Abstract Arbuscular mycorrhizas enhance the drought tolerance of host plants through several underlying mechanisms. Polyamines (PAs) are known to protect plant cells from the damages of drought by enhancing the antioxidant defense system, restricting ethylene synthesis, maintaining cell pH and ion homeostasis, preventing chlorophyll loss, and so on; concomitantly, the mechanism through which arbuscular mycorrhizal (AM) fungi modulate PA metabolism to enhance drought tolerance of plants remains unclear. A pot experiment was conducted to assess how an AM fungus, Funneliformis mosseae, affects root PA homeostasis, activities and gene expressions of PA-related synthesizing and degrading enzymes, hydrogen peroxide (H2O2, a PA metabolite) production, and antioxidant enzyme gene expressions in trifoliate orange (Poncirus trifoliata) exposed to drought stress (DS). AM seedlings showed higher growth traits, leaf water potential, two plasma membrane intrinsic protein aquaporin gene expressions, and chlorophyll concentrations than non-AM seedlings under well-watered (WW) and DS conditions. Mycorrhizal treatment induced higher putrescine and cadaverine but lower spermidine and spermine concentrations, with higher activity of PA catabolic enzymes (copper-containing diamine oxidase, CuAO; polyamine oxidase, PAO) and putrescine synthases (ornithine decarboxylaseby; arginine decarboxylase, ADC). Mycorrhizas up-regulated the expression of the spermine synthase gene, PtSPMS, under DS, and down-regulated the transcript levels of PA catabolic enzyme genes (PtCuAO1, PtCuAO2, PtCuAO6, and PtCuAO8) and PA synthase genes (PtADC1 and PtADC2) under DS. PtPAO1, PtPAO2, and PtPAO3 had higher expression levels in AMF-inoculated seedlings, as compared to non-AMF-inoculated seedlings, under DS, triggering reactive oxygen species-related signalling for stress responsiveness through low H2O2 levels by up-regulating the expression of PtMn-SOD, PtCu/Zn-SOD, and PtCAT1. This study demonstrated that mycorrhizas have the capacity to modulate PA metabolism to enhance the drought tolerance of plants.

中文翻译：

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丛枝菌根调节根多胺代谢增强三叶橙耐旱性

摘要 丛枝菌根通过多种潜在机制增强寄主植物的耐旱性。众所周知，多胺 (PA) 可以通过增强抗氧化防御系统、限制乙烯合成、维持细胞 pH 值和离子稳态、防止叶绿素损失等来保护植物细胞免受干旱损害；同时，丛枝菌根 (AM) 真菌调节 PA 代谢以增强植物耐旱性的机制尚不清楚。进行盆栽实验以评估 AM 真菌 Funneliformis mosseae 如何影响根 PA 稳态、PA 相关合成和降解酶的活性和基因表达、过氧化氢（H2O2，PA 代谢物）生产，和抗氧化酶基因在暴露于干旱胁迫 (DS) 的三叶橙 (Poncirus trifoliata) 中的表达。在充分浇水 (WW) 和 DS 条件下，AM 幼苗比非 AM 幼苗显示出更高的生长性状、叶水势、两种质膜内在蛋白水通道蛋白基因表达和叶绿素浓度。菌根处理诱导更高的腐胺和尸胺，但降低亚精胺和精胺的浓度，PA分解代谢酶（含铜二胺氧化酶，CuAO；多胺氧化酶，PAO）和腐胺合酶（鸟氨酸脱羧酶，精氨酸脱羧酶，ADC）的活性更高。菌根在 DS 下上调精胺合酶基因 PtSPMS 的表达，并下调 PA 分解代谢酶基因（PtCuAO1、PtCuAO2、PtCuAO6、和 PtCuAO8) 和 PA 合酶基因 (PtADC1 和 PtADC2) 在 DS 下。与未接种 AMF 的幼苗相比，PtPAO1、PtPAO2 和 PtPAO3 在接种 AMF 的幼苗中具有更高的表达水平，在 DS 下，通过上调PtMn-SOD、PtCu/Zn-SOD 和 PtCAT1。该研究表明，菌根具有调节 PA 代谢以增强植物耐旱性的能力。和 PtCAT1。该研究表明，菌根具有调节 PA 代谢以增强植物耐旱性的能力。和 PtCAT1。该研究表明，菌根具有调节 PA 代谢以增强植物耐旱性的能力。