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Chemical components in the hexane‐extract mixture from Phalaenopsis leaves were isolated and identified during the spike induction process. Several lipophilic components in the hexane‐extract mixture were isolated and identified as oleic acid, 1,2‐O‐dilinolenoyl‐MGDG, 1‐O‐linolenoyl‐2‐O‐linoleoyl‐MGDG, and α‐tocopherol by HPLC and NMR techniques. It is noteworthy that only one isomer of α‐tocopherol was isolated from Phalaenopsis leaves based on NMR spectra analysis. MGDG have a great potential to be a control factor in the regulation of spike process of Phalaenopsis. It is the first time to identify the chemical MGDG related to temperature‐controlled process of Phalaenopsis. These components have hydrophilic and hydrophobic moieties in the same molecule to act as potential amphiphiles. The use of the entire mixed hexane extract to form liposomes containing the dmbpyPtCl2 complex greatly enhanced the reactivity of the complex for inhibiting E. coli growth compared with the use of a single amphiphile. [ABSTRACT FROM AUTHOR]

The lignification of plant secondarywalls is an important process that provides plants with mechanical support. However, the presence of lignin in the secondary walls affects the readily availability of cellulose required in various industries, including the biofuel, paper, and textile industries. Thus, plants with less lignin are ideal for usage in such industries. Molecular studies have identified genes that regulate plant lignification, including group III plant-specific patatin-related phospholipase genes. Recent studies have reported decreased lignin content when pPLAIIIα, pPLAIIIγ (from Arabidopsis thaliana), and pPLAIIIβ (from Panax ginseng) were overexpressed in Arabidopsis. However, the role played by a closely related gene pPLAIIIδ in lignin biosynthesis has not yet been reported. In this study, we found that overexpression of the pPLAIIIδ significantly reduced the lignin content in secondary cell walls, whereas the silencing of the gene increased secondary walls lignification. Transcript level analysis showed that the key structural and regulatory genes involved in the lignin biosynthesis pathway decreased in overexpression, and increased in plants with silenced pPLAIIIδ. Further analysis revealed that pPLAIIIδ played an influential role in several physiological processes including seed germination, and chlorophyll accumulation. Moreover, the gene also influenced the size of plants and plant organs, including leaves, seeds, and root hairs. Generally, our study provides important insights toward the use of genetic engineering for lignin reduction in plants and provides information about the agronomical and physiological suitability of pPLAIIIδ transgenic plants for utilization in biomass processing industries. [ABSTRACT FROM AUTHOR]

The lignification of plant secondary walls is an important process that provides plants with mechanical support. However, the presence of lignin in the secondary walls affects the readily availability of cellulose required in various industries, including the biofuel, paper, and textile industries. Thus, plants with less lignin are ideal for usage in such industries. Molecular studies have identified genes that regulate plant lignification, including group III plant-specific patatin-related phospholipase genes. Recent studies have reported decreased lignin content when pPLAIIIα, pPLAIIIγ (from Arabidopsis thaliana), and pPLAIIIβ (from Panax ginseng) were overexpressed in Arabidopsis. However, the role played by a closely related gene pPLAIIIδ in lignin biosynthesis has not yet been reported. In this study, we found that overexpression of the pPLAIIIδ significantly reduced the lignin content in secondary cell walls, whereas the silencing of the gene increased secondary walls lignification. Transcript level analysis showed that the key structural and regulatory genes involved in the lignin biosynthesis pathway decreased in overexpression, and increased in plants with silenced pPLAIIIδ. Further analysis revealed that pPLAIIIδ played an influential role in several physiological processes including seed germination, and chlorophyll accumulation. Moreover, the gene also influenced the size of plants and plant organs, including leaves, seeds, and root hairs. Generally, our study provides important insights toward the use of genetic engineering for lignin reduction in plants and provides information about the agronomical and physiological suitability of pPLAIIIδ transgenic plants for utilization in biomass processing industries.

Abstract Background The cell wall and chloroplast are two fundamental structures determining plant mechanical strength and grain yield. Therefore, understanding mechanisms that improve plants’ ability to develop a robust cell wall and well-developed chloroplast is of utmost importance for agricultural activities. Results In this study, we report the functional characterization of a novel rice mutant, brittle stem and zebra leaf (bz1), which displays altered cell wall composition and collapsed chloroplast membrane. Molecular and biochemical analysis revealed that BZ1 encodes a functional UDP-galactose/glucose epimerase (UGE) and is ubiquitously expressed with higher expression in stem and leaf tissues. Multiple techniques analyses, including immunoblots, immuno-gold, and cryogenic scanning electron microscopy, demonstrated a significantly impaired glycosylation of arabinogalactan proteins (AGPs) and disordered cellulose microfibril deposition in bz1. Lipid profiling assay showed that the amount of monogalactosyldiacylglycerols (MGDG), a major chloroplast membrane glycolipid, was significantly decreased in bz1. Taken together, these results strongly demonstrate that BZ1 participates in UDP-galactose supply for the sugar chains biosynthesis of AGPs and MGDG, which thereby, respectively, results in altered cell wall and abnormal chloroplast development. Due to inferior mechanical strength and reduced photosynthesis, bz1 plants displayed detrimental agronomic traits, whereas BZ1 overexpressing lines showed enhanced plant growth. Transcriptome analysis of stems and leaves further showed that numerous key genes involved in AGPs biosynthesis and photosynthesis metabolism were substantially suppressed in bz1. Conclusions Our finding identifies BZ1 as a dual-targeting UGE protein for glycosylation of AGPs and MGDG and suggests a strategy for breeding robust elite crops.

Brown macroalgae, being important components of benthic communities in temperate regions, are frequently subjected to light limitation. To extend our understanding of their low light acclimation strategies to the regulation of membrane lipid environment, photosynthetic characteristics, lipid class, fatty acid profiles and chloroplast ultrastructure were compared in Undaria pinnatifida (Phaeophyceae, Ochrophyta) after long‐term exposure to low and moderate light intensities (LL, 100 and ML, 280 µmol photons · m−2 · s−1). We show that light limitation significantly increased PSII quantum efficiency and photosynthetic electron transport rate, enhanced pigment contents and concentration of thylakoid membranes in chloroplasts but decreased the distance between the thylakoid stacks. These physiological alterations at LL were accompanied by a selective remodeling of thylakoid membrane lipids driven by increases in monogalactosyldiacylglycerol (MGDG) and phosphatidylglycerol (PG) contents. Light limitation also induced active production of PG specific trans‐Δ3‐hexadecenoic acid and accumulation of n−3 polyunsaturated fatty acids (PUFA) mostly in PG and MGDG at the expense of the rise in 18:3n−3 and 20:5n−3, 18:4n−3, respectively. These changes in lipid and FA profiles are apparently responsible for supporting thylakoid biogenesis and efficient photosynthesis at light limitation, thus contributing to photoacclimation strategies in brown algae. The content of triacylglycerols (TAG) and the level of their PUFA were decreased at LL, suggesting the consumption of TAG as a source of PUFA and energy reserves. Thus, U. pinnatifida is able to successfully overcome periods of low irradiance through the effective light harvesting and utilization that are provided by high flexibility of lipid biosynthesis. [ABSTRACT FROM AUTHOR]

