Precise identification of photosynthetic glycerolipids in microalga Tetraselmis chuii by UPLC-ESI-Q-TOF-MS

Precise structural identification of photosynthetic polar glycerolipids in microalga Tetraselmis chuii has been established using Ultra Performance Liquid Chromatography-Electrospray ionization-Quadrupole-Time of Flight Mass Spectrometry (UPLC-ESI-Q-TOF-MS) by direct analysis of the total lipids extract. The mass spectrometry was performed in reflective time-of-flight using electron spraying ionization in both positive and negative modes. The structural determination was based on the characteristic product ions yielded by different glycerolipids under ESI-MS/MS mode, and confirmed the molecular species by the carboxylate anions produced by glycerolipids in the negative mode. As a result, more than 40 lipid molecular species, including 11 monogalactosyldiacylglycerols (MGDG), 7 digalactosyldiacylglycerols (DGDG), 16 sulfoquinovosyldiacylglycerols (SQDG), and 9 phosphatidylglycerols (PG), were detected in Tetraselmis chuii, which had never been identified before in this microalga. Furthermore, some intact lipid molecules with hydroxylated fatty acids that could not be detected by the traditional GC-MS method were found this time, providing novel information for the photosynthetic lipidome of Tetraselmis chuii. Comparative studies on fatty acids at the sn-2 position showed that SQDG and MGDG are dominantly biosynthesized through the prokaryotic pathway, PG is a typically mixed biosynthetic pathway, while DGDG is somewhat peculiar with C14:0 and C16:0 at its sn-2 position. This method could provide a full structural profile of intact photosynthetic lipid molecular species, which may be applied to study the physiological and ecological functions of lipid by monitoring their individual changes. Supported by the Program for Changjiang Scholars and Innovative Research Team in Universities (PCSIRT) (Grant No. IRT0734), Project of National Ocean Bureau (Grant No. 200805067), Project of Ministry of Science and Technology (Grant No. 2007BAD43B09), and K. C. Wong Magna Fund in Ningbo University     

Profiles of photosynthetic glycerolipids in three strains of <Emphasis Type="Italic">Skeletonema</Emphasis> determined by UPLC-Q-TOF-MS

An exhaustive qualitative and quantitative profiling of the photosynthetic glycerolipids in three strains of the marine diatom Skeletonema sp. was carried out by ultra performance liquid chromatography-electrospray ionization-quadrupole-time of flight-mass spectrometry. In the diatom thylakoid membrane, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) account for about 45–70% and 5–15% of the total membrane lipids, respectively. The anionic sulfoquinovosyldiacylglycerol (SQDG) as well as the likewise anionic phosphatidylglycerol (PG) contribute between 10–40% and 4–10% each. The predominant species of MGDG were those with C_16:3/C_16:3, C_20:5/_16:1, and C_20:5/C_16:3. Three main molecular species of DGDG contained C_20:5/C_16:1, C_20:5/C_16:2, and C_16:1/C_16:1. The major molecular species of SQDG were those containing combinations of C_14:0/C_14:0, C_14:0/C_16:0, C_14:0/C_16:1, and C_14:0/C_16:3. All the PG classes contained the C_18:1/C_18:1 as the main molecular species. Based on the fatty acid species in sn-2 position, it is indicated that MGDG and DGDG are biosynthesized through prokaryotic pathway exclusively within the chloroplast, whereas PG and SQDG have a typical mixed biosynthetic pathway (both prokaryotic pathway and eukaryotic pathways). The chemical characteristics of photosynthetic glycerolipids related with ecological physiology are discussed.     

集胞藻Synechocystis sp.PCC 6803脂质组的分析

以集胞藻Synechocystis sp.PCC 6803为研究对象,研究建立了基于超高效液相色谱耦合串联质谱技术脂质组学分析方法.鸟枪法脂质组学通过电喷雾离子化有效分离油脂粗提物中所含单个脂质分子,在三重四极杆扫描碎片离子,能够利用特征片段离子鉴定光合甘油酯的种类和酰基组成,具有高效、灵敏度高和质量准确度高等优点.对...     

