植物根部是首先反應重金屬侵害的植物器官，然而目前的研究多著重於植物地上部生理狀態與重金屬的
累積，較少有根部反應之生理研究，此可能是新舊根混合而取樣不易，或取樣時間過長而失去精確性。本研究採全盆(菸草與栽培介質)移植於石英砂盆之混合砂耕系統，嘗試建立可取得新根之研究平臺，並比較銅逆境下栽培介質與石英砂內菸草根部的生理反應。生理測試包括：根部水分、游離型脯胺酸、鍵結型脯胺酸、離層酸等之含量。結果顯示，新根 (石英砂內的新生根) 的水分含量高於混合根 (栽培介質內的新舊根)，但二者均不受銅處理影響。新根的游離脯胺酸含量原高於混合根，但於銅處理下二者均下降至同一含量。新根的鍵結型脯胺酸含量原與混合根相等，且二者均不受銅處理影響。由於新根之高水分與高脯胺酸含量皆符合新生根之特性，因此利用砂耕系統取得新根，適合進行根部生理研究。遂進行銅逆境下菸草根部離層酸的測定，結果顯示新根的含量原高於混合根，但於銅處理下新根之離層酸顯著增加，混合根則不受影響。本研究結論，利用混合砂耕系統發現銅逆境下菸草新根根部水分與鍵結型脯胺酸含量不受影響，其游離型脯胺酸含量下降，但離層酸含量增加。

Plant roots are the first organs to react to heavy metal stress. There are many studies investigating the effect of heavy metal accumulation in plant shoots but only few on plant roots. It might be because of the difficulties of separating new and old roots or time consuming of root sampling. In this study, the mixsand culture where the whole pot (tobacco and soil) was transferred to a bigger pot filled with sea sand was developed to provide an easy and fast method for studying the reaction of new roots against copper (Cu) stress. The measurement included the water content, free and conjugated proline and abscisic acid (ABA). The results showed that the water content of new roots (collected in sand) was higher than that of mixed root (collected in soil), but both were unaffected under Cu stress. The content of free proline was higher in new roots than in mixed roots, but both were down regulated to similar level under Cu stress. The conjugated proline content was the same in the new and mixed roots and both were unaffected under Cu stress. The higher water and free proline content in the roots collected from sand agree with the general characteristics of new roots, suggesting these root samples were suitable for physiological study on new roots. Furthermore, the analysis of ABA content of tobacco root under Cu stress was conducted. The results showed the ABA content was higher in new roots than in mixed roots under normal condition. Under Cu stress, the ABA content increased in new roots, but unaffected in mixed roots. In summary, this study revealed that the water and conjugated proline content of tobacco new roots were unaffected, but the free proline content decreased while the ABA content increased under Cu stress.