Auxin regulates cell division and elongation of the primordial cells through its concentration and then shaped the plant architecture. Cell division and elongation form the internode of soybean and result in different plant heights and lodging resistance. Yet the mechanisms behind are unclear in soybean. To elucidate the mechanism of the concentration difference of auxin related to stem development in soybean, samples of apical shoot, elongation zone, and mature zone from the developing stems of soybean seedlings, Charleston, were harvested and measured for auxin concentration distributions and metabolites to identify the common underlying mechanisms responsible for concentration difference of auxin. Distribution of indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), and methylindole-3-acetic acid (Me-IAA) were determined and auxin concentration distributions were found to have a complex regulation mechanism. The concentrations of IAA and Me-IAA in apical shoot were significantly different between elongation zone and mature zone resulting in an IAA gradient. Tryptophan dependent pathway from tryptamine directly to IAA or through indole-3-acetonitrile to IAA and from indole-3-propionic acid (IPA) to IAA were three primary IAA synthesis pathways. Moreover, some plant metabolites from flavonoid and phenylpropanoid synthesis pathways showed similar or reverse gradient and should involve in auxin homeostasis and concentration difference. All the data give the first insight in the concentration difference and homeostasis of auxin in soybean seedlings and facilitate a deeper understanding of the molecular mechanism of stem development and growth. The gathered information also helps to elucidate how plant height is formed in soybean and what strategy should be adopted to regulate the lodging resistance in soybean.

生长素通过其浓度调节原始细胞的细胞分裂和伸长，然后改变植物结构。细胞分裂和伸长形成大豆节间，导致不同的株高和抗倒伏性。然而，大豆的背后机制尚不清楚。为了阐明植物生长素浓度差异与大豆茎发育相关的机理，收集了大豆幼苗查尔斯顿发育中茎尖，伸长区和成熟区的样品，并测量了植物生长素的浓度分布和代谢产物，以鉴定导致植物生长素浓度差异的常见潜在机制。吲哚-3-乙酸（IAA），吲哚-3-丁酸（IBA）的分布，测定了甲基吲哚-3-乙酸（Me-IAA），发现生长素的浓度分布具有复杂的调节机制。根尖中IAA和Me-IAA的浓度在伸长区和成熟区之间显着不同，导致IAA梯度。从色胺直接到IAA或通过吲哚-3-乙腈到IAA和从吲哚-3-丙酸（IPA）到IAA的色氨酸依赖性途径是IAA的三个主要合成途径。此外，来自类黄酮和苯丙烷类合成途径的一些植物代谢物表现出相似或相反的梯度，应参与植物生长素的体内稳态和浓度差异。所有数据首次揭示了大豆幼苗中生长素的浓度差异和体内稳态，并有助于更深入地了解茎发育和生长的分子机制。所收集的信息还有助于阐明大豆的株高如何形成以及应采用何种策略来调节大豆的抗倒伏性。