SYNTHESIS OF TRILAURIN BY DEVELOPING PISA SEEDS (ACTINODAPHNE HOOKERI)

The developing seeds of Actinodaphne hookeri were investigated to deli neate their ability to synthesize large amounts of trilaurin. Until 88 days after flowering the embryos contained 71% neutral lipids (NL) an d 29% phospholipids (PL) and both these components contained C-16:0, C -18:0, C-18:2, and C-18:3 as the major fatty acids (FA). At 102 days a fter flowering the seeds began to accumulate triacylglycerols (TAG) an d to synthesize lauric acid (C-12:0). By 165 days after flowering, whe n the seeds were mature, they contained about 99% NL and 1% FL. At thi s stage the TAG contained exclusively C-12:0, while the PL consisted o f long-chain fatty acids (LCFA) only. Leaf lipids in contrast did not contain any C-12:0. Experiments on [1-C-14]acetate incorporation into developing seed slices showed that at 88 days after flowering only 4% of the label was in TAG, 1% in diacylglycerols (DAG), and 87% in FL. O ne hundred two days after flowering seeds incorporated only 2% of the label into TAG, 30% into DAG, and 64% into FL. In contrast at 114 days after flowering 71% of the label was incorporated into TAG, 25% into DAG, and only 2% into FL. Analysis of labeled FA revealed that up to 1 02 days after flowering it was incorporated only into LCFA, whereas at 114 days after flowering it was incorporated exclusively into C-12:0. Furthermore, 67% of the label in PL at 114 days after flowering was f ound to be dilaurylglycerophosphate. Analysis of the label in DAG at t his stage showed that it was essentially in dilaurin species. These ob servations indicate the induction of enzymes of Kennedy pathway for th e specific synthesis of trilaurin at about 114 days after flowering, H omogenates of seeds (114 days after flowering) incubated with labeled FA in the presence of glycerol-3-phosphate and coenzymes A and ATP inc orporated 84% of C-12:0 and 61% of C-14:0, but not C-16:0, C-18:2, and C-18:3, into TAG. In contrast the LCFA were incorporated preferential ly into FL. It is concluded that, between 102 and 114 days after flowe ring, a switch occurs in A. hookeri for the synthesis of C-12:0 and tr ilaurin which is tissue specific. Since the seed synthesizes exclusive ly C-12:0 at 114 days after flowering onwards and incorporates specifi cally into TAG, this system appears to be ideal for identifying the en zymes responsible for medium-chain fatty acid as well as trilaurin syn thesis and for exploiting them for genetic engineering. (C) 1994 Acade mic Press, Inc.