Changes in the content and composition of lipid fatty acids in tobacco leaves and roots at low-temperature hardening

Changes in the fatty acid (FA) composition of leaf and root lipids of heat-loving tobacco (Nicotiana tabacum L., cv. Samsun) plants during low-temperature hardening (8°C for 6 days) were studied. Hardening could improve leaf but not root cold tolerance. As this took place, the relative content of polyunsaturated (18:2n-6 and 18:3n-3) FAs increased and the proportion of saturated and monounsaturated FAs decreased. In contrast, in the roots hardening slightly increased the concentration of saturated FAs (16:0 and 18:0) and reduced the level of unsaturated FAs (18:1n-9, 18:2n-6, and 18:3n-3). At the same time, root lipids contained much C_20–24 FAs, and their content increased during hardening. It was suggested that an increased FA saturation and elevated proportion of C_20–24 FAs in the root lipids resulting in the lower membrane fluidity could be a reason for incapability of heat-loving tobacco plant roots of hardening and plant death at the lowtemperature stress.     

Cold acclimation of Ilex aquifolium under natural conditions with special regard to the photosynthetic apparatus

Frost resistance of leaves of holly ( Ilex aquifolium L.) increased from about −9°C in late summer to −24°C in mid-winter. The gradual rise in cold hardiness occurred when the minimum air temperature dropped to 0°C or below and was closely related to increase in the cellular sap concentration. Predominantly, the decrease in the osmotic potential of the cellular sap was caused by sugar accumulation, mainly of sucrose. The capacity of net photosynthesis of the leaves, as well as the total lipid and protein content and the proportion of individual lipids of the thylakoid membranes, did not significantly change during cold acclimation. The gradual shift towards desaturation in the fatty acids of the thylakoid lipids during the hardening period was neither correlated with alterations in the frost resistance nor did it affect the potential efficiency for various light-induced chloroplast membrane reactions such as linear photosynthetic electron transport, photophosphorylation and the proton gradient (ΔpH). It is suggested that in holly leaves reduction in cell volume changes during freeze-thawing and cryoprotection by sugars could play a dominant role for the increase in frost resistance. Seasonal changes in the degree of unsaturation of polar lipids of the thylakoids could contribute to maintain optimal functional efficiency of the membranes at low temperatures rather than to avoid freezing damage.     

Growth temperature effects on thylakoid membrane lipid and protein content of pea chloroplasts

The lipid composition and level of unsaturation of fatty acids has been determined for chloroplast thylakoid membranes isolated from Pisum sativum grown under cold (4°/7°C) or warm (14°/17°C) conditions. Both the relative amounts of lipid classes and degree of saturation were not greatly changed for the two growth conditions. In cold-grown plants, there was a slightly higher linolenic and lower linoleic acid content for the glycolipids monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), and sulfoquinovosyldiacylglycerol. In contrast to thylakoid membranes, a non-thylakoid leaf membrane fraction including the chloroplast envelope, had a higher overall level of fatty acid unsaturation in cold-grown plants due mainly to an increase in the linolenic acid content of MGDG, DGDG, phosphatidylglycerol, and phosphatidylcholine. The most clear cut change in the thylakoid membrane composition was the lipid to protein ratio which was higher in the cold-grown plants.     

Reorganization of membrane lipids during fast and slow cold hardening in Drosophila melanogaster

