許多重金屬是植物所需要，但是過量重金屬限制了許多農耕的土地。在台灣，水稻是主要的糧食，而台灣水稻也有被重金屬污染的紀錄。這些污染直接的限制了該土地中植物的生長和生物的存活，間接的影響人類的生活。鋅(Zn)是重金屬，也是植物生長所必須，但是過量的鋅對植物是有毒的，能導致生長的抑制、細胞死亡、細胞正常運作破壞等現象。這些現象的發生有部份是細胞主動產生的。細胞會先接收到外來的訊息，經過一連串的訊息傳遞而啟動許多反應來調節這些細胞主動產生的現象。本研究中，我們主要探討鋅和水稻之間的關係。包含：過量的鋅造成水稻根部和莖部的生長抑制情形、根尖的細胞死亡情形及細胞死亡可能的訊息傳導路徑、細胞內訊息傳遞物質：MAPK之活化情形、以及不同重金屬之間活化水稻根尖細胞MAPK的差異情形。
　　結果顯示：過量的鋅能抑制水稻根部和莖部的生長，也能誘導水稻根尖細胞死亡。鋅誘導水稻根尖細胞死亡可被細胞內鈣離子感應蛋白(sensor)、蛋白質激酶(protein kinase)、蛋白質去磷酸酶 (protein phosphatase)、蛋白質酶(protease)、ROS、粒線體等抑制劑所抑制；外加鈣離子、H2O2和細胞內的一氧化氮也能影響鋅所誘導的細胞死亡。3種tyrosine phosphatase：鋅、釩(V)和PAO(phenylarsine oxide)也都能抑制水稻根部和莖部的生長。PAO和釩能抑制鋅所誘導水稻根尖細胞死亡，但是，鋅所誘導的生長抑制卻沒有因為同時再外加處理PAO或釩而恢復。 細胞內，鋅能快速誘導31 kDa和42 kDa MAPK的TEY或TDY motif磷酸化，但是只有42 kDa MAPK被活化。MAPK蛋白質的活化和磷酸化作用在根尖比根基部還明顯，這可能是由於蛋白質量的差異所造成。並且猜測42 kDa MAPK磷酸化的條紋可能包含了OsMAPK2在內，而31 kDa 磷酸化條紋的MAPK可能是OsMAPK2剪切上的變異型(alternative splicing)，外加protease抑制劑能抑制31 kDa MAPK蛋白質的磷酸化。鋅、雙氧水(H2O2)、銅(Cu)和鎘(Cd)等逆境能誘導細胞42 kDa MAPK的TEY或TDY motif磷酸化，但是只有鋅能明顯誘導31 kDa MAPK蛋白質磷酸化。鋅、銅和H2O2逆境導致的細胞死亡程度並不等於42 kDa MAPK磷酸化的量。鋅誘導的細胞死亡可能經由MEK路徑，但是我們所偵測到的MAPK並沒有發現和細胞死亡有關。Cantharidin能增加鋅所誘導MAPK蛋白質的活化、但是抑制鎘所誘導MAPK蛋白質的活化。
　　由這些結果推測：鋅能抑制水稻生長和導致細胞死亡。這些現象可經由細胞的訊息傳遞來導致，也可被細胞外的一些物質所影響。鋅也能誘導細胞內42 kDa MAPK的活化，以及特有的31 kDa MAPK活化區磷酸化但不活化。鋅逆境導致的細胞死亡和所偵測到的MAPK活性並沒相關。不同重金屬誘導MAPK活化的路徑並不一樣。

　　Many heavy metals are necessary for plant, but excess heavy metals restrict the field of agriculture. Rice is a main cereal in Taiwan, and is polluted by heavy metals at one time. The pollution directly limits plant growth and survive of organisms, but also indirectly effect life of human. Zn (Zinc) is also a heavy metal and essential for the plant growth. Excess Zn is toxic for plants. It can cause plant growth retardation, inhibit physiological process and induce cell death. Some of these processes are active by cells themselves. These processes provoked by excess Zn are regulated by intercellular signal transduction. Here, we study the effect of excess Zn in rice root-tip, including cell death and the signaling pathway that leads to cell death in root-tip, the inhibition of the root growth, the activation of MAPKs induced by Zn in rice root-tip, and the difference in the active pathways of MAPKs induced by various heavy metal.
　　In rice root, we have shown that excess Zn can cause the inhibition of the growth as well as cell death. Pre-treatment of rice roots with calmodulin inhibitor W7, PI3K inhibitors LY294002 and wortmannin, protein phosphatase inhibitors cantharidin, endothall, PAO and sodium orthovanadate , protease inhibitor PMSF, MEK inhibitor PD098059, catalase inhibitor 3-AT, ROS inhibitor sodium benzoate, mitochondrial complexⅠinhibitor rotenone was able to effectively prevent cell death and CaCl2, EGTA, LaCl2, H2O2, SNP, PTIO effect Zn-induced cell death. We suggest that calmodulin or CDPK, PI3K, protein phosphatase, protease, MAPK pathway, ROS, mitochondrial electron transport chain, extracellular calcium ions, H2O2, NO are probably involved in zinc-induced cell death of rice root-tip cells. The other tyrosine phosphatase, PAO and sodium orthovanadate, can also inhibit rice root growth, suggest that tyrosine phosphatase can inhibit the growth of rice root-tip. Although pre-treatment with PAO and sodium orthovanadate could inhibit cell death of rice root induced by zinc, co-treatment with PAO and sodium orthovanadate did not recover the inhibition of rice root growth induced by zinc. Zn rapidly induced TEY or TDY motif phosphorylation of 31 kDa and 42 kDa MAPKs, but only 42 kDa MAPK was activated. TEY or TDY motif phosphorylation of 31 kDa and 42 kDa MAPKs in rice root-tip is more obvious than root-base. This difference may come from the different quantity of the proteins. We also suggest the band of the active 42 kDa MAPKs included OsMAPK2 and the band of the activated 31 kDa MAPK maybe alternative splicing of OsMAPK2. Treatment with Zn, H2O2, Cd and Cu all induced cellular TEY or TDY motif phosphorylation of 42 kDa MAPKs, but only Zn could induce TEY or TDY motif phosphorylation of 31 kDa MAPK. The quantities of the cell death caused by Zn, H2O2 and Cu are not equal to the quantities of 42 kDa MAPK phosphorylation. MAPK pathway probably involved in zinc-induced cell death of rice root-tip cells, but we found that not MAPK which was detected is involved in zinc-induced cell death. Cantharidin increased the activity of 42 kDa MAPK induced by Zn, but decreased the activity of 42 kDa MAPK induced by Cd.

　　In rice, we suggest that Zn inhibited the growth and caused cell death in rice root. The process of cell death was caused by cellular signal transduction and also effected by extracellular material. Zn could induce the activation and TEY or TDY motif phosphorylation of 42 kDa MAPK and TEY or TDY motif phosphorylation of special 31 kDa MAPK, which had no activity. The cell death caused by zinc was not involved in the activity of MAPK which we detected. The activities of MAPK pathways are different with distinct heavy metal.

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