不同地區之白茅對鹽分及淹水之生理生態反應

Abstract

在臺灣白茅（Imperata cylindrica var. major）是一種很常見的植物，一屬一種，族群分佈於各地。過去的研究，指出竹圍紅樹林族群與臺灣內陸的其他族群在形態、解剖、DNA結構上有顯著的不同，故竹圍的族群形成一個較特別的生態種（ecotype），然而其適應當地紅樹林環境的機制不明。 前人研究指出植物體之酒精去氫酵素ADH（alcohol dehydrogenase）與淹水有關，而植物體內脯胺酸（proline）及鈉含量與鹽分有關。為探究白茅之酒精去氫酵素、脯胺酸和鈉與鹽分及淹水之關係，作者選取竹圍白茅為研究對象，並比較沙崙及內湖白茅。對採自上述地區之白茅分析其於野外當地環境下葉中酒精去氫酵素的活性、脯胺酸及根、莖和葉中鈉含量。結果顯示竹圍白茅葉中之酒精去氫酵素活性最高，與淹水相關。並於大潮日中午赴竹圍紅樹林於淹水前後採取白茅葉片分析酒精去氫酵素活性之變化，結果顯示淹水後酒精去氫酵素活性升高，此亦與淹水相關。葉中之脯胺酸與根、莖中之鈉含量最高，與土壤鹽度相關。因此作者提出假說，認為竹圍白茅葉中之酒精去氫酵素、脯胺酸及根、莖中之鈉與其對淹水及鹽分之適應有關。 為了驗證酒精去氫酵素、脯胺酸及鈉確實參與竹圍白茅對淹水及鹽分之適應機制，作者設計水耕實驗，分別對各地區白茅做淹水及鹽分之處理，以觀淹水及鹽分對各地區白茅之影響。結果顯示竹圍白茅能生長在1％ NaCl鹽水中，淹水加速其生長速率，並且生長不受到抑制。其他地區白茅經淹水及鹽分處理後生長皆受到抑制。 進一步分析各地區白茅幼苗之酒精去氫酵素、脯胺酸及鈉對淹水及鹽分之反應，結果顯示淹水處理三個月後竹圍及沙崙白茅幼苗葉中酒精去氫酵素活性皆升高，但竹圍白茅比較高。淹水處理三天後竹圍白茅幼苗葉中酒精去氫酵素同功酵素活性大增，而沙崙白茅則活性不變。 以不同濃度鹽分處理四天後各族群之白茅幼苗葉中皆累積大量脯胺酸，但竹圍族群累積量比較高。以不同濃度鹽分處理八天後各地區之白茅幼苗根及莖中皆會累積大量鈉，但竹圍白茅累積量顯著比較高。以不同濃度鹽分處理二個月後各地區之白茅幼苗根及莖中皆會累積大量鈉，但竹圍白茅累積量亦顯著比較高。 由於在溫室內水耕試驗中白茅之酒精去氫酵素、脯胺酸及鈉對淹水及鹽分之生理反應與野外所得結果是吻合的，證實竹圍白茅葉中酒精去氫酵素確實與其對淹水之適應相關，而葉中累積之脯胺酸及根、莖中累積之鈉則與其對鹽分之適應相關。

Imperata cylindrica var. major, one of the commonest weeds, is widespread and distributed in Taiwan area. A previous study indicated that Chuwei population was grouped as an ecotype based on RAPD and anatomic data. The mechanism of physiological adaptation nevertheless remained unknown. Previous studies indicated that plant ADH (alcohol dehydrogenase) was involved in flooding. Plant proline and sodium contents were involved in saline. In order to identify the relationships of ADH, proline and sodium with flooding and saline, the Chuwei population as well as others from different locations were sampled. The ADH activity and proline content of leaf tissue and sodium content of roots, stems and leaves under native environment were analyzed. The I. cylindrica from Chuwei appeared to have the highest level of ADH activity, which may be respondent to flooding. In addition, the proline content of I. cylindrica from Chuwei is relatively higher than that of from others. The high level of proline may be ascribed to the concentrated salinity in soil. To clearify roles of ADH in relation to flooding and of proline and sodium in relation to saline, water culture experiment was conducted in greenhouse with flooding and salt treatment. I. cylindrica from Chuwei appeared to be tolerant of high salt with 1% NaCl coentration. Flooding may even have some effect on facilitating plant growth. In contrast, the growth of others was inhibited under saline and flooding treatment. After three months treatment of flooding and salinity on seedlings, the ADH level in leaf tissue of I. cylindrica from both Chuwei and Sallun becomed higher. Nevertheless, they responded differently. The ADH level increased dramatically in I. cylindrica from Chuwei after three-month flooding treatment. While the Adh level remained unaltered in I. cylindrica from Sallun. The salinity treatment with different concentrations on seedlings led to the accumulation of proline in leaf tissue and sodium in root and stem. The I. cylindrica from Chuwei appeared to have the highest level of sodium and proline after eight days as well as two months of treatment compared to others. Thus, there is correlation between ADH and adaptation to flooding of I. cylindrica from Chuwei. Also, there is correlation between proline and sodium and adaptation to saline of I. cylindrica from Chuwei.