Main conclusion: The compatible solute sucrose reduces the efficiency of the enzymatic de-epoxidation of violaxanthin, probably by a direct effect on the protein parts of violaxanthin de-epoxidase which protrude from the lipid phase of the thylakoid membrane. The present study investigates the influence of the compatible solute sucrose on the violaxanthin cycle of higher plants in intact thylakoids and in in vitro enzyme assays with the isolated enzyme violaxanthin de-epoxidase at temperatures of 30 and 10 °C, respectively. In addition, the influence of sucrose on the lipid organization of thylakoid membranes and the MGDG phase in the in vitro assays is determined. The results show that sucrose leads to a pronounced inhibition of violaxanthin de-epoxidation both in intact thylakoid membranes and the enzyme assays. In general, the inhibition is similar at 30 and 10 °C. With respect to the lipid organization only minor changes can be seen in thylakoid membranes at 30 °C in the presence of sucrose. However, sucrose seems to stabilize the thylakoid membranes at lower temperatures and at 10 °C a comparable membrane organization to that at 30 °C can be observed, whereas control thylakoids show a significantly different membrane organization at the lower temperature. The MGDG phase in the in vitro assays is not substantially affected by the presence of sucrose or by changes of the temperature. We conclude that the presence of sucrose and the increased viscosity of the reaction buffers stabilize the protein part of the enzyme violaxanthin de-epoxidase, thereby decreasing the dynamic interactions between the catalytic site and the substrate violaxanthin. This indicates that sucrose interacts with those parts of the enzyme which are accessible at the membrane surface of the lipid phase of the thylakoid membrane or the MGDG phase of the in vitro enzyme assays. [ABSTRACT FROM AUTHOR]

We used electrospray ionization tandem mass spectrometry to profile glycerolipids in the TOC159 null mutant of Arabidopsis, which is referred to as plastid protein import 2, or ppi 2. The goal was to evaluate the impact of a defective atToc159 receptor in the accumulation of plastid lipids. The ppi 2 mutant is severely impaired in the accumulation of monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG) and phosphatidylglycerol (PG), which are major components of the thylakoid membranes. Major molecular species of MGDG and DGDG are drastically decreased, which is consistent with our previous findings of decreased levels of hexadecatrienoic and linolenic acids. Under normal growth conditions, the ppi 2 mutant accumulated significantly lower levels of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylinositol (PI). In the cold-acclimated mutant, the amounts of PE and PI were similar to the wildtype level, which indicates that the ER pathway of lipid synthesis was functional in the mutant. The cold-acclimated ppi 2 mutant accumulated increased amounts of phosphatidic acid (PA), which was mirrored by an increase in phospholipase Dα (PLDα) transcript levels. These data suggest that PLDα activity contributed to the accumulation of cold-induced PA in the ppi 2 mutant. The accumulation of major molecular species in PA indicates that cold-induced PA originated from the degradation of both plastidial and extraplastidial lipids. Compared with the wildtype, the ppi 2 mutant had a low double bond index and high acyl chain length, which is indicative of decreased membrane fluidity. Taken together, these data indicate that a defective atToc159 receptor severely impaired the plastid pathway of lipid synthesis, which negatively affected the synthesis and/or accumulation of PC. Image 1 • The ppi 2 mutant is severely impaired in the accumulation of plastid lipids • Cold-acclimated ppi 2 mutant accumulates increased levels of phosphatidic acid • The ppi 2 mutant has a low double bond index and high acyl chain length [ABSTRACT FROM AUTHOR]

The xanthophyll cycles of higher plants and algae represent an important photoprotection mechanism. Two main xanthophyll cycles are known, the violaxanthin cycle of higher plants, green and brown algae and the diadinoxanthin cycle of Bacillariophyceae, Xanthophyceae, Haptophyceae, and Dinophyceae. The forward reaction of the xanthophyll cycles consists of the enzymatic de-epoxidation of violaxanthin to antheraxanthin and zeaxanthin or diadinoxanthin to diatoxanthin during periods of high light illumination. It is catalyzed by the enzymes violaxanthin or diadinoxanthin de-epoxidase. During low light or darkness the back reaction of the cycle, which is catalyzed by the enzymes zeaxanthin or diatoxanthin epoxidase, restores the epoxidized xanthophylls by a re-introduction of the epoxy groups. The de-epoxidation reaction takes place in the lipid phase of the thylakoid membrane and thus, depends on the nature, three dimensional structure and function of the thylakoid lipids. As the xanthophyll cycle pigments are usually associated with the photosynthetic light-harvesting proteins, structural re-arrangements of the proteins and changes in the protein-lipid interactions play an additional role for the operation of the xanthophyll cycles. In the present review we give an introduction to the lipid and fatty acid composition of thylakoid membranes of higher plants and algae. We introduce the readers to the reaction sequences, enzymes and function of the different xanthophyll cycles. The main focus of the review lies on the lipid dependence of xanthophyll cycling. We summarize the current knowledge about the role of lipids in the solubilization of xanthophyll cycle pigments. We address the importance of the three-dimensional lipid structures for the enzymatic xanthophyll conversion, with a special focus on non-bilayer lipid phases which are formed by the main thylakoid membrane lipid monogalactosyldiacylglycerol. We additionally describe how lipids and light-harvesting complexes interact in the thylakoid membrane and how these interactions can affect the structure of the thylakoids. In a dedicated chapter we offer a short overview of current membrane models, including the concept of membrane domains. We then use these concepts to present a model of the operative xanthophyll cycle as a transient thylakoid membrane domain which is formed during high light illumination of plants or algal cells.

Background: The cell wall and chloroplast are two fundamental structures determining plant mechanical strength and grain yield. Therefore, understanding mechanisms that improve plants' ability to develop a robust cell wall and well-developed chloroplast is of utmost importance for agricultural activities. Results: In this study, we report the functional characterization of a novel rice mutant, brittle stem and zebra leaf (bz1), which displays altered cell wall composition and collapsed chloroplast membrane. Molecular and biochemical analysis revealed that BZ1 encodes a functional UDP-galactose/glucose epimerase (UGE) and is ubiquitously expressed with higher expression in stem and leaf tissues. Multiple techniques analyses, including immunoblots, immuno-gold, and cryogenic scanning electron microscopy, demonstrated a significantly impaired glycosylation of arabinogalactan proteins (AGPs) and disordered cellulose microfibril deposition in bz1. Lipid profiling assay showed that the amount of monogalactosyldiacylglycerols (MGDG), a major chloroplast membrane glycolipid, was significantly decreased in bz1. Taken together, these results strongly demonstrate that BZ1 participates in UDP-galactose supply for the sugar chains biosynthesis of AGPs and MGDG, which thereby, respectively, results in altered cell wall and abnormal chloroplast development. Due to inferior mechanical strength and reduced photosynthesis, bz1 plants displayed detrimental agronomic traits, whereas BZ1 overexpressing lines showed enhanced plant growth. Transcriptome analysis of stems and leaves further showed that numerous key genes involved in AGPs biosynthesis and photosynthesis metabolism were substantially suppressed in bz1. Conclusions: Our finding identifies BZ1 as a dual-targeting UGE protein for glycosylation of AGPs and MGDG and suggests a strategy for breeding robust elite crops. [ABSTRACT FROM AUTHOR]

