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.     

Composition of galactolipids,betaine lipids and triglyceride-associated fatty acids of the symbiotic dinoflagellate Zooxanthella (Brandtodinium) nutricula: A glimpse into polyunsaturated fatty acids available to its polycystine radiolarian host

Zooxanthella nutricula is a photosynthetic dinoflagellate symbiont of polycystine radiolarians. As such, it is hypothesized to provide fixed organic carbon, including in the form of acylglycerolipids and sterols, to its non-photosynthetic host. We have previously characterized the sterols of Z. nutricula that may be transferred to its host and, in the present study, have turned our attention to three classes of fatty acid-containing lipids, chloroplast-associated galactolipids, betaine lipids, which are non-phosphorylated phospholipid analogs present in many eukaryotes, and triglycerides. Zooxanthella nutricula was observed using positive-ion electrospray/mass spectrometry (ESI/MS) and ESI/MS/MS to produce the galactolipids mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively) enriched in octadecapentaenoic (18:5(n-3)) and octadecatetraenoic (18:4(n-3)) acid to place it within a group of peridinin-containing dinoflagellates in a C₁₈/C₁₈ (sn-1/sn-2 fatty acid regiochemistry) cluster, as opposed to another cluster with C₂₀/C₁₈ MGDG and DGDG, where the C₂₀ fatty acid is eicosapentaenoic acid (20:5(n-3)) and the C₁₈ fatty acid is either 18:5(n-3) or 18:4(n-3). Zooxanthella nutricula was also observed to produce 38:10 (total number of fatty acid carbons:total number of double bonds), 38:6, and 44:7 diacylglycerylcarboxyhydroxymethylcholine (DGCC) as the sole type of betaine lipid. Although it is more difficult to determine which fatty acids are present in the sn-1 and sn-2 positions on the glycerol backbone of DGCC using ESI/MS/MS, gas chromatography/mass spectrometry (GC/MS)-based examination indicated the putatively DGCC-associated polyunsaturated fatty acid (PUFA) docosahexaenoic acid (22:6(n-3)). Coupled with the C₁₈ PUFAs of MGDG and DGDG, and fatty acids associated with triglycerides (also examined via GC/MS), Z. nutricula could serve as a rich source of PUFAs for its radiolarian host. These data demonstrate that Z. nutricula produces a similar set of PUFA-containing lipids as Symbiodinium microadriaticum, a photosynthetic dinoflagellate symbiont of cnidarians, indicating a metabolic commonality in these phylogenetically discrete dinoflagellate symbionts with unrelated host organisms.     

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 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.     

Mono- and digalactosyldiacylglycerol composition of dinoflagellates. VIII. Temperature effects and a perspective on the curious case of Karenia mikimotoi as a producer of the unusual, ‘green algal’ fatty acid hexadecatetraenoic acid [16:4(n-3)]

Previous studies have shown that dinoflagellates with different plastid ancestries have distinct differences in the fatty acid compositions and regiochemistries of their chloroplast-associated galactolipids, mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively), thus reflecting plastid origin as a major factor in plastid membrane composition. Specifically, dinoflagellates with aberrant plastids (e.g. Karenia brevis, Kryptoperidinium foliaceum and Lepidodinium chlorophorum) possess certain MGDG- and DGDG-associated fatty acids which are not found in peridinin-containing dinoflagellates (the largest group of photosynthetic dinoflagellates with a red algal plastid ancestry which is thought to be an evolutionary precursor to aberrant plastids), but which are common to other algal groups. For example, hexadecatetraenoic acid (16:4(n-3)) is common to green algae and is found in the MGDG and DGDG of L. chlorophorum, which agrees with its green algal plastid ancestry, while hexadecatrienoic acid (16:3) and hexadecadienoic acid (16:2) are found in the MGDG and DGDG of K. foliaceum, which agrees with its diatom plastid ancestry. Notably, 16:4 has been found by others in the total fatty acids and galactolipids of Karenia mikimotoi, but in no other examined members of the Kareniaceae (all of which have plastids of haptophyte origin). However, these findings lack information as to the regiochemistry of 16:4. We have utilized positive-ion electrospray ionization/mass spectrometry (ESI/MS) and ESI/MS/MS to demonstrate that 16:4, which aside from L. chlorophorum is not found conclusively in the MGDG and DGDG of any other dinoflagellates examined to date irrespective of plastid ancestry, is found in K. mikimotoi as 18:5/16:4 (sn-1/sn-2 regiochemistry) MGDG and DGDG, and that its presence is not modulated (i.e. does not become more saturated) with an increase in growth temperature. Considering an aberrant pigment composition as described by others, we present a perspective where galactolipid-associated 16:4 in K. mikimotoi indicates a plastid ancestry more convoluted than for other members of the Kareniaceae.     

