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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...

Photosystem I1 membrane fractions from dark-adapted mesophyll chloroplasts of maize were solubilized in different concentrations of dodecyl P-D-maltoside. Chlorophyll-binding proteins from photosystem I1 were isolated either by ultracentrifugation on a sucrose gradient, or by flat bed isoelectric focusing and identified by gel electrophoresis analysis for their polypeptide composition. Lipid and fatty acid compositions were determined in complexes prepared by both methods and also in purified light-harvesting complex 11, in minor chlorophyll alb binding complexes 29, 26, 24, in photosystem I1 antennae (chlorophyll-protein complexes 43, 47) and in the photosystem I1 reaction centers chlorophyll-protein complexes. Comparative analysis of the results suggests that a true heterogeneity exists in the lipid class distribution among the different chlorophyll-protein complexes in this region of the photosynthetic membrane. Photosystem I1 core fractions prepared either by ultra-centrifugation on a sucrose gradient or by isoelectric focusing were found significantly enriched in monogalactosyldiacylglycerol ; fractionation of the photosystem I1 core in its components showed that it was the chlorophyll-protein complexes 43 and 47 which were mainly responsible for this enrichment. One of them, the chlorophyll-protein complex 47, was found containing monogalactos yldiacylglycerol and having a very high level of saturated fatty acids. The minor chlorophyll alb binding linkers (chlorophyll-protein complexes 24, 26 and 29) retain a largely higher amount of lipids than all other complexes and especially of highly unsaturated galactolipids.Concerning the main light-harvesting antenna (LHCII), it is demonstrated that phosphatidylglycerol is strongly linked to the complex if it cannot be detached at high detergent concentration, while many galactolipids (which nevertheless represent the major lipid classes) are lost. This main light-harvesting complex has been fractionated into several families by isoelectric focusing showing a marked difference in lipid and polypeptide composition. A spectacular increase in the phosphatidylglycerol content was observed in the fraction migrating near the anode and enriched in a 26-kDa polypeptide; but this result is difficult to interpret in physiological terms as it was shown that phosphatidylglycerol alone, because of its negative charge, also migrates toward the anode in isoelectric focusing.In photosynthesis, the two major functions of light-harvesting and electron transport occur in a thylakoid which is the predominant membrane in the plant leaf cell representing up to 80% of the total cellular membranes (Forde and Steer, 1976). Thylakoids are organized into two major functional domains. The appressed or granal membranes and the nonappressed or stromal membranes contain different complements of electron transport and binding complexes participating in the photosynthetic process. The lipid composition of the thylakoid is unique since it always contains four lipids never found in other cellular m...

Growth of Synechococcus 6311 in the presence of 0.5 molar NaCI is accompanied by significant changes in membrane lipid composition. Upon transfer of the cells from a 'low salt' (0.015 molar NaCI) to 'high salt' (0.5 molar NaCI) growth medium at different stages of growth, a rapid decrease in palmitoleic acid (C16:1A9) content was accompanied by a concomitant increase in the amount of the two C18:1 acids (C18:1A9, C18:IAI1), with the higher increase in oleic acid C18:1A9 content. These changes began to occur within the first hour after the sudden elevation of NaCI and progressed for about 72 hours. The percentage of palmitic acid (C16:0) and stearic acid (C18:0) remained almost unchanged in the same conditions. High salt-dependent changes within ratios of polar lipid classes also occurred within the first 72 hours of growth. The amount of monogalactosyl diacylglycerol (bilayer-destabilizing lipid) decreased and that of the digalactosyl diacylglycerol (bilayer-stabilizing lipid) increased. Consequently, in the three day old cells, the ratio of monogalactosyl diacylglycerol to digalactosyl diacylglycerol in the membranes of high saltgrown cells was about half of that in the membranes of low saltgrown cells. The total content of anionic lipids (phosphatidylglycerol and sulfoquinovosyl diacylglycerol) was always higher in the isolated membranes and the whole cells from high salt-grown cultures compared to that in the cells and membranes from low salt-grown cultures. All the observed rearrangements in the lipid environment occurred in both thylakoid and cytoplasmic membranes. Similar lipid composition changes, however, to a much lesser extent, were also observed in the aging, low salt-grown cultures. The observed changes in membrane fatty acids and lipids composition correlate with the alterations in electron and ion transport activities, and it is concluded that the rearrangement of the membrane lipid environment is an essential part of the process by which cells control membrane function and stability. up to 0.6 M NaCl. Transfer from low salt (0.015 M NaCi) to high salt (0.5 M NaCI) medium initiates multiple changes in the composition of the cytoplasmic membrane and in activities of membrane-bound enzymes. These changes include alterations in the distribution of integral membrane proteins as seen by freeze-fracture electron microscopy ( 13), increased sodium/proton exchange activity (3) and an increase in the content and activity of Cyt c oxidase (8,19).It has been well recognized that membrane lipid composition modulates the physiological properties of membranes such as barrier function, transport, and signaling. As most protein-lipid interactions are achieved through direct contact ofthe given fatty acid, lipid, or lipid domains with the protein, changes in lipid environment will affect protein function. While changes in the lipid head group composition may alter electrostatic interactions between charged domains on the protein surface and the lipid head group, alterations in the hydrocarbon region will af...

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