The Mechanism of Formation of Polyunsaturated Fatty Acids by Photosynthetic Tissue

Gurr, M. I.; Robinson, Malcolm P.; James, A. T.

doi:10.1111/j.1432-1033.1969.tb00577.x

Cited by 142 publications

(40 citation statements)

References 13 publications

(15 reference statements)

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“…Furthermore, there was an appreciable light stimulation of PC synthesis in section E despite the greatly decreased quantitative importance of PC in the more mature tissue (9). Arising from turnover studies with older photosynthetic tissues, it has been suggested that PC may be of special significance in fatty acid biosynthesis (5,13). If PC is involved as an acyl carrier in the desaturation of 18:1 to 18:2 (5), increased labeling of PC could be expected to result from the greater demands for polyunsaturated fatty acids for the galactolipids and for PG which are required for granal formation.…”

Section: Discussionmentioning

confidence: 99%

Lipid Biosynthesis in Green Leaves of Developing Maize

Hawke

Rumsby²,

Leech³

1974

Plant Physiol.

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Only 4% of the newly synthesized fatty acids were 18: 3 but most of this was incorporated into monogalactolipid. In the distal sections, 20 to 25 % of the newly synthesized fatty acids in monogalactolipid were 18:3 compared with the endogenous proportions of 85 % . The differences in the composition of the newly synthesized fatty acids and the endogenous fatty acids appear to be related very largely to the low rate of 18 :3 biosynthesis from 18: 1 and 18: 2. Phosphatidyl choline and phosphatidyl ethanolamine, with lower proportions of 18:3, contained radioactive fatty acids which resembled the endogenous composition more closely.Phosphatidyl choline was quantitatively the most important acyl lipid synthesized under both light conditions. In addition, there was considerable stimulation of acetate incorporation into phosphatidyl glycerol and monogalactolipid, especially in the morphologically most mature regions of the tissue at the higher light intensity.Lipid biosynthesis in tissue where plastids are developing is of special interest because of the quantitative importance of lipids in the lamellae of differentiated chloroplasts. One system

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Section: Discussionmentioning

confidence: 99%

Lipid Biosynthesis in Green Leaves of Developing Maize

Hawke

Rumsby²,

Leech³

1974

Plant Physiol.

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“…More recently, Gurr, Robinson & James (1969) have shown that [1-14C]-oleic acid is incorporated almost exclusively into phosphatidylcholine in Chlorella and that desaturation to linoleic acid occurs only after a large proportion of the label has been incorporated into this lipid. My results are in agreement with this finding.…”

Section: Discussionmentioning

confidence: 99%

Turnover of the glycerolipids of pumpkin leaves. The importance of phosphatidylcholine

Roughan¹

1970

Biochemical Journal

118

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Between 1 and 5% of the 14C recovered from pumpkin leaves within 15-60min after pulse-labelling with 14C02 was in the lipids. The specific radioactivity of the phospholipids was higher than that of the glycolipids. Phosphatidylcholine had five times the specific radioactivity of monogalactosyl diglyceride, and the specific radioactivity of neither galactolipid changed significantly between 1 and 48 h after labelling. It therefore seemed unlikely that the galactose moieties of the galactolipids were involved in the transport of assimilated compounds across the chloroplast membrane. Within 60min of the application of [1-14C]acetate to the surfaces of mature, intact pumpkin leaves 70% of the recovered 14C was in the lipid fraction. Of the separated glycerolipids, phosphatidylcholine had by far the highest specific radioactivity at the shorter time-intervals, and the glycolipids again had the lowest specific radioactivities. Phosphatidylcholine was the only lipid to show a significant turnover of radiocarbon as judged by the decrease in specific radioactivity with time. From a comparison of the changes with time of the labelling of fatty acid fractions from phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol and monogalactosyl diglyceride, it is suggested that the primary site of linolenic acid biosynthesis in leaf cells is within the phosphatidylcholine molecule.