The xanthophyll cycles of higher plants and algae represent an important photoprotection mechanism. Two main xanthophyll cycles are known, the violaxanthin cycle of higher plants, green and brown algae and the diadinoxanthin cycle of Bacillariophyceae, Xanthophyceae, Haptophyceae, and Dinophyceae. The forward reaction of the xanthophyll cycles consists of the enzymatic de-epoxidation of violaxanthin to antheraxanthin and zeaxanthin or diadinoxanthin to diatoxanthin during periods of high light illumination. It is catalyzed by the enzymes violaxanthin or diadinoxanthin de-epoxidase. During low light or darkness the back reaction of the cycle, which is catalyzed by the enzymes zeaxanthin or diatoxanthin epoxidase, restores the epoxidized xanthophylls by a re-introduction of the epoxy groups. The de-epoxidation reaction takes place in the lipid phase of the thylakoid membrane and thus, depends on the nature, three dimensional structure and function of the thylakoid lipids. As the xanthophyll cycle pigments are usually associated with the photosynthetic light-harvesting proteins, structural re-arrangements of the proteins and changes in the protein-lipid interactions play an additional role for the operation of the xanthophyll cycles. In the present review we give an introduction to the lipid and fatty acid composition of thylakoid membranes of higher plants and algae. We introduce the readers to the reaction sequences, enzymes and function of the different xanthophyll cycles. The main focus of the review lies on the lipid dependence of xanthophyll cycling. We summarize the current knowledge about the role of lipids in the solubilization of xanthophyll cycle pigments. We address the importance of the three-dimensional lipid structures for the enzymatic xanthophyll conversion, with a special focus on non-bilayer lipid phases which are formed by the main thylakoid membrane lipid monogalactosyldiacylglycerol. We additionally describe how lipids and light-harvesting complexes interact in the thylakoid membrane and how these interactions can affect the structure of the thylakoids. In a dedicated chapter we offer a short overview of current membrane models, including the concept of membrane domains. We then use these concepts to present a model of the operative xanthophyll cycle as a transient thylakoid membrane domain which is formed during high light illumination of plants or algal cells. [ABSTRACT FROM AUTHOR]

The surface tension of xylem sap has been traditionally assumed to be close to that of the pure water because decreasing surface tension is thought to increase vulnerability to air seeding and embolism. However, xylem sap contains insoluble lipid-based surfactants, which also coat vessel and pit membrane surfaces, where gas bubbles can enter xylem under negative pressure in the process known as air seeding. Because of the insolubility of amphiphilic lipids, the surface tension influencing air seeding in pit pores is not the equilibrium surface tension of extracted bulk sap but the local surface tension at gas–liquid interfaces, which depends dynamically on the local concentration of lipids per surface area. To estimate the dynamic surface tension in lipid layers that line surfaces in the xylem apoplast, we studied the time-dependent and surface area-regulated surface tensions of apoplastic lipids extracted from xylem sap of four woody angiosperm plants using constrained drop surfactometry. Xylem lipids were found to demonstrate potent surface activity, with surface tensions reaching an equilibrium at ~25 mN m-1 and varying between a minimum of 19 mN m-1 and a maximum of 68 mN m-1 when changing the surface area between 50 and 160% around the equilibrium surface area. It is concluded that xylem lipid films in natural conditions most likely range from nonequilibrium metastable conditions of a supersaturated compression state to an undersaturated expansion state, depending on the local surface areas of gas–liquid interfaces. Together with findings that maximum pore constrictions in angiosperm pit membranes are much smaller than previously assumed, low dynamic surface tension in xylem turns out to be entirely compatible with the cohesion–tension and air-seeding theories, as well as with the existence of lipid-coated nanobubbles in xylem sap, and with the range of vulnerabilities to embolism observed in plants. [ABSTRACT FROM AUTHOR]

Monogalactosyldiacylglycerols (MGDGs) from microalgae containing a high proportion of polyunsaturated fatty acids (PUFAs) have enormous potential applications in various industries. In this study, the productivity and fatty acid composition of MGDGs from three microalgae in commercialized production, Chlorella sorokiniana GT, Nannochloropsis oceanica IMET1, and Arthrospira platensis, were evaluated under nitrogen-sufficient (+N) and nitrogen-deficient (−N) conditions. Under +N conditions, higher productivities of MGDGs from C. sorokiniana GT1, N. oceanica IMET1, and A. platensis were obtained with 16.3, 4.3, and 1.3 mg/L/day, respectively. In agreement with a high ratio of PUFAs in MGDGs, they accounted for 56%, 66%, and 47% of the total fatty acids in MGDG correspondingly. α-linoleic acid (ALA), eicosapentaenoic acid (EPA), and γ-linoleic acid (GLA) were the specific PUFAs of the three microalgae. The proportions of the specific PUFAs in MGDG accounted for 26%, 44%, and 63% of total specific PUFAs, respectively. Considering the production, cost of microalgae biomass and price of MGDG, the commercialized microalgae C. sorokiniana GT1 and A. platensis showed great potential to produce MGDGs with a high content of PUFAs, in contrast to N. oceanica IMET1, with its high biomass cost and low production. This study provides basic data for the extraction and separation of microalgae lipids from commercialized microalgae, which is helpful to promote the commercialization of microalgae. [ABSTRACT FROM AUTHOR]

Abstract Background Nitrogen (N) plays an important role in the formation of tea quality-related compounds, like amino acids and flavor/aroma origin compounds. Lipids, which have been reported to be affected by N deficiency, are precursors to the generation of flavor/aroma origin compounds in tea plant. However, there is no literature about the lipid profiles of tea plant affected by N fertilization. Hence, we hypothesize that the biosynthesis of flavor-related compounds in tea was affected by N through its regulation of lipid metabolism. Results In this study, mature leaves and new shoots of tea plant grown under three N levels at the rates of 0, 285 and 474 kg/ha were applied for ultra-performance liquid chromatography-mass spectrometry (UPLC/MS) based lipidomic analysis. Totally, 178 lipid species were identified. The results showed that the composition of lipid compounds in mature leaves and new shoots varied dramatically, which was also affected by N levels. The higher content of the storage lipid TAG and higher carbon (C)/N ratio in mature leaves than that of new shoots in tea plants grown under low N level (0 kg/ha) suggested that tea plants could remobilize the C stored in TAG to maintain their C/N balance and help to improve the quality of tea. N fertilization resulted in a higher content of the compounds 36:6 MGDG and 36:6 DGDG. Since these compounds contain linolenic acid (18:3), a precursor to the formation of aroma origin compounds, we suggested their increase could contribute to the quality of tea. Conclusions Taken together, the present work indicated that appropriate application of N fertilizer could balance the lipid metabolism and the formation of flavor/aroma origin compounds, which help to improve the quality of tea. Moreover, excess N fertilization might deteriorate the aroma quality of made tea due to increases of precursors leading to grassy odor.

Monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) are the two predominant galactolipids present in the photosynthetic membrane in many photosynthetic organisms, including algae and higher plants. These galactolipids are the main constituents of thylakoid membrane and are essential for chloroplast biogenesis and photoautotrophic growth. In silico analysis revealed that rice (Oryza sativa L.) genome has three genes encoding MGDG synthase (OsMGD1, 2, and 3). Although subcellular localization analysis demonstrated that OsMGD2 is localized to chloroplast, its expression was observed mainly in anther and endosperm, suggesting that MGDG might have an important role in the development of flower and grain in rice. Knock-out mutants of OsMGD2 were generated employing the CRISPR/Cas9 system and their morphology, yield and grain quality related traits were studied. The leaf of osmgd2 mutants showed reduced MGDG (∼11.6%) and DGDG (∼9.5%) content with chlorophyll a content decreased by ∼23%, consequently affecting the photosynthesis. The mutants also exhibited poor agronomic performance with plant height and panicle length decreased by ∼12.2 and ∼7.3%, respectively. Similarly, the number of filled grains per panicle was reduced by 43.8%, while the 1000 grain weight was increased by ∼6.3% in the mutants. The milled rice of mutants also had altered pasting properties and decreased linoleic acid content (∼26.6%). Put together, the present study demonstrated that OsMGD2 is the predominantly expressed gene encoding MGDG synthase in anther and grain and plays important roles in plant growth and development, as well as in grain quality.

Monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) are the two predominant galactolipids present in the photosynthetic membrane in many photosynthetic organisms, including algae and higher plants. These galactolipids are the main constituents of thylakoid membrane and are essential for chloroplast biogenesis and photoautotrophic growth. In silico analysis revealed that rice (Oryza sativa L.) genome has three genes encoding MGDG synthase (OsMGD1, 2 , and 3). Although subcellular localization analysis demonstrated that OsMGD2 is localized to chloroplast, its expression was observed mainly in anther and endosperm, suggesting that MGDG might have an important role in the development of flower and grain in rice. Knock-out mutants of OsMGD2 were generated employing the CRISPR/Cas9 system and their morphology, yield and grain quality related traits were studied. The leaf of osmgd2 mutants showed reduced MGDG (∼11.6%) and DGDG (∼9.5%) content with chlorophyll a content decreased by ∼23%, consequently affecting the photosynthesis. The mutants also exhibited poor agronomic performance with plant height and panicle length decreased by ∼12.2 and ∼7.3%, respectively. Similarly, the number of filled grains per panicle was reduced by 43.8%, while the 1000 grain weight was increased by ∼6.3% in the mutants. The milled rice of mutants also had altered pasting properties and decreased linoleic acid content (∼26.6%). Put together, the present study demonstrated that OsMGD2 is the predominantly expressed gene encoding MGDG synthase in anther and grain and plays important roles in plant growth and development, as well as in grain quality. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A unique feature of chloroplasts is their high content of the galactolipids monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), which constitute up to 80% of their lipids. These galactolipids are synthesized in the chloroplast envelope membrane through the concerted action of galactosyltransferases, the so-called ‘MGDG synthases (MGDs)’ and ‘DGDG synthases (DGDs),’ which use uridine diphosphate (UDP)-galactose as donor. In Arabidopsis leaves, under standard conditions, the enzymes MGD1 and DGD1 provide the bulk of galactolipids, necessary for the massive expansion of thylakoid membranes. Under phosphate limited conditions, plants activate another pathway involving MGD2/MGD3 and DGD2 to provide additional DGDG that is exported to extraplastidial membranes where they partly replace phospholipids, a phosphate-saving mechanism in plants. A third enzyme system, which relies on the UDP-Gal-independent GGGT (also called SFR2 for SENSITIVE TO FREEZING 2), can be activated in response to a freezing stress. The biosynthesis of galactolipids by these multiple enzyme sets must be tightly regulated to meet the cellular demand in response to changing environmental conditions. The cooperation between MGD and DGD enzymes with a possible substrate channeling from diacylglycerol to MGDG and DGDG is supported by biochemical and biophysical studies and mutant analyses reviewed herein. The fine-tuning of MGDG to DGDG ratio, which allows the reversible transition from the hexagonal II to lamellar α phase of the lipid bilayer, could be a key factor in thylakoid biogenesis.

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. [ABSTRACT FROM AUTHOR]

Monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) together constitute approximately 80% of chloroplast lipids. Apart from facilitating the photosynthesis light reaction in the thylakoid membrane, these two lipids are important for maintaining chloroplast morphology and for plant survival under abiotic stresses such as phosphate starvation and freezing. Recently it was shown that severe growth retardation phenotypes of the DGDG-deficient mutant dgd1 were due to jasmonate overproduction, linking MGDG and DGDG homeostasis with phytohormone production and suggesting MGDG as a major substrate for jasmonate biosynthesis. Induction of jasmonate synthesis and jasmonic acid (JA) signaling was also observed under conditions of phosphate starvation. We hypothesize that when DGDG is recruited to substitute for phospholipids in extraplastidic membranes during phosphate deficiency, the altered MGDG to DGDG ratio in the chloroplast envelope triggers the conversion of galactolipids into jasmonates. The conversion may contribute to rebalancing the MGDG to DGDG ratio rapidly to maintain chloroplast shape, and jasmonate production can reduce the growth rate and enhance predator deterrence. We also hypothesize that other conditions, such as suppression of dgd1 phenotypes by trigalactosyldiacylglycerol (tgd) mutations, may all be linked to altered jasmonate production, indicating that caution should be exercised when interpreting phenotypes caused by conditions that may alter the MGDG to DGDG ratio at the chloroplast envelope. [ABSTRACT FROM AUTHOR]

A unique feature of chloroplasts is their high content of the galactolipids monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), which constitute up to 80% of their lipids. These galactolipids are synthesized in the chloroplast envelope membrane through the concerted action of galactosyltransferases, the so-called 'MGDG synthases (MGDs)' and 'DGDG synthases (DGDs),' which use uridine diphosphate (UDP)-galactose as donor. In Arabidopsis leaves, under standard conditions, the enzymes MGD1 and DGD1 provide the bulk of galactolipids, necessary for the massive expansion of thylakoid membranes. Under phosphate limited conditions, plants activate another pathway involving MGD2/MGD3 and DGD2 to provide additional DGDG that is exported to extraplastidial membranes where they partly replace phospholipids, a phosphate-saving mechanism in plants. A third enzyme system, which relies on the UDP-Gal-independent GGGT (also called SFR2 for SENSITIVE TO FREEZING 2), can be activated in response to a freezing stress. The biosynthesis of galactolipids by these multiple enzyme sets must be tightly regulated to meet the cellular demand in response to changing environmental conditions. The cooperation between MGD and DGD enzymes with a possible substrate channeling from diacylglycerol to MGDG and DGDG is supported by biochemical and biophysical studies and mutant analyses reviewed herein. The fine-tuning of MGDG to DGDG ratio, which allows the reversible transition from the hexagonal II to lamellar α phase of the lipid bilayer, could be a key factor in thylakoid biogenesis. [ABSTRACT FROM AUTHOR]

Chronic inflammatory skin diseases such as psoriasis have a significant impact on society. Currently, the major topical treatments have many side effects, making their continued use in patients difficult. Microalgae have emerged as a source of bio-active molecules such as glycolipids with potent anti-inflammatory properties. We aimed to investigate the effects of a glycolipid (MGMG-A) and a glycolipid fraction (MGDG) obtained from the microalga Isochrysis galbana on a TPA-induced epidermal hyperplasia murine model. In a first set of experiments, we examined the preventive effects of MGMG-A and MGDG dissolved in acetone on TPA-induced hyperplasia model in mice. In a second step, we performed an in vivo permeability study by using rhodamine-containing cream, ointment, or gel to determinate the formulation that preserves the skin architecture and reaches deeper. The selected formulation was assayed to ensure the stability and enhanced permeation properties of the samples in an ex vivo experiment. Finally, MGDG-containing cream was assessed in the hyperplasia murine model. The results showed that pre-treatment with acetone-dissolved glycolipids reduced skin edema, epidermal thickness, and pro-inflammatory cytokine production (TNF-α, IL-1β, IL-6, IL-17) in epidermal tissue. The in vivo and ex vivo permeation studies showed that the cream formulation had the best permeability profile. In the same way, MGDG-cream formulation showed better permeation than acetone-dissolved preparation. MGDG-cream application attenuated TPA-induced skin edema, improved histopathological features, and showed a reduction of the inflammatory cell infiltrate. In addition, this formulation inhibited epidermal expression of COX-2 in a similar way to dexamethasone. Our results suggest that an MGDG-containing cream could be an emerging therapeutic strategy for the treatment of inflammatory skin pathologies such as psoriasis. [ABSTRACT FROM AUTHOR]