Profiles of glycerolipids in Pyropia haitanensis and their changes responding to agaro-oligosaccharides

A sensitive method based on electrospray ionization tandem mass spectrometry was used to profile glycerolipids in Pyropia haitanensis and their changes responding to agaro-oligosaccharides. Ten monogalactosyldiacylglycerols (MGDGs), twelve digalactosyldiacylglycerols (DGDGs), five sulfoquinovosyldiacylglycerols (SQDGs), five phosphatidylglycerols (PGs), fifteen phosphatidylcholins (PCs), three phosphatidic acids (PAs), and three phosphatidylethanolamines (PEs) were identified in P. haitanensis. We found the SQDG was the most abundant species, followed by MGDG, DGDG, PG, PC, PE, and PA of the total glycerolipids. The predominant lipid species contained C20 fatty acids at sn-1/sn-2 positions, which was different from higher plants. Changes in membrane lipid species occurred when P. haitanensis were treated with agaro-oligosaccharides. At first, agaro-oligosaccharides induced an increase in total glycerolipids including the galactolipids such as MGDG (20:5/20:5) and phospholipids such as PC (18:3/20:5), suggesting that agaro-oligosaccharides caused changes of lipids in chloroplasts and plasma membrane. With increased treatment time, a large decline in major plasma membrane lipids (PCs and PEs) was observed, but not galactolipids (MGDGs and DGDGs), suggesting that the lipid changes occurred mainly at the plasma membrane after prolonged treatment.     

Lipid compositions in diatom Conticribra weissflogii under static and aerated culture conditions

The diatom Conticribra weissflogii is a microalga with high nutrition value, rich in docosahexaenoic acids (DHA) and eicosapentaenoic acids (EPA). In order to study the effect of culture conditions on the changes of lipid compositions, the intact lipid structural profiles and fatty acids in C. weissflogii were monitored under static and aerated culture conditions. The results showed that, lipids identified in C. weissflogii were neutral lipid triacylglycerols (TAG), betaine lipid diacylglycerylcarboxy‐N‐hydroxymethyl‐choline (DGCC), phosphatidylcholine (PC) and four classes of photosynthetic glycerolipids. The profiles of lipid metabolites of C. weissflogii were different between two culture modes, with the following characteristics under aerated conditions: TAGs increased significantly, whereas the levels of sulfoquinovosyl diacylglycerol (SQDG), monogalactosyldiacylglycerol (MGDG), and DGCC decreased. Furthermore, higher contents of EPA‐rich TAG and EPA/DHA‐rich DGCC were detected at the end of stationary phase, while EPA/DHA‐rich PC, EPA‐rich MGDG and EPA‐rich digalactosyldiacylglycerol (DGDG) were obtained in the exponential phase under static conditions. Meanwhile, the contents of almost all classes of the essential fatty acids (EFAs)‐enriched lipids increased at onset of stationary phase under aerated conditions. Taken together, given that the high levels of EFAs are required for artificial rearing of marine organisms, aeration is critically important for increasing the production rate and the contents of EFA molecules and therefore increasing the nutritional value of the microalgae.     

Mono‐ and digalactosyldiacylglycerol composition of glaucocystophytes (Glaucophyta): A modern interpretation using positive‐ion electrospray ionization/mass spectrometry/mass spectrometry

Glaucocystophytes are freshwater algae that possess an almost‐intact cyanobacterium, referred to as a cyanelle, as their photosynthetic organelle. Because the cyanelle represents an intermediate state in plastid evolution, glaucocystophytes have been the subject of several studies to characterize the genetics and biochemistry of their cyanelles. However, only a small handful of older studies exist on the composition of their lipids, particularly two major plastid lipids, mono‐ and digalactosyldiacylglycerol (MGDG and DGDG, respectively), found in all photosynthetic life. Our study has used a modern mass spectrometry approach, namely positive‐ion electrospray ionization/mass spectrometry/mass spectrometry, to provide a fresh interpretation of the MGDG and DGDG composition of the species, Cyanophora paradoxa Korshikov and Glaucocystis nostochinearum Itzigsohn, representing two glaucocystophyte genera. We have found that the major forms of MGDG and DGDG (with sn‐1/sn‐2 regiochemistry) are 20:5/16:0 MGDG, 20:5/20:5 MGDG, 20:5/16:0 DGDG, and 20:5/20:5 DGDG. A comparison of these four forms, along with other more minor forms of MGDG and DGDG, to two examples of cyanobacteria has revealed that glaucocystophytes do not share intact forms of MGDG and DGDG with extant cyanobacteria, but may have maintained certain C₁₆ and C₁₈ cyanobacterial fatty acids.     