Mono‐ and digalactosyldiacylglycerol composition of the marennine‐producing diatom,Haslea ostrearia: Comparison to a selection of pennate and centric diatoms

Diatoms are one of the largest groups of primary producers in the oceans, yet despite their environmental importance little is known about their plastidial lipid biochemistry. It has been previously reported that Skeletonema species contain primarily C₁₆/C₁₆ and C₂₀/C₁₆ forms of mono‐ and digalactosyldiacylglycerol (MGDG and DGDG, respectively). Likewise, it was also reported that Phaeodactylum tricornutum contains primarily C₁₆/C₁₆ and C₂₀/C₂₀ forms of MGDG and DGDG. We seek to relate their studies to other diatoms, both in the centrics and pennates, with particular focus on the marennine‐producing pennate diatom, Haslea ostrearia. To this end, the composition and positional distribution of fatty acids of MGDG and DGDG were examined using positive‐ion electrospray ionization/mass spectrometry (ESI/MS). Two centric diatoms, Skeletonema marinoi and Thalassiosira weissflogii, and the pennate diatom, P. tricornutum, contained primarily C₂₀/C₁₆ (sn‐1/sn‐2) and C₁₈/C₁₆ forms of MGDG and DGDG. The other pennate diatoms, H. ostrearia and Navicula perminuta, contained primarily C₁₈/C₁₆ or C₁₈/C₁₈ forms of MGDG and DGDG, indicating a previously unrecognized fatty acid diversity in diatom MGDG and DGDG.     

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.     

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.     

Fatty Acid Composition of Polar Lipids in Ceratodon purpureus and Pleurozium schreberi

The total amount of fatty acids in the mono- (MGDG) and diglycosyl diglyceride (DGDG) and more polar lipid fractions of frozen Ceratodon purpureus shoots was 4.6, 3.4 and 4.0 mg/g dry weight, respectively. The respective values for the tops of frozen Pleurozium schreberi were 2.6, 3.3 and 3.8 mg/g dry weight. The molar ratios MGDG/DGDG and MGDG + DGDG/chlorophyll were 1.3 and 3.7, respectively, for C. purpureus and 0.8 and 3.5 for P. schreberi. In C. purpureus the main fatty acids in the MGDG fraction were C 18:3ω3 (44% of the total fatty acids) and C 16:3ω3 (26%); in the DGDG fraction C 18:3ω3 (70%); and in the more polar lipid fraction C 18: 3ω3 (26%) and C 16:0 (25%). The proportion of C 20 polyunsaturated fatty acids was 15, 12 and 19% of the total fatty acids found in the MGDG, DGDG and more polar lipid fractions, respectively. In P. schreberi the proportion of C 20 polyunsaturated fatty acids was high in all polar lipid fractions (47, 42 and 25% in MGDG, DGDG and more polar lipid fractions, respectively). In addition, MGDG and DGDG fractions contained abundantly C 18:3ω3 (32 and 45%, respectively), and the more polar lipid fraction both C 18: 3ω3 (24%) and C 16:0 (27%).     

