铵转运蛋白基因（AMT）调控菜薹硝酸盐积累的机制

Nitrate content is an important indicator for vegetable quality, and leafy vegetables tend to accumulate nitrate. Therefore research on nitrate regulation for leafy vegetable has always been taken seriously. Appropriate ammonium enhancement to solo nitrate as nitrogen source in nutrient solution can reduce nitrate content of vegetables, but the physiological basis and molecular mechanism of ammonium regulation is unclear. Flowering Chinese cabbage (Brassica campestris L. ssp. chinesis (L.) Makino var. utilis Tsen et Lee) is a special and important vegetable in South China, and 2 types of cultivars for high and low nitrate accumulation in product organs were obtained in our former experiment. With these 2 materials, the following studies will be carried out. Experiments for nitrogen dynamic monitoring in nutrient solution and nitrogen type analysis in xylem sap will be conducted, in order to discuss the physiological basis of ammonium in its reduction of nitrate accumulation in product organs. Ammonium transporter gene (AMT) and nitrate transporter gene (NRT) in flowering Chinese cabbage are to be cloned, and the function of AMT gene is to be identified. The interaction expression pattern of AMT and NRT will be analyzed under different nitrogen treatments. AMT overexpression mutant and gene knockout mutant will be built, in order to research nitrogen absorption function by AMT with transgenic plants. The results could clarify the physiological and molecular mechanisms in nitrate accumulation regulation by AMT in flowering Chinese cabbage, and provide the basis of molecular improvement in vegetable quality and screening high nitrogen efficient cultivars. Thus the project has important theoretical and practical values.

硝酸盐含量是蔬菜品质的重要标志，而叶菜类蔬菜最易积累硝酸盐，对叶菜类蔬菜硝酸盐调控的研究历来受到重视。全硝态氮营养液中适量添加铵态氮能降低蔬菜的硝酸盐含量，但铵态氮调控的生理基础和分子机理还不清楚。本项目以华南地区特产的重要蔬菜——菜薹(菜心)为材料，选用前期筛选获得的高、低硝酸盐积累类型的2个品种进行以下研究：通过氮素营养动态监测和植株伤流液中氮素形态分析试验，探讨铵态氮降低产品器官硝酸盐积累的生理基础；克隆菜薹铵转运蛋白基因AMT和硝转运蛋白基因NRT，并鉴定AMT基因的功能，分析不同氮源处理下AMT和NRT基因的互作表达规律；构建AMT基因的超表达突变体和基因敲除突变体，研究AMT转基因植株的氮素吸收功能。研究结果能阐明AMT调控菜薹硝酸盐积累的生理和分子机制，并为蔬菜品质的分子改良和氮素高效品种的筛选提供依据，具有重要的理论和实践意义。

硝酸盐含量是蔬菜品质的重要标志，而叶菜类蔬菜最易积累硝酸盐，对叶菜类蔬菜硝酸盐调控的研究历来受到重视。全硝态氮营养液中适量添加铵态氮能降低蔬菜的硝酸盐含量，但铵态氮调控的生理基础和分子机理还不清楚。本项目以华南地区特产的重要蔬菜——菜薹（菜心）为材料，进行了以下研究：通过氮素营养动态监测和植株伤流液中氮素形态分析试验，探讨铵态氮降低产品器官硝酸盐积累的生理基础；克隆菜薹铵转运蛋白基因AMT和硝转运蛋白基因NRT，并鉴定AMT基因的功能，分析不同氮源处理下AMT和NRT基因的互作表达规律；构建AMT基因的超表达突变体和基因敲除突变体，研究AMT转基因植株的氮素吸收功能。. 研究结果表明，与全硝对照相比，铵硝比25：75的处理降低了菜薹的硝态氮含量，提高了氮素利用效率，促进了植株生长及其对氮素的吸收和积累。主要原因是菜薹对铵态氮的吸收补偿了对硝态氮吸收的减少，导致总氮吸收的显著增加。NH4+不仅是作为营养物质还很可能作为信号分子调控菜心生长和氮素吸收，且BcAMT1;3很可能参与了菜心NH4+调控途径，正向调控BcAMT1;1和BcAMT1;5以及BcNRT1;1和BcNRT2;1在根系的表达以及菜心根系对NH4+和NO3-的吸收。.项目揭示了铵态氮降低菜薹硝酸盐积累的生理机制；通过分析AMT和NRT基因的互作表达规律，揭示了AMT调控菜薹硝酸盐积累的分子机制；并为蔬菜品质的分子改良和氮素高效品种的筛选提供依据，具有重要的理论和实践意义。