中文摘要
生物性和非生物性逆境，如致病物的感染、熱、乾旱、鹽害以及過量的重金屬，會影響植物生長及代謝。植物會發展出耐受性來對抗各種逆境，而交互耐受性是指當生物體發展某種逆境的耐受性時，對其他的逆境也產生相同的耐受性。預先使用適度的熱處理已知可以從重金屬逆境中保護生物細胞，然而目前對熱逆境是利用哪些訊息傳遞分子與重金屬逆境作連結尚未明瞭。因此，本論文將把目標定在尋找出參與在熱所誘導的重金屬耐受性之中的訊息傳遞分子。在我們的研究中，預先使用熱處理水稻根部細胞可以降低由銅所引起的細胞死亡及活性氧化物 (reactive oxygen species, ROS)的產生，若以亞胺環己酮 (cycloheximide)，一種蛋白質合成抑制劑做前處理，結果發現會阻礙熱所誘導的保護作用，從這個結果推論出由熱處理所誘導的保護作用必須要重新合成蛋白質。實驗室早期的實驗結果已指出銅會引起MAPK (mitogen-activated protein kinase) 大量活化，除此之外，鎳也能夠大量增加MAPK的活性。然而，我們發現一小時的熱處理能夠抑制銅和鎳所誘發的MAPK活性。另外，在in-vitro 激活脢活性分析中，直接加入純化過的Hsp72就能夠降低銅所誘發的MAPK活性。綜合以上研究結果，我們推論預先的熱處理能夠提高水稻對重金屬的耐受性，而Hsp72對MAPK活性的抑制效果能夠幫助重金屬耐受性的增加，而是否有其他分子參與在交互耐受性的機制中，則有待進一步研究探討。

Abstract
Environmental stresses including biotic and abiotic stresses, such as pathogen infection, heat, drought, salinity, and heavy metals, are important factors that affect growth and metabolism of plants. Plants developed tolerances to respond to multiple environmental stresses. Cross tolerance is the phenomenon by which a plant resistance to a stress results in resistance to another form of stress. Pretreatment with nonlethal heat shock is known to protect cells from heavy metal stress. However, very little is known about how heat stress interacts with heavy metal stresses, and which are the signalling components that interrelate the response. The aim of this study was to search for the signaling components involved in heat induced metaltolerance. In our investigation, preheating attenuates copper (Cu) induced cell death and accumulation of reactive oxygen species (ROS) in rice root cells. Pre-treatment of rice roots with protein synthesis inhibitor, cyclohexiamide (CHX) is able to effectively blocked heat shock protection. This result suggests that protection by heat shock was dependent on protein de novo synthesis. Our prior work showed that Cu elicited a remarkable increase in mitogen-activated protein kinase (MAPK) activities. In addition, Ni also induces MAPK activation in rice root cells. Here, we found that MAPKs activities are down regulated in response to Cu and Ni treatment after 1 hour preheating. Moreover, addition of a purified recombinant HSP72 directly down- regulates Cu-induced MAPK activities in in-vitro kinase assay. Thus, we suggest that preheating enhances tolerance to heavy metal stress in rice and inhibitory effect of HSP72 on MAPKs appears to be a contributor to increased metaltolerance. These results provide for some information for further studies on the mechanisms of cross tolerance in plants.

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