丛枝菌根增强植物铬耐性机理研究
文献类型：学位论文
| 作者 | 伍松林 |
| 学位类别 | 博士 |
| 答辩日期 | 2015-11 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 陈保冬 |
| 关键词 | 丛枝菌根 真菌 铬 耐性 重金属 迁移转化 同步辐射 X射线光谱 |
| 其他题名 | Mechanisms underlying the enhanced plant chromium tolerance by arbuscular mycorrhizal symbiosis |
| 学位专业 | 生态学 |
| 中文摘要 | 丛枝菌根在植物适应重金属胁迫中具有重要作用，因而在重金属污染土壤的植物修复及生态恢复中具有极高的潜在应用价值。然而，关于丛枝菌根对植物耐受铬的影响鲜有报道，相关机理研究更是匮乏。本论文证实了丛枝菌根对植物适应铬污染环境的积极作用，同时深入研究了铬在菌根共生界面的迁移转化过程，揭示了丛枝菌根增强植物铬耐性机制。论文主 要研究内容及结论如下： （1）丛枝菌根能够增强植物铬耐性 模拟研究了不同程度土壤铬污染水平[Cr(VI)添加量: 0、5、10、20 mg kg-1]下，丛枝菌根真菌（Rhizophagus irregularis）对蒲公英（Taraxacum platypecidum Diels.）和狗牙根（Cynodon dactylon (Linn.) Pers.）生长及吸收累积铬的影响。结果发现，丛枝菌根显著促进了蒲公英和狗牙根的生长，但对植物磷和铬吸收分配的影响因植物种类而异。蒲公英是铬敏感性植物，其菌根依赖性较高，而狗牙根对铬的耐受性较强，菌根依赖性相对较低。丛枝菌根能够显著促进蒲公英吸收磷，同时降低其对铬的吸收和向地上部运输，从而缓解蒲公英铬毒害。相反，丛枝菌根并没有改善狗牙根磷营养，但能够降低其对铬的吸收，同时在高浓度铬污染下抑制铬自根系向地上部的运输，以此来缓解植物铬毒害。研究同时也发现，丛枝菌根能够改变根际土壤中铬的形态及生物有效性。 （2）丛枝菌根根外菌丝在菌根固持铬中起着重要作用 对比研究了不同磷添加水平（0、30、60、150 mg kg-1）和接种丛枝菌根真菌（Rhizophagus irregularis）对蒲公英（Taraxacum platypecidum Diels.）铬耐性的影响。发现添加磷处理并不 能达到接种丛枝菌根真菌对植物所产生的积极效果，丛枝菌根在促进磷吸收的同时增强了根系对铬的固持能力。基于同步辐射光源的微区 X射线荧光分析（SRμ-XRF）发现铬在非接种植物主根中主要分布于皮层和维管束部位，而在接种植物主根中则主要分布在皮层部位，表明丛枝菌根能够抑制铬经由木质部向植物地上部运输。研究进一步通过三分室植物培养装置探究了丛枝菌根根外菌丝对铬的吸收及转运作用，发现丛枝菌根根外菌丝能够吸收铬并转运到菌根根系中，但似乎并没有将铬进一步转运到植物地上部，而是更多的固持在根系，说明丛枝菌根根外菌丝在菌根固持铬中起着重要作用。 （3）铬在丛枝菌根共生界面的微观行为过程研究 利用丛枝菌根真菌与 Ri T-DNA转化胡萝卜根双重培养体系，结合透射电子显微镜-能谱分析（TEM-EDS）和基于同步辐射光源的 X射线近边吸收精细结构（XAFS）技术深入研究了丛枝菌根根外菌丝对铬的吸收、转运和转化作用。在排除其它微生物干扰的情况下，证实了丛枝菌根根外菌丝能够通过主动运输方式吸收铬并转运至菌根根系，但同时将70%以上铬固持在根外菌丝中。进一步利用 XAFS分析发现，丛枝菌根真菌能够将Cr(VI)还原成Cr(III)，并以磷酸铬类似物的形式固持在菌丝表面，而吸收进去的铬（以 Cr(VI)或 Cr(III)形式吸收）很可能以组氨酸结合态及其类似物的形式在菌丝中转运。进一步通过场发射扫描电子显微镜-能谱分析（FE-SEM-EDS）、扫描透射 X射线显微分析（STXM）及XAFS分析共同证实这些以磷酸铬类似物为主的铬化合物（还有少量羧基或组氨酸结合态铬）主要分布于菌丝表面的胞外聚合物（EPS）中，表明 EPS在菌丝还原固持 Cr(VI)中具有重要作用。STXM分析同时发现， Cr(VI)胁迫下（组培情况）菌根根系中铬主要分布于丛枝、根内菌丝及细胞壁等部位，这一现象同时在土培试验蒺藜苜蓿（Medicago truncatula）根系中再现，说明丛枝菌根真菌结构在菌根根系中起到铬的“区室化”作用，并由此降低铬自真菌结构经由共生界面向植物细胞的转运，从而减轻植物铬毒害。 论文深入揭示了菌根介导的铬在植物-土壤系统中的生物地球化学过程，阐明了菌根通过直接作用缓解植物铬毒害的机制，为菌根在铬污染土壤生态修复中的应用提供了重要理论基础，同时也为推测其他金属在菌根界面的环境行为提供了借鉴。 |
| 英文摘要 | Arbuscular mycorrhizal fungi (AMF) play an important role in plant resistance to heavy metal stress, and therefore are potentially valuable for phytoremediation or ecological restoration of metal contaminated soils. However, few studies focus on the role of AMF in relieving chromium (Cr) phytotoxicity and the underlying mechanisms. The present study confirmed the importance of AMF in alleviation of Cr phytotoxicity, and investigated the underlying mechanisms with focus on biotranslocation and transformation of chromium by AM symbiosis. The key findings are as follows: (1) AM symbiosis can enhance plant Cr tolerance In a greenhouse pot experiment, we investigated the effects of arbuscular mycorrhizal fungus (AMF) Rhizophagus irregularis on the growth of dandelion (Taraxacum platypecidum Diels.) and bermudagrass [Cynodon dactylon (Linn.) Pers.] in Cr(VI)-amended soils [0 mg kg-1, 5 mg kg-1, 10 mg kg-1, and 20 mg kg-1]. The results showed that the dry weights of the two plant species were dramatically increased by AM symbiosis. AMF inoculation increased plant P concentrations, while decreased Cr concentrations and Cr translocation from roots to shoots for dandelion. However, as for bermudagrass, AM symbiosis decreased plant Cr concentrations without improvement of P uptake. Besides, the study also revealed that AM symbiosis changed Cr species and bioavailability in the rhizosphere. The study confirmed the protective effects of AMF on host plants under Cr(VI)contaminations. (2) Extraradical mycelium contributes to Cr stabilization in mycorrhizal roots We explored if applying exogenous P to the Cr contaminated soil could match the positive effects of AM symbiosis on plant growth under Cr contaminations for the highly mycorrhizal dependent plant-dandelion (Taraxacum platypecidum Diels.). The results indicated that P application could not increase plant dry weights as well as AM symbiosis did. Besides enhancement of P acquisition, AM symbiosis can