The role of chloroplasts and microsomal fractions in polar-lipid synthesis from [1-14C]acetate by cell-free preparations from spinach (<i>Spinacia oleracea</i>) leaves

Roughan, P. G.; Holland, Ross; Slack, C. R.

doi:10.1042/bj1880017

Cited by 125 publications

(90 citation statements)

References 48 publications

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“…Whereas lipids derived from the prokaryotic pathway are predominantly C 18 C 16 , those derived from the eukaryotic pathway are either C 18 C 18 or C 16 C 18 (Browse and Somerville, 1991). In order to approximate the flux of acyl groups from cytosolic to plastid lipids, we predict the compositions of labeled chloroplast lipids from the labeled fatty acid distribution by assuming that both positions are equally labeled, an observation based on equal labeling of the sn-1 and sn-2 positions of PC, MGDG, and PG in spinach (Spinacia oleracea) leaves (Roughan et al, 1980). We also use the finding that Arabidopsis DGDG contains about 8% C 18 C 16 species and 25% C 16 C 18 species .…”

Section: Analysis Of Labeled Polar Lipid Classes In Wild-type and Fatmentioning

confidence: 99%

Metabolic Responses to the Reduction in Palmitate Caused by Disruption of the FATB Gene in Arabidopsis

et al. 2004

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Disruption of the FATB gene in Arabidopsis results in a two-thirds reduction in saturated fatty acids, largely palmitate, in the leaf extra-plastidic phospholipids and a reduction in the growth rate of the mutant compared to wild type (Bonaventure G, Salas JJ, Pollard MR, Ohlrogge JB [2003] Plant Cell 15: 1020-1033. In this study, we report that although fatb-ko seedlings grow more slowly than wild type, the rate of fatty acid synthesis in leaves of the mutant increases by 40%. This results in approximately the same amount of palmitate exported from the plastid as in wild type but an increase in oleate export of about 55%. To maintain constant amounts of fatty acids in leaves, thereby counterbalancing their higher rate of production, the mutant also increases its rate of fatty acid degradation. Although fatb-ko leaves have higher rates of fatty acid synthesis and turnover, the relative proportions of membrane lipids are similar to wild type. Thus, homeostatic mechanisms to preserve membrane compositions compensate for substantial changes in rates of fatty acid and glycerolipid metabolism in the mutant. Pulse-chase labeling studies show that in fatb-ko leaves there is a net increase in the synthesis of both prokaryotic and eukaryotic lipids and consequently of their turnover. The net loss of palmitate from phosphatidylcholine plus phosphatidylethanolamine is similar for wild type and mutant, suggesting that mechanisms are not present that can preferentially preserve the saturated fatty acids. In summary, the leaf cell responds to the loss of saturated fatty acid production in the fatb-ko mutant by increasing both fatty acid synthesis and degradation, but in doing so the mechanisms for increased fatty acid turnover contribute to the lowering of the percentage of saturated fatty acids found in eukaryotic lipids.In plants, the major site for de novo fatty acid synthesis (FAS) occurs in the plastid (Ohlrogge et al., 1979). Fatty acids are either utilized in this organelle or exported to supply diverse cytoplasmic biosynthetic pathways and cellular processes. Production of fatty acids for export depends on the activity of acyl-ACP thioesterases (FATs) that hydrolyze acyl-acyl carrier protein (acyl-ACP) to release free fatty acids and ACP (for review, see Voelker et al., 1997). After export, the free fatty acids are re-esterified to CoA to form the cytosolic acyl-CoA pool (Pollard and Ohlrogge, 1999). In mesophyll cells, acyl-CoAs are primarily used for the biosynthesis of membrane glycerolipids in the endoplasmic reticulum (Browse and Somerville, 1991). However, in other cell types exported fatty acids have different fates. For example, in embryo cells of oilseeds, the major fraction is incorporated into triacylglycerols, while in epidermal cells a large fraction is utilized for the synthesis of waxes and cutin (Post-Beittenmiller, 1996;Kolattukudy, 2003). Furthermore, all cells synthesize sphingolipids (Lynch, 1993), and we recently estimated that as much as 30% to 40% of exported palmitate is needed for sphingoid ba...