Biosynthesis and desaturation of prokaryotic galactolipids in leaves and isolated chloroplasts from spinach

Mono- and digalactosyldiacylglycerol (MGDG and DGDG) were isolated from the leaves of sixteen 16:3 plants. In all of these plant species, the sn-2 position of MGDG was more enriched in C₁₆ fatty acids than sn-2 of DGDG. The molar ratios of prokaryotic MGDG to prokaryotic DGDG ranged from 4 to 10. This suggests that 16:3 plants synthesize more prokaryotic MGDG than prokaryotic DGDG. In the 16:3 plant Spinacia oleracea L. (spinach), the formation of prokaryotic galactolipids was studied both in vivo and in vitro. In intact spinach leaves as well as in chloroplasts isolated from these leaves, radioactivity from [1-¹⁴C]acetate accumulated 10 times faster in MGDG than in DGDG. After 2 hours of incorporation, most labeled galactolipids from leaves and all labeled galactolipids from isolated chloroplasts were in the prokaryotic configuration. Both in vivo and in vitro, the desaturation of labeled palmitate and oleate to trienoic fatty acids was higher in MGDG than in DGDG. In leaves, palmitate at the sn-2 position was desaturated in MGDG but not in DGDG. In isolated chloroplasts, palmitate at sn-2 similarly was desaturated only in MGDG, but palmitate and oleate at the sn-1 position were desaturated in MGDG as well as in DGDG. Apparently, palmitate desaturase reacts with sn-1 palmitate in either galactolipid, but does not react with the sn-2 fatty acid of DGDG. These results demonstrate that isolated spinach chloroplasts can synthesize and desaturate prokaryotic MGDG and DGDG. The finally accumulating molecular species, MGDG(18:3/16:3) and DGDG(18:3/16:0), are made by the chloroplasts in proportions similar to those found in leaves.     

Temperature modulation and the presence of C20 fatty acids in mono‐ and digalactosyldiacylglycerol of Euglena gracilis and Lepocinclis acus: A modern interpretation of euglenid galactolipids using positive‐ion electrospray ionization/mass spectrometry

Mono‐ and digalactosyldiacylglycerol (MGDG and DGDG, respectively) are important galactolipids that comprise photosynthetic membranes in almost all photosynthetic organisms. Intact forms of MGDG and DGDG of Euglena gracilis and Lepocinclis acus, two example euglenids with secondary plastids of green algal origin, were elucidated with fatty acid regiochemistry via positive‐ion electrospray ionization/mass spectrometry at two growth temperatures. At 20°C, E. gracilis and L. acus produced predominantly 18:3/16:4 (sn‐1/sn‐2) MGDG, whereas at 30°C this was supplanted by 18:2/16:2 MGDG. At both temperatures were also observed a variety of other MGDG and DGDG forms, including C₂₀ fatty acid‐containing forms not expected in a green algal‐derived plastid. In addition to providing structural details of MGDG and DGDG not available in past studies, these results suggest a previously unknown relationship between these two organisms and the red algae. This study also illustrates that temperature modulation of galactolipids occurs via modification of unsaturation of both the sn‐1 and sn‐2 fatty acids; this is fundamentally different from previously published studies from our laboratory on other algal classes.     

Plasma membrane lipid composition of the halophilic cyanobacterium Aphanothece halophytica

The plasma membrane from Aphanothece halophytica was isolated using both glycerol and sucrose gradient centrifugation. The isolated membrane was characterized for lipid content by TLC and isolated lipids were quantified by chemical analysis. The plasma membrane of A. halophytica was composed of MGDG, DGDG and PG. The sulfur containing lipid SQDG was not detected. The mole percent of each lipid in the plasma membrane varied with the external salinity of the media. MGDG was the most abundant lipid in the plasma membrane of cells grown at one molar external NaCl. At three molar external NaCl, PG was the most abundant lipid. The ratio of uncharged to charged lipids comprising the plasma membrane decreased as the external salinity increased. It is possible that the alteration in lipid composition is of major importance in the adaptation of A. halophytica to changing external salinity.Abbreviations TLC Thin-layer chromatography - MGDG momogalactosyldiacylglycerol - DGDG digaloctosyldiacylglycerol - PG phosphatidylglycerol - SQDG sulphoquinovosyldiacylglycerol     

Influence of thylakoid membrane lipids on the structure of aggregated light‐harvesting complexes of the diatom Thalassiosira pseudonana and the green alga Mantoniella squamata