Red (hot) algae: modulation of mono- and digalactosyldiacylglycerol-associated fatty acids of Polysiphonia sp. and Porphyridium sp. in response to growth temperature

ABSTRACT

There is a dearth of surveys examining the direct effects of temperature on red algal galactolipids, and none which examine regiochemistry modulation with respect to growth temperature. Therefore, forms of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), the two most commonly found galactolipids in chloroplast membranes, were determined in two model red algae, Polysiphonia sp. and Porphyridium sp., via positive-ion electrospray ionization/mass spectrometry (ESI/MS) and ESI/MS/MS. We sought to compare modulation of galactolipid forms in response to growth temperature between these two red algae and selected descendants with red algal plastid ancestry, and have proposed the following hypothesis: Polysiphonia sp. and Porphyridium sp. would modulate desaturations in the sn-2 position in accordance with previously examined descendant organisms. It was observed that both red algae produced C₂₀/C₁₆ (sn-1/sn-2 regiochemistry) and C₂₀/C₂₀ forms of MGDG and DGDG as their most abundant galactolipids under two growth temperatures, 20°C and 30°C. Furthermore, temperature-induced modulation of the major forms of MGDG and DGDG was more complex than what has been observed previously in selected representatives of red algal plastid ancestry. Porphyridium sp. modulated levels of desaturation in the sn-1 position of C₂₀/C₁₆ forms of MGDG and DGDG and in the sn-1 and sn-2 positions of C₂₀/C₂₀ forms of MGDG and DGDG. Polysiphonia sp. displayed trends suggesting it modulates levels of desaturation in the sn-1 and sn-2 positions of C₂₀/C₂₀ forms of MGDG and DGDG, thus indicating a different approach to regulating plastid membrane fluidity from that which has been observed in algae with secondary, red algae-derived plastids.     

Mono- and digalactosyldiacylglycerol composition of dinoflagellates. V. The galactolipid profile of Alexandrium tamarense (Dinophyceae) during the course of infection by the parasitic syndinian dinoflagellate Amoebophrya sp.

Amoebophrya is a parasitic, syndinian dinoflagellate genus that must infect another host dinoflagellate in order to reproduce. Work by Park et al. [Mar. Ecol. Prog. Ser., 227: 281–292 (2002)] has led to the hypothesis that Amoebophrya's development within a host cell nucleus disrupts the flow of genetic information involved in plastidial function. The possibility that genetic disruption by this parasite could lead to alterations in plastidial lipid composition during the course of an infection has not yet been elucidated. Our primary objective in this lipidomic study was to examine the chloroplast membrane galactolipid composition of Alexandrium tamarense infected by an Amoebophrya species in order to determine whether infection of A. tamarense causes a phenotypic alteration in the composition of mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively), two galactolipids that comprise the majority of photosynthetic membranes. Our secondary objective was to determine if non-photosynthetic Amoebophrya sp. either incorporated host cell MGDG and DGDG, and/or itself produced forms of MGDG and DGDG, as has been observed previously in heterotrophic apicomplexan parasites distantly related to Amoebophrya. We found that, despite development of Amoebophrya sp. within the nucleus, the composition of A. tamarense MGDG and DGDG did not change throughout the infection process. The predominant forms of these galactolipids were 18:5/18:4 (sn???1/sn?2) and 20:5/18:4 DGDG, which were present at similar abundances in both an uninfected host and a host late in the infection process just prior to release of Amoebophrya sp. dinospores. Amoebophrya sp. did not possess appreciable amounts of any forms of MGDG and DGDG.     

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.     

Biosynthesis of digalactosyldiacylglycerol in plastids from 16:3 and 18:3 plants

Intact chloroplasts isolated from leaves of eight species of 16:3 and 18:3 plants and chromoplasts isolated from Narcissus pseudonarcissus L. flowers synthesize galactose-labeled mono-, di-, and trigalactosyldiacylglycerol (MGDG, DGDG, and TGDG) when incubated with UDP-[6-³H]galactose. In all plastids, galactolipid synthesis, and especially synthesis of DGDG and TGDG, is reduced by treatment of the organelles with the nonpenetrating protease thermolysin. Envelope membranes isolated from thermolysin-treated chloroplasts of Spinacia oleracea L. (16:3 plant) and Pisum sativum L. (18:3 plant) or membranes isolated from thermolysin-treated chromoplasts are strongly reduced in galactolipid:galactolipid galactosyltransferase activity, but not with regard to UDP-Gal:diacylglycerol galactosyltransferase. For the intact plastids, this indicates that thermolysin treatment specifically blocks DGDG (and TGDG) synthesis, whereas MGDG synthesis is not affected. Neither in chloroplast nor in chromoplast membranes is DGDG synthesis stimulated by UDP-Gal. DGDG synthesis in S. oleracea chloroplasts is not stimulated by nucleoside 5′-diphospho digalactosides. Therefore, galactolipid:galactolipid galactosyltransferase is so far the only detectable enzyme synthesizing DGDG. These results conclusively suggest that the latter enzyme is located in the outer envelope membrane of different types of plastids and has a general function in DGDG synthesis, both in 16:3 and 18:3 plants.     