Abstract Rapid cold hardening is a naturally occurring phenomenon in insects that is thought to be responsible for increased cold tolerance during diurnal variations in temperature. The underlying physiological mechanisms are still not fully resolved but, in Drosophila melanogaster (Meigen 1830), rapid cold hardening is accompanied by specific changes in the membrane lipid composition. To further understand the link between rapid cold hardening and adjustments in the membrane lipid composition, the present study investigates how different rates of cooling affect thermotolerance and the composition of phospholipid fatty acids. Female Drosophila are cooled gradually from 25 to 0 °C at 0.01, 0.05, 0.1 or 0.5 °C min^?1, respectively, and, subsequently, phospholipid fatty acid composition and survival after a 1‐h cold shock at ?5 °C is measured. The rapid cold hardening treatments all influence cold tolerance differently so that short and intermediate rapid cold hardening treatments (0.05, 0.1 or 0.5 °C min^?1 cooling rates) increase cold shock survival, whereas the slow cooling treatment (0.01 °C min^?1) decreases survival relative to an untreated control. The intermediate rapid cold hardening treatments (0.05 or 0.1 °C min^?1) induce a similar type of response characterized by an increase in the molar percentage of linoleic acid, 18:2(n‐6), at the expense of 16:0 and 18:1(n‐9), which leads to an increase in the degree of unsaturation. The slowest cooling treatment (0.01 °C min^?1) results in a large increase in cis‐16:1(n‐7) and significant reductions in the saturated phospholipid fatty acids 16:0, 18:0 and the unsaturated 16:1(n‐9) and 18:2(n‐6) fatty acids. These changes cause a slight decrease in the average length of the phospholipid fatty acids and an increase in the overall ratio of unsaturated vs. saturated fatty acids. These findings demonstrate that the rate of cooling is important for both the reorganization of membrane lipids, and for the degree of acquired cold tolerance during rapid cold hardening, and they suggest an important role for rapid cold hardening during diurnal rather than seasonal temperature changes.     

The effect of low temperatures on fatty acid composition of crops with different cold resistance

The study was focused on fatty acid (FA) composition of lipids from the seedlings and roots of crops having different cold resistance and grown at 27°C or 4°C. Biosynthesis of FA in the lipids of seedlings and roots of cold-susceptible maize (Zea mays L.) at both growth temperatures was controlled by chloroplast ω6 desaturase and microsomal ω6 desaturase, respectively. The content of linoleic acid was 56.2% and 43.3% in the coleoptiles of maize seedlings grown at 4 and 27°C, respectively, and in the roots it was 52.2% and 38.5%, respectively. The content of α-linolenoic acid in the coleoptiles was 6.7–6.8% at both temperatures, while in the root lipids it was higher at low temperature (3.15% at 27°C vs. 4.7% at 4°C). FA biosynthesis in the seedling coleoptiles of wheat (Triticum aestivum L.) and Siberian wild rye (Elymus sibiricus L.) grown at low temperature was controlled by the chloroplast ω3 desaturase. A minor increase in the content of α-linolenoic acid was observed at low temperature: 29.7% to 30.2% in wheat and 22.8% to 25.8% in wild rye. In the root tissues of these species, the biosynthesis of α-linolenoic acid was controlled by the microsomal ω3 desaturase. The content of α-linolenoic acid was higher at low temperature: in wheat it was 6.1% at 27°C and 17.1%, and 4°C, while in Siberian wild rye, 7.1% and 12.0% at 4 and 27°C, respectively.     

Characterization of the main lipid components of chloroplast membranes and cold induced changes in Coffea spp.

Low temperatures affect many plant physiological and biochemical components, amongst them the lipid phase of membranes. The present work aimed to characterize the lipid composition of chloroplast membranes of three Coffea genotypes, representing three agronomic valuable species (Coffea arabica cv. Icatu, Coffea canephora cv. Conilon clone 02 and Coffea dewevrei), under adequate environmental conditions and to relate its cold tolerance ability to the adjustments triggered during a gradual temperature decrease, after chilling exposure and upon a recovery period. Under adequate temperature (25/20 °C, day/night) the lipid composition of chloroplast membranes was fairly similar amongst the genotypes concerning the total fatty acid (TFA) content and individual FAs (both globally or within the classes), suggesting a close lipid composition amongst Coffea species, which can be considered as “C18:3” plants. Under cold exposure and subsequent recovery the genotypes undergo adjustments, some of them with acclimation potential. The genotypes displayed some ability to increase lipid synthesis, increasing their FA content. However, under cold exposure (even at 4 °C), Icatu and C. dewevrei plants performed qualitative adjustments, including preferential synthesis of phospholipids (especially PG) instead of galactolipids and increases in the unsaturation degree of DGDG and phospholipid classes (PG, PC and PI). Clone 02 maintained almost all lipid characteristics, what explains its higher cold sensitivity. Furthermore, differences that contribute to explain contrasting cold sensitivity in Icatu (more tolerant) and C. dewevrei emerged when analyzing PA content (taken as a stress metabolite) and the FA composition within MGDG and PG classes. C. dewevrei presented the higher increase, absolute value and relative weight of PA, while Icatu was the solely genotype to show a rise in the unsaturation degree of MGDG and PG, displaying as well the highest DBI values for these classes. We conclude that lipid qualitative and quantitative adjustments constitute a flexible mechanism that decisively contributes to cold acclimation in Coffea spp., working in tandem with others that minimize oxidative stress damages.     

