质外体在龙葵植物镉耐性中的作用

Contamination of soil by heavy metals is a severe environmental problem worldwide. Cadmium (Cd) is considered to be one of the most phytotoxic heavy metal pollutants，As a widespread trace pollutant with a better water solubility, Cd can enter the food chain through uptake into plant such as Solanum nigrum L tissues and pose a serious hazard to human health. The research on Cd tolerance mechanism of plant contributes to controlling the toxicity of Cd. Apoplast is important signal source and organelle of the plant cell. It play a important role in plant environmental adaptation and was increasingly concerned by the people. Although there have been many studies on apoplast, including the change of cell wall component under biotic and abiotic stress, the study on its role in plant Cd tolerance have been little studied. Therefore, the main aims of this work are to enucleate the role of apoplast in Cd tolerance by investigating (1) Cd distribution and accumulation in cell wall and apoplastic fluid，(2) the changes of apoplastic component（lignin，proteins，phytochelatin（PCs），amino acids and active oxygen（ROS，H2O2）etc, (3) the activity changes be involved in enzymes（coniferyl alcohol peroxidase (CAPX) and NADH peroxidase（NADH-POD），guaiacol peroxidase (GPOD), antioxidant enzymes SOD, CAT, APX, and GR）with the leaves or roots of Solanum nigrum L. as cadmium hyperaccumulator and with high biomass, Solanum photeinocarpum Nakam. & Odash, Solanum alatum Moench and Solanum nigrum L. va. flavovirns S. Z. Liouet W. Q. Wang under Cd stress. Based on these work, the relativity between Cd accumulation and these changes were discussed. These work will help prove the Cd-tolerance role of apoplast in longkui, provide the useful data for unraveling the Cd tolerance mechanisms of plant, accumulation candidate materials for phytoremediation of Cd contaminated soil, and provide scientific and technological supports for local economic development.

土壤重金属污染已成为严重的全球性环境问题。镉（Cd）被认为是毒性最强的重金属污染物之一，它一旦进入农产品便可通过食物链对人体健康造成危害。对植物Cd耐性机理研究有助于防治Cd污染。质外体是植物细胞的重要信号源和细胞器，其在植物环境适应性中可能具有重要作用。本研究以Cd超富集植物龙葵及其近缘种少花龙葵、红果龙葵和黄果龙葵为材料对比研究Cd在质外体（细胞壁和质外体汁液）中的分布积累以及质外体成分木质素、蛋白质种类、植物螯合肽（PCs）、氨基酸和活性氧等物质含量及细胞壁结合酶松柏醇过氧化物酶、NADH过氧化物酶和抗氧化酶活性变化及其相关性，以阐明质外体在龙葵Cd耐性中的作用，为全面阐明植物Cd耐性机理积累有用资料，为Cd污染土壤植物修复提供理论依据。

质外体是植物细胞的重要信号源和细胞器，其在植物环境适应性中可能具有重要作用，并越来越受人们的关注。然而，其作用机理目前还不十分清楚。本研究以中国境内常见的茄科植物龙葵（Solanum nigrum L.）、红果龙葵（Solanum villosum Miller）、矮株龙葵（Solanum nigrum L. var. humile）、黄果龙葵（Solanum villosumＬ. var.suaveolens）、少花龙葵（Solanum photeinocarpum）为试验材料，采用基质培养法进行了Cd耐性对比研究，考察五种龙葵生长和生理指标、活性氧产生积累和抗氧化酶同工酶谱及其活性等指标，综合各项指标表明：五种龙葵对Cd均有良好的耐性。相比之下，龙葵（Solanum nigrum L.）是Cd较耐植物，红果龙葵（Solanum villosum Miller）是Cd较敏感植物。以龙葵和红果龙葵为材料对比研究了Cd在质外体中的分布、积累以及质外体成分如果胶、木质素、蛋白质种类、活性氧等物质含量及其相关细胞壁结合酶活性变化。结果表明：两种龙葵根、叶亚细胞中的Cd积累均表现出可溶性组分＞细胞壁＞细胞器；龙葵根、叶中及各亚细胞组分中积累的Cd较多，其根叶中的Cd多以果胶质或蛋白质结合态存在；叶片细胞壁组分中Cd积累的多少顺序为果胶＞半纤维素；果胶各组分中的Cd积累顺序为螯合态果胶＞水溶性果胶＞碱溶性果胶；两种龙葵叶片质外体汁液中O 2–•产生和H2O2积累与抗氧化酶同工酶谱及其活性变化间有良好的相关性。基于 iTRAQ的研究结果表明，红果龙葵共有 369个蛋白对Cd响应，其中 140 个丰度上调蛋白和 229 个丰度下调蛋白。黑果龙葵中共有 292 个蛋白对Cd响应，其中207 个丰度上调蛋白和85个丰度下调蛋白。龙葵中丰度上调的蛋白主要参与逆境响应、活性氧代谢对有毒物质的响应；红果龙葵丰度上调的蛋白主要参与转运、细胞对逆境的应激反应，丰度下调的蛋白主要参与单个有机体代谢、小分子代谢过程。以龙葵为材料的研究结果表明，其表现出对Cd的耐性，叶片细胞壁果胶含量和结合酶GPOD以及质外体汁液中APX、CAT活性升高有关。.综上，细胞壁果胶及相关结合酶活性升高、质外体抗氧化酶活性升高和逆境响应蛋白的产生或丰度上调、活性氧代谢对有毒物质的响应对龙葵植物Cd耐性有贡献。