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.     

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.     

Glycerolipid synthesis in Chlorella kessleri 11h: I. Existence of a eukaryotic pathway

The fatty acid distributions at the sn-1 and sn-2 positions in major chloroplast lipids of Chlorella kessleri 11h, monogalactosyl diacylglycerol (MGDG) and digalactosyl diacylglycerol (DGDG), were determined to show the coexistence of both C₁₆ and C₁₈ acids at the sn-2 position, i.e. of prokaryotic and eukaryotic types in these galactolipids. For investigation of the biosynthetic pathway for glycerolipids in C. kessleri 11h, cells were fed with [¹⁴C]acetate for 30 min, and then the distribution of the radioactivity among glycerolipids and their constituent fatty acids during the subsequent chase period was determined. MGDG and DGDG were labeled predominantly as the sn-1-C₁₈-sn-2-C₁₆ (C₁₈/C₁₆) species as early as by the start of the chase, which suggested the synthesis of these lipids within chloroplasts via a prokaryotic pathway. On the other hand, the sn-1-C₁₈-sn-2-C₁₈ (C₁₈/C₁₈) species of these galactolipids gradually gained radioactivity at later times, concomitant with a decrease in the radioactivity of the C₁₈/C₁₈ species of phosphatidylcholine (PC). The change at later times can be explained by the conversion of the C₁₈/C₁₈ species of PC into galactolipids through a eukaryotic pathway. The results showed that C. kessleri 11h, distinct from most of other green algal species that were postulated mainly to use a prokaryotic pathway for the synthesis of chloroplast lipids, is similar to a group of higher plants designated as 16:3 plants in terms of the cooperation of prokaryotic and eukaryotic pathways to synthesize chloroplast lipids. We propose that the physiological function of the eukaryotic pathway in C. kessleri 11h is to supply chloroplast membranes with 18:3/18:3-MGDG for their functioning, and that the acquisition of a eukaryotic pathway by green algae was favorable for evolution into land plants.     

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)     

Glycolipid composition of Hevea brasiliensis latex

Glycolipids of fresh latex from three clones of Hevea brasiliensis were characterized and quantified by HPLC/ESI-MS. Their fatty acyl and sterol components were further confirmed by GC/MS after saponification. The four detected glycolipid classes were steryl glucosides (SG), esterified steryl glucosides (ESG), monogalactosyl diacylglycerols (MGDG) and digalactosyl diacylglycerols (DGDG). Sterols in SG, ESG and total latex unsaponifiable were stigmasterol, β-sitosterol and Δ⁵-avenasterol. The latter was found instead of fucosterol formerly described. Galactolipids were mainly DGDG and had a fatty acid composition different from that of plant leaves as they contained less than 5% C18:3. Glycolipids, which represented 27–37% of total lipids, displayed important clonal variations in the proportions of the different fatty acids. ESG, MGDG and DGDG from clone PB235 differed notably by their higher content in furan fatty acid, which accounted for more than 40% of total fatty acids. Clonal variation was also observed in the relative proportions of glycolipid classes except MGDG (8%), with 43–51% DGDG, 30–34% SG and 7–19% ESG. When compared with other plant cell content, the unusual glycolipid composition of H. brasiliensis latex may be linked to the peculiar nature of this specialized cytoplasm expelled from laticiferous system, especially in terms of functional and structural properties.     

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.