Dietary fatty acid composition changes mitochondrial phospholipids and oxidative capacities in rainbow trout red muscle

Dietary conditioning of juvenile trout changed the acyl chain composition of mitochondrial phospholipids and the oxidative capacities of muscle mitochondria. Trout were fed three diets differing only in fatty acid (FA) composition. The highly unsaturated 22:6 n-3 (DHA) accounted for 0.4, 14, and 30% of fatty acids in Diets 1, 2 and 3. After 10 weeks of growth, the dietary groups differed markedly in FA composition of mitochondrial phospholipids, with significant dietary effects for virtually all FA. Mean mitochondrial DHA levels were 19, 40 and 33% in trout fed Diets 1, 2 and 3. Mitochondrial oxidative capacities changed with diet, while mitochondrial concentrations of cytochromes and of the adenylate nucleotide translocase (nmol mg¹ protein) did not. Mitochondria from fish fed Diet 1 had higher non-phosphorylating (state 4) rates at 5°C than those fed other diets. When phosphorylating (state 3) rates differed between dietary groups, rates at 5 and 15°C were higher for fish fed the more unsaturated diets. Stepwise multiple regressions indicated that FA composition could explain much (42–70%) of the variability of state 4 rates, particularly at 5°C. At 15°C, FA composition explained 16–42% of the variability of states 3 and 4 rates. Similar conclusions were obtained for the complete data set (trout fed diets 1, 2 and 3) and for the data from trout achieving similar growth rates (e.g. those fed Diets 1 and 2). Neither general characteristics of membrane FA, such as % saturates, unsaturation index, n-3, n-6 or n-3/n-6 nor levels of abundant unsaturated FA such as DHA or 18:1(n-9 + n-7), were systematically correlated with mitochondrial capacities even though they differed considerably between trout fed the different diets. Relatively minor FA (20:5n-3, 20:0, 18:2n-6, 18:3n-3, 18:0 and 15:0) showed better correlations with mitochondrial oxidative capacities. This supports the concept that acyl chain composition modulates mitochondrial capacities via interactions between membrane proteins and specific FA of particular phospholipid classes in their microenvironment.     

Fatty acids composition in erythrocyte membranes of athletes after one and after a series of whole body cryostimulation sessions

Whole body cryotherapy (WBC) is a treatment often used by athletes as part of biological renewal. Despite the large interest in this form therapy there is still a lack of information on the effects of WBC on the concentration of fatty acids in erythrocyte membranes. Our study aimed at comparing the fatty acids (FA) composition of erythrocyte membranes of athletes after one session and after a series of sessions of whole body cryostimulation. In our study small changes in the level of total cholesterol (decrease) were observed 24 h after a single session. After the twelfth session of whole body cryostimulation, the level of saturated fatty acids (SFA), mainly palmitic acid (C16:0) and n-3 fatty acid eicosapentaenoic (EPA, C20:5n-3) increased almost two-times fold in the red blood cell membranes. The level of n-6 polyunsaturated fatty acids (PUFA n-6), mainly gamma-linolenic acid (C18:3n-6) as well as trans fatty acids (elaidic acid) decreased in the erythrocyte membranes from men after a series of session in a cryochamber, when compared to the control sample. The n-3/n-6 FA ratio in the erythrocyte membranes was higher after twelfth session in a cryochamber in comparison to the control sample.The data obtained during our study will be important for further research regarding the biochemistry of lipids in men after sessions of whole body cryostimulation.     