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Section: Analysis Of Labeled Polar Lipid Classes In Wild-type and Fatmentioning

confidence: 99%

Metabolic Responses to the Reduction in Palmitate Caused by Disruption of the FATB Gene in Arabidopsis

et al. 2004

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“…60th pathways are initiated by the synthesis of 16:O-acyl carrier protein (ACP) and 18:l-ACP by the combined action of a type II fatty acid synthase (Shimakata and Stumpf, 1982) and a soluble stearoyl-ACP desaturase (McKeon and Stumpf, 1982;Shanklin and Somerville, 1991) located in the chloroplasts or other plastids. The prokaryotic pathway (Roughan et al, 1980) located in the chloroplast inner envelope uses 18:l-ACP and 16:O-ACP for the sequential acylation of glyceral-3-phosphate and synthesis of glycerolipid components for the chloroplast membranes (Frentzen, 1993;Joyard et al, 1993). The eukaryotic pathway involves export of 16:O and 18:l fatty acids from the chloroplast to the endoplasmic reticulum and their incorporation into phosphatidylchsline and other phospholipids that are the principal structural lipids of a0 the membranes of the cell except for the chloroplast.…”

Section: Introductionmentioning

confidence: 99%

“…There are two dlstinct pathways in plant 6811s for the biosynthesis of glycerolipids Rnd the associated praduction To whom correspondence should be addressed. of polyunsaturated fatty acids (Roughan et al, 1980;Browse and Somerville, 1991). 60th pathways are initiated by the synthesis of 16:O-acyl carrier protein (ACP) and 18:l-ACP by the combined action of a type II fatty acid synthase (Shimakata and Stumpf, 1982) and a soluble stearoyl-ACP desaturase (McKeon and Stumpf, 1982;Shanklin and Somerville, 1991) located in the chloroplasts or other plastids.…”

Section: Introductionmentioning

confidence: 99%

The Critical Requirement for Linolenic Acid Is Pollen Development, Not Photosynthesis, in an Arabidopsis Mutant.

1996

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The very high proportlons of trlenolc fatty acids found in chloroplast membranes of all higher plants suggest that these llpld otructurtis mlght be essentlal for photosynthasis. We report here on the productisn of Arabidopsis triple mutants that contaln negllglble levels of trlenolc fatty acids. Photosynthesls at 22OC was barely affected, and vegetative growth of the mutants was ldentlcal wlth that of tha wlld type, dm"StratIng that any requlrement for trienoic acyl groups in membrane structure and functlon 1s relatively subtle. Although vegetative growth and development were unaffected, the triple mutants are male sterlle and produce no seed under normal conditlons. Comparisons of psllen development In wlld-type and triple mutant flowersestablished that pallan gralns in the mutant develeped to the tslcellular stege. Exogenous applicatlens of a-llnolenata or jasmonate restered fertlllty. T a k n tsgether, the results demonstrate that the critical role of trlenolc acids ln tha llfe cycle of plants 1s as the precursor of sxylipln, a signallng compound that regulates final maturatlon processes and the release of pollen. INTRODUCTIONThe biophysical reactions of light harvesting and electron transport during photosynthesis take place in a uniquely constructed bilayer membrane, the thylakoid. In all photosynthetic eukaryotes, the complement of atypical glyceralipid molecules that form the foundation of this membrane are characterized by sugar headgroups and avery high leve1 of unsaturation in the fatty acid chains, which compose the central portion of the thylakoid lamella bilayer. For example, menogalactosyldiacylglycerol, the major thylakoid lipid, typically contains >90% af a-linolenic acid (183) er a combination of 183 and hexadecatrienoic (163) acids, depending on the plant species (Jamieson and Reid, 1971). These very high levels of trienoic fatty asids are noteworthy because free radicals that are byproducts of the photosynthetic llght reactions stimulate oxidation of polyunsaturated fatty acids. Because this oxidation might be expected ta medlate against a high degree of unsaturation, it has been inferred that there is a strong selective advantage to having such high levels of trienoic fatty acids in the thylakoid. Therefore, it could be reasoned that these lipid structures must have some critical role in maintaining photosynthetic functlon.To test this line of reasoning directly, we set out to develop Arabldopsis llnes with reduced levels of 18:3 and 163 fatty acids. There are two dlstinct pathways in plant 6811s for the biosynthesis of glycerolipids Rnd the associated praduction To whom correspondence should be addressed. of polyunsaturated fatty acids (Roughan et al., 1980;Browse and Somerville, 1991). 60th pathways are initiated by the synthesis of 16:O-acyl carrier protein (ACP) and 18:l-ACP by the combined action of a type II fatty acid synthase (Shimakata and Stumpf, 1982) and a soluble stearoyl-ACP desaturase (McKeon and Stumpf, 1982;Shanklin and Somerville, 1991) located in the chloroplasts or other p...

