Betaine Lipids in Lower Plants. Biosynthesis of DGTS and DGTA in Ochromonas danica (Chrysophyceae) and the Possible Role of DGTS in Lipid Metabolism

Membrane lipids and fatty acids of Ochromonas danica were analyzed. Of the two betaine lipids, the homoserine lipid DGTS mainly contains 14:0 and 18:2 fatty acids, while the alanine lipid DGTA is enriched in 18:0, 18:2 and 22:5 fatty acids. Of the polar moiety of DGTA, improved NMR data are presented. On incubation of cells with [3,4-14C]methionine, DGTS as well as DGTA were labelled. With [1-14C]methionine as a substrate, the label appeared in DGTS only. If double labelled [3H](glycerol)/[14C](polar part)DGTS was used as a precursor, radioactivity was incorporated specifically into DGTA in which the isotope ratio was unchanged compared to the precursor. Thus, the glyceryltrimethylhomoserine part of DGTS acts as the precursor of the polar group of DGTA. Labelling of cells with [1-14C]oleate in a pulse-chase manner and subsequent analysis of the label in the fatty acids and molecular species of different lipids including DGTS and DGTA, suggested a clearly different role of the two betaine lipids: DGTS acts as a i) primary acceptor for exogenous C18 monoene acid, ii) substrate for the desaturation of 18:1 to 18:2 acid, and iii) donor of mainly 18:2 fatty acid to be distributed among PE and other membrane lipids. Into DGTA, in contrast, fatty acids are introduced only after elongation and desaturation. As a result, the biosynthesis of DGTA from DGTS involves a decarboxylation and recarboxylation of the polar part and a simultaneous deacylation and reacylation of the glycerol moiet

Lipid and Fatty Acid Composition of the Marine Brown Alga Dictyopteris membranacea

Glycerolipids and fatty acids of D. membranacea (Dic-tyotales) were analysed. The betaine lipid DGTA and the glycolipids MGOG, DGDG and SQDG were major components. The phospholipids PE, PG, PI and PHEG were present in minor amounts only. This lipid pattern, which is characterised by the presence of DGTA and the absence of PC, has been found exclusively in brown algae belonging to the orders Dictyotales, Durvillaeales and Fucales. Major fatty acids were 16:0, 18:1, 18:2, α18:3, 18:4 and 20:4 acids. MGDG was the most unsaturated lipid with high levels of 18:4 acid. SQDG showed the highest degree of saturation containing a considerable proportion of 16:0 acid. DGTA contained 14 : 0,18:1,18:2 and 20:4 as major fatty acids. Among phospholipids, PE and PHEG had a very similar pattern which was enriched in 20:4 acid. Analysis of the positional distribution of fatty acids revealed that DGTA and MGDG were almost exclusivly of the "euka-ryotic” type, whereas SQDG was predominantly of the "prokaryotic” type. For the first time, molecular species of selected lipids have been analysed in a brown alga. In DGTA, 14:0/18:1, 14:0/18:2 and 14:0/20:4 were the main molecular species. In MGDG the highly unsaturated erl8:3/18:4, 18:4/18:4 and 18:4/20:5 were predominan

Radiolabelling Studies on the Lipid Metabolism in the Marine Brown Alga Dictyopteris membranacea

The lipid metabolism of the marine brown alga D. membranacea was investigated using [2−14C]acetate, [1−14C]myristate, [l−I4C]oleate and [l−14C]arachidonate as precursors. On incubation with [2−14C]acetate, 18:1 and 16:0 were the main products formed by de novo synthesis and incorporated into polar lipids. With all the exogenous substrates used, DGTA was strongly labelled and the subsequent rapid turnover of radioactivity suggested a key role for this lipid in the redistribution of acyl chains and most likely also in the biosynthesis of the eukaryotic galacto-lipids produced in the absence of PC. In the glycolipids a continuous accumulation of radioactivity was observed with all the substrates used. The labelling kinetics of molecular species of MGDG suggested the desaturation of 18:1 to 18:4 and of 20:4 (n-6) to 20:5 (n−3) acids on this lipid. Both PG and PE were primary acceptors of de novo synthesized fatty acids and exogenous [l−14C]oleate, but no evidence exists for a further processing of acyl chains on these lipids. TAG, although strongly labelled with all exogenous [l−14CJacids, was not labelled when [2−14C]acetate was used as a precursor indicating the flux of endogenous fatty acids to be different of that of exogenously supplied fatty acid