Frost hardening and photosynthetic performance of Scots pine (Pinus sylvestris L.). II. Seasonal changes in the fluidity of thylakoid membranes

The fluidity of chloroplast thylakoid membranes of frost-tolerant and frost-sensitive needles of␣three- to four-year-old Scots pine (Pinus sylvestris L.) trees, of liposomes produced from the lipids of the thylakoids of these needles, and of liposomes containing varying amounts of light-harvesting complex (LHC) II protein was investigated by means of electron paramagnetic resonance (EPR) measurements using spin-labelled fatty acids as probes. Broadening of the EPR-resonance signals of 16-doxyl stearic acid in chloroplast membranes of frost-sensitive needles and changes in the amplitudes of the peaks were observed upon a decrease in temperature from +30 °C to −10 °C, indicating a drastic loss in rotational mobility. The lipid molecules of the thylakoid membranes of frost-tolerant needles exhibited greater mobility. Moderate frost resistance could be induced in Scots pine needles by short-day treatment (Vogg et al., 1997, Planta, this issue), and growth of the trees under short-day illumination (9 h) resulted in a higher mobility of the chloroplast membrane lipids than did growth under long-day conditions (16 h). The EPR spectrum of thylakoids from frost-tolerant needles at −10 °C was typical of a spin label in highly fluid surroundings. However, an additional peak in the low-field range appeared in the subzero temperature range for the chloroplast membranes of frost-sensitive needles, which represents spin-label molecules in a motionally restricted surrounding. The EPR spectra of thylakoids and of liposomes of thylakoid lipids from frost-hardy needles were identical at +30 °C and −10 °C. The corresponding spectra from frost-sensitive plants revealed an additional peak for the thylakoids, but not for the pure liposomes. Hence, the domains with restricted mobility could be attributed to protein-lipid interactions in the membranes. Broadening of the spectrum and the appearance of an additional peak was observed with liposomes of pure distearoyl phosphatidyl glycerol modified to contain increasing amounts of LHC II. These results are discussed with respect to a loss of chlorophyll and chlorophyll-binding proteins in thylakoids of Scots pine needles under winter conditions. Received: 3 March 1997 / Accepted: 16 July 1997     

Cadmium-Induced Changes in Chloroplast Lipids and Photosystem Activities in Barley Plants

Fatty acid content and composition of chloroplast membranes, ethylene production associated with thylakoid lipids degradation as well as photosynthetic electron transport involving photosystems 1 and 2 were used to determine the effects of increasing Cd concentrations in the growth medium [0, 14, 28, and 42 mg (Cd) kg^–1(sand)] on the photosynthetic performance of barley plants (H. vulgare L., cv. CE9704). High concentrations of Cd triggered serious disturbances of the chloroplast membranes. Ethylene production increased whereas a drop of 18:3 fatty acid content occurred, indicating that Cd mediates lipid peroxidation in the thylakoids. The enhanced ethylene production could be used as an early indicator of Cd-induced membrane degradation, yet at very high concentration (42 mg kg^–1) Cd decreased ethylene production.     

Effect of water stress on the lipid and fatty acid composition of cotton (Gossypium hirsutum) chloroplasts

In order to investigate the effects of water stress on the photosynthetic compartment, analysis of chloroplast polar lipids and their fatty acid composition was made. Cotton ( Gossypium hirsutum L. cv. Reba) plants were submitted to water stress by witholding irrigation. Chloroplasts were purified on a Percoll gradient and three fractions were collected: intact, apparently intact and broken chloroplasts. The percentage of broken chloroplasts increased with a decrease in leaf water potential, indicating a greater weakness of the membrane. Galactolipid content (expressed as mg lipid per mg chlorophyll), particularly digalactosyldiglyceride, decreased with decreasing water potential. Phospholipid content decreased in the broken chloroplast fraction. The fatty acid composition of chloroplasts was also affected. The perecentage of linolenic acid (18:3), the major fatty acid of thylakoids, decreased, whereas that of linoleic acid(18:2) and oliec acid (18:1) increased. An accumulation of fatty acids having less than 16 carbon atoms was also observed. These changes in the lipid and fatty acid composition of cotton chloroplasts under water stress might affect the properties of the thylakoid membrane and thereby the photosynthetic activity and the compartmentation of the leaf cells.     

