硼介导根系细胞壁对蔬菜镉吸收的调控效应及其机制研究

As an essential trace element for vegetable growth and development, boron plays an irreplaceable role in promoting plant cell wall formation, carbohydrate synthesis and transportation, protein synthesis and gene expression. Many previous studies indicated that the processes, including localization, retention, polysaccharide adsorption and cadmium inhibition gene expression of root cell wall, play a key role in the mechanism of cadmium detoxification and tolerance. Thus, whether boron would regulate the cadmium absorption of vegetables through its influences on the above-mentioned processes with the medium of the root cell wall? In this project, with Chinese flowering cabbage as the research object, which is the special vegetable in Guangdong, it will be aimed to investigate the regulating effect of exogenous boron addition on cadmium absorption characteristics of vegetables. Combining with the technologies such as scanning electron microscopy-energy spectrum analysis, synchrotron radiation microprobe X-ray fluorescence spectrometry analysis and Q-PCR assay, it will deeply probe into the regulation mechanism of boron on vegetable cadmium absorption processes through the root absorption, Cd compartmentation of cell walls, carbohydrate metabolism and cadmium inhibition gene expression, from the multiple levels as the organs, cells, metabolic and molecular. The results would provide scientific references for safety planting of vegetable in medium and mild cadmium contaminated soils, solving the current situation as low boron and high cadmium of soils and cadmium pollution of vegetables in South China.

硼是蔬菜生长发育的必需微量元素，对促进植物细胞壁的形成、糖类合成和运输、参与蛋白合成和基因表达等都有不可替代的重要作用。大量研究表明在植物镉吸收机制中根系细胞壁区室化隔离、细胞壁滞留、细胞壁多糖吸附、细胞壁镉滞留相关基因表达等过程起着关键作用。硼元素会否以根系细胞壁为媒介，通过对细胞壁合成、糖代谢、基因表达等过程的影响来调控蔬菜对镉的吸收特性？本项目针对华南地区土壤低硼高镉和蔬菜镉污染日益严重的现状，以广东特色蔬菜菜心为研究对象，研究外源硼添加对蔬菜镉吸收特性的调控效应，结合扫描电镜-能谱分析、同步辐射微束X射线荧光分析以及Q-PCR等技术，从器官、细胞、代谢和分子等多个水平，深入探讨硼通过根部吸收、细胞壁区室化、多糖组分代谢和镉滞留相关基因表达等过程调控蔬菜镉吸收的内在机理，为利用合理施用硼肥改善华南地区农田土壤低硼高镉现状和保障蔬菜质量安全提供科学依据。

作为蔬菜生长必需的微量元素之一，硼在参与细胞壁形成、糖类合成和运输、蛋白合成和基因表达等过程中具有不可替代的重要作用。而这些过程同样与蔬菜镉吸收有着紧密联系。因此，硼可能以根系细胞壁为媒介，通过上述过程来影响植物镉吸收累积。针对华南地区土壤低硼高镉和蔬菜镉污染日益严重的现状，本项目以广东特色蔬菜菜心为研究对象，利用营养液培养试验探讨不同外源硼添加浓度对蔬菜生长和镉吸收特性的调控效应及其内在机理。研究发现，镉胁迫情况下，10μM以上的硼添加比常规硼添加能促进蔬菜根系长度和生物量显著增长，而镉累积量下降7.78%~24.0%，外源硼能有效促进镉胁迫下的蔬菜根系生长。同时分析了镉胁迫下外源硼添加对蔬菜根系抗氧化酶活性、根系亚细胞组分、细胞壁多糖镉分布和镉滞留相关基因表达等过程的影响，从而揭示硼调控蔬菜镉吸收的内在机理。结果表明，镉胁迫下适宜浓度的硼添加可有效提高蔬菜根系的抗氧化酶活性，通过增强根系的抗氧化能力，促进其GSH-AsA 循环，降低镉对蔬菜根系的胁迫作用。外源硼添加使蔬菜根系各亚细胞组分镉含量下降，但更趋向固定在细胞壁和液泡内，从而降低镉对根系细胞器等活性较强区域的伤害，增加植物对镉毒害的耐性。细胞壁果胶含量在10μM以上的硼添加处理下比常规硼添加增加16.96%~67.81%，增加了根系细胞壁镉的结合位点。研究蔬菜根系镉累积相关基因表达量发现，HMA2、IRT1、IRT2、MAN3、NRAMP1等基因的相对表达量在1μM镉处理下，随外源硼的增加这4个基因的相对表达量持续下降，表明硼对蔬菜根系中镉吸收和耐性相关基因的表达起一定的调控作用。该研究为进一步完善植物镉吸收机理研究，并利用合理施用硼肥改善华南地区农田土壤低硼高镉现状并保障蔬菜质量安全提供了科学依据。