DSE促进镉滞留在作物根系皮层的作用机理研究

Dark septate endophytes (DSE) are ubiquitiously distributed in the root cortex of crops grown in the farmland polluted by cadmium (Cd). The DSE strain isolated from the Cd polluted soils can enhance the cadmium retention in the crop roots, which is considered to be the key mechanism of DSE enhancing Cd tolerance of crops. However, its mechanism is unknown. In this project the consortium of a Cd tolerant DSE strain with maize was cultivated in a pot under cadmium stresses with different concentrations. The research objects include: (1) To investigate the physiological and molecular mechanisms of DSE regulating the cortex material synthesis in the crop roots. The measurements included the contents, key enzymes activity related with the biosynthesis and differential gene expression in metabolic pathways of the root cortex material (lignin, suberin, cell-wall polysaccharides, and intracellular sulfhydryl compounds) using techniques such as histochemical stain, fractional centrifugation, transcriptomics, and quantitative real-time PCR. (2) To clarify the effect of DSE on enhancing the Cd retention in the root cortex included Cd deposition in the root cortex, adsorption by cell wall and intracellular complexation. The measurements included the micro-distribution and chemical forms of Cd in the outer cortex, functional groups of the cell wall polysaccharides and the adsorption of Cd, intracellular chelation forms of Cd binding to the sulfhydryl compounds using methods included sequential chemical extraction, transmission electron microscopy - X ray energy spectrum (TEM-EDS), Fourier transform infrared spectroscopy (FTIR), size exclusion chromatography – high performance liquid chromatography – inductively coupled plasma mass spectrometry (SEC-HPLC-ICP-MS). (3) To expound the mechanism of DSE regulating the substances biosynthesis in the root cortex, and then enhancing the Cd retention in the root cortex of crops, by comprehensively analyzing the relationship between the DSE colonization, substances in the root cortex and the Cd retention in roots. Finally, the study results will provide a new understanding of the physiological and ecological function of root endophytes, and enrich the theory of the relationship between root endophytes and Cd tolerance in crops.

深色有隔内生真菌（DSE）广泛定殖在镉污染农田作物的根系皮层，促进镉滞留在作物根部，但机理尚不清楚。项目拟在不同浓度镉胁迫下，构建DSE与玉米的联合体，采用组织化学染色、分级离心、转录组学、qRT-PCR技术，分析根系皮层物质（木质素、木栓质、细胞壁多糖、细胞内巯基化合物）含量、合成酶活性与合成通路差异基因表达，探讨DSE调节根系皮层物质合成的生理与分子机理。采用逐步提取、TEM-EDS、FTIR、SEC-HPLC-ICP-MS技术，分析镉在根系皮层质外体的微区分布与化学形态、细胞壁多糖官能团与镉吸附、细胞内巯基-镉的络合形态，解析DSE促进镉在根系皮层质外体沉积、细胞壁吸附和细胞内络合的滞留效应。综合分析“DSE—根系皮层物质—镉滞留”间的关系，阐释DSE调节根系皮层物质合成、促进镉滞留在作物根系皮层的作用机理。为植物根部内生菌的生理生态提供新认识，丰富根部内生菌与植物镉耐性关系的理论。

深色有隔内生真菌（DSE）广泛定殖在镉污染农田作物的根系皮层，促进镉滞留在作物根部，但机理尚不清楚。项目拟在不同浓度镉胁迫下，构建DSE与玉米的联合体，采用组织化学染色、分级离心、转录组学、qRT-PCR技术，分析根系皮层物质（木质素、木栓质、细胞壁多糖、细胞内巯基化合物）含量、合成酶活性与合成通路差异基因表达，探讨DSE调节根系皮层物质合成的生理与分子机理。采用逐步提取、TEM-EDS、FTIR等技术，分析镉在根系皮层质外体的微区分布与化学形态、细胞壁多糖官能团与镉吸附、细胞内巯基-镉的络合形态，解析DSE促进镉在根系皮层质外体沉积、细胞壁吸附和细胞内络合的滞留效应。.结果表明：（1）镉胁迫下，接种DSE会增加玉米植株生物量和株高，降低玉米地上部镉含量，增加玉米根系PME活性，降低果胶甲基酯化度；导致MYB DNA－结合域超家族蛋白基因表达量、热激蛋白１基因表达量、纤维素合酶基因表达量和内切葡聚糖酶基因表达量基因表达增加；此外，细胞壁中的果胶和半纤维素等组分、羟基、氨基和酯基等官能团，在玉米根细胞壁吸附镉中起着重要作用。（2）DSE会调控玉米根系内源激素含量，改善玉米GSH代谢与矿质营养，降低地上部镉含量，提高植株的镉耐性；IAA与GA在DSE增强植物镉耐性中起着重要的调节作用。（3）DSE会增加根系皮层质外体屏障结构关键合成酶活性、编码基因表达与主要化学组分含量，促进根系皮层质外体屏障结构的形成，将镉沉积在根系皮层上，改变根系皮层镉化学形态，从而提高植物镉耐性。.总之，“DSE—根系皮层物质—镉滞留”间存在内在联系，DSE通过调节根系皮层物质合成，起着促进镉滞留在作物根系皮层的生态作用。为植物根部内生菌的生理生态提供新认识，丰富根部内生菌与植物镉耐性关系的理论。

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