Two varieties of turnip, Laurentian and Wye, were examined for their lipid and fatty acid composition. Lipids extracted with 80% ethanol contained variable quantities of phosphatidic acid, which was considered to be an artifact. Crude lipids were fractionated by TLC, and fatty acids and sterols were analyzed by GLC. Among the common phospholipids, cardiolipid and phosphatidyl glycerol were abundant components. Linolenic acid comprised 60% of the total fatty acids. beta-Sitosterol was the principal sterol, and about half of the carotenoids was lycopene. No great differences between the two varieties studied were observed however.
After 7 days of germination in the dark, the three sections of pea seedlings studied (cotyledons, stems, and young leaves) are rich in linoleic acid; after illumination of the seedlings a very significant increase in linolenic acid is observed in the young leaves section, whereas only small variations are noted in the fatty acid composition of the other sections. The increase in linolenic acid results from the increase in galactolipid content of the young leaves; these already linolenic acid-rich galactolipids are present but onl-in small amounts in the etiolated seedlings (10% of total lipid).Variations in composition of the otlher lipid classes (phospholipids and neutral fats) were also studied. The possibility of fatty acid transport from the cotyledons toward the young leaves during the synthesis of the photosynthetic apparatus is discussed.or clover leaves (17) have shown that during greening the incorporation of acetate-1-'4C into linolenic acid does not clearly indicate how this fatty acid is synthesized as the chloroplast matures. We may assume that linolenic acid is not mainly formed de novo, but from an endogenous precursor already present in the etiolated seedling (perhaps from another fatty acid present in large quantities in the cotyledon). However, the low incorporation of radioactive tracers in the fatty acid portion does not permit us to define further the metabolic pathways of the galactolipid biosynthesis.In this study, we have followed the changes in fatty acid composition of each lipid class during the greening of the etiolated pea seedlings (in which the cotyledons and the young leaves are clearly cut) in order to elucidate the biosynthetic pathways of chloroplast galactolipids as well as the action of light on the formation of these lipids, and to show the relationship between storage lipids and structural lipids during greening.
MATERIAL AND METHODSVariations in lipid metabolism as related to greening and formation of the photosynthetic apparatus have been studied mainly in algae, Chllorella and Euglena (5,(12)(13)(14). But it is known that the greening of higher plants differs markedly from that of photosynthetic algae. Whereas algae pass from a heterotrophic metabolism to an autotrophic or semiautotrophic metabolism during greening and this transformation is largely reversible, in higher plants the etiolated seedlings subsist only at the expense of food reserves made by the plant, and greening is essential for its survival and presents an irreversible feature. Moreover, although the lipid compositions of green algae and higher plants have common characteristics such as high levels of galactolipids with polyunsaturated fatty acids and presence of phosphatidylglycerol with trans-3-hexadecenoic acid (7), appreciable differences are encountered between them: (a) in algae, the galactolipid polyunsaturated fatty acids consist of 16 and 18 carbon chain fatty acids, whereas in higher plants, y-linolenic acid alone accounts for 80% of the galactolipid fatty acid (7); (b) For germination...
Four Canadian varieties of potatoes were examined for their lipid composition. Lipids, extracted with chloroformmethanol, were shown by TLC and column chromatography to consist of 16.5% neutral lipids, 45.5% phospholipids and 38.1% glycolipids. Among the phospholipids and glycolipids, phosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl inositol, the galactolipids and the sterol glucosides were the major lipids. The predominant fatty acids were palmitic (19.5%), linoleic (44.8%) and linolenic (30.4%, in Kennebec). Analyses of the fatty acids of stored potatoes showed a marked decrease in linoleic acid and an increase in linolenic acid, in the Irish Cobbler and Sebago potatoes. beta-sitosterol comprised 85.0% of total sterols. Nearly half of the carotenoids was lutein (xanthophyll), the others being alpha-carotene, beta-carotene, an unidentified pigment and lutein epoxide.
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