Membrane lipids: It’s only a phase

Lee, Anthony G.

doi:10.1016/s0960-9822(00)00477-2

Cited by 107 publications

(79 citation statements)

References 14 publications

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“…It is noteworthy, however, that although breakdown of thylakoid membranes is initiated early in the leaf senescence cascade, the chloroplast envelope remains relatively intact until the very late stages of senescence (Peoples et al, 1980). Thylakoids are the most abundant membrane in nature (Lee, 2000) and, as such, constitute a rich source of carbon in the form of lipid fatty acids for remobilization during leaf senescence. The galactolipids monogalactosyldiacylglycerol and digalactosyldiacylglycerol collectively comprise approximately 80% of the lipid content of thylakoids (Lee, 2000).…”

Section: Discussionmentioning

confidence: 99%

“…Thylakoids are the most abundant membrane in nature (Lee, 2000) and, as such, constitute a rich source of carbon in the form of lipid fatty acids for remobilization during leaf senescence. The galactolipids monogalactosyldiacylglycerol and digalactosyldiacylglycerol collectively comprise approximately 80% of the lipid content of thylakoids (Lee, 2000). As chloroplasts senesce, galactolipid fatty acids are de-esterified and converted to phloem-mobile Suc for translocation out of the senescing leaf.…”

Section: Discussionmentioning

confidence: 99%

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A Role for Diacylglycerol Acyltransferase during Leaf Senescence

2002

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Lipid analysis of rosette leaves from Arabidopsis has revealed an accumulation of triacylglycerol (TAG) with advancing leaf senescence coincident with an increase in the abundance and size of plastoglobuli. The terminal step in the biosynthesis of TAG in Arabidopsis is catalyzed by diacylglycerol acyltransferase 1 (DGAT1; EC 2.3.1.20). When gel blots of RNA isolated from rosette leaves at various stages of development were probed with the Arabidopsis expressed sequence tag clone, E6B2T7, which has been annotated as DGAT1, a steep increase in DGAT1 transcript levels was evident in the senescing leaves coincident with the accumulation of TAG. The increase in DGAT1 transcript correlated temporally with enhanced levels of DGAT1 protein detected immunologically. Two lines of evidence indicated that the TAG of senescing leaves is synthesized in chloroplasts and sequesters fatty acids released from the catabolism of thylakoid galactolipids. First, TAG isolated from senescing leaves proved to be enriched in hexadecatrienoic acid (16:3) and linolenic acid (18:3), which are normally present in thylakoid galactolipids. Second, DGAT1 protein in senescing leaves was found to be associated with chloroplast membranes. These findings collectively indicate that diacylglycerol acyltransferase plays a role in senescence by sequestering fatty acids de-esterified from galactolipids into TAG. This would appear to be an intermediate step in the conversion of thylakoid fatty acids to phloem-mobile sucrose during leaf senescence.Diacylglycerol (DAG) acyltransferase (DGAT; EC 2.3.1.20) mediates the final acylation step in the synthesis of triacylglycerol (TAG). It is present in most plant organs, including leaves, petals, fruits, anthers, and developing seeds (Hobbs et al., 1999). In seeds, TAG is thought to be synthesized within the membranes of the endoplasmic reticulum and subsequently released into the cytosol in the form of oil bodies, which bleb from the cytoplasmic surface of the endoplasmic reticulum (Huang, 1992). The stored TAG is localized in the interior of the oil body, and the surfaces of oil bodies are coated with a monolayer of phospholipid associated with oleosin, the major protein of oil bodies. The acyl chains of the phospholipid monolayer are embedded in the TAG interior of the oil body. Oleosin is a structural protein that is thought to prevent coalescence of oil bodies during seed dehydration (Huang, 1996). That oil bodies originate from the endoplasmic reticulum is consistent with the finding that enzymes of TAG synthesis, including DGAT, are present in microsomal membrane fractions, which are known to contain vesicles of endoplasmic reticulum (Kwanyuen and Wilson, 1986). In addition, TAG can be synthesized in vitro in the presence of microsomes isolated from developing seeds (Lacey et al., 1999).Although TAG formation in seeds is believed to occur in the ER, there have been several reports indicating that purified chloroplast envelope membranes from leaves are also capable of synthesizing this storage lipid (Siebe...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

