Effect of Changed Environmental Conditions on Glycolipids of the Mosses Pleurozium Schreberi and Ceratodon purpureus

The effect of changed environmental conditions on the content of glycolipids and component fatty acids was studied in the moss species Pleurozium schreberi and Ceratodon purpureus. The mosses were collected from their natural habitats when frozen and covered by snow. After one week's exposure to rhythmic light (150 μE m^?2 s^?1, 12 h 17°C) no changes were observed in the absolute amount of fatty acids in either mono- (MGDG) or diglycosyl diglyceride (DGDG) fractions. Some changes were recorded in the content of individual fatty acids, however. The long chain, polunsaturated fatty acids (mainly 20:4ω6 and 20:5ω3 in P. schreberi and in addition 16:3ω3 and 18:3ω3 in C. purpureus) tended to decrease and the shorter chain, more saturated ones increased correspondingly. Under continuous light conditions (17°C) the total amount of fatty acids decreased in both MGDG and DGDG fractions, more significantly at 150 than at 75 μE m^?2 s^?1. This was due to the accelerated degradation and/or decreased synthesis of polyunsaturated fatty acids, which in this case was not totally compensated by the increase in shorter chain, more saturated ones.     

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.     

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.     

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.     

Mono- and digalactosyldiacylglycerol composition of dinoflagellates. III. Four cold-adapted,peridinin-containing taxa and the presence of trigalactosyldiacylglycerol as an additional glycolipid

Despite their importance in marine and freshwater microalgal assemblages, cold-adapted dinoflagellates have been the subject of few comprehensive lipid studies, particularly with respect to those lipids that comprise plastid membranes. In an effort to understand the differences between warm- and cold-adapted dinoflagellate glycolipid composition, four peridinin-containing, cold-adapted dinoflagellates were surveyed for intact forms of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), two common plastid lipids, using positive-ion electrospray ionization/mass spectrometry (ESI/MS) and electrospray ionization/mass spectrometry/mass spectrometry (ESI/MS/MS). It was determined that the dominant forms of MGDG and DGDG in these cold-adapted, peridinin-containing dinoflagellates possessed C₁₈ fatty acids and did not, with the exception of a 20:5/18:5 form of DGDG in a cold-adapted Gymnodinium sp. from the Baltic Sea, have C₂₀ fatty acids. This finding is in contrast to an earlier study of 35 peridinin-containing, warm-adapted dinoflagellates, which discovered a cluster dominated by C₁₈ fatty acids and a cluster dominated by both C₂₀ and C₁₈ fatty acids. The key difference in MGDG and DGDG production between the former group and the cold-adapted dinoflagellates examined in this study is that the cold-adapted species’ DGDG fatty acids were less saturated. Each cold-adapted dinoflagellate possessed both 18:5/18:5 and 18:5/18:4 DGDG, while most of the warm-adapted dinoflagellates contained only 18:5/18:4 DGDG. This survey also revealed the presence of a putative 18:1/14:0 trigalactosyldiacylglycerol (TGDG) as a dominant glycolipid in Gymnodinium sp. TGDG, previously unreported in dinoflagellates, was also discovered in Gymnodinium sp. in the forms of 18:1/16:0 and 18:1/18:1 TGDG, as minor lipids. Since the fatty acids associated with TGDG are not those found with dominant forms of MGDG or DGDG, TGDG may be produced by a different biosynthetic pathway.     

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.     

Wounding stimulates the accumulation of glycerolipids containing oxophytodienoic acid and dinor-oxophytodienoic acid in Arabidopsis leaves

Although oxylipins can be synthesized from free fatty acids, recent evidence suggests that oxylipins are components of plastid-localized polar complex lipids in Arabidopsis (Arabidopsis thaliana). Using a combination of electrospray ionization (ESI) collisionally induced dissociation time-of-flight mass spectrometry (MS) to identify acyl chains, ESI triple-quadrupole (Q) MS in the precursor mode to identify the nominal masses of complex polar lipids containing each acyl chain, and ESI Q-time-of-flight MS to confirm the identifications of the complex polar lipid species, 17 species of oxylipin-containing phosphatidylglycerols, monogalactosyldiacylglycerols (MGDG), and digalactosyldiacylglycerols (DGDG) were identified. The oxylipins of these polar complex lipid species include oxophytodienoic acid (OPDA), dinor-OPDA (dnOPDA), 18-carbon ketol acids, and 16-carbon ketol acids. Using ESI triple-Q MS in the precursor mode, the accumulation of five OPDA- and/or dnOPDA-containing MGDG and two OPDA-containing DGDG species were monitored as a function of time in mechanically wounded leaves. In unwounded leaves, the levels of these oxylipin-containing complex lipid species were low, between 0.001 and 0.023 nmol/mg dry weight. However, within the first 15 min after wounding, the levels of OPDA-dnOPDA MGDG, OPDA-OPDA MGDG, and OPDA-OPDA DGDG, each containing two oxylipin chains, increased 200- to 1,000-fold. In contrast, levels of OPDA-hexadecatrienoic acid MGDG, linolenic acid (18:3)-dnOPDA MGDG, OPDA-18:3 MGDG, and OPDA-18:3 DGDG, each containing a single oxylipin chain, rose 2- to 9-fold. The rapid accumulation of high levels of galactolipid species containing OPDA-OPDA and OPDA-dnOPDA in wounded leaves is consistent with these lipids being the primary products of plastidic oxylipin biosynthesis.     