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“…The chloroplasts isolated from the four different plants incorporated acetate into fatty acids under conditions which had been optimized for spinach (18). The maximum rates of about 1 pmol/mg Chl.h are lower than those of spinach for which rates in excess of 2 ,umol/mg Chl.…”

mentioning

confidence: 99%

“…In photosynthetically active cells of 16:3 plants which are represented, for example, by members of Apiaceae and Brassicaceae (9), two pathways operate in parallel (18) to provide thylakoids with MGD. The cooperative 'eucaryotic' sequence (4) is supplemented to various extents by a 'procaryotic' pathway.…”

mentioning

confidence: 99%

Similarities and Differences in Lipid Metabolism of Chloroplasts Isolated from 18:3 and 16:3 Plants

Heinz¹,

Roughan²

1983

Plant Physiol.

261

167

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Photosynthetically active chloroplasts reting high rates of fatty acid synthesis from i1-"4Clacetate were purifie from leaves of both 16:3 (Solaum nodiforuu, Chenopodiwm album) and 183 plants (Amaranthu lividus, Pisum sativum). A comparson of lipids into which newly synthesized fatty acids were incorporated revealed that, in 183 chloroplasts, enzymic activities catalyzing the conversion of phosphatidate to diacylglycerol and of diacyiglycerol to monogalactosyl diacylglycerol (MGD) were significantiy less active than in 16:3 chloroplasts. In contrast, labeling rates of MGD from UDP-I14Cigal were similar for both types of chloroplasts. having two linoleoyl groups results in an accordingly unsaturated MGD. The MGD-linked acyl groups are substrates for the introduction of the third double bonds (16) to yield MGD with two linolenoyl residues. This galactolipid is characteristic of 18:3 plants such as Asteraceae and Fabaceae, for example (9). It is called eucaryotic MGD, because the nucleocytoplasmic part of the cell controls the construction of the DAG backbone which carries C 18 fatty acids at both C-1 and C-2 positions of glycerol (7), whereas C 16:0, if present, is excluded from C-2.In photosynthetically active cells of 16:3 plants which are represented, for example, by members of Apiaceae and Brassicaceae (9), two pathways operate in parallel (18) to provide thylakoids with MGD. The cooperative 'eucaryotic' sequence (4) is supplemented to various extents by a 'procaryotic' pathway. Its reactions are confined to the chloroplast and result in a typical arrangement of acyl groups as well as their complete desaturation once they are esterified to MGD. Procaryotic DAG backbones carry C 16:0 and its desaturation products at C-2 (7) from which position C18: fatty acids are excluded. The C-l position is occupied by C 18 fatty acids and to a small extent by C16 groups. The similarity in DAG backbones of lipids from blue-green algae (22, 30) with those synthesized by the chloroplast-confmed pathway in 16:3 plants suggests a phylogenetic relation and justifies the term procaryotic.The different pathways just mentioned were deduced from labeling experiments with leaves from a small selection of 18:3 and 16:3 plants (17,24,26,29), whereas studies with isolated chloroplasts were mainly confined to organelles from the 16:3 plant spinach (14,20). To provide additional evidence for the roles ascribed to chloroplasts in pro-or eucaryotic pathways during MGD biosynthesis in different plants, we carried out experiments with chloroplasts isolated from 18:3 as well as 16:3 plants. Our data suggest that chloroplasts from these two groups of plants have similarities and differences in enzymic equipment explaining some of the above mentioned complications in lipid biosynthesis. Chloroplast Isolation. The medium (12) used for isolating chloroplasts, forming gradients, measuring O2 evolution and lipid synthesis contained 25 mm Hepes, 10 mm KHCO3, 2 mm EDTA, 1 mM MgCl2, 1 mm MnCl2, 0.3 mm KH2PO4, and 0.33 M sorbitol, adjusted to ...

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The role of chloroplasts and microsomal fractions in polar-lipid synthesis from [1-14C]acetate by cell-free preparations from spinach (Spinacia oleracea) leaves

Cited by 125 publications

References 48 publications

Metabolic Responses to the Reduction in Palmitate Caused by Disruption of the FATB Gene in Arabidopsis

Metabolic Responses to the Reduction in Palmitate Caused by Disruption of the FATB Gene in Arabidopsis

The Critical Requirement for Linolenic Acid Is Pollen Development, Not Photosynthesis, in an Arabidopsis Mutant.

Similarities and Differences in Lipid Metabolism of Chloroplasts Isolated from 18:3 and 16:3 Plants

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