Chlamydomonas reinhardtii of the microalgal model species lacks phosphatidylcholine (PC), and PC is replaced by diacylglyceryl N , N , N -trimethylhomoserine (DGTS). DGTS is a betaine lipid that is placed in the endoplasmic reticulum (ER) and is synthesized by a single gene, BTA1 . In this study, we aimed to ascertain the turnover between membrane and neutral lipids via BTA1 knockdown transformants. Transgenic lines CrBta-hm13 and CrBta-hm31 were 80% and 60% downregulated in BTA1 gene expression levels, respectively. Both transformants had half the amount of DGTS, which coincided with decreased monogalactosyldiacylglycerol (MGDG), which was increased approximately threefold in neutral lipids. While the reduction of DGTS was shown to arise from inhibition of DGTS synthesis, decreased MGDG was affected by internal stress, such as ER stress, which was induced to have a decreased amount of DGTS in the ER. However, galactolipids, except for MGDG, and phospholipids in the transformants were maintained at similar levels. In the transformants, the molar proportion of C16:4 and C18:3(9,12,15), which are the major fatty acids of MGDG, was significantly increased in triacylglycerol (TAG) because of MGDG degradation. Thus, lipid turnover arising from the downregulation of DGTS and induction of ER stress caused a decrease in DGTS and MGDG, which generated a synergy effect on the accumulation of TAG. This study implies that genetic modification of a membrane lipid synthesis pathway could not only be a suitable approach to target accumulation of TAG, but could also suggest a mechanism for the lipid turnover between membrane lipids and neutral lipids. [ABSTRACT FROM AUTHOR]

Main conclusion: A special domain of the thylakoid membrane of higher plants has been isolated which carries out the de-epoxidation of the xanthophyll cycle pigment violaxanthin to zeaxanthin. Recent models indicate that in the chloroplast of higher plants, the violaxanthin (V) cycle takes place within specialized domains in the thylakoid membrane. Here, we describe a new procedure to directly isolate such a domain in functional state. The procedure consists of a thylakoid membrane isolation at a pH value of 5.2 which realizes the binding of the enzyme V de-epoxidase (VDE) to the membrane throughout the preparation process. Isolated thylakoid membranes are then solubilized with the very mild detergent n-dodecyl α- d-maltoside and the pigment-protein complexes are separated by sucrose gradient ultracentrifugation. The upper main fraction of the sucrose gradient represents a V cycle domain which consists of the major light-harvesting complex of photosystem II (LHCII), a special lipid composition with an enrichment of the galactolipid monogalactosyldiacylglycerol (MGDG) and the VDE. The domain is isolated in functional state as evidenced by the ability to convert the LHCII-associated V to zeaxanthin. The direct isolation of a V cycle domain proves the most important hypotheses concerning the de-epoxidation reaction in intact thylakoid membranes. It shows that the VDE binds to the thylakoid membrane at low pH values of the thylakoid lumen, that it binds to membrane regions enriched in LHCII, and that the domain contains high amounts of MGDG. The last point is in line with the importance of the galactolipid for V solubilisation and, by providing inverted hexagonal lipid structures, for VDE activity. [ABSTRACT FROM AUTHOR]

Monogalactosyldiacylglycerol ( MGDG) and digalactosyldiacylglycerol ( DGDG) are the major lipid components of photosynthetic membranes, and hence the most abundant lipids in the biosphere. They are essential for assembly and function of the photosynthetic apparatus. In Arabidopsis, the first step of galactolipid synthesis is catalyzed by MGDG synthase 1 ( MGD1), which transfers a galactosyl residue from UDP-galactose to diacylglycerol ( DAG). MGD1 is a monotopic protein that is embedded in the inner envelope membrane of chloroplasts. Once produced, MGDG is transferred to the outer envelope membrane, where DGDG synthesis occurs, and to thylakoids. Here we present two crystal structures of MGD1: one unliganded and one complexed with UDP. MGD1 has a long and flexible region (approximately 50 amino acids) that is required for DAG binding. The structures reveal critical features of the MGD1 catalytic mechanism and its membrane binding mode, tested on biomimetic Langmuir monolayers, giving insights into chloroplast membrane biogenesis. The structural plasticity of MGD1, ensuring very rapid capture and utilization of DAG, and its interaction with anionic lipids, possibly driving the construction of lipoproteic clusters, are consistent with the role of this enzyme, not only in expansion of the inner envelope membrane, but also in supplying MGDG to the outer envelope and nascent thylakoid membranes. [ABSTRACT FROM AUTHOR]

Chronic inflammatory skin diseases such as psoriasis have a significant impact on society. Currently, the major topical treatments have many side effects, making their continued use in patients difficult. Microalgae have emerged as a source of bio-active molecules such as glycolipids with potent anti-inflammatory properties. We aimed to investigate the effects of a glycolipid (MGMG-A) and a glycolipid fraction (MGDG) obtained from the microalga Isochrysis galbana on a TPA-induced epidermal hyperplasia murine model. In a first set of experiments, we examined the preventive effects of MGMG-A and MGDG dissolved in acetone on TPA-induced hyperplasia model in mice. In a second step, we performed an in vivo permeability study by using rhodamine-containing cream, ointment, or gel to determinate the formulation that preserves the skin architecture and reaches deeper. The selected formulation was assayed to ensure the stability and enhanced permeation properties of the samples in an ex vivo experiment. Finally, MGDG-containing cream was assessed in the hyperplasia murine model. The results showed that pre-treatment with acetone-dissolved glycolipids reduced skin edema, epidermal thickness, and pro-inflammatory cytokine production (TNF-α, IL-1β, IL-6, IL-17) in epidermal tissue. The in vivo and ex vivo permeation studies showed that the cream formulation had the best permeability profile. In the same way, MGDG-cream formulation showed better permeation than acetone-dissolved preparation. MGDG-cream application attenuated TPA-induced skin edema, improved histopathological features, and showed a reduction of the inflammatory cell infiltrate. In addition, this formulation inhibited epidermal expression of COX-2 in a similar way to dexamethasone. Our results suggest that an MGDG-containing cream could be an emerging therapeutic strategy for the treatment of inflammatory skin pathologies such as psoriasis.

Marine macroalgae, or seaweeds, are a formidable source of natural compounds with diverse biological activities. In the last five decades it has been estimated that more than 3,000 natural compounds were discovered from these organisms. The great majority of the published works have focused on terpenoids. In comparison, glycolipids are a neglected class of macroalgal secondary metabolites therefore remaining as a largely unknown reservoir of molecular diversity. Nevertheless, the interest regarding these compounds has been growing fast in the last decades as activities of ecological or pharmaceutical interest have been highlighted. This paper will review recent work regarding isolation and structural characterization of glycolipids from seaweeds and their prospective biological activities.

Plant galactolipid synthesis on the outer envelope membranes of chloroplasts is an important biosynthetic pathway for sustained growth under conditions of phosphate (Pi) depletion. During Pi starvation, the amount of digalactosyldiacylglycerol (DGDG) is increased to substitute for the phospholipids that are degraded for supplying Pi. An increase in DGDG concentration depends on an adequate supply of monogalactosyldiacylglycerol (MGDG), which is a substrate for DGDG synthesis and is synthesized by a type-B MGDG synthase, MGD3. Recently, sucrose was suggested to be a global regulator of plant responses to Pi starvation. Thus, we analyzed expression levels of several genes involved in lipid remodeling during Pi starvation in Arabidopsis thaliana and found that the abundance of MGD3 mRNA increased when sucrose was exogenously supplied to the growth medium. Sucrose supplementation retarded the growth of the Arabidopsis MGD3 knockout mutant mgd3 but enhanced the growth of transgenic Arabidopsis plants overexpressing MGD3 compared with wild type, indicating the involvement of MGD3 in plant growth under sucrose-replete conditions. Although most features such as chlorophyll content, photosynthetic activity, and Pi content were comparable between wild-type and the transgenic plants overexpressing MGD3, sucrose content in shoot tissues decreased and incorporation of exogenously supplied carbon to DGDG was enhanced in the MGD3-overexpressing plants compared with wild type. Our results suggest that MGD3 plays an important role in supplying DGDG as a component of extraplastidial membranes to support enhanced plant growth under conditions of carbon excess.