The effect of phosphate starvation on the lipid and fatty acid composition of the fresh water eustigmatophyte Monodus subterraneus

Phosphate limitation caused significant changes in the fatty acid and lipid composition of Monodus subterraneus. With decreasing phosphate availability from 175 to 52.5, 17.5 and 0 microM (K2HPO4), the proportion of the major VLC-PUFA, eicosapentaenoic acid (EPA), gradually decreased from 28.2 to 20.8, 19.4 and 15.5 mol% (of total fatty acids), respectively. The cellular total lipid content of starved cells increased, mainly due to the dramatic increase in triacylglycerols (TAG) levels. Among polar lipids, cellular contents of digalactosyldiacylglycerol (DGDG) and diacylglyceroltrimethylhomoserine (DGTS) increased sharply from 0.29 and 0.19 to 0.60 and 0.38 fg cell(-1), respectively, while that of monogalactosyldiacylglycerol (MGDG) was not significantly changed. In the absence of phosphate, the proportion of phospholipids was significantly reduced from 8.3% to 1.4% of total lipids, and the proportion of triacylglycerols (TAG) increased from 6.5% up to 39.3% of total lipids. The share of MGDG was substantially reduced, from 35.7% to 13.3%, while that of DGDG and DGTS reduced less from 18.3% to 15.1%, and 12.2% to 8.6%, respectively. The most distinctive change in the fatty acid composition was noted in that of DGDG, where the proportion of EPA, located exclusively at the sn-1 position, increased from 11.3% to 21.5% at the expense of 16:0, 16:1 and 18:1. In MGDG, however, the proportion of EPA did not change appreciably. In contrast to higher plants, DGDG accumulated under P-deprivation in M. subterraneus, did not resemble PC and the positional distribution of its fatty acids was not altered, preserving the C20/C16 structure of its molecular species. We suggest that under phosphate starvation DGTS is a likely source of C20 acyl groups that can be exported to the sn-1 position of DGDG and can partially compensate for the decrease in PE, the apparent source of C20 acyl-containing diacylglycerols in this alga. Moreover, accumulation of non-esterified 18:0 indicates that no polar lipid can replace PC, which appears to be the only lipid capable of C18 desaturation in this alga.     

The effect of cadmium on lipid and fatty acid biosynthesis in tomato leaves

This research aims to examine the effect of cadmium uptake on lipid composition and fatty acid biosynthesis, in young leaves of tomato treated seedlings (Lycopersicon esculentum cv. Ibiza F1). Results in membrane lipids investigations revealed that high cadmium concentrations affect the main lipid classes, leading to strong changes in their composition and fatty acid content. Thus, the exposure of tomato plants to cadmium caused a concentration-related decrease in the unsaturated fatty acid content, resulting in a lower degree of fatty acid unsaturation. The level of lipid peroxides was significantly enhanced at high Cd concentrations. Studies of the lipid metabolism using radioactive labelling with [1-¹⁴C]acetate as a major precursor of lipid biosynthesis, showed that levels of radioactivity incorporation in total lipids as well as in all lipid classes were lowered by Cd doses. In total lipid fatty acids, [1-¹⁴C]acetate incorporation was reduced in tri-unsaturated fatty acids (C16:3 and C18:3); While it was enhanced in the palmitic (C16:0), palmitoleic (C16:1), stearic (C18:0) and linoleic (C18:2) acids. [1-¹⁴C]acetate incorporation into C16:3 and C18:3 of galactolipids [monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG)] and some phospholipids [phosphatidylcholine (PC) and phosphatidylglycerol (PG)] was inhibited by Cd stress. Our results showed that in tomato plants, cadmium stress provoked an inhibition of polar lipid biosynthesis and reduced fatty acid desaturation process.     

