Storage oil breakdown during embryo development of Brassica napus (L.)

In this study it is shown that at least 10% of the major storage product of developing embryos of Brassica napus (L.), triacylglycerol, is lost during the desicca tion phase of seed development. The metabolism of this lipid was studied by measurements of the fate of label from [1-14C]decanoate supplied to isolated em bryos, and by measurements of the activities of en zymes of fatty acid catabolism. Measurements on desiccating embryos have been compared with those made on embryos during lipid accumulation and on germinating seedlings. Enzymes of s-oxidation and the glyoxylate cycle, and phosphoenolpyruvate carboxyki nase were present in embryos during oil accumulation, and increased in activity and abundance as the seeds matured and became desiccated. Although the activ ities were less than those measured during germina tion, they were at least comparable to the in vivo rate of fatty acid synthesis in the embryo during development. The pattern of labelling, following metabolism of dec anoate by isolated embryos, indicated a much greater involvement of the glyoxylate cycle during desiccation than earlier in oil accumulation, and showed that much of the 14C-label from decanoate was released as C02 at both stages. Sucrose was not a product of decanoate metabolism during embryo development, and therefore lipid degradation was not associated with net gluco neogenic activity. These observations are discussed in the context of seed development, oil yield, and the synthesis of novel fatty acids in plants.