Glyco- and Phospholipids of Biomembranes in Higher Plants

Three cultivars of citrus with different sensitivities to freezing temperatures (citron, Citrus medica L.; rough lemon, C. limo, Burm. F; sour orange, C. aurwantium L.) were cold hardened for 4 weeks. Lipids from leaves of hardened and control seedlins were fractionated and analyzed for fatty acids. The absolute amount of triglycerides and phospholipids increased in the leaves upon hardening. With hardening, total linoleic acid also increased 141% in citron, 210% in rough lemon, and 233% in sour orange. Specific increases in linoleic acid were found in triglycerides, in the four phospholipids (phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylglycerol), and in neutral lipids more polar than triglycerides. Trans-3-hexadecenoic acid was found only in phosphatidylglycerol.In plants, fatty acids have been postulated to play a role in hardening processes. The membrane-fluidity theory is based on the fact that membranes from chill-resistant plants are often richer in unsaturated fatty acids than those from chill-sensitive plants (8). Accumulation of unsaturated fatty acids during temperature acclimation has been observed in a number ofgenera, e.g. linolenic in wheat shoots (1) and apple leaves (5); linoleic in alfalfa (7) and bean leaves (21); and hexadecatrienoic in thistle (15).A number of studies (14,20,23), however, do not show this relationship between cold-hardiness or ability to be hardened and high fatty acid unsaturation. Raison (18) has concluded that these studies do not rule out a relationship between lipids in membranes and cold-hardiness. Wilson (21), comparing chill and drought hardening studies on bean leaves, indicated that chilling injury is not solely due to phase transitions in the membrane lipids; the increase in unsaturation with chill hardening may be due to a general response to low temperature growth conditions such as altered desaturase activity. A possible relationship between cold hardiness in a citrus rootstock and its lipid content was reported by Kuiper (6) when he found that a cold hardy mandarin rootstock had a higher content of phospholipids than less hardy rootstocks.Our study was planned to determine the following: Do fatty acids in citrus leaves undergo desaturation upon hardening as has been observed in field crops and weeds? Is this desaturation limited to one Control trees were left in the greenhouse during the hardening treatment. Freeze tolerance tests were conducted on control and hardened seedlings in the dark with 50% ± 10%o RH. Plants were equilibrated for 1 h at 4.4°C followed by 1.1°C/h cooling temperatures to -6.7°C which was maintained for 4 h. Thawing was a return to 4.4°C at 1.1°C/h. Plants were kept at 25°C for 3 h and then returned to the greenhouse for 5 weeks of injury observation.Trees were rated for percentage of leaves killed and dieback of the main stem.Tissue Sampling. Ten leaf samples were obtained from hardened and control trees by removing one leaf randomly selected from the top five leaves of ten trees. Duplicate ...

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confidence: 99%

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confidence: 99%

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confidence: 99%

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Relationships of Leaf Fatty Acids to Cold Hardening of Citrus Seedlings

Nordby¹,

Yelenosky²

1982

“…In addition, the enzymes involved in galactolipid synthesis are located primarily in the chloroplast envelope membranes (14). Inasmuch as galactolipids constitute 60 to 90%o of chloroplast membrane polar lipids (18), and the chloroplast membranes constitute about 70%o of total leaf cell membranes (17), it follows that galactolipids are major lipids in green tissues and that plastid galactolipid synthesis represents a considerable portion of leaf cell lipid metabolism.…”

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confidence: 99%

Acyl-CoA Synthetase Is Located in the Outer Membrane and Acyl-CoA Thioesterase in the Inner Membrane of Pea Chloroplast Envelopes

Andrews

Keegstra²

1983

102

Both acyl-CoA synthetase and acyl-CoA thioesterase activities are present in chloroplast envelope membranes. The functions of these enzymes in lipid metabolism remains unresolved, although the synthetase has been proposed to be involved in either plastid galactolipid synthesis or the export of plastid-synthesized fatty acids to the cytoplasm. We have examined the locations of both enzymes within the two envelope membranes of pea (Pisum sativum var Laxton's Progress No. 9) chloroplasts. Inner and outer envelope membranes were purified from unfractionated envelope preparations by linear density sucrose gradient centrifugation. Acyl-CoA synthetase was located in the outer envelope membrane while acyl-CoA thioesterase was located in the inner envelope membrane. Thus, it seems unlikely that the synthetase is directly involved in galactolipid assembly. Instead, its localization supports the hypothesis that it functions in the transport of plastid-synthesized fatty acids to the endoplasmic reticulum.

“…Plant researchers have studied chloroplast and mitochondrial membranes extensively (12,18,21), but comparatively little work has been done to elucidate the composition of plasma membrane from higher plants. Plasma (28), sterol (27), and protein composition (5) with development.…”

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confidence: 99%

Phospholipid Composition of a Plasma Membrane-Enriched Fraction from Developing Soybean Roots

Whitman¹,

Travis²

1985

ABSTRACFPhospholipid polar head group and fatty acid composition were determined for plasma membrne enriched fractions from developing soybean root (Glycine max [L.1 Meff. cult. Wells II). Plasma membrane vesicles were isolated from meristematic and mature sections of four-day-old dark grown soybean roots at pH 7.8 and in the presence of 5 miflimolar ethylenediaminetetraacetate, 5 millimolar ethyleneglycol-bis (l-aminoethyl (27), and protein composition (5) with development. These changes may reflect alterations in membrane composition associated with differentiation of the average cell in the representative root segment and/or aging effects which may be common to all cells.The inability to prepare highly enriched fractions of plasma membranes from plants in quantities sufficient for analysis has hindered efforts to characterize plasma membrane composition. In a previous communication (28) we reported the isolation of a highly enriched plasma membrane fraction. Comparisons of isolated vesicles stained with the phosphotungstic acid-chromic acid procedure, specific for the plasma membrane, with vesicles stained with the general membrane stain uranyl acetate-lead citrate indicated these preparations were approximately 75% pure (2). Additional electron microscope studies with concana-