The study investigated the effect of the thylakoid membrane lipids monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), sulphoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG) on the structure of two algal light‐harvesting complexes (LHCs). In contrast to higher plants whose thylakoid membranes are characterized by an enrichment of the neutral galactolipids MGDG and DGDG, both the green alga Mantoniella squamata and the centric diatom Thalassiosira pseudonana contain membranes with a high content of the negatively charged lipids SQDG and PG. The algal thylakoids do not show the typical grana–stroma differentiation of higher plants but a regular arrangement. To analyze the effect of the membrane lipids, the fucoxanthin chlorophyll protein (FCP) complex of T. pseudonana and the LHC of M. squamata (MLHC) were prepared by successive cation precipitation using Triton X‐100 as detergent. With this method, it is possible to isolate LHCs with a reduced amount of associated lipids in an aggregated state. The results from 77 K fluorescence and photon correlation spectroscopy show that neither the neutral galactolipids nor the negatively charged lipids are able to significantly alter the aggregation state of the FCP or the MLHC. This is in contrast to higher plants where SQDG and PG lead to a strong disaggregation of the LHCII whereas MGDG and DGDG induce the formation of large macroaggregates. The results indicate that LHCs which are integrated into thylakoid membranes with a high amount of negatively charged lipids and a regular arrangement are less sensitive to lipid‐induced structural alterations than their counterparts in membranes enriched in neutral lipids with a grana–stroma differentiation.     

The lipid dependence of diadinoxanthin de-epoxidation presents new evidence for a macrodomain organization of the diatom thylakoid membrane

The present study shows that thylakoid membranes of the diatom Cyclotella meneghiniana contain much higher amounts of negatively charged lipids than higher plant or green algal thylakoids. Based on these findings, we examined the influence of SQDG on the de-epoxidation reaction of the diadinoxanthin cycle and compared it with results from the second negatively charged thylakoid lipid PG. SQDG and PG exhibited a lower capacity for the solubilization of the hydrophobic xanthophyll cycle pigment diadinoxanthin than the main membrane lipid MGDG. Although complete pigment solubilization took place at higher concentrations of the negatively charged lipids, SQDG and PG strongly suppressed the de-epoxidation of diadinoxanthin in artificial membrane systems. In in vitro assays employing the isolated diadinoxanthin cycle enzyme diadinoxanthin de-epoxidase, no or only a very weak de-epoxidation reaction was observed in the presence of SQDG or PG, respectively. In binary mixtures of the inverted hexagonal phase forming lipid MGDG with the negatively charged bilayer lipids, comparable suppression took place. This is in contrast to binary mixtures of MGDG with the neutral bilayer lipids DGDG and PC, where rapid and efficient de-epoxidation was observed. In complex lipid mixtures resembling the lipid composition of the native diatom thylakoid membrane, we again found strong suppression of diadinoxanthin de-epoxidation due to the presence of SQDG or PG. We conclude that, in the native thylakoids of diatoms, a strict separation of the MGDG and SQDG domains must occur; otherwise, the rapid diadinoxanthin de-epoxidation observed in intact cells upon illumination would not be possible.     

Squishy lipids: Temperature effects on the betaine and galactolipid profiles of a C18/C18 peridinin‐containing dinoflagellate,Symbiodinium microadriaticum (Dinophyceae), isolated from the mangrove jellyfish,Cassiopea xamachana

Previous work from our laboratory has shown dinoflagellates, which possess the carotenoid peridinin, have been divided into two clusters based on plastid galactolipid fatty acid composition. In one cluster major forms of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), lipids that comprise the majority of photosynthetic membranes, were C₁₈/C₁₈ (sn‐1/sn‐2), with octadecapentaenoic [18:5(n‐3)] and octadecatetraenoic [18:4(n‐3)] acid as principal fatty acids. The other cluster contained C₂₀/C₁₈ major forms, with eicosapentaenoic acid [20:5(n‐3)] being the predominant sn‐1 fatty acid. In this study, we have found that Symbiodinium microadriaticum isolated from the jellyfish, Cassiopea xamachana, when grown at 30°C, produced MGDG and DGDG with a more saturated fatty acid, 18:4(n‐3), at the sn‐2 carbon than when grown at 20°C where 18:5(n‐3) predominates. This modulation of the sn‐2 fatty acid's level of saturation is mechanistically similar to what has been observed in Pyrocystis, a C₂₀/C₁₈ dinoflagellate. We have also examined the effect of growth temperature on the betaine lipid, diacylglycerylcarboxyhydroxymethylcholine (DGCC), which has been observed by others to be the predominant non plastidial polar lipid in dinoflagellates. Temperature effects on it were minimal, with very few modulations in fatty acid unsaturation as observed in MGDG and DGDG. Rather, the primary difference seen at the two growth temperatures was the alteration of the amount of minor forms of DGCC, as well as a second betaine lipid, diacylglyceryl‐N,N,N‐trimethylhomoserine.     