Lipids of Chlamydomonas reinhardtii. Incorporation of [14C]Acetate, [14C]Palmitate and [14C]Oleate into Different Lipids and Evidence for Lipid-Linked Desaturation of Fatty Acids

Chlamydomonas reinhardtii, parent strain (ssf), was pulse-labelled with [14C]acetate, [14C]-palmitate or [14C]oleate. Lipids were separated by TLC and HPLC. Radioactivity was measured in each class of lipids and in its fatty acids and molecular species. After 1 hour of incubation with acetate, the label was incorporated mainly into phosphatidylglycerol (PG), diacylglyceryl(N,N,N-trimethyl)homoserine (DGTS), digalactosyldiacylglycerol (DGDG) and monogalactosyldiacylglycerol (MGDG). Saturated, monoene and diene fatty acids were strongly labelled. Within 10 hours of incubation in the absence of labelled precursor, the label shifted from monoenes and dienes to trienes and tetraenes. The transfer of radioactivity from mono- to polyunsaturated MGDG and DGDG molecular species suggests a lipid-linked desaturation of the C-l position (and, in MGDG, also of the C-2 position) of these prokaryotic lipids. In the eukaryotic DGTS, all the species present were labelled simultaneously. On incubation with [14C]-palmitate or [14C]oleate, most of the label appeared in DGTS. Palmitate was immediately incorporated into the polyene species of DGTS, while oleate first appeared in the monoene species and then shifted to the polyene species. From these results it is concluded that, in DGTS, the acyl groups in the C-l position (mostly 16:0) were rapidly exchanged, while those in the C-2 position (mostly C18) became desaturated to give 18:3(5,9,12) and 18:4(5,9,12,15) acid

Lipid Bodies in Eremosphaera viridis De Bary (Chlorophyceae)

Under conditions of stress, e.g., nitrogen deficiency, Eremosphaera viridis De Bary (Chlorophyceae, Chlorococcales) synthesized secondary carotenoids and large amounts of triacylglycerols forming orange-red, cytosolic lipid bodies. Additionally, four polypeptides (28, 26, 25 and 23 kDa) as well as traces of chlorophyll a and b, of violaxanthin, neoxanthin and zeaxanthin, and of membrane lipids could be demonstrated in isolated lipid bodies. No membrane could be shown around the lipid bodies by the use of electron microscopy. The formation of lipid bodies in Eremosphaera is discussed as a bulging of the chloroplast envelope membrane

Lipids of Chlamydomonas reinhardtii. Analysis of Molecular Species and Intracellular Site(s) of Biosynthesis

Membrane lipids of Chlamydomonas reinhardtii were separated into the major components, MGDG, DGDG, SQDG, DGTS, PG, PE, PI, and the molecular species of each lipid were isolated and analyzed. The fatty acid composition was determined for the total lipid, the particular lipid classes and the molecular species. The positional distribution of fatty acids between the C-1 and C-2 position of the glycerol moiety was also determined. MGDG, DGDG, SQDG, PG and probably PI were found to be of plastidic (prokaryotic) origin, while DGTS and PE were found to be of cytoplasmic (eukaryotic) origin. Prokaryotic lipids mainly contained 18:3(9,12,15), 18:2,16:4 and 16:3, while DGTS and PE were rich in 18:3(5,9,12), 18:4(5,9,12,15), 18:2 and 18:1(11) fatty acids. From the fact that each lipid class was characterized by an individual pattern of molecular species, we conclude that during their biosynthesis, all the lipids act individually as substrates for the lipid-linked desaturation of fatty acids. Moreover, our results suggest that in Chlamydomonas, 18:3(5,9,12) and 18:4(5,9,12,15) are formed in the cytoplasm using DGTS and PE as substrate