Temperature-dependent impact of 24-epibrassinolide on the fatty acid composition and sugar content in winter oilseed rape callus

The aim of this experiment was to study the effect of 24-epibrassinolide (BR₂₇) on fatty acids composition and sugar content in winter oilseed rape callus cultured at 20 and 5°C. Studies have showed that BR₂₇ action is highly temperature-dependent. The increase in sugar content (sucrose, glucose and fructose) by BR₂₇ in concentration 100 nM was observed only in calli cultured at 20°C. At 5°C, quite the opposite effect of BR₂₇ action was observed; where cold increased the sugar content, BR₂₇ decreased it. BR₂₇ at 20°C had a similar effect on the fatty acid composition of phospholipids (PL) as the cold in the process of frost hardening of oilseed rape calli. BR₂₇ decreased the 16:0, 18:1 and 18:2 and increased the 18:3 fatty acid content. At 5°C, BR₂₇ (100 nM) generally did not influence the fatty acid composition of PL. In case of digalactosyl diacylglycerols and monogalactosyl diacylglycerols, the influence of BR₂₇ on the fatty acid composition is ambiguous but still depends on temperature.     

Homeoviscous and functional adaptations of mitochondrial membranes to growth temperature in soybean seedlings

The present study investigated whether the cold‐sensitive character of soybean is reflected at the level of mitochondrial membranes. When exposed to an increase of temperature (from 25 to 35 °C), mitochondrial membranes were characterized by a higher phosphatidylcholine : phosphatidylethanolamine ratio and a lower content in 18 : 3 fatty acid. After a reduction of temperature (from 25 to 18 °C) the opposite changes were found. Lipid lateral diffusion and local microviscosity appeared to be comparable in mitochondria from plantlets grown at 25 or 35 °C when assayed at the respective growth temperatures. Some functional aspects (cytochrome c oxidase activity or membrane conductance) tended to this behaviour whereas others (respiration rate or maximum membrane potential) did not. On the other hand, membranes from plants grown at 18 °C were more rigid. Moreover, as illustrated by cytochrome c oxidase activity or respiration rate, functional measurements suggested that these membranes were less active at this temperature. Thus the dynamic characteristics and functional properties measured in mitochondrial membranes were in favour of an adaptive trend at 35 °C, but not at 18 °C despite changes in lipid composition, in accordance with the cold‐sensitive character of the plant.     

Chloroplast lipid synthesis and lipid trafficking through ER-plastid membrane contact sites

Plant chloroplasts contain an intricate photosynthetic membrane system, the thylakoids, and are surrounded by two envelope membranes at which thylakoid lipids are assembled. The glycoglycerolipids mono- and digalactosyldiacylglycerol, and sulfoquinovosyldiacylglycerol as well as phosphatidylglycerol, are present in thylakoid membranes, giving them a unique composition. Fatty acids are synthesized in the chloroplast and are either directly assembled into thylakoid lipids at the envelope membranes or exported to the ER (endoplasmic reticulum) for extraplastidic lipid assembly. A fraction of lipid precursors is reimported into the chloroplast for the synthesis of thylakoid lipids. Thus polar lipid assembly in plants requires tight co-ordination between the chloroplast and the ER and necessitates inter-organelle lipid trafficking. In the present paper, we discuss the current knowledge of the export of fatty acids from the chloroplast and the import of chloroplast lipid precursors assembled at the ER. Direct membrane contact sites between the ER and the chloroplast outer envelopes are discussed as possible conduits for lipid transfer.     

Arabidopsis mutants deficient in polyunsaturated fatty acid synthesis. Biochemical and genetic characterization of a plant oleoyl-phosphatidylcholine desaturase.

