The establishment of the nitrogen‐fixing symbiosis between soybean and Bradyrhizobium japonicum is a complex process. To document the changes in plant metabolism as a result of symbiosis, we utilized laser ablation electrospray ionization‐mass spectrometry (LAESI‐MS) for in situ metabolic profiling of wild‐type nodules, nodules infected with a B. japonicum nifH mutant unable to fix nitrogen, nodules doubly infected by both strains, and nodules formed on plants mutated in the stearoyl‐acyl carrier protein desaturase (sacpd‐c) gene, which were previously shown to have an altered nodule ultrastructure. The results showed that the relative abundance of fatty acids, purines, and lipids was significantly changed in response to the symbiosis. The nifH mutant nodules had elevated levels of jasmonic acid, correlating with signs of nitrogen deprivation. Nodules resulting from the mixed inoculant displayed similar, overlapping metabolic distributions within the sectors of effective (fix⁺) and ineffective (nifH mutant, fix⁻) endosymbionts. These data are inconsistent with the notion that plant sanctioning is cell autonomous. Nodules lacking sacpd‐c displayed an elevation of soyasaponins and organic acids in the central necrotic regions. The present study demonstrates the utility of LAESI‐MS for high‐throughput screening of plant phenotypes. Overall, nodules disrupted in the symbiosis were elevated in metabolites related to plant defense.

中文翻译：

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使用激光烧蚀电喷雾电离质谱法对野生型和突变型大豆根瘤进行代谢组学分析，揭示了代谢的改变。


大豆与日本慢生根瘤菌之间固氮共生关系的建立是一个复杂的过程。为了记录共生导致的植物代谢变化，我们利用激光烧蚀电喷雾电离质谱 (LAESI-MS) 对野生型根瘤进行原位代谢分析，感染日本B. japonicum nifH突变体的根瘤无法修复氮，两种菌株双重感染的根瘤，以及在硬脂酰酰基载体蛋白去饱和酶（ sacpd-c ）基因突变的植物上形成的根瘤，这些基因先前被证明具有改变的根瘤超微结构。结果表明，脂肪酸、嘌呤和脂质的相对丰度因共生而发生显着变化。 nifH突变根瘤的茉莉酸水平升高，与氮缺乏的迹象相关。由混合接种物产生的结节在有效（fix ⁺ ）和无效（ nifH突变体，fix ^- ）内共生体区域内表现出相似的、重叠的代谢分布。这些数据与植物制裁是细胞自主的概念不一致。缺乏sacpd-c 的结节在中央坏死区域显示大豆皂苷和有机酸的升高。本研究证明了 LAESI-MS 在植物表型高通量筛选中的实用性。总体而言，共生破坏的根瘤中与植物防御相关的代谢物升高。