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- Andersson, Mats X., 1977, et al.
(författare)
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Chloroplast biogenesis. Regulation of lipid transport to the thylakoid in chloroplasts isolated from expanding and fully expanded leaves of pea.
- 2001
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Ingår i: Plant physiology. - 0032-0889. ; 127:1, s. 184-93
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Tidskriftsartikel (refereegranskat)abstract
- To study the regulation of lipid transport from the chloroplast envelope to the thylakoid, intact chloroplasts, isolated from fully expanded or still-expanding pea (Pisum sativum) leaves, were incubated with radiolabeled lipid precursors and thylakoid membranes subsequently were isolated. Incubation with UDP[(3)H]Gal labeled monogalactosyldiacylglycerol in both envelope membranes and digalactosyldiacylglycerol in the outer chloroplast envelope. Galactolipid synthesis increased with incubation temperature. Transport to the thylakoid was slow below 12 degrees C, and exhibited a temperature dependency closely resembling that for the previously reported appearance and disappearance of vesicles in the stroma (D.J. Morré, G. Selldén, C. Sundqvist, A.S. Sandelius [1991] Plant Physiol 97: 1558-1564). In mature chloroplasts, monogalactosyldiacylglycerol transport to the thylakoid was up to three times higher than digalactosyldiacylglycerol transport, whereas the difference was markedly lower in developing chloroplasts. Incubation of chloroplasts with [(14)C]acyl-coenzyme A labeled phosphatidylcholine (PC) and free fatty acids in the inner envelope membrane and phosphatidylglycerol at the chloroplast surface. PC and phosphatidylglycerol were preferentially transported to the thylakoid. Analysis of lipid composition revealed that the thylakoid contained approximately 20% of the chloroplast PC. Our results demonstrate that lipids synthesized at the chloroplast surface as well as in the inner envelope membrane are transported to the thylakoid and that lipid sorting is involved in the process. Furthermore, the results also indicate that more than one pathway exists for galactolipid transfer from the chloroplast envelope to the thylakoid.
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| 2. |
- Andersson, Mats X., 1977, et al.
(författare)
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The involvement of cytosolic lipases in converting phosphatidyl choline to substrate for galactolipid synthesis in the chloroplast envelope :
- 2004
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Ingår i: Biochimica et Biophysica Acta-Molecular and Cell Biology of Lipids. - : Elsevier BV. - 1388-1981. ; 1684:1-3, s. 46-53
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Tidskriftsartikel (refereegranskat)abstract
- Here we report that cytosolic phospholipases are involved in the utilization of phosphatidylcholine (PC) as substrate for chloroplast-localized synthesis of monogalactosyldiacylglycerol (MGDG). Isolated chloroplasts were pre-incubated with lysoPC and [C-14]18:0-CoA to form [C-14]PC. When soluble plant proteins (cytosol) and UDP-galactose were added, [C-14] MGDG was formed. An inhibitor of phospholipase D markedly lowered the formation of [C-14]MGDG, whereas thermolysin pretreatment of the chloroplasts was without effect. The cytosolic activity resided in the >100-kDa fraction. In a second approach, [C-14]PC-containing lipid mixtures were incubated with cytosol. Degradation of [C-14]PC to [C-14]diacylglycerol was highest when the lipid composition of the mixture mimicked that of the outer chloroplast envelope. We also investigated whether PC of extraplastidic origin could function as substrate for MGDG synthesis. Isolated chloroplasts were incubated with enriched endoplasmic reticulum containing radiolabelled acyl lipids. In the presence of cytosol and UDPgalactose, there was a time-dependent transfer of [C-14]PC from this fraction to chloroplasts, where [C-14]MGDG was formed. We conclude that chloroplasts recruit cytosolic phospholipase D and phosphatidic acid phosphatase to convert PC to diacylglycerol. Apparently, these lipases do not interact with chloroplast surface proteins, but rather with outer membrane lipids, either for association to the envelope or for substrate presentation. (C) 2004 Elsevier B.V. All rights reserved.
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| 3. |
- Kjellberg, J. Magnus, 1972, et al.
(författare)
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Acyl-CoA dependent acylation of phospholipids in the chloroplast envelope.
