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Phosphate deprivation induces transfer of DGDG galactolipid from chloroplast to mitochondria.

Jouhet J, Maréchal E, Baldan B, Bligny R, Joyard J, Block MA - J. Cell Biol. (2004)

Bottom Line: Mitochondria do not synthesize this pool of DGDG, which structure is shown to be characteristic of a DGD type enzyme present in plastid envelope.This transfer does not apparently involve the endomembrane system and would rather be dependent upon contacts between plastids and mitochondria.Contacts sites are favored at early stages of phosphate deprivation when DGDG cell content is just starting to respond to phosphate deprivation.

View Article: PubMed Central - PubMed

Affiliation: Laboratoire de Physiologie Cellulaire Végétale, UMR 5168 (CNRS/CEA/Université Jseph Fourier/INRA), DRDC-PCV, CEA-Grenoble, Grenoble, France.

ABSTRACT
In many soils plants have to grow in a shortage of phosphate, leading to development of phosphate-saving mechanisms. At the cellular level, these mechanisms include conversion of phospholipids into glycolipids, mainly digalactosyldiacylglycerol (DGDG). The lipid changes are not restricted to plastid membranes where DGDG is synthesized and resides under normal conditions. In plant cells deprived of phosphate, mitochondria contain a high concentration of DGDG, whereas mitochondria have no glycolipids in control cells. Mitochondria do not synthesize this pool of DGDG, which structure is shown to be characteristic of a DGD type enzyme present in plastid envelope. The transfer of DGDG between plastid and mitochondria is investigated and detected between mitochondria-closely associated envelope vesicles and mitochondria. This transfer does not apparently involve the endomembrane system and would rather be dependent upon contacts between plastids and mitochondria. Contacts sites are favored at early stages of phosphate deprivation when DGDG cell content is just starting to respond to phosphate deprivation.

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1H-NMR galactolipid analysis. The α-peak is characterized by a doublet at 4.7 ppm and the β-peak by a doublet at 4.0 ppm. (A) β-MGDG from A. thaliana control cells. (B) α-β DGDG from A. thaliana control cells. (C) DGDG from Spinacia oleracea purified chloroplast envelope. In envelope fraction, two DGDG types are visible: α-β and β1-β2. (D) α-β DGDG from A. thaliana Pi-deprived cells. (E) Mitochondrial α-β DGDG from A. thaliana Pi-deprived cells.
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fig5: 1H-NMR galactolipid analysis. The α-peak is characterized by a doublet at 4.7 ppm and the β-peak by a doublet at 4.0 ppm. (A) β-MGDG from A. thaliana control cells. (B) α-β DGDG from A. thaliana control cells. (C) DGDG from Spinacia oleracea purified chloroplast envelope. In envelope fraction, two DGDG types are visible: α-β and β1-β2. (D) α-β DGDG from A. thaliana Pi-deprived cells. (E) Mitochondrial α-β DGDG from A. thaliana Pi-deprived cells.

Mentions: To characterize the overall structure of the mitochondria-associated DGDG, we analyzed its fatty acid composition and its polar head structure. Fig. 3 B shows that fatty acid composition of mitochondrial DGDG was fairly similar to that of Pi-deprived cell DGDG. Compared with DGDG present in control cells, the main characteristic of fatty acid composition of mitochondrial DGDG was an increase in 16C/18C ratio (0.09–0.13) with more 16:0 and an increase in more saturated species of C18, but globally DGDG remained highly enriched in 18:3. The anomeric structure of the polar head of mitochondrial DGDG was resolved by nuclear magnetic resonance (NMR). In 1H-NMR, the anomeric proton in α- or β-glycosidic configuration gives characteristic doublet signals respectively at high chemical shift (∼5.0 ppm) or at low chemical shift (∼4.0 ppm). The exact position of these signals depends on solvent, temperature, and molecular environment. To identify the precise position of these α- and β-doublet signals, several galactolipid molecules were analyzed by NMR and compared. Higher plant MGDG was reported to contain only a β-glycosidic bond (Carter et al., 1956), and indeed Arabidopsis cell MGDG gave a doublet signal at 4.0 ppm (Fig. 5 A). Two forms of DGDG have previously been reported in plants (Kojima et al., 1990; Xu et al., 2003); the main form containing a β-glycosidic bond on the first galactose and an α-glycosidic bond on the second galactose (Carter et al., 1956). DGDG extracted from either control or Pi-deprived Arabidopsis cells corresponded to this main form, with a doublet signal at 4.0 ppm for the β-bond and at 4.7 ppm for the α-bond (Fig. 5, B and D). In addition to the 4.7 ppm α-doublet, DGDG extracted from an isolated fraction of spinach chloroplast envelope contained three doublet signals in the range of the β signal (exact position at 4.0, 4.05, and 4.1 ppm; Fig. 5 C) that were indicative of presence of both α-β and β-β DGDG structures, the later structure very likely resulting from the activation of the galactolipid–galactolipid galactosyltransferase during the course of envelope isolation (Xu et al., 2003). In NMR spectra of mitochondrial DGDG, we observed only doublet signals characteristic for an α-glycosidic bond at 4.7 ppm and for a β-glycosidic bond at 4.0 ppm, with no signal at 4.1 ppm (Fig. 5 E). We concluded from these results that mitochondrial DGDG structure is 1,2-diacyl-3-O-(α-d-galactopyranosyl-(1→6)-O-β-d-galactopyranosyl)-sn-glycerol.


