超积累植物东南景天根系质外体屏障发育特征及其对镉吸收积累的影响机制

Root apoplast is an important transport way for water and ions, which plays an important role in regulating the adaptation of plants to different environment. For many years, most studies have found that metal ions can only reach the xylem through the symplastic pathway. There are few reports on the contribution of the apoplastic pathway in the uptake and accumulation of heavy metals in hyperaccumulator. Sedum alfredii (Crassulaceae), a species native to China, has been characterized as a Cd hyperaccumulator. To date, studies on the mechanism of metal tolerance and hyperaccumulation in S. alfredii mainly focused on the uptake, transport, and subcellular distribution characteristics, while no information is available about the interactions between the development of the apoplastic barrier and Cd accumulation in this plant. In this project, pot experiment, as well as techniques like frozen section, fluorescent staining, stable isotopic tracer techniques, confocal laser scanning microscopy (CLSM), scanning ion-selective electronic technique (SIET), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), gas chromatography-mass spectrometer (GC-MS) and reverse transcription quantitative PCR (RT-qPCR) were used to: (1) investigate the effect of Cd on horizontal and vertical development of root apoplastic barrier, as well as lignin and suberin monomer content, and then reveal the response characteristics of root apoplastic barrier development and composition to cadmium; (2) investigate the effect of endogenous hormone abscisic acid and ethylene on the development and chemical composition of root apoplastic barrier; (3) study the effect of cadmium on the activity of key enzymes and the expression of related gene involved in the development of the root apoplastic barrier. Based on these studies, we aimed to reveal the regulation mechanism of the development of root apoplastic barrier in S. alfredii, and to elucidate the effect and mechanism of the development of root apoplastic barrier on cadmium uptake, transport and accumulation. Results of this project will help to understand the mechanisms of heavy metal hyperaccumulation, improve the theory of phytoremediation, and it is of great importance for improving the efficiency of phytoextraction and protecting the health of soil ecosystem.

根系质外体是水分和离子运输的重要途径，对植物环境适应性具有重要调节作用。目前，有关超积累植物根系质外体屏障发育特征的研究报道很少，对质外体屏障发育在重金属吸收积累中的作用机制并不清楚。本项目以超积累植物东南景天（Sedum alfredii）为材料，综合运用冷冻切片、荧光染色、稳定同位素示踪、CLSM、SIET、LA-ICP-MS、GC-MS及RT-qPCR等技术，研究不同镉处理对根系横向和纵向质外体屏障发育及木质素、木栓质单体含量的影响，揭示根系质外体屏障发育和组成对镉的响应特征；研究内源激素脱落酸、乙烯对根系质外体屏障发育及化学组成的影响，研究根系质外体屏障发育关键酶活性及相关基因表达对镉的响应特征，揭示东南景天根系质外体屏障发育特征及调控机理，阐明质外体屏障发育对镉吸收积累的影响机制，为揭示植物重金属超积累机理，完善植物修复理论，提高植物修复效率和保障土壤生态系统健康提供科学依据。

根系质外体是水分和离子运输的重要途径，对植物环境适应性具有重要调节作用。目前，有关超积累植物根系质外体屏障发育特征的研究报道很少，对质外体屏障发育在重金属吸收积累中的作用机制并不清楚。本项目主要系统研究不同镉污染土壤中两种生态型东南景天根系内皮层分化形成的凯氏带和木栓质发育和化学组成特点，结合质外体示踪剂PI染色和Cd特异性荧光探针定位，揭示东南景天根系内皮层分化对Cd吸收、运输及积累的影响；研究东南景天内源脱落酸和乙烯对镉的响应，揭示根系内源激素对根系质外体屏障发育的调控机制及对Cd吸收运输的影响机理；研究不同镉处理浓度对东南景天根系内皮层分化关键酶活性及相关基因相对表达量的影响，揭示内皮层分化调控Cd吸收积累的分子机制。研究结果表明，相较于非超积累（NHE）生态型东南景天，超积累（HE）生态型东南景天在Cd处理下，根系维持较低的脱落酸（ABA）和较高的乙烯（Eth）水平，诱导SaCASP、SaCYP86A1、SaGPAT5、SaKCS20基因和POD/PAL酶活性显著下调，使得凯氏带（CS）和木栓质（SL）合成单体减少以及CS和SL远离根尖，从而使得HE具有更大的质外体自由空间，导致木质部导管中质外体示踪剂PI和Cd含量以及地上部Cd积累量显著增加。通过本项目研究，揭示了东南景天根系质外体屏障发育特征及调控机理，阐明了质外体屏障发育对镉吸收积累的影响机制。为揭示植物重金属超积累机理，完善植物修复理论，提高植物修复效率和保障土壤生态系统健康提供科学依据。本项目共产出SC论文6篇，超额完成预期目标。此外，参加学术会议3次，培养在读硕士研究生2名，在读博士研究生3名。

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