Fatty-acid composition of polar lipids in fruit and leaf chloroplasts of “16:3”- and “18:3”-plant species

The fatty-acid composition of polar lipids from fruit and leaf chloroplasts was compared in five Solanaceous and two cucurbit species. The acylated fatty acids in monogalactosyl diglycerides (MGDG) from leaf chloroplasts of all five Solanaceous species included substantial amounts of ^7,10,13-hexadecatrienoic acid (16:3). In contrast, the MGDG from fruit chloroplasts of the Solanaceae contained very little of this plastid-specific polyunsaturate, and instead included a proportionately greater percentage of linoleic acid (18:2). In MGDG from leaf chloroplasts of two cucurbits, -linolenic acid (18:3) constituted 94–95% of the acylated fatty acids. Fruit-chloroplast galactolipids of the cucurbits had a greater abundance of 18:2, and hence a higher 18:2/18:3 ratio, than found in the corresponding leaf lipids. Among the phosphoglycerides, the unusual fatty acid 3-trans-hexadecenoate (trans-16:1) constituted from 15 to 24% of the acylated fatty acids in phosphatidyl glycerol (PG) from leaf chloroplasts (all species). In sharp contrast, trans-16:1 was virtually absent in PG from fruit chloroplasts of both Solanaceous and cucurbit species, and was replaced by a proportionate increase in the content of palmitate (16:0). The observed differences in the polar lipid fatty-acid composition of fruit and leaf chloroplasts are discussed in terms of the relative activity of several intrachloroplastic enzymes involved in lipid synthesis and fatty-acyl desaturation.Abbreviations MGDG monogalactosyldiglyceride - DGDG digalactosyl diglyceride - PC phosphatidyl choline - PE phosphatidyl ethanolamine - PG phosphatidyl glycerol     

Mono- and digalactosyldiacylglycerol composition of dinoflagellates. VI. Biochemical and genomic comparison of galactolipid biosynthesis between Chromera velia (Chromerida), a photosynthetic alveolate with red algal plastid ancestry,and the dinoflagellate,Lingulodinium polyedrum

Chromera velia is a recently discovered, photosynthetic, free-living alveolate that is the closest free-living relative to non-photosynthetic apicomplexan parasites. Most plastids, regardless of their origin, have membranes composed chiefly of two galactolipids, mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively). Because of the hypothesized shared red algal origin between the plastids of C. velia and dinoflagellates, our primary objectives were to examine how growth temperature affects MGDG and DGDG composition via positive-ion electrospray/mass spectrometry (ESI/MS) and positive ion/electrospray/mass spectrometry/mass spectrometry (ESI/MS/MS), and to examine galactolipid biosynthetic genes to determine if shared ancestry translates into shared MGDG and DGDG composition. When growing at 20°C, C. velia produces eicosapentaenoic acid-rich 20:5(n-3)/20:5(n-3) (sn-1/sn-2) MGDG and 20:5(n-3)/20:5(n-3) DGDG as its primary galactolipids, with relative percentage compositions of approximately 35 and 60%, respectively. At 30°C these are lessened by approximately 5 and 8%, respectively, by the corresponding production of 20:5/20:4 forms of these lipids. The presence of 20:5 at the sn-1 position is similar to what has been observed previously in a cluster of peridinin-containing dinoflagellates, but the presence of 20:5(n-3) at the sn-2 position is extremely rare. Thus, the forms of MGDG and DGDG in C. velia displayed similarities and differences to what has been observed in peridinin-containing dinoflagellates, such as Lingulodinium polyedrum, which produces 20:5/18:5 and 20:5/18:4 as the major forms of MGDG and DGDG. We develop conceptual models from the galactolipids observed and galactolipid-relevant gene annotations to explain the presence of polyunsaturated fatty acid-containing MGDG and DGDG in both L. polyedrum and C. velia.     

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.     

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)     

Determination of Fatty Acid Composition of Spore Lipids of the Moss Polytrichum commune by Glass Capillary Column Gas Chromatography

Fatty acid methyl esters of Polytrichum commune spore triglyceride and mono- and diglycosyl diglyceride fractions were analysed by glass capillary column gas chromatography provided with a precolumn system. The composition of the fatty acids in the lipid fractions differed only quantitatively: the diglycosyl diglyceride fraction was characterized by a high content of C 18: 3ω3 (67.7%), and the triglyceride and monoglycosyl diglyceride fractions by about 35%. The monoglycosyl diglyceride fraction contained a high proportion of C 14: 0 (18.4%). In all fractions the content of polyunsaturated C 20 acids was low, ranging from trace amounts to 4.9%.     

