Studies on Seed‐Oil Triglycerides Factors Controlling the Biosynthesis of Fatty Acids and Acyl Lipids in Subcellular Organelles of Maturing Crambe abyssinica Seeds

1 The acetyl‐CoA carboxylase activity of all Crambe abyssinica subcellular fractions is very low as indicated by poor conversion of acetate and acetyl‐CoA and a requirement for malonyl‐CoA as the substrate for fatty acid synthesis. 2 Erucic acid (C 22:1 ) biosynthesis is most active in the oil body fraction, quite active in the denser nuclear/plastid and mitochondrial fractions and absent from the microsomal and cytoplasmic fractions. Erucic acid is formed by direct elongation of oleic acid, not by synthesis from acetate de novo.3 Desaturation of added stearyl‐CoA was not demonstrated. 4 Incorporation of 14 C‐labelled acyl groups from fatty acyl‐CoA thioesters into phospholipids occurred in all subcellular fractions except the supernatant from centrifugation at 105000 × g.5 Triglyceride synthesis from 14 C‐labelled stearyl‐CoA occurred in all subcellular fractions except the supernatant fraction from centrifugation at 105000 × g.6 Incubations of halved seeds with labelled precursors, followed by subcellular fractionation, supported these findings except that the intact seeds had functional acid‐CoA ligase and acetyl‐CoA carboxylase. 7 Incubation of halved seeds in the presence of trichloroacetic acid (2.5 mM and 12.5 mM) resulted in substantial inhibition of the biosynthesis of erucic acid but not of other fatty acids. Higher levels of trichloroacetic acid resulted in general inhibition of fatty acid and acyl lipid synthesis.