Figure 1.

Overview of the analytical techniques used for the measurement of ¹³C labeling in amino acids and fatty acids (see also “Materials and Methods”). After extraction of labeled embryos, the seed protein was hydrolyzed and the amino acids derivatized to their N,O-t-butyl-dimethylsilyl (TBDMS) derivatives. By GC/MS, the amino acid molecule is represented by the fragment M-57. For most amino acids, additional fragments were measured that represent parts of the amino acid molecule. The abundances of mass isotope isomers (isotopomers) of a measured fragment (m₀, m₁, m₂… m_n) were corrected for isotopomer content in the derivatization reagent and for heteroatoms (¹H, ¹³C, ¹⁵N, ¹⁷O, ¹⁸O, ²⁹Si, and ³⁰Si) as well as for natural ¹³C in the derivatized molecule fragment. Finally, the relative abundance of mass isotopomers (¹³C₁, ¹³C₂, ¹³C₃… ¹³C_n) was obtained. After transmethylation of seed oil, fatty acid methyl esters were analyzed by GC/MS. The molecular ion and the McLafferty fragment (m/z 74) were measured and the relative abundance of mass isotopomers was obtained as described for the amino acids.