Plants phosphatidylglycerol

Figure 21-3 Major pathways of synthesis of fatty acids and glycerolipids in the green plant Arabidopsis. The major site of fatty acid synthesis is chloroplasts. Most is exported to the cytosol as oleic acid (18 1). After conversion to its coenzyme A derivative it is converted to phosphatidic acid (PA), diacylglycerol (DAG), and the phospholipids phosphatidylcholine (PC), phosphatidylinositol (PI), phosphatidylglycerol (PG), and phosphatidylethanolamine (PE). Desaturation also occurs, and some linoleic and linolenic acids are returned to the chloroplasts. See text also. From Sommerville and Browse.106 See also Figs. 21-4 and 21-5. Other abbreviations monogalactosyldiacylglycerol (MGD), digalactosyldiacylglycerol (DGD), sulfolipid (SL), glycerol 3-phosphate (G3P), lysophosphatidic acid (LPA), acyl carrier protein (ACP), cytidine diphosphate-DAG (CDP-DAG).

Roughan, P.G. (1985). Phosphatidylglycerol and chilling sensitivity in plants. Plant Physiology 77, 740-6. 

Phosphodiesterase (Hydrolysis) Activity. A rather broad substrate specificity is exhibited by the purified phospholipase D (phosphodiesterase activity). It can attack phosphatidylcholine, phosphatidylethanolamine, phospha-tidylserine, and phosphatidylglycerol. In most cases, Ca2+ was an activator, but variable results were obtained on the positive influence of diethyl ether on the catalytic activity of different sources of this enzyme. Usually the optimum pH was in the range from 5.0 to 7.0. Mammalian phospholipase D, containing both the phosphodiesterase and transphosphatidylase activities, exhibited a broad-range substrate specificity similar to that of the plant enzyme. However, the mammalian enzyme showed a dependency for the presence of oleic acid in the reaction system (Kobayashi and Kanfer, 1991). 

Straight- or normal-chain (even-numbered) monoenoic fatty acids (with one double bond) amount to a significant proportion of the total fatty acids in most natural lipids. The double bond is usually of the cis- or Z-configuration, but some fatty acids with trans- or -double bonds are found. For example, a major fatty acid esterified to phosphatidylglycerol in the photosynthetic membranes of higher plants and algae is trans-3-hexadecenoic acid. Often the cis bond is present at the A9 position. 

Associate Professor, Professor of Agricultural and Biological Chemistry, The Pennsylvania State University. Research on lipid metabolism, neutron activation analysis, sulfocarbohydrate metabolism. Discovery of phosphatidylglycerol and the plant suhbhpid. 

Phosphatidylglycerol (PG) is predominant in higher plants (30%) and is located in chloroplasts, It is localised in mitochondria in mammalian cells. 

FIGURE 11-2 Lipid composition of the plasma membrane and organelle membranes of a rat hepatocyte. The functional specialization of each membrane type is reflected in its unique lipid composition. Cholesterol is prominent in plasma membranes but barely detectable in mitochondrial membranes. Cardiolipin is a major component of the inner mitochondrial membrane but not of the plasma membrane. Phosphatidylserine, phosphatidylinositol, and phosphatidylglycerol are relatively minor components (yellow) of most membranes but serve critical functions phosphatidylinositol and its derivatives, for example, are important in signal transductions triggered by hormones. Sphingolipids, phosphatidylcholine, and phosphatidylethanolamine are present in most membranes, but in varying proportions. Clycolipids, which are major components of the chloroplast membranes of plants, are virtually absent from animal cells. 

Fig. 3. Schematic showing potential routes whereby G-proteins may mediate Ca and other ion channels within plant cells. The dashed line (—) separates regulation via activation of PLC and channel gating via IP3 (right hand side) from direct regulation (left hand side) in which G or Gp interact directly with the particular ion channels. Phospholipase D which generates IP2 and phosphatidylglycerol (and by the action of other enzymes IP, and DAG respectively) may also be G-protein regulated but is omitted for clarity.

Figure 11.14 Phospholipid synthesis in plants. For simplicity the full systematic names for enzymes and co-factor requirements are not given. Details can be found in Mudd (1980). Phosphatidylglycerol is mainly formed in photosynthetic tissues. Methylation pathway to phosphatidylcholine has only been demonstrated in a few plants. Cardiolipin synthesis is probably confined to mitochondria. Other possible sources of diacylglycerol include phospholipase C action, demonstrated in many plants and plant tissues. Reproduced from Harwood and Russell (1984) with permission.

Constit. of many plant systems including spinach leaves, red clover (as phosphatidylglycerol ester) and Aster spp. Mp 53-54 . 

In many families of angiosperms, phosphatidylglycerol (9) is the only major product of the prokaryotic pathway. Other chloroplast lipids in these plants are synthesized only by the eukaryotic pathway. In some primitive angiosperm families, both pathways contribute to the s)mthesis of mono-galactosyldiacylglycerol (10) and other lipids (Browse and Somerville, 1991). 

Mitochondria have been prepared from plant tissues by a number of different techniques. Unfortunately, the variations in technique may also be reflected in the somewhat different compositions reported. Mitochondria, in general, have membranes containing a high concentration of phospholipids. Phosphatidylcholine and phosphatidylethanolamine are major components and are fairly evenly apportioned between the inner and outer membranes. Cardiolipin is found in high amounts in the inner membrane, while phospha-tidylinositol is mainly in the outer membrane. Phosphatidylglycerol is a minor component. These results are illustrated in Table XV. 

Wu, J. and Browse, (1995) Elevated levels of high-melting-point phosphatidylglycerols do not induce chilling sensitivity in an Arabidopsis mutant. J. Plant Cell, 1, 17-27. 

Krol M, Huner NPA, Williams JP, and Maissan EE. Prior accumulation of phosphatidylglycerol high in trans-A -hexadecenoic acid enhances the in vitro stability of oligomeric light harvesting complex II. J Plant Physiol. 1989 135 75-90. 

Molecular species of phosphatidylglycerol from plant chloroplasts were fractionated by HPLC on a column (4.6 X 250 mm) containing Rainin Microsorb reversed-phase packing material, and with 1-ethyl-propylamine-acetic acid-methanol-acetonitrile (0.3-0.5-34.7-64.5 by volume) as the mobile phase at a flow-rate of 0.8 mL/min [674,860]. Of particular interest here was what appears to have been the first published application of the Tracer transport-flame ionization detector to lipid analysis. Excellent baseline stability was recorded in spite of the presence of ionic species in the mobile phase, and minor components present at a level of as little as 1.2 nmole could be determined. It was confirmed that direct quantification of components by integration of peaks from the detector gave results which were comparable to those obtained by alternative methods. A stream splitter ahead of the detector enabled fractions to be collected for determination of radioactivity or for GC analysis of the fatty acid constituents. In the sample studied, species eluted in the order 16 1M8 3,16 1M8 2 and 16 0-18 2. 

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