also stabilize Cr in mycorrhizal roots and thus restrain Cr transport to shoots. Synchrotron radiation micro-focused X-ray fluorescence (SR μ-XRF) analysis of metal distribution in principal roots also confirmed the immobilization of Cr in mycorrrihzal roots. Furthermore, by using a three-compartment cultivation system, we demonstrated that extraradical mycelium (ERM) can take up and transport Cr to mycorrhizal roots from distance, but may not translocate these Cr from roots to shoots, and therefore contributed to Cr stabilization in mycorrhizal roots and relieved Cr phytotoxicity. (3) Cr translocation and transformation in AM symbiotic interface In a two-compartment root-organ culture system, the uptake, translocation, and transformation of Cr(VI) by ERM of AM association was investigated using inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscope equipped with energy dispersive spectroscopy (SEM-EDS), transmission electron microscope equipped with energy dispersive spectroscopy (TEM-EDS) and X-ray absorption fine structure (XAFS) technologies. The results showed that ERM can actively take up and transport Cr [either in the form of Cr(VI) or Cr(III)] to roots but retains above 70% of the total Cr in the fungal biomass. The XAFS analysis further showed that Cr(VI) in the ERM was reduced completely to Cr(III) and subsequently precipitated mainly by phosphate analogues likely on fungal surface. Besides, through comparison of Cr speciation between living hyphae and inactivated hyphae, we also proposed that Cr(III)-histidine analogues may exist in the living hyphae. In order to investigate the detailed biochemical processes of Cr immobilization by AM symbiosis, we further investigated the cellular distribution and speciation of Cr in both ERM and mycorrhizal roots treated with Cr(VI) by using FE-SEM-EDS, scanning transmission soft X-ray microscopy (STXM) and XAFS techniques. The results indicated that AMF can produce numerous extracellular polymeric substances (EPS) on the fungal surface upon Cr(VI) stress, and Cr mainly existed in these EPS, which indicated that those EPS potentially contribute to Cr(VI) reduction and immobilization on fungal surface. The significant positive relationship between Cr and P concentration (analyzed by EDS) on hyphal surface further indicated that phosphate groups may act as counter ions of Cr, which was also revealed by the XAFS analysis showing that the Cr in fungal biomass was in the form of mainly Cr(III)-phosphate analogues. Take together the results of both STXM and XAFS analysis, we concluded that AMF can adsorb and reduce Cr(VI) to Cr(III), and then complex Cr(III) mainly by phosphate groups on fungal surface due to the functions of EPS produced by AMF upon Cr(VI) stress. In addition, the STXM analysis on sections of mycorrhizal roots (grown both in vitro and in vivo) exposed to Cr(VI) also indicated that AMF structures (arbuscules, intraradical mycelium, etc) in mycorrhizal roots can also reduce Cr(VI) to Cr(III) and precipitate Cr(III) possibly by phosphate groups, and thus restrain Cr translocation to plant cells across the symbiotic interface. All in all, the present work provided strong evidences of Cr immobilization by ERM and Cr compartmentation by fungal structures in mycorrhizal roots at cellular level, and therefore unraveled the mechanisms by which AM symbiosis immobilize Cr and enhance plant Cr tolerance. The study has demonstrated the important role of AMF in Cr biogeochemical processes in plant-soil continuum. Besides, the present work has also provided essential evidences of the direct way AM symbiosis enhances plant Cr tolerance, which indicates that AM symbiosis can be used in ecological restoration of Cr contaminated soils. |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/37026]  |
| 专题 | 生态环境研究中心_城市与区域生态国家重点实验室 |
| 推荐引用方式 GB/T 7714 | 伍松林. 丛枝菌根增强植物铬耐性机理研究[D]. 北京. 中国科学院研究生院. 2015. |
入库方式： OAI收割
来源：生态环境研究中心
浏览0
下载0
收藏0
其他版本
除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。