Formula omitted] biosynthesis of a-linolenic acid in plants

Abstract

[1- 14C]acetate was readily incorporated into unsaturated fatty acids by leaf slices of spinach, barley and whole cells of Chlorella pyrenoidosa and Candida bogoriensis . In these systems the [ 14C] label in newly synthesized oleate and linoleate was approximately equally distributed in the C 1–9 and the C 10–18 fragments obtained by reductive ozonolysis of these acids, whereas in a-linolenic acid over 90% of the total [ 14C] was localized in the C 1–9 fragment. While [1- 14C]oleic acid was converted by whole cells of Chlorella to [1- 14C]linoleic and [1- 14C]linolenic acids, [U- 14C]oleic acid yielded [U- 14C]linoleic acid but a-linolenic acid was labeled only in the carboxyl terminal carbon atoms. When spinach leaf slices were supplied with carboxyl labeled octanoic, decanoic, dodecanoic, tetradecanoic and octadecanoic acids, only the first three acids were converted to a-linolenic acids while the last two acids were ineffective. Thus we suggest that (a) linoleic acid is not the precursor of a-linolenic acid and (b) 12:3(3, 6, 9) is the earliest permissible trienoic acid which is then elongated to a-linolenic acid.