Incorporation of14C-radioactivity into various lipid classes at different growth-stages of culturedLaminaria japonica

A study is reported on the incorporation of¹⁴C-acetate into lipid classes from three different growth stages ofLaminaria japonica, a species long used for food in Japan. This was done because of the possible utilization of its lipids.Radioactivity incorporated into whole lipids in the three growth stages under the same experimental conditions (10 °C, 500 lux) increased with maturity of the thalli. The radioactivity was found mainly in PC, TG and 1,2-DG and subsequently distributed into other lipid classes (PG,PI,PE,MGDG,SQDG and DGDG) to a lesser extent. The incorporation patterns of the former group were similar at all stages, but those of the latter group differed slightly according to growth stage.In juvenile thalli,¹⁴C was incorporated to a much higher extent into PG, MGDG, PI and fucosterol than PE, SQDG, DGDG and MG, while the¹⁴C-incorporation into MG, SQDG, DGDG and PS in the mature growth stage was higher than into the other lipid classes. The absolute level of incorporation was higher for all these compounds in mature thalli than the thalli of other growth stages.     

Lipid Compositions of Photomixotrophic Green Calluses and Chlorophyll Deficient Leaves of Tobacco

Among photomixotrophic green calluses tested (N. rustica. N. tobacum L. cv. BY-4 and Samsun), the callus of Samsun had the highest contents of chlorophyll and chloroplast lipids, such as monogalactosyldiglyceride (MGDG), digalactosyldiglyceride (DGDG), sulfoquinovosyldigly-ceride (SQDG) and phosphatidylglycerol (PG). However, the chlorophyll and chloroplast lipids in the green callus of Samsun were still 1/6 and 1/3 of that in the parent leaves, respectively. The relative content of a-linolenate in MGDG, DGDG and SQDG of the green calluses were higher than that of the white calluses. The ratios of hexadecatrienoate in MGDG and hexadeceno-ate (Δ³-trans) in PG in the green calluses were trace or less compared with that of the parent leaves. The crude lipids and total fatty acid contents of the chlorophyll deficient leaves (N. taba-cum L. cv. Consolation 402 and Dominant Aurea Su/su) were almost the same as those of the normal leaves (cv. BY-4 and Samsun), although the chlorophyll contents of the chlorophyll deficient leaves were 1/3 ~ 1/4 of that of the normal leaves. The ratios of chloroplast lipids in the total polar lipids in the chlorophyll deficient leaves were a little lower than that in the normal green leaves, but the former had a slightly higher ratio of phospholipids such as phosphatidylcholine and phosphatidylethanolamine than the latter. There were few differences in the fatty acid compositions of each individual lipid betweeen both types of leaves.     

Osmoregulation in Escherichia coli by accumulation of organic osmolytes: betaines,glutamic acid,and trehalose

Like other cyanobacteria, Chlorogloeopsis fritschii contained as major lipid classes monogalactosyldiacyl-glycerols, digalactosyldiacylglycerols, sulfoquinovosyldiacylglycerols and diacylglycerophosphoglycerols. In addition to these lipid classes this cyanobacterium also contained small amounts of diacylglycerophosphocholines and sterols, predominantly lanosterol, thus showing similarity to photosynthetic eukaryotes. Dark incubated cells contained larger proportions of the latter two lipid classes than light grown cells. Like other prokaryotes, C. fritschii lacked linolenic acid (18:3) in its lipids. Lipids from the thylakoids were richer in palmitoleic acid (16:1) than those of whole cells. There was no effect of light on the patterns of constituent fatty acids of lipids from C. fritschii, in contrast to photosynthetic eukaryotes.Abbreviations MGDG Monogalactosyldiacylglycerols - PA Phosphatidic acids - PE Diacylglycerophosphoethanolamines - PG Diacylglycerophosphoethanolamines - DGDG Digalactosyldiacylglycerols - SQDG Sulfoquinovosyldiacylglycerols - PC Diacylglycerophosphocholines     

