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Title: | 維他命C調控文心蘭南茜品系開花誘導之研究 The ascorbate level mediates the floral initiation of Oncidium Gower ramsey |
Authors: | Chin-Hui Shen 沈金輝 |
Advisor: | 葉開溫 |
Keyword: | 文心蘭,開花調控,維他命C, Oncidium,Regulation of flowering time,Ascorbate, |
Publication Year : | 2010 |
Degree: | 博士 |
Abstract: | 維他命C是植物對抗環境逆境時所需的抗氧化劑,亦是多種植物荷爾蒙生合成酵素的輔助因子(cofactor),近年來的研究發現植物內生性維他命C的含量多寡具有顯著調控植物花期的功能。文心蘭在營養生長階段,假球莖會累積大量的維他命C,但在進入生殖生長階段時,其含量會明顯地下降。利用0.1M維他命C每日施加於文心蘭假球莖基部的花莖芽,結果發現可有效抑制開花相關基因LEAFY的表現量,並明顯延緩花莖生長,因此可知維他命C在文心蘭開花機制中扮演著抑制者的角色。維他命C含量生合成路徑如Smirnoff-Wheeler路徑與半乳醣醛酸路徑(galacturonate pathway)的基因在營養生長階段都有明顯的表現量,然而當進入生殖生長階段時,僅半乳醣醛酸路徑上的基因表現量有明顯的下降,分析其酵素活性亦呈現相同結果。再進一步轉殖半乳醣醛酸路徑中的果膠甲酯酶(pectin methylesterase)於阿拉伯芥中,發現轉殖植物亦會累積維他命C並且延遲開花。由此可知半乳糖醛酸路徑同時調控植物維他命C含量與開花生理。甲醇是半乳糖醛酸路徑的副產物,處理50mM甲醇於文心蘭擬原球體 protocorm like body,PLB )中發現可提高維他命C 相關基因的表現與維他命C含量。利用羥胺(hydroxylamine)與DPI分別抑制代謝甲醇產生過氧化氫的乙醇氧化酶(alcohol oxidase)與NADPH氧化酶,發現原本受甲醇誘導的維他命C相關基因表現量也會受到抑制,因此認為過氧化氫為植物誘導維他命C相關基因表現的重要次級傳遞訊
息者 (secondary messenger)。綜合這些結果可知文心蘭營養生長階段因具有較高活性的果膠甲酯酶可產生甲醇並進一步產生過氧化氫而誘導維他命C相關基因表現,此訊息傳遞之生理意義在於緩和該階段因為生長而累積的氧化逆境。而當植物細胞壁的果膠含量因為細胞延長而逐漸減少時,果膠甲酯酶活性降低,進而降低維他命C含量而促進開花基因的表現量,而使植物進入生殖生長階段。本論文主要在解析維他命C在文心蘭開花生理中扮演負調控的角色,而果膠甲酯酶則 為調控文心蘭不同生長階段維他命C含量重要的基因 We investigated the alteration in L-ascorbate (AsA, reduced form) content and the expression pattern of its related genes during the phase transition in Oncidium orchid. During the vegetative growth, a high hydrogen peroxide (H2O2) level was associated with a high content of the reduced form of AsA. At the bolting period, the AsA content and H2O2 level were greatly reduced in parallel with increased expression of OgLEAFY, the gene encoding a key transcription factor integrating different flowering-inducing pathways. This observation suggests that the reduced AsA content, resulted from the consumption of H2O2, is a prerequisite for mediating the phase transition in Oncidium. A survey of the AsA biosynthetic pathway revealed that the gene expressions and enzymatic activities of the relevant genes in the galacturonate (GalUA) pathway were markedly decreased at the bolting period, as compared with at the vegetative stage. However, the genes involved in the Smirnoff-Wheeler pathway retained a similar expression level in the two growth stages. Moreover, MeOH produced form the demethylation of pectin by pectin methylesterase (OgPME) also could trigger the synthesis of H2O2 and was effective in enhancing the expression of AsA-biosynthetic genes. It suggested that OgPME of the GalUA pathway was the pivotal gene in regulating AsA biosynthesis during the bolting period. Further elucidation by overexpressing OgPME in Arabidopsis demonstrated a considerable increase in AsA content, as well as a resulting delayed-flowering phenotype. We proposed a model in controlling the phase transition by ascorbate homeostasis which is associated with the functional role of PME in Oncidium. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/8693 |
Fulltext Rights: | 同意授權(全球公開) |
Appears in Collections: | 植物科學研究所 |
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