Leibniz-Institut für Pflanzengenetik und Kulturpflanzenforschung, 06466 Gatersleben, Germany.
Plant Cell. 2011 Aug;23(8):3041-54. doi: 10.1105/tpc.111.087015. Epub 2011 Aug 19.
The starchy endosperm of cereals is a priori taken as a metabolically uniform tissue. By applying a noninvasive assay based on (13)C/(1)H-magnetic resonance imaging (MRI) to barley (Hordeum vulgare) grains, we uncovered metabolic compartmentation in the endosperm. (13)C-Suc feeding during grain filling showed that the primary site of Ala synthesis was the central region of the endosperm, the part of the caryopsis experiencing the highest level of hypoxia. Region-specific metabolism in the endosperm was characterized by flux balance analysis (FBA) and metabolite profiling. FBA predicts that in the central region of the endosperm, the tricarboxylic acid cycle shifts to a noncyclic mode, accompanied by elevated glycolytic flux and the accumulation of Ala. The metabolic compartmentation within the endosperm is advantageous for the grain's carbon and energy economy, with a prominent role being played by Ala aminotransferase. An investigation of caryopses with a genetically perturbed tissue pattern demonstrated that Ala accumulation is a consequence of oxygen status, rather than being either tissue specific or dependent on the supply of Suc. Hence the (13)C-Ala gradient can be used as an in vivo marker for hypoxia. The combination of MRI and metabolic modeling offers opportunities for the noninvasive analysis of metabolic compartmentation in plants.
谷物的淀粉胚乳从前被认为是一种代谢均匀的组织。通过对大麦（Hordeum vulgare）籽粒应用一种基于（13）C/（1）H-磁共振成像（MRI）的非侵入性测定方法，我们揭示了胚乳中的代谢区室化现象。在灌浆期间用（13）C-蔗糖进行喂养表明，Ala 合成的主要部位是胚乳的中央区域，这是颖果经历缺氧水平最高的部分。通过通量平衡分析（FBA）和代谢物分析对胚乳中的区域特异性代谢进行了表征。FBA 预测，在胚乳的中央区域，三羧酸循环转变为非循环模式，伴随着糖酵解通量的增加和 Ala 的积累。胚乳内的代谢区室化有利于谷物的碳和能量经济，Ala 氨基转移酶起着重要作用。对具有遗传扰动组织模式的颖果的研究表明，Ala 的积累是氧状态的结果，而不是组织特异性的，也不依赖于 Suc 的供应。因此，（13）C-Ala 梯度可以作为体内缺氧的标志物。MRI 和代谢建模的结合为植物代谢区室化的非侵入性分析提供了机会。