A null and heterozygous mutant for the Arabidopsis thaliana TOC 132 and TOC 120 genes accumulates increased levels of 16:0 and decreased 16:3, suggesting altered homeostasis in fatty acid synthesis. The FAD 5 gene encodes a plastid desaturase that catalyzes the first step in the synthesis of 16:3 in monogalactosyldiacylglycerol (MGDG). In non-acclimated toc 132 toc 120+/− mutant plants, the FAD 5 gene was repressed and this correlated with decreased levels of 16:3. In cold-acclimated mutant however, the FAD 5 gene was upregulated and there was a small increase in 16:3 levels relative to the non-acclimated mutant plants. The MGD 1 gene was expressed at control levels and the mutant accumulated levels of MGDG that were similar to the wild type. In the mutant however, MGDG had decreased 16:3 levels, suggesting that the activity of FAD5 desaturase was compromised. In the mutant, the FAD 2 and FAD 3 genes were downregulated but levels of 18:3-PC were increased, suggesting posttranscriptional regulation for the ER-localized fatty acid desaturases. The Toc120 or Toc159 receptor is likely to compensate for a defective Toc132 receptor. In the cold-acclimated mutant, the TOC 159 gene was repressed ca. 300-fold, whereas the TOC 120 gene was repressed 7-fold relative to the non-acclimated wild type. Thus, the TOC 159 gene is more sensitive to cold-stress and might not compensate for defect in the TOC 132 gene under these conditions. Overall, these data show that a mutation in the TOC 132 gene results in decreased 16:3 levels, indicating the need for an intact Toc132/Toc120 receptor, presumably to facilitate the import of the FAD5 preprotein into chloroplasts. [ABSTRACT FROM AUTHOR]

A method that uses marker fatty acids (FAs) is widely applied in investigations of trophic and symbiotic relationships. In a search for new lipid markers, we determined the total lipid FA composition, as well as the composition of molecular species of mono- and digalactosyl diacylglycerols (MGDGs and DGDGs), which are specific galactolipids of thylakoid membranes, in zooxanthellae (endosymbiotic dinoflagellates) of the tropical soft coral Capnella sp. Some FAs of zooxanthellae were suggested for use as marker polyunsaturated FAs (PUFAs). Thirteen molecular species of MGDGs and ten molecular species of DGDGs were detected using the method of high-resolution tandem mass spectrometry. All marker PUFAs of zooxanthellae were found in acyl groups of galactolipids. The major molecular species of DGDGs (18:4/18:4, 18:4/20:5, and 16:2/22:6) and the unique molecular species of MGDGs (16:4/18:5) were described. The identification of several polyunsaturated molecular species of galactolipids that contain marker FAs allowed us to propose that this lipid group be used as molecular lipid markers of zooxanthellae for the study of symbiont-host interactions in soft corals. [ABSTRACT FROM AUTHOR]

We evaluated whether the TOC159 mutant of Arabidopsis called plastid protein import 2-2 ( ppi 2-2) accumulates normal levels of fatty acids, and transcripts of fatty acid desaturases and galactolipid synthesis enzymes. The ppi 2-2 mutant accumulates decreased pigments and total fatty acid content. The MGD1 gene was downregulated and the mutant accumulates decreased levels of monogalactosyldiacylglycerol (MGDG) and 16:3, which suggests that the prokaryotic pathway was impaired in the mutant. The HY5 gene, which encodes long hypocotyl5 transcription factor, was upregulated in the mutant. The DGD1 gene, an HY5 target was marginally increased and the mutant accumulates digalactosyldiacylglycerol at the control level. The mutant had increased expression of 3-ketoacyl-ACP synthase II gene, which encodes a plastid enzyme that elongates 16:0 to 18:0. Interestingly, glycerolipids in the mutant accumulate increased levels of 18:0. A gene that encodes stearoyl-ACP desaturase (SAD) was expressed at the control level and 18:1 was increased, which suggest that SAD may be strongly regulated at the posttranscriptional level. The molar ratio of MGDG to bilayer forming plastid lipids was decreased in the cold-acclimated wild type but not in the ppi 2-2 mutant. This indicates that the mutant was unresponsive to cold-stress, and is consistent with increased levels of 18:0, and decreased 16:3 and 18:3 in the ppi 2-2 mutant. Overall, these data indicate that a defective Toc159 receptor impaired the synthesis of MGDG, and affected desaturation of 16 and 18-carbon fatty acids. We conclude that expression of the MGD1 gene and synthesis of MGDG are tightly linked to plastid biogenesis. [ABSTRACT FROM AUTHOR]

Phosphate (Pi) limitation causes drastic lipid remodeling in plant membranes. Glycolipids substitute for the phospholipids that are degraded, thereby supplying Pi needed for essential biological processes. Two major types of remodeling of membrane lipids occur in higher plants: whereas one involves an increase in the concentration of sulfoquinovosyldiacylglycerol in plastids to compensate for a decreased concentration of phosphatidylglycerol, the other involves digalactosyldiacylglycerol (DGDG) synthesis in plastids and the export of DGDG to extraplastidial membranes to compensate for reduced abundances of phospholipids. Lipid remodeling depends on an adequate supply of monogalactosyldiacylglycerol (MGDG), which is a substrate that supports the elevated rate of DGDG synthesis that is induced by low Pi availability. Regulation of MGDG synthesis has been analyzed most extensively using the model plant Arabidopsis thaliana, although orthologous genes that encode putative MGDG synthases exist in photosynthetic organisms from bacteria to higher plants. We recently hypothesized that two types of MGDG synthase diverged after the appearance of seed plants. This divergence might have both enabled plants to adapt to a wide range of Pi availability in soils and contributed to the diversity of seed plants. In the work presented here, we found that membrane lipid remodeling also takes place in sesame, which is one of the most common traditional crops grown in Asia. We identified two types of MGDG synthase from sesame (encoded by SeMGD1 and SeMGD2) and analyzed their enzymatic properties. Our results show that both genes correspond to the Arabidopsis type-A and -B isoforms of MGDG synthase. Notably, whereas Pi limitation up-regulates only the gene encoding the type-B isoform of Arabidopsis, low Pi availability up-regulates the expression of both SeMGD1 and SeMGD2. We discuss the significance of the different responses to low Pi availability in sesame and Arabidopsis.

