汞已經成為農業用地中導致污染的重要有毒重金屬污染源之ㄧ，汞的累積在植物中會從許多分子的層面干擾其功能進而抑制植物的生長及發育，但其機轉目前尚未釐清。本研究主要探討汞逆境下，水稻根部其分子、生化及蛋白質體的變化。在根部汞濃度逐漸增加的情形下，根的生長素率下降，但活性含氧物(ROS)、丙二醛(MDA)的含量以及脂氧合酶(lipoxygenase)的活性卻顯著增加。研究發現在汞逆境下，植物根尖部位的榖胱苷肽(glutathione)總含量、超氧化物歧化酶(SOD)、植物抗壞血酸過氧化物酶(APX)、過氧化氫酶(CAT)以及過氧化酶(POD)的活性會隨時間而有變化，二維電泳法顯示出以汞處理根尖後共有25個不同蛋白質的表現，其中14個蛋白質的點顯示為正調控而11個蛋白質的點顯示為負調控，以ESI-MS/MS法鑑定出的這些不同的表現蛋白參與包含氧化還原作用、賀爾蒙的恒定、chaperone活性、代謝及轉錄作用的調節等的分子功能。本研究結果可以提供對植物在汞逆境下分子基礎反應的新觀點。此外，本研究亦完成水稻transcriptome在短時間暴露於汞逆境下的大量分析，包含細胞壁形成、化學性的去毒性作用、次級代謝、訊息傳遞以及生命性的逆境基因反應。在汞處理過的水稻根部其基因表現的資料顯示出訊息的正調節、ethylene的生合成以及生物素的去活化作用。此外，汞逆境也會產生誘發鈣的累積以及活化有絲分裂原激活蛋白質的激酶的現象。這些現象回應汞逆境所產生的相關基因改變並進一步的幫助我們了解在水稻於汞逆境下的分子機轉。

Mercury (Hg) has become one of the major causes of toxic metal pollution in agricultural lands. Accumulation of mercury (Hg) in plants disrupts many cellular-level functions and inhibits growth and development, but the mechanism is not fully understood. We investigated cellular, biochemical and proteomic changes in rice roots under Hg stress. Root growth rate was decreased and Hg, reactive oxygen species (ROS), and malondialdehyde (MDA) content and lipoxygenase activity were increased significantly with increasing Hg concentration in roots. Our research showed a time-dependent alteration in total glutathione content and enzymatic activity of superoxide dismutase (SOD), ascorbate peroxides (APX), catalase (CAT) and peroxidase (POD) during Hg stress. 2-D electrophoresis revealed differential expression of 25 spots with Hg treatment of roots: 14 spots were up-regulated and 11 spots down-regulated. These differentially expressed proteins were identified by ESI-MS/MS to be involved in cellular functions including redox and hormone homeostasis, chaperone activity, metabolism, and transcription regulation. These results may provide new insights into the molecular basis of the Hg stress response in plants. We also performed a large-scale analysis of the rice transcriptome during Hg stress. Genes induced with short-term exposure represented functional categories of cell-wall formation, chemical detoxification, secondary metabolism, signal transduction and abiotic stress response. Gene expression profiling indicated upregulation of signaling and biosynthesis of ethylene and inactivation of cytokinins in Hg-treated rice roots. In addition, Hg induced calcium accumulation and activated mitogen-activated protein kinase. Further characterization of the identified Hg-responsive genes may be helpful for a better understanding of the mechanisms of Hg in plants.

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