Lipids of Ectocarpus fasciculatus (Phaeophyceae). Incorporation of [l-14C]Oleate and the Role of TAG and MGDG in Lipid Metabolism

Lipids and fatty acids of Ectocarpus fasciculatus (Ectocarpales, Phaeophyceae) were analyzed. Major polar lipids are monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), sulfoquinovosyldiacylglycerol (SQDG), diacylglycerylhydroxymethyl-N,N,N-trimethyl-rβ-alanine (DGTA), phosphatidylcholine (PC), phospha-tidylethanolamine (PE), phosphatidylglycerol (PG) and phosphatidylinositol (PI). Diphosphatidylglycerol (DPG), phosphatidic acid (PA) and phosphatidyl-O-[N-(2-hydroxy-ethyl)glycine] (PHEG) were also present in small amounts. Nonpolar lipids mainly consist of triacylglycerol (TAG) and diacylglycerol (DAG). Major fatty acids are 16:0,18:1, α18:3, 18:4, 20:4 and 20:5. The positional distribution of fatty acids showed that molecular species of eukaryotic structure account for 99% in MGDG, 98% in DGDG, 62% in PG and 23% in SQDG. On incubation with [1-14C]18:1 for 30 min, 33% of the total label was detected in TAG, 16% in PG, 14% in PE, 10% in PC and 8% in MGDG. During 7 days of chase, the label in TAG, PG, PE and PC decreased and simultaneously increased in MGDG up to 41% of the total. In SQDG, labelled fatty acids were found in prokaryotic as well as in eukaryotic molecular species. During the experiment, the label shifted from 18:1 to 18:2, 18:3, 18:4 and, to a minor extent, to 20:4 and 20:5 acids indicating 18:1 to be processed by elongation and/or desaturation. These results suggest TAG to act as a major primary acceptor of exogenous oleate and to be involved in the transfer of fatty acids to MGDG and other polar lipid

High Performance Liquid Chromatography of Molecular Species from Free Sterols and Sterylglycosides Isolated from Oat Leaves and Seeds

Free sterols and sterylglycosides (SG) from oat leaves and seeds were isolated by conventional thin layer chromatography (TLC) and subjected to high performance liquid chromatography (HPLC) for resolution of molecular species. Acylsterylglycosides, isolated by TLC, were converted to SG by mild alkaline hydrolysis and determined as SG. Sterols and SG were injected onto the column without any chemical treatment and the separated species were detected at 200 nm. The separation of SG-species follows exactly the separation of free sterols. Though gas liquid chromatography still is the method of choice, advantages of HPLC is to analyse directly the SG-species without hydrolysis and derivatization as compared to GLC. After TLC the sterol- and the SG-fraction are injected directly onto the column. This is extremely important for labile sterylglycosides or sterols, as demonstrated for the avenasterol

Distribution of Diacylglycerylhydroxymethyltrimethyl-β-alanine (DGTA) and Phosphatidylcholine in Brown Algae

Lipids were analyzed in thirteen species of brown algae collected at the seashore near Tokyo, Japan. Diacylglycerylhydroxymethyltrimethyl-β-alanine (DGTA), a recently identified betaine lipid, was found as a major lipid component in eight species of brown algae examined, namely, Ishige okamurai, Dictyota dichotoma, Pachydictyon coriaceum, Padina arborescens, Hizikia fusiformis, Sargassum horneri, S. ringgoldianum and S. thunbergii. However, phosphatidylcholine (PC) was not detected in any of these algae except I. okamurai. By contrast, PC was found as a major lipid component in five other species, namely, Colpomenia sinuosa, Endarachne binghamiae, Scytosiphon lomentarius, Eisenia bicyclis, Undaria pinnatifida. These algae in turn did not contain detectable amounts of DGTA. The fatty acid composition of four selected species, S. lomentarius, U. pinnatifida, D. dichotoma and H. fusiformis, was also studied. The fatty acid components of DGTA in D. dichotoma and H. fusiformis were similar to those of PC in U. pinnatifida, the major components being 16:0, 18:2 and 20:4ω6 (also 16:1 in D. dichotoma