超积累植物东南景天根系细胞壁多糖修饰对镉积累的影响及机制

Cell wall is the first barrier for any ions to enter the cell, which play a key role in resisting metal toxicity in plant. Although extensive efforts have been directed to uncover the mechanisms of metal-induced cell wall modification in tolerant plant, little is known concerning the structural modifications of root cell walls in hyperaccumulator. Sedum alfredii (Crassulaceae), a species native to China, has been characterized as a Zn/Cd cohyperaccumulator. To date, studies on the mechanism of metal tolerance and hyperaccumulation of S. alfredii were mainly focused on the uptake and subcellular distribution characteristics, while no information is available about the root cell wall polysaccharide modifications of this plant. In this project, hydroponic experiments, as well as new techniques such as stable isotope tracing, LA-ICP-MS, scanning ion-selected electrode technique (SIET), synchrotron radiation techniques, immunofluorescence and RT-PCR were used to (1) investigate the compartmention of Cd in root cell and it efflux to the xylem; (2) investigate the polysaccharide content (cellulose, hemicellulose and pectin) of root cell walls of S. alfredii tereated with different Cd and Cd content in different components of root cell walls; (3) study the influence of Cd on the components of root cell wall pectin, as well was the degree of pectin methylation; (4) investigate the influence of Cd on the activity of XET and XEH, as well as the XTH gene expression in the root cell wall of S. alfredii. Results of this project will contribute to reveal the polysaccharides modification features of root cell wall and its influence on cadmium accumulation and will help to understand the mechanisms of metal hyperaccumulation in S. alfredii and will optimize the management practices for maximum metal phytoextraction, and it is of great importance for protecting soil ecosystem health.

细胞壁是金属离子进入细胞质的第一道屏障，在植物抵抗金属离子毒害的过程中发挥着重要作用。尽管围绕植物金属诱导的细胞壁多糖修饰机制做了大量工作，然而目前有关超积累植物根系细胞壁多糖修饰特征还未见报道，其在植物重金属超积累中的作用机制也不清楚。该项目以镉超积累植物东南景天（Sedum alfredii）为材料，综合应用稳定同位素示踪、LA-ICP-MS、非损伤微测技术、同步辐射、免疫荧光及分子生物学等技术手段，研究东南景天根系镉的区隔特征及其向木质部的转运特点，分析东南景天根系细胞壁多糖组成及其对镉的结合特性，研究镉对东南景天根系细胞壁果胶多糖组成、甲基化程度的影响，以及镉对根系细胞壁XET和XEH活性、XTH基因表达水平的影响，揭示超积累植物东南景天根系细胞壁多糖修饰特征及其对镉积累的影响及机制。研究结果对于揭示超积累植物重金属超积累机理、完善植物修复理论具有重要意义。

项目以镉超积累植物东南景天（Sedum alfredii）为材料，综合应用稳定同位素示踪、LA-ICP-MS、非损伤微测技术、同步辐射、GC-MS、FTIR、SEM-EDS、NMR以及免疫荧光及分子生物学等技术手段，综合揭示了超积累植物东南景天根系细胞壁多糖修饰特征及其对镉积累的影响及机制。研究结果对于揭示超积累植物重金属超积累机理、完善植物修复理论具有重要意义。取得的主要研究成果如下：.①阐明两种生态型东南景天根系细胞壁对镉的区隔特征及其向木质部的再转运特点，超积累生态型地上部转移的Cd为非超积累生态型的5倍，说明超积累生态型东南景天根系积累的镉更容易向地上部转移利用；.②明确两种生态型东南景天根系细胞壁多糖组成差异及对镉吸附解吸特点，发现非超积累生态型东南景天根系细胞壁所积累的镉量远大于超积累生态型根细胞壁，进一步证明吸附于超积累生态型东南景天根系细胞壁上的大部分镉结合松散，容易被解吸下来。.③明确了东南景天细胞壁代谢关键酶活性及基因表达水平对镉处理的响应特点，发现东南景天根系质外体空间的镉主要和细胞壁中的果胶结合，而根系细胞壁果胶修饰参与了质外体镉的固定和再利用调控；.④证实了超积累型东南景天根系部分镉能通过质外体途径进入木质部向地上部转移，明确了根尖和侧根是超积累型东南景天的重要入口，质外体屏障发育特点及其对镉胁迫的响应特征；.⑤阐明非超积累型中与木葡聚糖合成相关基因表达的上调及由此调控的酶活性增强，造成了其根系细胞壁中半纤维素含量的升高，又由于半纤维素中存在大量可以结合镉离子的官能团，从而导致镉离子紧密结合在根系中，而超积累型中半纤维素的响应完全相反，所以大量镉离子可以向木质部装载，在地上部超积累。.综上，初步探明东南景天根系细胞壁多糖修饰对镉积累的影响及调控机制。.四年来，本项目已发表SCI收录学术论文8篇，完成预期目标。此外，参加国际会议2次，国内学术会议17次。