- 2000
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Ingår i: Biochimica et biophysica acta. - 0006-3002. ; 1485:2-3, s. 100-10
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Tidskriftsartikel (refereegranskat)abstract
- Acyl-CoAs are substrates for acyl lipid synthesis in the endoplasmic reticulum. In addition, they may also be substrates for lipid acylation in other membranes. In order to assess whether lipid acylation may have a role in plastid lipid metabolism, we have studied the incorporation of radiolabelled fatty acids from acyl-CoAs into lipids in isolated, intact pea chloroplasts. The labelled lipids were phosphatidylcholine (PC), phosphatidylglycerol (PG), phosphatidylinositol and free fatty acids. With oleoyl-CoA, the fatty acid was incorporated preferably into the sn-2 position of PC and the acylation activity mainly occurred in fractions enriched in inner chloroplast envelope. Added lysoPC stimulated the activity. With palmitoyl-CoA, the fatty acid was incorporated primarily into the sn-1 position of PG and the reaction occurred at the surface of the chloroplasts. As chloroplast-synthesized PG generally contains 16C fatty acids in the sn-2 position, we propose that the acylation of PG studied represents activities present in a domain of the endoplasmic reticulum or an endoplasmic reticulum-derived fraction that is associated with chloroplasts and maintains this association during isolation. This domain or fraction contains a discreet population of lipid metabolizing activities, different from that of bulk endoplasmic reticulum, as shown by that with isolated endoplasmic reticulum, acyl-CoAs strongly labelled phosphatidic acid and phosphatidylethanolamine, lipids that were never labelled in the isolated chloroplasts.
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| 4. |
- Kjellberg, J. Magnus, 1972, et al.
(författare)
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GTP-dependent phosphorylation and GTPγS-dependent thiophosphorylation of proteins and lipids in chloroplasts isolated from leaves of spinach (Spinacia oleracea)
- 2004
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Ingår i: Plant Science. - : Elsevier BV. - 0168-9452. ; 166:3, s. 601-607
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the interaction of GTP and its slowly-hydrolysable analogue, GTPγS, with isolated chloroplast envelope, stroma and thylakoids from spinach (Spinacia oleracea). We used a filter assay to monitor [35S]GTPγS-dependent labelling of the chloroplast fractions. All fractions were labelled by [35S]GTPγS and the labelling was competed by unlabelled GTPγS, GTP and GDP over ATP and GMP. The label associated with the chloroplast fractions was, at least partly, covalent thiophosphate labelling of proteins as well as traces of lipid labelling. The pattern of [35S]GTPγS-dependent protein thiophosphorylation differed from [35S]ATPγS dependent thiophosphorylation as well as from [γ-32P]GTP and [γ-32P]ATP dependent protein phosphorylation. Incubation of chloroplast fractions with [γ-32P]GTP also resulted in heavy labelling of several lipids and lipid phosphorylation was markedly more prominent than lipid thiophosphorylation. The results are discussed in relation to the possible roles of guanine nucleotides in the regulation of thylakoid biogenesis
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| 5. |
- Larsson, Karin E., 1958, et al.
(författare)
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LysoPC acyltransferase/PC transacylase activities in plant plasma membrane and plasma membrane-associated endoplasmic reticulum
- 2007
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Ingår i: BMC Plant Biology. - 1471-2229.
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Tidskriftsartikel (refereegranskat)abstract
- Background The phospholipids of the plant plasma membrane are synthesized in the endoplasmic reticulum (ER). The majority of these lipids reach the plasma membrane independently of the secretory vesicular pathway. Phospholipid delivery to the mitochondria and chloroplasts of plant cells also bypasses the secretory pathway and here it has been proposed that lysophospholipids are transported at contact sites between specific regions of the ER and the respective organelle, followed by lysophospholipid acylation in the target organelle. To test the hypothesis that a corresponding mechanism operates to transport phospholipids to the plasma membrane outside the secretory pathway, we investigated whether lysolipid acylation occurs also in the plant plasma membrane and whether this membrane, like the chloroplasts and mitochondria, is in close contact with the ER. Results The plant plasma membrane readily incorporated the acyl chain of acyl-CoA into phospholipids. Oleic acid was preferred over palmitic acid as substrate and acyl incorporation occurred predominantly into phosphatidylcholine (PC). Phospholipase A2 stimulated the reaction, as did exogenous lysoPC when administered in above critical micellar concentrations. AgNO3 was inhibitory. The lysophospholipid acylation reaction was higher in a membrane fraction that could be washed off the isolated plasma membranes after repeated freezing and thawing cycles in a medium with lowered pH. This fraction exhibited several ER-like characteristics. When plasma membranes isolated from transgenic Arabidopsis expressing green fluorescent protein in the ER lumen were observed by confocal microscopy, membranes of ER origin were associated with the isolated plasma membranes. Conclusions We conclude that a lysoPC acylation activity is associated with plant plasma membranes and cannot exclude a PC transacylase activity. It is highly plausible that the enzyme(s) resides in a fraction of the ER, closely associated with the plasma membrane, or in both. We suggest that this fraction might be the equivalent of the mitochondria associated membrane of ER origin that delivers phospholipids to the mitochondria, and to the recently isolated ER-derived membrane fraction that is in close contact with chloroplasts. The in situ function of the lysoPC acylation/PC transacylase activity is unknown, but involvement in lipid delivery from the ER to the plasma membrane is suggested.
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