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“…Such studies usirig whole plant tissues and green algae have been previously conducted to demonstrate the in vivo activity of desa-turases that use fatty acids bound to glycerolipids or COA as substrates (e.g. Gurr et al, 1969;Pollard and Stumpf, 1980;Stymne and Stobart, 1986).…”

Section: E Tabolism Of Exogenous 14c-fatty Acids By Coriander Endosmentioning

confidence: 99%

“…The most common desaturation mechanism in plants involves the insertion of double bonds into acyl moieties esterified to glycerolipids. Examples of this include the desaturation of oleic acid to linoleic acid on PC (Gurr et al, 1969;Slack et al, 1978;Stymne and Appelqvist, 1978) and the desaturation of palmitic acid to transa3-hexadecenoic acid on phosphatidylglycerol (Bartels et al, 1967). In addition, fatty acid unsaturation may arise from reactions that use saturated acyl chains bound to ACP.…”

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confidence: 99%

Metabolic Evidence for the Involvement of a [delta]4-Palmitoyl-Acyl Carrier Protein Desaturase in Petroselinic Acid Synthesis in Coriander Endosperm and Transgenic Tobacco Cells

Cahoon

Ohlrogge

1994

Plant Physiol.

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We have previously demonstrated that the double bond of petroselinic acid ( 18:1Akis) in coriander (Coriandrum safivum L.) seed results from the activity of a 36-kD desaturase that is structurally related to the Ag-stearoyl-acyl carrier protein (ACP) desaturase (E.B. Cahoon, J. Shanklin, J.B. Ohlrogge [1992] Proc Natl Acad Sci USA 89: 11 184-1 1188). To further characterize the biosynthetic pathway of this unusual fatty acid, 14C-labeling experiments were conducted using developing endosperm of coriander. Studies were also performed using suspension cultures of transgenic tobacco (Nicotiana tabacum L.) that express the coriander 36-kD desaturase, and as a result produce petroselinic acid and A4-hexadecenoic acid. When supplied exogenously to coriander endosperm slices, [I -14C]palmitic acid and stearic acid were incorporated into glycerolipids but were not converted to petroselinic acid. This suggested that petroselinic acid is not formed by the desaturation of a fatty acid bound to a glycerolipid or by reactions involving acyl-coenzyme As (COA). Instead, evidence was most consistent with an acyl-ACP route of petroselinic acid synthesis. For example, the exogenous feeding of [l-'4C]lauric acid and myristic acid to coriander endosperm slices resulted in the incorporation of the radiolabels into long-chain fatty acids, including primarily petroselinic acid, presumably through acyl-ACP-associated reactions. In addition, using an in vitro fatty acid biosynthetic system, homogenates of coriander endosperm incorporated [2-'4C]malonyl-CoA into petroselinic acid, of which a portion was detected in a putative acyl-ACP fraction. Furthermore, analysis of transgenic tobacco suspension cultures expressing the coriander 36-kD desaturase revealed significant amounts of petroselinic acid and A4-hexadecenoic acid in the acyl-ACP pool of these cells. Also presented is evidence derived from [U-'4C]nonanoic acid labeling of coriander endosperm, which demonstrates that the coriander 36-kD desaturase positions double bonds relative to the carboxyl end of acyl-ACP substrates. l h e data obtained in these studies are rationalized in terms of a biosynthetic pathway of petroselinic acid involving the A4 desaturation of palmitoyl-ACP by the 36-kD desaturase followed by two-carbon elongation of the resulting A4-hexadecenoyl-ACP.

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The Mechanism of Formation of Polyunsaturated Fatty Acids by Photosynthetic Tissue

Cited by 142 publications

References 13 publications

Lipid Biosynthesis in Green Leaves of Developing Maize

Lipid Biosynthesis in Green Leaves of Developing Maize

Turnover of the glycerolipids of pumpkin leaves. The importance of phosphatidylcholine

Metabolic Evidence for the Involvement of a [delta]4-Palmitoyl-Acyl Carrier Protein Desaturase in Petroselinic Acid Synthesis in Coriander Endosperm and Transgenic Tobacco Cells

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