Department of Chemical and Biological Engineering, Iowa State University, Ames, IA 50010, USA.
J Exp Bot. 2013 Jul;64(10):2985-95. doi: 10.1093/jxb/ert138. Epub 2013 Jun 5.
Soybean [Glycine max (L.) Merr.] seed are valued for their protein and oil content. Soybean somatic embryos cultured in Soybean Histodifferentiation and Maturation (SHaM) medium were examined for their suitability as a model system for developing an understanding of assimilate partitioning and metabolic control points for protein and oil biosynthesis in soybean seed. This report describes the growth dynamics and compositional changes of SHaM embryos in response to change in the carbon to nitrogen ratio of the medium. It was postulated that at media compositions that were sufficient to support maximal growth rates, changes in the C:N ratio are likely to influence the partitioning of resources between the various storage products, especially protein and oil. As postulated, at steady-state growth rates, embryo protein content was strongly correlated with decreasing C:N ratios and increasing glutamine consumption rates. However, oil content remained relatively unchanged across the C:N ratio range tested, and resources were instead directed towards the starch and residual biomass (estimated by mass balance) pools in response to increasing C:N ratios. Protein and oil were inversely related only at concentrations of sucrose in the medium <88 mM, where carbon limited growth and no starch was found to accumulate in the tissues. These observations and the high reproducibility in the data indicate that SHaM embryos are an ideal model system for the application of metabolic flux analysis studies designed to test hypotheses regarding assimilate partitioning in developing soybean seeds.
大豆（Glycine max (L.) Merr.）种子因其蛋白质和油含量而受到重视。在大豆组织分化和成熟（SHaM）培养基中培养的大豆体细胞胚被检查其是否适合作为一个模型系统，以了解大豆种子中同化产物分配和蛋白质及油脂生物合成的代谢控制点。本报告描述了 SHaM 胚胎对培养基中碳氮比变化的生长动态和组成变化的响应。据推测，在足以支持最大生长速率的培养基组成下，C:N 比的变化可能会影响各种储存产物（尤其是蛋白质和油脂）之间资源的分配。正如假设的那样，在稳定的生长速率下，胚胎蛋白质含量与 C:N 比的降低和谷氨酰胺消耗速率的增加呈强烈相关。然而，油含量在整个 C:N 比测试范围内相对不变，资源则被引导到淀粉和剩余生物量（通过质量平衡估计）池中，以响应 C:N 比的增加。只有在培养基中蔗糖浓度 <88mM 时，蛋白质和油脂才呈负相关，因为此时碳限制了生长，并且在组织中没有发现淀粉积累。这些观察结果和数据的高度重现性表明，SHaM 胚胎是应用代谢通量分析研究的理想模型系统，这些研究旨在测试关于发育中的大豆种子中同化产物分配的假设。
