过渡金属元素如Cu、Zn和Mn对植物来说是必需的，其它的过渡金属元素如Cd和Pb则是有毒的，当在植物体内处于高浓度时，即使是必需的过渡金属元素也是有毒的。在拟南芥中，HMA2和HMA4主要在维管系统表达，在Zn和Cd从根部到地上部分的转运中起重要作用。软件预测结果表明AtHMA4在C-末端有一个长的细胞质中的结构域，该结构域可能具有调节功能。在酵母体内单独表达AtHMA4的游离C-末端能提高酵母的Cd耐受性。然而，植物HMA4的游离长C-末端的生理功能尚不清楚。为了探究BjHMA4转运蛋白C-末端结构域的位置和功能，本项目拟在前期工作基础上，利用C-末端缺失和单碱基突变技术研究印度芥菜BjHMA4 突变体的底物专一性和转运活性。具体来讲，本研究的目标是确定BjHMA4的C-末端缺失和单碱基突变会对其生理功能造成何种影响，并确定BjHMA4突变体在将来用于生物强化和植物修复的可能性。

Transition metals such as Cu, Zn and Mn are essential for plants. Other transition metals such as Cd and Pb are toxic, and even the essential transition metals can be poisonous at elevated levels. In Arabidopsis thaliana, HMA2 and HMA4 are expressed in the vascular system and are important for the translocation of Zn and Cd from roots to shoots. AtHMA4 is predicted to possess a long cytoplasmic domain at the C-terminus that may play regulatory roles. The C-terminal region expressed alone in yeast conferred tolerance to Cd. However, the functional role of the long cytoplasmic C-terminus of plant HMA4 has not been established. To explore the position and function of BjHMA4 transporter C-terminal domain, based on our previous experimental results, we will focus on the substrate specificity and activity rate of various mutant version of BjHMA4 transporting protein by the truncation of the C-terminal sequence and a single base-pair mutation. In particular, the aim was to determine whether C-terminal truncation and mutation of BjHMA4 had any effect on its function in plant and to determine whether the HMA4 mutant versions had potential in future biofortification and phytoremediation strategies.