Polyunsaturated Fatty Acids and Betaine Lipids from Pavlova lutheri

The polar lipids and fatty acids of the microalgae Pavlova lutheriwere analyzed. The principal polar lipid components were monogalactosyldiacylglycerol(MGDG), digalactosyldiacylglycerol (DGDG), sulfoquinovosyldiacylglycerol(SQDG), 1,2-diacylglyceryl-O-2'-hydroxymethyl-(N,N,N-trimethyl)-rß-alanine(DGTA) and 1,2-diacylglyceryl-3-O-carboxyhydroxymethylcholine(DGCC). Each polar lipid had a different set of combinationsof fatty acids, the most characteristic feature being the localizationof polyunsaturated fatty acids in the betaine lipids. The percentagesof polyunsaturated fatty acids in DGTA and DGCC were 70% and50%, respectively, and these fatty acids were localized at theC-2 position in the betaine lipids. An analysis of the incorporationof ¹⁴C-labelled compounds into the algal cells indicated theinvolvement of DGCC in acyl exchange. (Received October 17, 1994; Accepted October 2, 1995)     

Enriching marine macroalgae with eicosatetraenoic (arachidonic) and eicosapentaenoic acids by chilling

Summary Twelve macroalgae belonging to the Chlorophyta, Phaeophyta and Rhodophyta were collected from the Arabian Gulf. Field samples and samples that were first incubated at 5° C and 24° C in the light for 1 week were analysed for lipids and fatty acids. The lipid contents varied according to the macroalga and, within the Chlorophyta and Phaeophyta, some representatives accumulated more lipids at 5° C and others at 24° C. All samples of algae had similar lipid composition with only quantitative differences. The temperature did not have a common effect on the lipid composition of representative algae, although changes in the relative concentration of specific classes were recorded. The Phaeophyta and Rhodophyta were as a rule richer than the Chlorophyta in eicosatetranoic (20:4) and eicosapentaenoic (20:5) but poorer in linolenic (18:3) acids. In most of the algae, incubation at 5° C was associated with lowering the proportion of palmitic acid (16:0) in the total lipids, and, but only in the Phaeophyta and Rhodophyta, increasing the concentration of 20:4 and 20:5. These polyunsaturated fatty acids occurred in high levels in monogalactosyldiacylglycerols (MGDG) and digalactosyldiacylglycerols (DGDG) of the Phaeophyta and Rhodophyta but not the Chlorophyta, the MGDG and DGDG of which were rich in 18:3 and hexadecatrienoic acid (16:3). Offprint requests to: R. H. Al-Hasan     

Chlorophyll-sensitized Photooxidation Products of Spinach Galactolipids

Spinach monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) were oxidized with singlet molecular oxygen by the use of chlorophyll a as the photosensitizer. The oxidation products were separated from the unoxidized MGDG and DGDG by reverse-phase high performance liquid chromatography (HPLC). The products separated by HPLC were identified to be mono- and di-hydroperoxides formed by ¹O₂ oxidation of the 16:3 or 18:3 component of MGDG and DGDG. Each unsaturated fatty acid moiety in the MGDG and DGDG produced isomeric hydroperoxides in a manner similar to the corresponding fatty acid methyl ester.     

Precise identification of photosynthetic glycerolipids in microalga <Emphasis Type="Italic">Tetraselmis chuii</Emphasis> 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.     

The Effect of Light Intensity, Day Length, and Temperature on Fatty Acid Synthesis and Desaturation in Vicia faba L.

Some effects of light intensity, day length, and temperatureon the fatty acid composition of the major glycerolipids ofleaves of Vicia faba L. (cv. Giant Windsor) were observed. Increasinglight intensity caused an increase in the relative concentrationsof 16 : 1 in PG and 18 : 3 in MGDG and DGDG. Increasing daylength during growth (and continuous illumination of leaf tissue)had no effect on 16 : 1 in PG but caused a decrease in the 18: 3 content of PG, PC, MGDG, and DGDG. Since the quantitiesof these lipids increased under these conditions, the decreasewas not due to photodestruction but to the differences in therelative rates of biosynthesis and desaturation of fatty acids.Incubation of leaf tissue in the dark for 4 d had little effecton the fatty acid composition of MGDG, DGDG, and PG. Temperaturealso controls fatty acid synthesis and desaturation. Above theoptimum growth temperature (20 °C), the 18 : 3 content ofMGDG, DGDG, PG, and PC decreased. In mature leaf tissue, thedegree of unsaturation of MGDG may be modified upward in responseto temperature changes. When plants were grown at 30 °Cand transferred to 20 °C the level of 18 : 3 in MGDG ofthe leaf tissue increased to levels found in plants grown onlyat 20 °C. The level of 18 : 3 in MGDG does not decreaseas rapidly when plants grown at 20 °C were transferred to30 °C. This suggests that the lower temperature induceddesaturation of 18 : 2 to 18 : 3.