Fatty acid composition and lipid synthesis in developing safflower seeds

Linoleic acid predominated in every lipid class during the whole period of seed development of safflower, while linolenic acid decreased with increasing maturation and it was not detected in mature seeds. Just before the initiation of triacylglycerol accumulation, the fatty acid composition of triacylglycerols changed more rapidly than those of phospholipids and glycolipids. Saturated fatty acids tended to accumulate at the 1- and 3-positions of the glycerol molecule and the more highly unsaturated acids at the 2-position. The fatty acid compositions at the 1- and 3-positions were similar in all cases investigated, but in none of the triacylglycerols was the distribution completely symmetrical. The positional distribution of linolenic acid in triacylglycerols prepared from the immature seeds 2 days after flowering and from the leaves was unusual; in spite of its highest degree of unsaturation, it was preferentially esterified at the 1- and 3-positions. When triacylglycerol was most rapidly accumulated (14–18 days after flowering), the incorporation of acetate-[U- ¹⁴C] into total lipids was also maximum and dienoic fatty acids were the principal acids labelled. Diacylglycerols and compound lipids reached the highest rate of synthesis 15 days after flowering, and then a maximum incorporation into triacylglycerol occurred 18 days after flowering. Incubation temperature affected the synthesis of individual lipid classes. Triacylglycerol was more rapidly synthesized at 32° than at 10°, while diacylglycerols and compound lipids were accumulated under the low-temperature condition. A rise of incubation temperature caused a depression in dienoic acid synthesis.