Marine macroalgae, or seaweeds, are a formidable source of natural compounds with diverse biological activities. In the last five decades it has been estimated that more than 3000 natural compounds were discovered from these organisms. The great majority of the published works have focused on terpenoids. In comparison, glycolipids are a neglected class of macroalgal secondary metabolites therefore remaining as a largely unknown reservoir of molecular diversity. Nevertheless, the interest regarding these compounds has been growing fast in the last decades as activities of ecological or pharmaceutical interest have been highlighted. This paper will review recent work regarding isolation and structural characterization of glycolipids from seaweeds and their prospective biological activities. [ABSTRACT FROM AUTHOR]

The purpose of this study was to examine the effect of different growth temperatures on the fatty acid compositions of the photosynthetically important galactolipids, mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively), of the 'blue' pennate diatom, Haslea ostrearia, and the model pennate diatom, Phaeodactylum tricornutum, with the hypothesis that their sn-2 fatty acids would be modulated in the same manner as for dinoflagellates. Positive-ion electrospray ionization/mass spectrometry/mass spectrometry was used to characterize the galactolipids of each diatom. At 20°C, H. ostrearia and P. tricornutum were rich in eicosapentaenoic acid (EPA; C) at the sn-1 position and in C fatty acids at the sn-2 position of MGDG and DGDG. At 30°C, however, H. ostrearia and P. tricornutum contained no EPA or other C fatty acids, but rather contained higher percentages of C fatty acids at sn-1. At 30°C, no galactolipid in either diatom contained more than three unsaturations on any of its fatty acids. While these two species differ in galactolipid composition, they both possess a similar method of acclimating their galactolipids to a higher growth temperature: reducing the numbers of the longest and shortest fatty acid chains, as well as decreasing the total number of unsaturations. [ABSTRACT FROM AUTHOR]

In the present study, the influence of Mg ions and low pH values on the aggregation state of the diatom FCP and the LHCII of vascular plants was studied. In addition, the concentration of thylakoid membrane lipids associated with the complexes was determined. The results demonstrate that the FCP, which contained a significantly higher concentration of the negatively charged lipids SQDG and PG, was less sensitive to Mg and low pH values than the LHCII which was characterized by lower amounts of SQDG and a higher concentration of MGDG. High MgCl concentrations and pH values below pH 6 induced significant changes of the absorption and 77K fluorescence emission spectra of the LHCII, indicating a strong aggregation of the light-harvesting complex. This aggregation was also visible as a pellet after centrifugation on a sucrose cushion. Although the FCP responded with changes of the absorption and fluorescence spectra to low pH and Mg incubation, these spectral changes were less pronounced than those observed for the LHCII. In addition, the FCP complexes did not show a visible pellet after incubation with either low pH values or high Mg concentrations. Only the combined action of Mg and pH 5 led to FCP aggregates of a size that could be pelleted by centrifugation. The decreased sensitivity of FCP aggregation to Mg and low pH is discussed with respect to the differences in the concentration of the lipids surrounding the FCP and LHCII and the different thylakoid membrane organizations of diatoms and vascular plants. [ABSTRACT FROM AUTHOR]

Abstract: Previous studies have shown that a mutant of Arabidopsis that lacks the Toc159 receptor is impaired in chloroplast biogenesis. The mutant is referred as plastid protein import 2 or ppi2 and has an albino phenotype due to its inability to import the photosynthetic proteins. In this study, we measured fatty acid composition and transcript levels of plastid-localized fatty acid desaturases in the wild type and ppi2 mutant. The objective was to evaluate whether the Toc159 receptor was critical in the import of lipid-synthesizing enzymes. The ppi2 mutant accumulated decreased levels of oleic acid (18:1) and α-linolenic acid (18:3). The mutant accumulated drastically reduced amounts of the chloroplast lipid monogalactosyldiacylglycerol (MGDG), which contains more than 80% of 18:3. The expression of genes that encode stearoyl-ACP desaturase and MGD1 synthase were down-regulated in the ppi2 mutant, and this corresponded to decreased levels of 18:1 and MGDG, respectively. We conclude that in the ppi2 mutant the impaired synthesis of MGDG resulted in decreased amounts of 18:3. The mutant however, had a 30-fold increase in fad5 transcript levels; this increase was mirrored by a 16- to 50-fold accumulation of hexadecatrienoic acid (16:3), a fatty acid found exclusively in MGDG. Taken together, these data suggest that the Toc159 receptor is required in the import of stearoyl-ACP desaturase and MGD1 synthase into the chloroplasts. Since the expression of fad5 gene was up-regulated in the ppi2 mutant, we propose that fad5 desaturase is imported into plastids through the atToc132/atToc120 protein import pathway. [Copyright &y& Elsevier]

We investigated the effects of osmotic downshift induced by the transfer of Nannochloropsis oceanica CCALA 804 from artificial seawater medium (27 g L NaCl) to the same medium without NaCl or freshwater modified BG-11 medium (mBG-11) as a function of photosynthetically active radiation (170, 350, or 700 μmol photon m s). Alterations in growth, total fatty acid (FA) content and FA composition of individual lipid classes, and in relative contents of metabolites relevant to osmotic adjustments were studied. Cells displayed remarkable tolerance to the osmotic downshift apart from some swelling, with no substantial lag or decline in cell division rate. Biomass accumulation and chlorophyll a content were enhanced upon downshifting, especially under the highest irradiance. The highest chlorophyll a and eicosapentaenoic acid (EPA) biomass and culture contents were determined in the cultures grown in mBG-11. Two days after transfer to 0 g L NaCl, the proportion in total acyl lipids of the major chloroplast galactolipid monogalactosyldiacylglycerol, a major depot of EPA, increased twofold, along with a modest change in the proportion of digalactosyldiacylglycerol (DGDG). EPA percentage decreased in DGDG and increased in the extraplastidial lipid phosphatidylethanolamine. Metabolite profiling by GC-MS analysis revealed a sharp decrease in metabolites potentially involved in osmoregulation, such as mannitol and proline, while proline-cycle intermediates and some free sugars increased. The stress-induced polyamine spermidine decreased ca. one order of magnitude, while its catabolic product-the non-protein amino acid γ-amino butyric acid-increased twofold, as did the stress-related sugars trehalose and talose. Biochemical mechanisms governing osmotic plasticity and implications for optimization of EPA production by N. oceanica CCALA 804 under variable cultivation conditions are discussed. [ABSTRACT FROM AUTHOR]

Chromera veliais 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 ofC. veliaand 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. veliaproduces 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 thesn-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 thesn-2 position is extremely rare. Thus, the forms of MGDG and DGDG inC. veliadisplayed similarities and differences to what has been observed in peridinin-containing dinoflagellates, such asLingulodinium 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 bothL. polyedrumandC. velia. [ABSTRACT FROM AUTHOR]

The heterotrophic genusOxyrrhiscontains two species,O. marinaandO. maritima, which occupy positions basal to the dinoflagellate lineage.Oxyrrhisis also related to apicomplexan parasites, which have recently been shown to have a non-photosynthetic, relic plastid referred to as the apicoplast. A recent study by Slamovits & Keeling (2008) demonstrated the presence of plastid-targeted proteins withinO. marina. We hypothesized that ifO. marinadoes indeed have plastids, then mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively), which are the two most prominent plastidial membrane lipids, would be present. Therefore, we examined three isolates ofO. marinato determine if they can produce MGDG and DGDG. We observed thatO. marina, when fed the chlorophyteDunaliella tertiolecta, possessed forms of MGDG and DGDG containing a C18:3fatty acid at thesn-1 position and most containing a C16:3-4fatty acid at thesn-2 position; these were derived solely from the prey itself. Examination of published expressed sequence tag (EST) and transcriptome databases ofO. marinafor the genes encoding MGDG and DGDG synthases, two enzymes integral to the incorporation of galactose in the final forms of these lipids, failed to reveal their presence. Taken together, these results indicate thatO. marinadoes not produce a non-photosynthetic, relictual plastid. However, the presence of plastid-targeted proteins may indicate thatO. marinamaintains, however briefly, plastids acquired from its prey in a form of kleptoplasty that has been observed previously in dinoflagellates. [ABSTRACT FROM AUTHOR]

