- 學位論文
水稻幼苗鎘逆境生理之研究：鎂或熱休克之效應
Studies on the Cd stress of Rice Seedlings:Effects of Magnesium or Heat Shock
摘要
本論文係以水稻品種台中在來1號 (Oryza sativa L. cv. Taichung Native 1, TN1) 為材料，探討 (一) 缺鎂狀況下鎘對水稻幼苗之影響； (二) 熱休克處理與鎘處理對水稻幼苗葉片OsGR與OsAPX基因表現之影響。 缺鎂處理之水稻幼苗，其地上部、第二片葉片及根部之鎂含量明顯下降，但不影響蛋白質及葉綠素含量。以OsRab16A偵測ABA表現，缺鎂導致葉片Rab16A基因明顯表現，進一步以ELISA偵測ABA含量，缺鎂亦明顯使ABA含量增加。缺鎂葉片內H2O2以及ascorbate (ASC)含量增加，但不影響GSH含量。缺鎂同時也使抗氧化酵素superoxide dismutase (SOD)、glutathione reductase (GR)、ascorbate peroxidase (APX)以及catalase (CAT)活性增加。取自缺鎂幼苗之切離葉片可克服巴拉刈(paraquat, PQ)與鎘所引起之毒害。缺鎂幼苗亦可克服後續鎘處理所產生之毒害。不論是取自缺鎂幼苗之切離葉片或缺鎂幼苗，經鎘處理後，其葉片或根部鎘含量明顯增加，顯示缺鎂幼苗可克服後續鎘逆境毒害，不是藉由降低鎘之吸收。缺鎂幼苗根部經鎘處理後，降低鐵與鋅之含量，促進鐵轉運蛋白基因 (iron-regulated transporter, OsIRT1)及鋅轉運蛋白基因 (Zn-regulated transporter, iron (Fe)-regulated transporter-like protein, OsZIP1、OsZIP3)表現。此說明，水稻幼苗缺鎂後，鎘可能藉由鐵與鋅轉運通道輸送鎘，而使鎘吸收增加。 水稻幼苗經HS（45℃黑暗下，3小時）處理可降低後續鎘毒害。HS處理可誘導OsAPX2表現，同時增加GR與APX活性。HS亦可明顯誘導Oshsp17.3基因之表現。HS處理可導致H2O2累積，但其累積發生在OsAPX2與Oshsp17.3基因表現之後，此說明 HS處理所誘導之OsAPX2與Oshsp17.3基因表現並非受H2O2所調控。水稻幼苗經鎘處理可誘導葉片GR與APX活性上升，但不影響OsGR與OsAPX基因表現。因此，鎘處理所誘導之水稻幼苗葉片GR與APX活性上升，似乎與OsGR與OsAPX基因之轉錄無關。
並列摘要
Rice (Oryza sativa L. cv. Taichung Native 1) seedlings were used to investigate (a) the effect of magnesium (Mg) deficiency on Cd toxicity and (b) the effect of heat shock (HS, 45℃, 3h, dark) and Cd treatment on the expression of OsGR and OsAPX genes. The Mg deficiency treatment caused reduction in Mg concentration in shoots, second leaves, and roots, but had no effect on the content of chlorophyll and protein. The expression of OsRab16A and the accumulation of ABA were observed to be increased in Mg-deficient leaves. Rice seedlings grown under Mg deficiency conditions showed an increase in the contents of hydrogen peroxide and ascorbate, as well as the activities of SOD, APX, GR and CAT. Mg deficiency enhanced the tolerance of leaves or seedlings to subsequent Cd and/or paraquat (PQ) stress. However, Cd concentration could be increased in Mg-deficient seedlings or detached leaves than those in Mg-sufficient seedlings or detached leaves. Cd treatment resulted in a decrease in Fe and Zn concentrations and an increase in OsIRT1, OsZIP1 and OsZIP3 expression under Mg deficiency conditions, suggesting that iron-regulated and zinc transporters can be used for enhancing Cd uptake in roots of rice seedling grown under Mg deficiency conditions. Rice seedlings pretreated with HS resulted in protection against subsequent of Cd stress. HS up-regulated the expression OsAPX2 and Oshsp17.3 and the activities of GR and APX. The expression of OsAPX2 and Oshsp17.3 induced by HS prior to the accumulation of H2O2. It appears that H2O2 is not involved in the regulation of HS-induced OsAPX2 and Oshsp17.3 expression. Cd treatment resulted in an increase in GR and APX activity, but had no effect on OsGR and OsAPX expression. Thus, the regulation of Cd-induced GR and APX activity is not under transcriptional control.