Fat metabolism in higher plants XXVII. Synthesis of long-chain fatty acids by preparations of Hordeum vulgare L. and other graminae.

Abstract

The incorporation of acetate-1-C14 into the long-chain fatty acids was examined in the seedling tissues of a number of Gramineae. A novel feature of the synthesis was that a large proportion of the total fatty acids were normal saturated fatty acids in the range C20-C26. Further experiments with seedling tissues of Hordeum vulgare showed that the capacity to synthesize these longer chain fatty acids was greatest with 3-day-old tissue. The synthesis of these fatty acids occurred rapidly during the first 2-3 hours of incubation and then leveled off. The capacity to synthesize C20 to C26 fatty acids from acetate-l-C14 was shared by etiolated and green tissue slices and by whole excised shoots. The C14-iabeled long chain fatty acids were incorporated into the particulate fraction of the cell and were absent from the supernatant fraction after centrifuging at 110,000 x g. Moreover, the labeled long-chain fatty acids predominated in the nonpolar lipids, including the mono- and digalactosyl lipids. Only a little occurred in the wax esters. The polar lipids contained predominantly the monoene fatty acids synthesized from acetate. The distribution of label in the 20:0 and 26:0 fatty acids was consistent with the synthesis occurring via the primary fatty acid palmitate by the successive addition of 2-carbon moieties, probably acetate. An additional novel feature was the synthesis of up to 50% of the labeled 18:1 fatty acid as vaccenic. Palmitoleic acid also was synthesized from acetate.