Quantitative flux maps describing glycerolipid synthesis can be important tools for rational engineering of lipid content and composition in oilseeds. Lipid accumulation in cultured embryos of Camelina sativa is known to mimic that of seeds in terms of rate of lipid synthesis and composition. To assess the kinetic complexity of the glycerolipid flux network, cultured embryos were incubated with [14C/13C]glycerol, and initial and steady state rates of [14C/13Cglyceryl] lipid accumulation were measured. At steady state, the linear accumulations of labeled lipid classes matched those expected from mass compositions. The system showed an apparently simple kinetic precursor-product relationship between the intermediate pool, dominated by diacylglycerol (DAG) and phosphatidylcholine (PC), and the triacylglycerol (TAG) product. We also conducted isotopomer analyses on hydrogenated lipid class species. [13C3glyceryl] labeling of DAG and PC, together with estimates of endogenous [12C3glyceryl] dilution, showed that each biosynthetically active lipid pool is ∼30% of the total by moles. This validates the concept that lipid sub-pools can describe lipid biosynthetic networks. By tracking the kinetics of [13C3glyceryl] and [13C2acyl] labeling, we observed two distinct TAG synthesis components. The major TAG synthesis flux (∼75%) was associated with >95% of the DAG/PC intermediate pool, with little glycerol being metabolized to fatty acids, and with little dilution from endogenous glycerol; a smaller flux exhibited converse characteristics. This kinetic heterogeneity was further explored using postlabeling embryo dissection and differential lipid extractions. The minor flux was tentatively localized to surface cells across the whole embryo. Such heterogeneity must be recognized in order to construct accurate gene expression patterns and metabolic networks describing lipid biosynthesis in developing embryos.

中文翻译：

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亚麻荠发育中胚胎中三酰甘油积累的动力学复杂性为多种生物合成系统提供了证据。

描述甘油脂合成的定量通量图可以成为合理设计油籽中脂质含量和组成的重要工具。众所周知，亚麻荠培养胚中的脂质积累在脂质合成速率和组成方面与种子相似。为了评估甘油脂流动网络的动力学复杂性，将培养的胚胎与[14C/13C]甘油一起孵育，并测量[14C/13C甘油基]脂质积累的初始和稳态速率。在稳定状态下，标记脂质类别的线性累积与质量成分的预期相符。该系统显示出以二酰甘油（DAG）和磷脂酰胆碱（PC）为主的中间体池与三酰甘油（TAG）产物之间明显简单的动力学前体-产物关系。我们还对氢化脂质类物质进行了同位素异构体分析。DAG 和 PC 的 [13C3 甘油] 标记以及内源性 [12C3 甘油] 稀释度的估计表明，每个生物合成活性脂质库占总摩尔数的约 30%。这验证了脂质子池可以描述脂质生物合成网络的概念。通过跟踪[13C3甘油基]和[13C2酰基]标记的动力学，我们观察到两种不同的TAG合成成分。主要的 TAG 合成通量 (~75%) 与 >95% 的 DAG/PC 中间池相关，几乎没有甘油被代谢为脂肪酸，并且很少被内源甘油稀释；较小的通量表现出相反的特性。使用标记后胚胎解剖和差异脂质提取进一步探讨了这种动力学异质性。较小的通量暂时定位于整个胚胎的表面细胞。必须认识到这种异质性，以便构建准确的基因表达模式和描述发育胚胎中脂质生物合成的代谢网络。