Limits...
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.

Show MeSH

Related in: MedlinePlus

Electron microscopy observation of chloroplasts and mitochondria in A. thaliana cells grown in suspension. (A) Comparison of cells grown for different times (6 h or 3 d) in standard or −Pi medium. (B) Serial cross sections of a cell grown for 6 h in −Pi medium. Arrows indicate position of contact between mitochondria and chloroplasts. (C) Three-dimensional interpretation of relative position of chloroplasts P1 and P2 (referring to P1 and P2 in B) and two mitochondria (in light gray). Numbers of cross sections refer to numbers displayed in B. Bars, 1 μm.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2172463&req=5

fig6: Electron microscopy observation of chloroplasts and mitochondria in A. thaliana cells grown in suspension. (A) Comparison of cells grown for different times (6 h or 3 d) in standard or −Pi medium. (B) Serial cross sections of a cell grown for 6 h in −Pi medium. Arrows indicate position of contact between mitochondria and chloroplasts. (C) Three-dimensional interpretation of relative position of chloroplasts P1 and P2 (referring to P1 and P2 in B) and two mitochondria (in light gray). Numbers of cross sections refer to numbers displayed in B. Bars, 1 μm.

Mentions: Lipid transfer between organelles and/or membrane vesicles can be activated by contact between membranes (Achleitner et al., 1999; Voelker, 2003). To investigate a possible increase of contact sites between plastids and mitochondria during Pi deprivation, we performed an EM survey of Arabidopsis cell suspensions. In cells that were subcultured into a standard medium for 3 d, we observed numerous round or elongated mitochondria and plastids containing a big starch grain and scarce thylakoid membranes with limited grana stacks. Cells are indeed photosynthetic (Axelos et al., 1992) but not fully autotrophic, and their growth is dependent on presence of sugar. In cells subcultured in −Pi medium for 3 d, mitochondria come across globally similar but plastids look distorted with a fragmented starch grain, further reduced thylakoid membranes, and loose internal membranes. Plastid envelope seems slack as if the inner volume of plastids had been suddenly reduced. When cells are observed only 6 h after subculture, they look roughly similar whenever Pi is present or not. Starch grains in plastids are not quite as developed as in 3-d control cells. Thylakoids are present although scarce. Numerous round or elongated mitochondria can also be observed (Fig. 6 A). In all conditions mitochondria and chloroplasts are rather close to each other, but in Pi-deprived cells tight contacts are more frequent (Fig. 6 B). Indeed, although a close apposition of mitochondria and chloroplasts occurs even under normal growth conditions, the number of contacts between mitochondria and chloroplasts increases approximately three times in Pi-deprived cells compared with control cells (Table II). Analysis of images obtained by a serial cut of a Pi-deprived cell indicates that such contacts cover a rather broad area and are not just localized at focal points between plastids and mitochondria (Fig. 6, B and C). In addition, in cells grown for 6 h in −Pi medium numerous figures of partition are visible on chloroplasts with clear constriction regions. We observed that mitochondria are often present in the vicinity of the chloroplast constrictions (Fig. 6 B). Altogether, the global organization of the cell appears to be modified in the early phase after transfer to Pi-deprived medium. This early response consists particularly in a movement of mitochondria toward chloroplasts or vice-versa and enhanced apposition of mitochondria and plastid membranes.


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)

Electron microscopy observation of chloroplasts and mitochondria in A. thaliana cells grown in suspension. (A) Comparison of cells grown for different times (6 h or 3 d) in standard or −Pi medium. (B) Serial cross sections of a cell grown for 6 h in −Pi medium. Arrows indicate position of contact between mitochondria and chloroplasts. (C) Three-dimensional interpretation of relative position of chloroplasts P1 and P2 (referring to P1 and P2 in B) and two mitochondria (in light gray). Numbers of cross sections refer to numbers displayed in B. Bars, 1 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172463&req=5

fig6: Electron microscopy observation of chloroplasts and mitochondria in A. thaliana cells grown in suspension. (A) Comparison of cells grown for different times (6 h or 3 d) in standard or −Pi medium. (B) Serial cross sections of a cell grown for 6 h in −Pi medium. Arrows indicate position of contact between mitochondria and chloroplasts. (C) Three-dimensional interpretation of relative position of chloroplasts P1 and P2 (referring to P1 and P2 in B) and two mitochondria (in light gray). Numbers of cross sections refer to numbers displayed in B. Bars, 1 μm.
Mentions: Lipid transfer between organelles and/or membrane vesicles can be activated by contact between membranes (Achleitner et al., 1999; Voelker, 2003). To investigate a possible increase of contact sites between plastids and mitochondria during Pi deprivation, we performed an EM survey of Arabidopsis cell suspensions. In cells that were subcultured into a standard medium for 3 d, we observed numerous round or elongated mitochondria and plastids containing a big starch grain and scarce thylakoid membranes with limited grana stacks. Cells are indeed photosynthetic (Axelos et al., 1992) but not fully autotrophic, and their growth is dependent on presence of sugar. In cells subcultured in −Pi medium for 3 d, mitochondria come across globally similar but plastids look distorted with a fragmented starch grain, further reduced thylakoid membranes, and loose internal membranes. Plastid envelope seems slack as if the inner volume of plastids had been suddenly reduced. When cells are observed only 6 h after subculture, they look roughly similar whenever Pi is present or not. Starch grains in plastids are not quite as developed as in 3-d control cells. Thylakoids are present although scarce. Numerous round or elongated mitochondria can also be observed (Fig. 6 A). In all conditions mitochondria and chloroplasts are rather close to each other, but in Pi-deprived cells tight contacts are more frequent (Fig. 6 B). Indeed, although a close apposition of mitochondria and chloroplasts occurs even under normal growth conditions, the number of contacts between mitochondria and chloroplasts increases approximately three times in Pi-deprived cells compared with control cells (Table II). Analysis of images obtained by a serial cut of a Pi-deprived cell indicates that such contacts cover a rather broad area and are not just localized at focal points between plastids and mitochondria (Fig. 6, B and C). In addition, in cells grown for 6 h in −Pi medium numerous figures of partition are visible on chloroplasts with clear constriction regions. We observed that mitochondria are often present in the vicinity of the chloroplast constrictions (Fig. 6 B). Altogether, the global organization of the cell appears to be modified in the early phase after transfer to Pi-deprived medium. This early response consists particularly in a movement of mitochondria toward chloroplasts or vice-versa and enhanced apposition of mitochondria and plastid membranes.

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