Phosphate deprivation induces transfer of DGDG galactolipid from chloroplast to mitochondria.

Jouhet J, Maréchal E, Baldan B, Bligny R, Joyard J, Block MA - J. Cell Biol. (2004)

1H-NMR galactolipid analysis. The α-peak is characterized by a doublet at 4.7 ppm and the β-peak by a doublet at 4.0 ppm. (A) β-MGDG from A. thaliana control cells. (B) α-β DGDG from A. thaliana control cells. (C) DGDG from Spinacia oleracea purified chloroplast envelope. In envelope fraction, two DGDG types are visible: α-β and β1-β2. (D) α-β DGDG from A. thaliana Pi-deprived cells. (E) Mitochondrial α-β DGDG from A. thaliana Pi-deprived cells.
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Related In: Results  -  Collection

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fig5: 1H-NMR galactolipid analysis. The α-peak is characterized by a doublet at 4.7 ppm and the β-peak by a doublet at 4.0 ppm. (A) β-MGDG from A. thaliana control cells. (B) α-β DGDG from A. thaliana control cells. (C) DGDG from Spinacia oleracea purified chloroplast envelope. In envelope fraction, two DGDG types are visible: α-β and β1-β2. (D) α-β DGDG from A. thaliana Pi-deprived cells. (E) Mitochondrial α-β DGDG from A. thaliana Pi-deprived cells.
Mentions: To characterize the overall structure of the mitochondria-associated DGDG, we analyzed its fatty acid composition and its polar head structure. Fig. 3 B shows that fatty acid composition of mitochondrial DGDG was fairly similar to that of Pi-deprived cell DGDG. Compared with DGDG present in control cells, the main characteristic of fatty acid composition of mitochondrial DGDG was an increase in 16C/18C ratio (0.09–0.13) with more 16:0 and an increase in more saturated species of C18, but globally DGDG remained highly enriched in 18:3. The anomeric structure of the polar head of mitochondrial DGDG was resolved by nuclear magnetic resonance (NMR). In 1H-NMR, the anomeric proton in α- or β-glycosidic configuration gives characteristic doublet signals respectively at high chemical shift (∼5.0 ppm) or at low chemical shift (∼4.0 ppm). The exact position of these signals depends on solvent, temperature, and molecular environment. To identify the precise position of these α- and β-doublet signals, several galactolipid molecules were analyzed by NMR and compared. Higher plant MGDG was reported to contain only a β-glycosidic bond (Carter et al., 1956), and indeed Arabidopsis cell MGDG gave a doublet signal at 4.0 ppm (Fig. 5 A). Two forms of DGDG have previously been reported in plants (Kojima et al., 1990; Xu et al., 2003); the main form containing a β-glycosidic bond on the first galactose and an α-glycosidic bond on the second galactose (Carter et al., 1956). DGDG extracted from either control or Pi-deprived Arabidopsis cells corresponded to this main form, with a doublet signal at 4.0 ppm for the β-bond and at 4.7 ppm for the α-bond (Fig. 5, B and D). In addition to the 4.7 ppm α-doublet, DGDG extracted from an isolated fraction of spinach chloroplast envelope contained three doublet signals in the range of the β signal (exact position at 4.0, 4.05, and 4.1 ppm; Fig. 5 C) that were indicative of presence of both α-β and β-β DGDG structures, the later structure very likely resulting from the activation of the galactolipid–galactolipid galactosyltransferase during the course of envelope isolation (Xu et al., 2003). In NMR spectra of mitochondrial DGDG, we observed only doublet signals characteristic for an α-glycosidic bond at 4.7 ppm and for a β-glycosidic bond at 4.0 ppm, with no signal at 4.1 ppm (Fig. 5 E). We concluded from these results that mitochondrial DGDG structure is 1,2-diacyl-3-O-(α-d-galactopyranosyl-(1→6)-O-β-d-galactopyranosyl)-sn-glycerol.

Bottom Line: Mitochondria do not synthesize this pool of DGDG, which structure is shown to be characteristic of a DGD type enzyme present in plastid envelope.This transfer does not apparently involve the endomembrane system and would rather be dependent upon contacts between plastids and mitochondria.Contacts sites are favored at early stages of phosphate deprivation when DGDG cell content is just starting to respond to phosphate deprivation.

View Article: PubMed Central - PubMed

Affiliation: Laboratoire de Physiologie Cellulaire Végétale, UMR 5168 (CNRS/CEA/Université Jseph Fourier/INRA), DRDC-PCV, CEA-Grenoble, Grenoble, France.

ABSTRACT
In many soils plants have to grow in a shortage of phosphate, leading to development of phosphate-saving mechanisms. At the cellular level, these mechanisms include conversion of phospholipids into glycolipids, mainly digalactosyldiacylglycerol (DGDG). The lipid changes are not restricted to plastid membranes where DGDG is synthesized and resides under normal conditions. In plant cells deprived of phosphate, mitochondria contain a high concentration of DGDG, whereas mitochondria have no glycolipids in control cells. Mitochondria do not synthesize this pool of DGDG, which structure is shown to be characteristic of a DGD type enzyme present in plastid envelope. The transfer of DGDG between plastid and mitochondria is investigated and detected between mitochondria-closely associated envelope vesicles and mitochondria. This transfer does not apparently involve the endomembrane system and would rather be dependent upon contacts between plastids and mitochondria. Contacts sites are favored at early stages of phosphate deprivation when DGDG cell content is just starting to respond to phosphate deprivation.

Show MeSH
Related in: MedlinePlus