Regulation of triacylglycerol biosynthesis in embryos and microsomal preparations from the developing seeds of Cuphea lanceolata

Abstract

Embryos of Cuphea lanceolata have more than 80 mol% of decanoic acid (‘capric acid’) in their triacylglycerols, while this fatty acid is virtually absent in phosphatidylcholine (PtdCho). Seed development was complete 25-27 days after pollination, with rapid triacylglycerol deposition occurring between 9 and 24 days. PtdCho amounts increased until day 15 after pollination. Analysis of embryo lipids showed that the diacylglycerol (DAG) pool consisted of mainly long-chain molecular species, with a very small amount of mixed medium-chain/long-chain glycerols. Almost 100% of the fatty acid at position sn-2 in triacylglycerols (TAG) was decanoic acid. When equimolar mixtures of [14C]decanoic and [14C]oleic acid were fed to whole detached embryos, over half of the radioactivity in the DAG resided in [14C]oleate, whereas [14C]decanoic acid accounted for 93% of the label in the TAG. Microsomal preparations from developing embryos at the mid-stage of TAG accumulation catalysed the acylation of [14C]glycerol 3-phosphate with either decanoyl-CoA or oleoyl-CoA, resulting in the formation of phosphatidic acid (PtdOH), DAG and TAG. Very little [14C]glycerol entered PtdCho. In combined incubations, with an equimolar supply of [14C]oleoyl-CoA and [14C]decanoyl-CoA in the presence of glycerol 3-phosphate, the synthesized PtdCho species consisted to 95% of didecanoic and dioleic species. The didecanoyl-glycerols were very selectively utilized over the dioleoylglycerols in the production of TAG. Substantial amounts of [14C]oleate, but not [14C]decanoate, entered PtdCho. The microsomal preparations of developing embryos were used to assess the acyl specificities of the acyl-CoA:sn-glycerol-3-phosphate acyltransferase (GPAT, EC 2.3.1.15) and the acyl-CoA:sn-1-acyl-glycerol-3-phosphate acyltransferase (LPAAT, EC 2.3.1.51) in Cuphea lanceolata embryos. The efficiency of acyl-CoA utilization by the GPAT was in the order decanoyl = dodecanoyl greater than linoleoyl greater than myristoyl = oleoyl greater than palmitoyl. Decanoyl-CoA was the only acyl donor to be utilized to any extent by the LPAAT when sn-decanoylglycerol 3-phosphate was the acyl acceptor. sn-1-Acylglycerol 3-phosphates with acyl groups shorter than 16 carbon atoms did not serve as acyl acceptors for long-chain (greater than or equal to 16 carbon atoms) acyl-CoA species. On the basis of the results obtained, we propose a schematic model for triacylglycerol assembly and PtdCho synthesis in a tissue specialized in the synthesis of high amounts of medium-chain fatty acids.

Biosynthesis and function of polyacetylenes and allied natural products

“…For example, isoforms of LPAAT selectively generate 10:0/10:0-and long-chain phosphatidic acids [127]. With the decanoyl lipids segregated, the action of a 10:0/10:0-specific DAGAT completes the channeling of these medium-chain lipids to tricaproin.…”

Compartmentation of Triacylglycerol Accumulation in Plants

“…1. FA production by plastids can limit TAG accumulation in seeds (5,6), so increasing flux through FA biosynthesis may perhaps have the single greatest influence on the amount of TAG produced in plant tissues. As in bacteria, fungi, and animals, both in vitro and in vivo evidence indicates that acetylCoA carboxylase (ACCase) is a key rate-determining step that controls FA biosynthesis.…”

A Novel Pathway for Triacylglycerol Biosynthesis Is Responsible for the Accumulation of Massive Quantities of Glycerolipids in the Surface Wax of Bayberry (Myrica pensylvanica) Fruit

“…Each point in the graphs represents the mean of three to four replicates 6 SE. substantial lag in acyl chain incorporation into [ 14 C]-DAG and the even longer lag in [ 14 C]-TAG production is not observed with acyl chain labeling for plants which accumulate primarily saturated and monounsaturated fatty acids (e.g., Cacao, Cuphea, and avocado mesocarp) (Stobart and Stymne, 1985;Griffiths et al, 1988;Bafor et al, 1990;Griffiths and Harwood, 1991;Bates and Browse, 2012). In these tissues, rather than initial incorporation into PC, newly synthesized fatty acids apparently enter a common acylCoA pool where they have an equal chance of reacting with G3P, lysophosphatidic acid, or DAG via the Kennedy pathway and thus produce [ 14 C]-DAG and [ 14 C]-TAG at similar initial rates.…”