PAHs胁迫下根系分泌物的释放特征及其主要组分的种间差异研究

Polycyclic aromatic hydrocarbons(PAHs) is one kind of persistent organic pollutants，previous researches have indicated plant could facilitate the dissipation of PAHs in soil．Root exudates are exchange carriers of substance, energy and information in rhizosphere, and plays an important role in the interaction mechanisms among plants, soil, and microorganisms, so it is in favor of revealing the mechanisms of remediation by studying the root exudates of plants with different phytoremediation potential under the stress of PAHs．To assess the characteristics of root exudates and their interspecies difference in main component under PAHs stress, phenanthrene and pyrene are selected as representative PAHs, and three native species are screened from 15 plant species of Festuca L. after having examined their phytoremediation potential by pot experiments. According to their phytoremediation ability for the cleanup of PAH-contaminated soil, they are divided into three classes, and differentiation of PAHs removal efficiency between adjacent classes ranges from 25% to 30%. Root exudates of screened plants in seeding 35d, seeding 65d and seeding 95d are collected by means of a new device for continuous collecting plant root exudates under the stress of series concentration of PAHs in culture solution, respectively, and TOC, organic acids, total carbohydrate and amino acids in root exudates are investigated. Types and quantity of low molecule weight organic compounds in root exudates, which are extracted by n-butanol, petroleum ether, chloroform and ethyl acetate respectively, are identified by GC-MS. Meanwhile, high molecule weight organic compounds including polysaccharides, uronic acid, proteins and ecotoenzymes are also identified using HPAEC-PAD or Shotgun protein identification techniquesin. On these basis, comparing characteristics of root secretion of plants, and probing into interspecies difference in main component of root exudates of plants with different phytoremediation potential ; we hope to provide insight into the mechanisms responsible for plant-enhanced bioremediation of PAHs in soil on molecular level.

根系分泌物的释放特征与有机污染物的植物修复密切相关，研究PAHs胁迫下根系分泌物的释放特征及其主要组分的种间差异，有助于从分子水平上揭示植物修复的内在机制。据此，拟以菲、芘为PAHs代表物，借助自制的根系分泌物连续收集装置，分别收集不同修复潜力的3种羊茅属植物在系列浓度PAHs胁迫下各生长时期(35、65、95d)的根系分泌物，检测分泌物中总糖、总有机碳、有机酸、氨基酸等组分的释放特征；采用6种不同属性的萃取介质对根系分泌物进行多元分离、GC-MS检测，从不同侧面对比分析分泌物中各种低分子化合物的组成成分、数量比例；借助HPAEC-PAD、Shotgun等技术检测分泌物中各种高分子化合物的组成成分、数量比例。在此基础上，进一步分析PAHs胁迫下根系分泌物的释放特征及其变化规律，揭示不同修复潜力植物间根系分泌物主要组分的种间差异，为深入探讨植物修复的内在机制提供科学依据。

本项目以菲、芘、苯并芘为多环芳烃(PAHs)代表物，借助自制根系分泌物连续收集装置及现代检测手段，对比研究了PAHs胁迫下不同修复潜力的5种羊茅属植物根系分泌物的释放特征及其主要组分的种间差异。结果显示，1）PAHs胁迫增强了根系对可溶性糖的分泌：随胁迫水平地升高、胁迫期地延长,其含量呈先上升后下降波动；2）PAHs胁迫促进了对低分子量有机酸的释放，植物的修复潜力越强，有机酸高峰值出现时的胁迫浓度越高；试验期间，有机酸组分无明显变化，且主要以草酸、乙酸、乳酸和苹果酸为主，但修复潜力较强植物的根系分泌物中却检测到微量反丁烯二酸；3）PAHs胁迫对氨基酸种类影响不大，但对分泌量的影响较大。其中，苏氨酸、丝氨酸、甘氨酸、丙氨酸的分泌量随胁迫水平地升高而剧增；脯氨酸、羟脯氨酸和天冬氨酸近乎以功能群形式参与植物对PAHs的胁迫响应：参与应激响应的功能群组分的分泌量随胁迫水平的升高而剧增，不同水平间差异显著；植物的修复潜力越强,参与响应的组分数则越多；4）PAHs胁迫促进了12种黄酮类化合物的分泌，其含量随着胁迫强度增大、胁迫期延长呈现“先升后降”变化，在污染水平为79.94mg•kg-1(T4)、生长期为60 d 时出现“峰值”；修复潜力越高，差异越显著，但修复潜力较差的植物分泌的酮类物质并没有明显变化；5) PAHs胁迫促进了对红景天多糖、壳多糖、蛋白聚糖的分泌活动，其释放量变化趋势与所在土壤中PAHs去除率呈显著正相关；6）PAHs胁迫下根系分泌物中蛋白信息数明显高于非胁迫条件下的对照组，修复潜力越强，新出现的蛋白信息数越多，且主要参与物质代谢、防御功能及信号传导等途径。该研究成果有助于从分子水平上揭示不同植物修复潜力种间差异的生物学原因，为深入探讨植物修复的内在机制、科学筛选修复植物、改善修复效率提供依据。