Biosynthesis of Lipids Containing Isoricinoleic (9-Hydroxy-cis-12-octadecenoic) Acid in Seeds of Wrightia Species

Abstract

Seeds of two Wrightia species, i.e. W. tinctoria and W. coccinea, synthesize triacylglycerols containing isoricinoleoyl (9-hydroxy-cis-12-octadecenoyl, 9-OH-Δ1218:1) moieties as the major lipid constituents. Seed maturation is accompanied by lipid accumulation and steep increase in the level of 9-OH-Δ1218:1 in the total lipids, while relative proportions of palmitic (16:0), oleic (18:1), and linoleic (18:2) acids decrease. 9-Hydroxy stearic acid (9-OH-18:0) is also detected in these seed lipids, and both 9-OH-Δ1218:1 and 9-OH-18:0 occur exclusively in the neutral lipids of mature and developing seeds. Developing seeds of both Wrightia species synthesize upon incubation with sodium [1-14C]acetate, besides common long-chain fatty acids, considerable proportions of 9-OH-Δ1218:1 and 9-OH-18:0, which are predominantly esterified in triacylglycerols. Substantial proportions of radiolabeled 9-OH-Δ1218:1 and 9-OH-18:0 are also formed upon anaerobic incubation of the developing seeds with the ammonium salts of [1-14C]18:2 and [1-14C]18:1, respectively. The data presented suggest that hydration of the Ay olefinic bond of 18:2 is a possible pathway of synthesis of 9-OH-Δ1218:1, however, hydration of the Δ9 olefinic bond of 18:1 followed by Δ12 desaturation of 9-OH-18:0 cannot be ruled out.