centre of nucellus makes sporogenous cell. One of the sporogenous cell grows into a megaspore mother-cell in middle April. At that time, megaspore mother cell processes meiosis to form megaspore tetrad. Three of them degenerate to leave the one most nearest to chalaza end to form funtional megaspore. The funtional megaspore begin to go on karyokinesis to create free nucleus. In middle April, pollen chamber is build up in nucellus. In late May, the amount of free nucleus in female gametophyte is estimated to several thousands. Archigonium initial come appears on micropylar end of female gametophyll. Archigonium initial forms two primary neck cell and one central cell after abruption. In early June, central cell divides to a egg and a ventral-canal nucleus . Impregnation occurs in middle August. Proembryo starts to develop in late August. Germ matures in the coming February, including two cotyledons.