Abstract In south China, Magnesium (Mg) deficiency is commonly found in Citrus orchard due to soil acidification. However, less information is available discussing the global metabolic profile of Mg-deficient leaves in Citrus species. In the study, seedlings of ‘Xuegan’ [Citrus sinensis (L.) Osbeck] were treated with Mg-plus (2 mM, as Control) or Mg-deficiency (0 mM) for 16 weeks by sandy culture, respectively. The untargeted metabolomics based on UHPLC-Q-TOF/MS were investigated to reveal the metabolic responses to Mg-deficiency in leaves of C. sinensis. The results indicated severe growth inhibition and obvious leaf chlorosis in Mg-deficient seedlings of C. sinensis compared to control. The principal component analysis (PCA) and orthogonal partial least squares-discriminate analysis (OPLS-DA) on the LC/GC data demonstrated a clear discrimination between the profiles of metabolites in control leaves and Mg-deficient leaves of C.sinensis. Besides, the identification and classification of those differential expressed metabolites (DEMs) revealed Mg-deficiency upregulated relative abundances of 78.42 % lipids and lipid-like molecules. In contrast, Mg-deficiency downregulated 89.42 % phenylpropanoids and polyketides in leaves of C.sinensis. Remarkably, relative abundances of most monosaccharides and amino acids increased while relative abundances of most leaf pigment compounds and organic acids decreased in response to Mg-deficiency in C. sinensis leaves. Those results support both primary and secondary metabolic modifications in C. sinensis leaves exposed to Mg-deficiency. Overall, the findings of present study contribute to a better understanding on the metabolic changes of Mg-deficient Citrus species, which will provide references for nutrient management and quality control in Citrus production.

中文翻译：

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基于 UHPLC-Q-TOF/MS 的代谢组学揭示了柑橘缺镁叶片中代谢谱的改变

摘要 在华南地区，柑橘园因土壤酸化而普遍缺乏镁（Mg）。然而，关于柑橘属物种缺镁叶片的全球代谢特征的讨论较少。在这项研究中，'雪干' [Citrus sinensis (L.) Osbeck] 的幼苗分别用加镁（2 mM，作为对照）或缺镁（0 mM）通过沙质培养处理 16 周。研究了基于 UHPLC-Q-TOF/MS 的非靶向代谢组学，以揭示中华白菜叶片缺镁时的代谢反应。结果表明，与对照相比，C. sinensis 缺镁幼苗严重的生长抑制和明显的叶片萎黄。LC/GC 数据的主成分分析 (PCA) 和正交偏最小二乘判别分析 (OPLS-DA) 表明，对照叶片和缺镁叶片中的代谢物谱具有明显的区别。此外，这些差异表达代谢物 (DEM) 的鉴定和分类显示，缺镁会上调 78.42% 脂质和脂质样分子的相对丰度。相比之下，缺镁会下调 C.sinensis 叶子中 89.42% 的苯丙烷类化合物和聚酮化合物。值得注意的是，大多数单糖和氨基酸的相对丰度增加，而大多数叶色素化合物和有机酸的相对丰度随着 C. sinensis 叶片中镁的缺乏而减少。这些结果支持 C 中的初级和次级代谢修饰。sinensis 叶片暴露于镁缺乏。总体而言，本研究结果有助于更好地了解缺镁柑橘的代谢变化，为柑橘生产中的营养管理和质量控制提供参考。