Aims Populus can tolerant high concentration Al stress. However, the mechanisms of Mg alleviation to Al toxicity in populus remain unknown. Methods In the present study, adequate Mg was supplied to poplar under high concentration Al toxicity stress, and the pH gradients of root surface, Mg and Al uptake from root apex were detected using electrophysiological analysis, fluorescence staining, etc. Furthermore, auxin distribution and transport dynamic kinetics in root tips were also detected. Results In the present study, we found that adequate supply of Mg alleviated high concentration Al toxicity to populus root growth. Mg promoted the pH gradients of root surface in populus, leading to alkalization in the root transition zone, which prevented Al toxicity to root elongation. The auxin distribution in root tips of populus was detected using DR5:GFP reporter. The transport and distribution of polar auxin in root transition zone were inhibited by Al toxicity, but partially alleviated by Mg supply. Further electrophysiological experiments using auxin transporter mutant pin-formed 2 ( pin2 ) showed that Mg alleviated Al toxicity by PIN2-based polar auxin transport, which regulated root surface alkalization in the transition zone. Transcriptomic analysis and yeast complementation experiments using mrs2 mutants also reveals same relationships among Mg, auxin and Al. Conclusions The present study suggests that Mg promotes polar auxin transport and distribution, which leads to the elevated root surface pH regulation, and further alleviates the Al toxicity. Our results partially clarify the mechanism of Mg in alleviating the toxicity of high concentration Al in woody plants.

中文翻译：

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镁通过促进杨树根尖的极性生长素转运和分布以及根碱化来减轻铝的毒性

目的 杨树能耐受高浓度铝胁迫。然而，镁减轻杨树中铝毒性的机制仍然未知。方法本研究在高浓度铝毒胁迫下给杨树提供充足的镁，采用电生理分析、荧光染色等方法检测根表面pH梯度、根尖吸收镁和铝。还检测到根尖中的运输动态动力学。结果在本研究中，我们发现充足的镁供应减轻了高浓度铝对杨树根系生长的毒性。镁促进了杨树根表面的 pH 梯度，导致根过渡区碱化，从而防止铝对根伸长的毒性。使用DR5检测杨树根尖中的生长素分布：GFP 记者。极性生长素在根过渡区的运输和分布受到铝毒性的抑制，但部分被镁供应缓解。使用生长素转运蛋白突变体 pin-formed 2 ( pin2 ) 进行的进一步电生理实验表明，Mg 通过基于 PIN2 的极性生长素转运减轻了铝的毒性，从而调节了过渡区的根表面碱化。使用 mrs2 突变体的转录组学分析和酵母互补实验也揭示了镁、生长素和铝之间的相同关系。结论 本研究表明，Mg 促进生长素极性转运和分布，导致根表面 pH 调节升高，并进一步减轻 Al 毒性。我们的研究结果部分阐明了镁减轻高浓度铝对木本植物毒性的机制。极性生长素在根过渡区的运输和分布受到铝毒性的抑制，但部分被镁供应缓解。使用生长素转运蛋白突变体 pin-formed 2 ( pin2 ) 进行的进一步电生理实验表明，Mg 通过基于 PIN2 的极性生长素转运减轻了铝的毒性，从而调节了过渡区的根表面碱化。使用 mrs2 突变体的转录组学分析和酵母互补实验也揭示了镁、生长素和铝之间的相同关系。结论 本研究表明，Mg 促进生长素极性转运和分布，导致根表面 pH 调节升高，并进一步减轻 Al 毒性。我们的研究结果部分阐明了镁减轻高浓度铝对木本植物毒性的机制。极性生长素在根过渡区的运输和分布受到铝毒性的抑制，但部分被镁供应缓解。使用生长素转运蛋白突变体 pin-formed 2 ( pin2 ) 进行的进一步电生理实验表明，Mg 通过基于 PIN2 的极性生长素转运减轻了铝的毒性，从而调节了过渡区的根表面碱化。使用 mrs2 突变体的转录组学分析和酵母互补实验也揭示了镁、生长素和铝之间的相同关系。结论 本研究表明，Mg 促进生长素极性转运和分布，导致根表面 pH 调节升高，并进一步减轻 Al 毒性。我们的研究结果部分阐明了镁减轻高浓度铝对木本植物毒性的机制。