Comparisons of Floral Ontogeny and Microsporogenesis in Oncidium flexuosum Sims and Oncidium Gower Ramsey
| Autor: | Ming-Hsiang Chuang, 莊茗翔 |
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| Rok vydání: | 2003 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 91 There are more than 700 species of Oncidium (Orchidaceae) distributed in the region ranged from Brazil to Peru principally. The floral morphology and ontogeny of orchid are very different from the other angiosperms. Some hypotheses about the floral ontogeny of orchid have been proposed. However, quite a few questions about the issue are still needed to be elucidated. The microspore development of orchids is different from the other angiosperms. The orchids’ androecia produce hard pollinia instead of free pollens. The developmental processes of pollinia and free pollens are identical from the beginning to the tetrad stage. After tetrad stage, difference begins. In this study, we observed the floral and microspore development of Oncidium flexuosum Sims and its male-sterile line Oncidium Gower Ramsey with light microscopy, scanning electron microscopy, and transmitting electron microscopy. Based on the results of the above observation, we compared the two taxa’s floral and microspore develoment and tried to find out what caused O. Gower Ramsey to become male-sterile. Both the two above Oncidium taxa have similar process of floral development. The primodia of floral and bud were both differentiated from the inflorescence primodium. Then, six perianth primodia, including three calyx primodia, two petal primodia and one lip primodium, were differentiated from floral primodia. At last, the primodia of one fertile stamen, two vestige stamens, and three carpels were differentiated at the center of floral primodium. The stamens and carpels develop together into the column. A part of filament derived from vestige stamens becomes into the wings. The anther wall structure of Oncidium is very different from the other angiosperms. It includes one layer of epidermis, two or three layers of endothecium, two or three layers of middle layer, two layers of secretory tapetum. The microspore development of Oncidium is different from the other angiosperms, too. For example, O. flexuosum does not produce free spores. Instead, the outer pollinium tetrads and the inner pollinium tetrads were differentiated. The exine was formed outside of the layer of pollinium. The difference of the microspore development between O. flexuosum and O. Gower Ramsey are the earlier degeneration of tapetum at meiosis stage, the absence of exine, and the existence of mitochondria and plastids in some generative cell, etc. We speculate the above difference might be the reason of the male-sterility of O. Gower Ramsey. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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