探討銅離子進入金魚藻的路徑

Study on the route of entry of copper ions in Ceratophyllum demersum L.

謝秀芬

指導教授 ： 徐邦達

國立清華大學/生命科學院/生物資訊與結構生物研究所/碩士(2010年)

https://doi.org/10.6843/NTHU.2010.00231

摘要

重金屬植生整治是利用具有重金屬累積能力的植物，去吸收並蓄積環境中過量的重金屬污染。由於經濟實用以及價格低廉，這項技術在近幾年快速發展。許多水生植物具有吸收且累積重金屬的能力。深入瞭解重金屬的吸收路徑，可以幫助增進植生整治的功能。金魚藻是一種沉水草本植物，其根部已經退化，能懸浮養殖於水體中，並且具有吸收以及累積重金屬的能力。本研究的目的主要是利用葉綠素螢光儀，以及感應耦合電漿質譜儀去探討銅離子進入金魚藻植物體的路徑。
從葉綠素螢光以及ROS偵測的實驗，我們發現葉片是銅離子的主要攻擊目標。葉綠素螢光的圖像則顯現銅所造成的抑制是從葉尖開始逐漸向葉基推進。質譜儀的測量也顯示有高濃度的銅堆積於葉片中，其中又以葉片尖端含量最高；莖部的銅含量則幾乎不變。我們也發現，ATPase抑制劑以及蛋白質合成抑制劑都可以使銅的累積量以及對光合作用的抑制現象明顯下降。此外，從顯微鏡的觀察，我們也發現過量的銅離子會破壞細胞間的黏著，使葉片脫落。
綜合以上，我們可以知道銅離子可能是經由位於葉尖細胞膜上的ATPase進入植株，但在葉片與莖之間的環狀區域卻有阻隔銅離子入侵的能力，這種阻隔會鬆動該區域內細胞間的黏著而使葉片脫落。這似乎是一種保護莖和頂芽的機制，避免過多的銅離子進入植物的莖主體。

關鍵字

銅離子 ； 金魚藻 ； 光合作用 ； 葉綠素螢光 ； 質譜儀

並列摘要

The phytoremediation of metals, with an increasing development recently, is a cost-effective green technology based on the use of metal-accumulating plants to remove toxic metals. Many aquatic plants are reported to bioconcentrate heavy metals in natural water areas as well as upon exposure to wastewater. A further understanding of metal uptake and entry by aquatic plants can enhance the performance of metal removal from polluted water. Coontail (Ceratophyllum demersum L.) is a submerged, floating rootless macrophyte, which can accumulate heavy metals. In this study, entry of copper ions into coontail plants was investigated using chlorophyll fluorometer and ICP-MS.
From the chlorophyll fluorescence and ROS detection experiments, it was found that leaf is the major site attacked by copper ions. Besides, chlorophyll fluorescence image indicated that the fluorescence signal decayed starting from the apical to the basal part of leaves. The result of ICP-MS analysis confirmed that the highest copper accumulation was in the leaf, especially the tip part, while the copper content in stem remained unchanged after Cu2+ treatment. We also found that both ATPase inhibitor and protein synthesis inhibitor could alleviate the inhibition of photosynthesis and decrease copper uptake. Moreover, microscopic observation revealed that excess copper could loose binding between cell walls at a zone closed to the base of leaves, causing defoliation.
We thus suggest that copper ions might be taken up by binding to the ATPase located in the apical part of leaf. However, there seems to be a barrier at the leaf base that prevents translocation of copper ions to stem. The impediment could decrease the interaction between cell walls, followed by leaf detachment. It may represent a protective response of the plants to prevent further uptake of copper ions.

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