MONO‐ AND DIGALACTOSYLDIACYLGLYCEROL COMPOSITION OF RAPHIDOPHYTES (RAPHIDOPHYCEAE): A MODERN INTERPRETATION USING POSITIVE‐ION ELECTROSPRAY/MASS SPECTROMETRY/MASS SPECTROMETRY1

Raphidophyte algae (Raphidophyceae) can be divided according to pigment composition and plastid ancestry into two categories, brown‐ and green‐pigmented taxa. We sought to examine if there are any biochemical differences in plastid lipid composition between the two groups. To this end, the composition and positional distribution of fatty acids of the chloroplast lipids, mono‐ and digalactosyldiacylglycerol (MGDG and DGDG, respectively), were examined using positive‐ion electrospray/mass spectrometry (ESI/MS) and electrospray/mass spectrometry/mass spectrometry (ESI/MS/MS). Brown‐pigmented strains from the genera Chattonella, Fibrocapsa, and Heterosigma primarily consisted of 20:5/18:4 (sn‐1/sn‐2) MGDG and 20:5/18:4 DGDG, while isolates of the green‐pigmented raphidophyte Gonyostomum semen (Ehrenb.) Diesing contained these as well as 18:3/18:4 MGDG and DGDG, thus underscoring its green algal plastid lineage. Although previously unseen without the regiochemical information provided by ESI/MS/MS, Chattonella subsalsa Biecheler possessed 20:5/18:3 DGDG as a major form, a potential biosynthetic intermediate in the production of 20:5/18:4 DGDG. These results provide a modern interpretation of the fatty acid regiochemistry of MGDG and DGDG.     

Effects of Cadmium on Polar Lipid Composition and Unsaturation in Maize （Zea mays） in Hydroponic Culture

This study aimed to evaluate the effect of Cd exposure （100 μmol/L） on polar lipid composition, and to examine the level of fatty acid unsaturation in maize （Zea mays L.）. In roots, the level of 16：0 and monounsaturated fatty acids （16：1 ＋ 18：1） decreased in phosphatidylcholine （PC） and phosphatidylethanolamine （PE）. In contrast, the proportion of unsaturated 18-C fatty acid species showed an opposite response to Cd. The content, on the other hand, of PC, PE, digalactosyldiacylglycerol （DGDG）, and steryl lipids increased in roots （2.9-, 1.6-, 5.3-, and 1.7-fold increase, respectively）. These results suggest that a more unsaturated fatty acid composition than found in control plants with a concomitant increase in polar lipids may favor seedling growth during Cd exposure. However, the observed increase in the steryl lipid （SL） ： phospholipid （PL） ratio （twofold）, the decrease in monogalactosyldiacylglycerol （MGDG） ： DGDG ratio, as well as the induction of lipid peroxidation in roots may represent symptoms of membrane injury. In shoots, the unsaturation level was markedly decreased in PC and phosphatidylglycerol （PG） after Cd exposure, but showed a significant increase in sulfoquinovosyldiacylglycerol （SQDG）, MGDG and DGDG. The content of PG and MGDG was decreased by about 65%, while PC accumulated to higher levels （4.4-fold increase）. Taken together, these changes in the polar lipid unsaturation and composition are likely to be due to alterations in the glycerolipid pathway. These results also support the idea that the increase in overall unsaturation plays some role in enabling the plant to withstand the metal exposure.     

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-rß-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 mainlyconsist of triacylglycerol (TAG) and diacylglycerol (DAG). Majorfatty acids are 16:0,18:1, 18:3, 18:4, 20:4 and 20:5. The positionaldistribution of fatty acids showed that molecular species ofeukaryotic structure account for 99% in MGDG, 98% in DGDG, 62%in PG and 23% in SQDG. On incubation with [1-¹⁴C]18:1 for 30min, 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 simultaneouslyincreased in MGDG up to 41% of the total. In SQDG, labelledfatty acids were found in prokaryotic as well as in eukaryoticmolecular species. During the experiment, the label shiftedfrom 18:1 to 18:2, 18:3, 18:4 and, to a minor extent, to 20:4and 20:5 acids indicating 18:1 to be processed by elongationand/or desaturation. These results suggest TAG to act as a majorprimary acceptor of exogenous oleate and to be involved in thetransfer of fatty acids to MGDG and other polar lipids. (Received March 24, 1997; Accepted June 11, 1997)