Root oxygen deficiency that is induced by flooding (waterlogging) is a common situation in many agricultural areas, causing considerable loss in yield and productivity. Physiological and metabolic acclimation to hypoxia has mostly been studied on roots or whole seedlings under full submergence. The metabolic difference between shoots and roots during waterlogging, and how roots and shoots communicate in such a situation is much less known. In particular, the metabolic acclimation in shoots and how this, in turn, impacts on roots metabolism is not well documented. Here, we monitored changes in the metabolome of roots and shoots of barrel clover (Medicago truncatula), growth, and gas-exchange, and analyzed phloem sap exudate composition. Roots exhibited a typical response to hypoxia, such as γ-aminobutyrate and alanine accumulation, as well as a strong decline in raffinose, sucrose, hexoses, and pentoses. Leaves exhibited a strong increase in starch, sugars, sugar derivatives, and phenolics (tyrosine, tryptophan, phenylalanine, benzoate, ferulate), suggesting an inhibition of sugar export and their alternative utilization by aromatic compounds production via pentose phosphates and phosphoenolpyruvate. Accordingly, there was an enrichment in sugars and a decline in organic acids in phloem sap exudates under waterlogging. Mass-balance calculations further suggest an increased imbalance between loading by shoots and unloading by roots under waterlogging. Taken as a whole, our results are consistent with the inhibition of sugar import by waterlogged roots, leading to an increase in phloem sugar pool, which, in turn, exert negative feedback on sugar metabolism and utilization in shoots.

中文翻译：

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苜蓿根与芽之间对涝渍的代谢响应及反映韧皮部转运的变化。

在许多农业地区，水灾（涝灾）引起的根系缺氧现象很普遍，导致单产和生产力大大降低。对缺氧的生理和代谢适应主要是在完全浸没的根或整个幼苗上进行的。渍水过程中，枝条和根部之间的代谢差异以及在这种情况下根部和枝条如何进行通信尚不清楚。尤其是，芽中的新陈代谢及其对根系代谢的影响尚无充分文献记载。在这里，我们监测了桶三叶草（Medicago truncatula）的根和芽的代谢组中的变化），生长和气体交换，并分析了韧皮部汁液渗出液的组成。根表现出对缺氧的典型反应，例如γ-氨基丁酸酯和丙氨酸积累，以及棉子糖，蔗糖，己糖和戊糖的强烈下降。叶片的淀粉，糖，糖衍生物和酚类（酪氨酸，色氨酸，苯丙氨酸，苯甲酸酯，阿魏酸酯）的含量显着增加，这表明糖的出口受到抑制，并被戊糖磷酸酯和磷酸烯醇酯生产的芳香族化合物替代利用丙酮酸。因此，在涝灾下，韧皮部汁液渗出物中的糖分富集，有机酸下降。质量平衡计算进一步表明，在渍水条件下，枝条的负载与根部的负载之间的不平衡增加。总的来说，我们的结果与淹水根对糖的进口抑制作用一致，导致韧皮部糖池增加，从而对芽的糖代谢和利用产生负面反馈。