The freshwater dinoflagellate Borghiella dodgei is adapted to cold temperatures. We investigated the effects of small temperature changes on its galactolipid composition, choosing 3 and 7°C as deviations from its optimal growth temperature (5°C). The galactolipid profile, important for maintenance of membrane fluidity, was determined by liquid chromatography-mass spectrometry and the influence of temperature on galactolipids was investigated by one-way ANOVA. We found 24 different galactolipid species, including novel tri-galactosyldiacylglycerols (TGDGs). The overall amount of mono- (MGDG), di- (DGDG) and tri- (TGDG) galactosyldiacylglycerols remained stable while single galactolipids varied with temperature. Few changes were found from 3 to 5°C, instead 11 galactolipid species changed from 5 to 7°C. Concomitantly with the unsaturation index of MGDGs, the more unsaturated galactolipids decreased at higher temperature, and the less abundant and less unsaturated galactolipids in each lipid class accumulated. Changes in the galactolipid profile of Borghiella underlined its cold-stenothermal nature: it can adapt to relatively 'higher' temperatures by reducing the synthesis of the more unsaturated MGDGs, DGDGs and TGDGs, but remains restricted by its lower growth rate. Based on our results, we predict that with climate change the galactolipid profile of cold-stenothermal algae will change with important repercussions on their consumers. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

Abstract: The composition of plant membrane lipids was investigated by reversed-phase high performance liquid chromatography mass spectrometry with accurate mass measurement. The data dependent methods for the analysis of monogalactosyldiacylglycerols (MGDGs) and digalactosyldiacylglycerols (DGDGs) have been developed. The optimised chromatographic systems were based on a 2.0mm i.d. Nucleosil C18 column with methanol/water (MGDGs) or acetonitrile/methanol/water (DGDGs) gradients. The galactolipids were ionised by electrospray operated in the positive ion mode and identified based on their MS/MS spectra. High resolution spectra with accurate masses were found to be essential for correct interpretation of the MS data. The elution order of non-oxidised MGDGs and DGDGs followed the equivalent carbon numbers. The methods were applied for detailed characterisation of the MGDGs and DGDGs in the leaves of Arabidopsis thaliana and Melissa officinalis. [Copyright &y& Elsevier]

Abstract: The interaction of monogalactosyldiacylglycerol (MGDG) with cytochrome b6f complex (cyt b6f), a major component of the photosynthetic apparatus, was studied in Langmuir monolayers during compression/expansion cycling and at constant surface pressure mode. The surface pressure/area isotherms of the mixed films were analyzed in terms of surface compressional modulus and two-dimensional virial equation of state. The morphology and the surface potential of the monolayers were monitored by Brewster angle microscopy and vibrating plate sensor respectively. Our results suggested that there is a specific interaction between MGDG and cyt b6f which resulted in depletion of lipid molecules from the interface. The current work sheds light on the still unclear question how b6f complex gets in touch with the major compound of the thylakoid membranes, the non-charged lipid MGDG. The interaction occured even at very low sub-nanomolar concentration of the complex. This effect most probably could be attributed to hydrogen bonding between the galactose headgroup of the lipid and the protein moiety of cyt b6f. [Copyright &y& Elsevier]

Abstract: In the present study the influence of the lipid environment on the organization of the main light-harvesting complex of photosystem II (LHCII) was investigated by 77K fluorescence spectroscopy. Measurements were carried out with a lipid-depleted and highly aggregated LHCII which was supplemented with the different thylakoid membrane lipids. The results show that the thylakoid lipids are able to modulate the spectroscopic properties of the LHCII aggregates and that the extent of the lipid effect depends on both the lipid species and the lipid concentration. Addition of the neutral galactolipids monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) seems to induce a modification of the disorganized structures of the lipid-depleted LHCII and to support the aggregated state of the complex. In contrast, we found that the anionic lipids sulfoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG) exert a strong disaggregating effect on the isolated LHCII. LHCII disaggregation was partly suppressed under a high proton concentration and in the presence of cations. The strongest suppression was visible at the lowest pH value (pH 5) and the highest Mg2+ concentration (40mM) used in the present study. This suggests that the negative charge of the anionic lipids in conjunction with negatively charged domains of the LHCII proteins is responsible for the disaggregation. Additional measurements by photon correlation spectroscopy and sucrose gradient centrifugation, which were used to gain information about the size and molecular mass of the LHCII aggregates, confirmed the results of the fluorescence spectroscopy. LHCII treated with MGDG and DGDG formed an increased number of aggregates with large particle sizes in the μm-range, whereas the incubation with anionic lipids led to much smaller LHCII particles (around 40nm in the case of PG) with a homogeneous distribution. [Copyright &y& Elsevier]

Abstract: In higher plants, the major part of the xanthophyll cycle pigment violaxanthin (Vx) is non-covalently bound to the main light-harvesting complex of PSII (LHCII). Under saturating light conditions Vx has to be released from its binding site into the surrounding lipid phase, where it is converted to zeaxanthin (Zx) by the enzyme Vx de-epoxidase (VDE). In the present study we investigated the influence of thylakoid lipids on the de-epoxidation of Vx, which was still associated with the LHCII. We isolated LHCII with different concentrations of native, endogenous lipids and Vx by sucrose gradient centrifugation or successive cation precipitation. Analysis of the different LHCII preparations showed that the concentration of LHCII-associated Vx was correlated with the concentration of the main thylakoid lipid monogalactosyldiacylglycerol (MGDG) associated with the complexes. Decreases in the MGDG content of the LHCII led to a diminished Vx concentration, indicating that a part of the total Vx pool was located in an MGDG phase surrounding the LHCII, whereas another part was bound to the LHCII apoproteins. We further studied the convertibility of LHCII-associated Vx in in-vitro enzyme assays by addition of isolated VDE. We observed an efficient and almost complete Vx conversion in the LHCII fractions containing high amounts of endogenous MGDG. LHCII preparations with low concentrations of MGDG exhibited a strongly reduced Vx de-epoxidation, which could be increased by addition of exogenous, pure MGDG. The de-epoxidation of LHCII-associated Vx was saturated at a much lower concentration of native, endogenous MGDG compared with the concentration of isolated, exogenous MGDG, which is needed for optimal VDE activity in in-vitro assays employing pure isolated Vx. [Copyright &y& Elsevier]

Members of the dinoflagellate genus Pyrocystis possess forms of mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively) that have the C20 fatty acid eicosapentaenoic acid [20:5(n-3)] at the sn-1 position and either octadecapentaenoic acid [18:5(n-3)] or octadecatetraenoic acid [18:4(n-3)] at the sn-2 position. We have examined the effect of growth at 15°C, 20°C, and 25°C on modulation of the fatty acids associated with MGDG and DGDG in two strains of each of three species of Pyrocystis, P. fusiformis, P. lunula, and P. noctiluca and have observed using positive-ion electrospray ionization/mass spectrometry (ESI/MS) and electrospray ionization/mass spectrometry/mass spectrometry (ESI/MS/MS) that modulation of the sn-2 fatty acid of DGDG was the only consistent, statistically significant temperature response across all three species. Only one strain of P. lunula displayed a statistically significant temperature-induced modulation of MGDG. In addition, the effect of growth temperature on two forms of the recently identified lipid, trigalactosyldiacylglycerol (TGDG), was examined; TGDG displayed a statistically significant temperature response in only one strain of P. noctiluca. The results presented herein demonstrate how DGDG is modified preferentially over MGDG and TGDG in response to growth temperature by modulating the sn-2 fatty acid of DGDG between the 18:5(n-3) and 18:4(n-3) forms, while the sn-1 fatty acid, 20:5(n-3), remained constant. [ABSTRACT FROM AUTHOR]