A Role for Diacylglycerol Acyltransferase during Leaf Senescence

2002

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“…These galactolipids are also major lipid constituents of the inner and outer envelope membranes of plastids and are rarely detected in other cell membranes (1). MGDG has a small galactose head group and splayed polyunsaturated fatty acid tails, which together give this molecule a cone-like shape and the ability to induce curvature in lamellar membranes (3). In contrast to MGDG, which forms nonbilayer hexagonal phases, pure DGDG forms bilayer membranes (3).…”

mentioning

confidence: 99%

“…MGDG has a small galactose head group and splayed polyunsaturated fatty acid tails, which together give this molecule a cone-like shape and the ability to induce curvature in lamellar membranes (3). In contrast to MGDG, which forms nonbilayer hexagonal phases, pure DGDG forms bilayer membranes (3). These unique galactolipid characteristics may be important for the organization of highly stacked thylakoid membranes (3).…”

mentioning

confidence: 99%

“…In contrast to MGDG, which forms nonbilayer hexagonal phases, pure DGDG forms bilayer membranes (3). These unique galactolipid characteristics may be important for the organization of highly stacked thylakoid membranes (3). In addition, x-ray crystallographic analyses of photosystems I and II (PSI and PSII) revealed that galactolipids are tightly bound to these reaction centers (4)(5)(6), which suggests that these lipids are required not only as bulk constituents of photosynthetic membranes but also for the photosynthetic reaction itself.…”

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confidence: 99%

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Galactolipid synthesis in chloroplast inner envelope is essential for proper thylakoid biogenesis, photosynthesis, and embryogenesis

Kobayashi

Kondo

Fukuda

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

268

224

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The biogenesis of thylakoid membranes, an indispensable event for the photoautotrophic growth of plants, requires a significant increase in the level of the unique thylakoid membrane lipid monogalactosyldiacylglycerol (MGDG), which constitutes the bulk of membrane lipids in chloroplasts. The final step in MGDG biosynthesis occurs in the plastid envelope and is catalyzed by MGDG synthase. Here we report the identification and characterization of an Arabidopsis mutant showing a complete defect in MGDG synthase 1. The mutant seeds germinated as small albinos only in the presence of sucrose. The seedlings lacked galactolipids and had disrupted photosynthetic membranes, leading to the complete impairment of photosynthetic ability and photoautotrophic growth. Moreover, invagination of the inner envelope, which is not seen in mature WT chloroplasts, was observed in the mutant, supporting an old hypothesis that envelope invagination is a major event in early chloroplast biogenesis. In addition to the defective seedling phenotype, embryo development was arrested in the mutant, although seeds with impaired embryos could germinate heterotrophically. These results demonstrate the importance of galactolipids not only in photosynthetic growth but also in embryogenesis.glycosyltransferase ͉ thylakoid membrane ͉ monogalactosyldiacylglycerol ͉ monogalactosyldiacylglycerol synthase T he photosynthetic reactions of higher plants rely on a well developed thylakoid membrane system inside chloroplasts. The biogenesis of thylakoid membranes, an indispensable event for photoautotrophic growth, is closely linked to the development of chloroplasts from other plastids such as proplastids. This drastic morphological change within chloroplasts requires a significant increase in the levels of the nonphosphorus glycolipids monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), which account for Ϸ50 and 25 mol% of total thylakoid lipids, respectively (1). These relative abundance levels are also found in cyanobacteria, which suggests that MGDG and DGDG are important for all oxygenic photosynthetic organisms (2). These galactolipids are also major lipid constituents of the inner and outer envelope membranes of plastids and are rarely detected in other cell membranes (1). MGDG has a small galactose head group and splayed polyunsaturated fatty acid tails, which together give this molecule a cone-like shape and the ability to induce curvature in lamellar membranes (3). In contrast to MGDG, which forms nonbilayer hexagonal phases, pure DGDG forms bilayer membranes (3). These unique galactolipid characteristics may be important for the organization of highly stacked thylakoid membranes (3). In addition, x-ray crystallographic analyses of photosystems I and II (PSI and PSII) revealed that galactolipids are tightly bound to these reaction centers (4-6), which suggests that these lipids are required not only as bulk constituents of photosynthetic membranes but also for the photosynthetic reaction itself.The biosynthesis of both MGDG...

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