The overall fatty acid composition of leaf lipids in a mutant of Arabidopsis thaliana was characterized by reduced levels of polyunsaturated 18-carbon fatty acids and an increased proportion of oleate as a consequence of a single recessive nuclear mutation. Quantitative analysis of the fatty acid composition of individual lipids demonstrated that all the major phospholipids of the extrachloroplast membranes are affected by the mutation, whereas the chlorplast lipids show fatty acid compositions only slightly different from those of wild type plants. These results are consistent with the parallel operation of two pathways of lipid synthesis in plant leaf cells (the prokaryotic pathway in the chloroplast and the eukaryotic pathway in the endoplasmic reticulum) and with genetic evidence (Browse, J., Kunst, L., Anderson, S., Hugly, S., and Somerville, C.R. (1989) Plant Physiol 90, 522-529) that an independent 18:1/16:1 desaturase operates on chloroplast membrane lipids. Direct enzyme assays confirmed that the mutant plants are deficient in the activity of a microsomal oleoyl-phosphatidycholine desaturase and demonstrated that this desaturase is the major enzyme responsible for the synthesis of polyunsaturated phospholipids. Despite this deficiency in 18:1-desaturase activity, mutant plants contained relatively high levels of 18:3 in their leaf phospholipids. This finding is interpreted as additional evidence that considerable two-way exchange of lipid occurs between the chloroplast and endoplasmic reticulum and that this exchange allows the chloroplast desaturases to provide lipids containing 18:3 to the extrachloroplast compartment, thus partially alleviating the deficiency in 18:1 desaturase activity.     

The effects of reduced amounts of lipid unsaturation on chloroplast ultrastructure and photosynthesis in a mutant of Arabidopsis

A mutant of Arabidopsis thaliana with reduced content of C_18:3 and C_16:3 fatty acids in membrane lipids exhibited a 45% reduction in the cross-sectional area of chloroplasts and had a decrease of similar magnitude in the amount of chloroplast lamellar membranes. The reduction in chloroplast size was partially compensated by a 45% increase in the number of chloroplasts per cell in the mutant. When expressed on a chlorophyll basis the rates of CO₂-fixation and photosynthetic electron transport were not affected by these changes. Fluorescence polarization measurements indicated that the fluidity of the thylakoid membranes was not significantly altered by the mutation. Similarly, on the basis of temperature-induced fluorescence yield enhancement measurements, there was no significant effect on the thermal stability of chlorophyll-protein complexes in the mutant. These observations suggest that the high content of trienoic fatty acids in chloroplast lipids may be an important factor regulating organelle biogenesis but is not required to support normal levels of the photosynthetic activities associated with the thylakoid membranes.     

A mutant of Arabidopsis deficient in c(18:3) and c(16:3) leaf lipids

Leaf tissue of a mutant of Arabidopsis thaliana contains reduced levels of both 16:3 and 18:3 fatty acids and has correspondingly increased levels of the 16:2 and 18:2 precursors due to a single recessive nuclear mutation. The kinetics of in vivo labeling of lipids with [¹⁴C]acetate and quantitative analysis of the fatty acid compositions of individual lipids suggests that reduced activity of a glycerolipid n-3 desaturase is responsible for the altered lipid composition of the mutant. The effects of the mutation are most pronounced when plants are grown at temperatures above 26°C but are relatively minor below 18°C, suggesting a temperature-sensitive enzyme. Since the desaturation of both 16- and 18-carbon fatty acids is altered, it appears that the affected enzyme lacks specificity with respect to acyl group chain length and that it is located in the chloroplast where 16:3-monogalactosyldiglyceride is synthesized. Because the degree of unsaturation of all the major glycerolipids was similarly affected by the mutation, it is inferred that either the affected desaturase does not exhibit head group specificity or there is substantial transfer of trienoic acyl groups between different lipid classes. Both chloroplast and extrachloroplast lipids are equally affected by the mutation. Thus, either the desaturase is located both outside and inside the chloroplast, or 18:3 formed inside the chloroplast is reexported to other cellular sites.     

Enhancement of low-temperature tolerance in transgenic tomato plants overexpressing Lefad7 through regulation of trienoic fatty acids

We studied how tomato (Lycopersicon esculentum Mill.) chloroplast omega-3 fatty acid desaturase gene (Lefad7) overexpression enhanced low-temperature (LT) tolerance in transgenic tomato plants. In these plants, the content of linolenic acid (18:3) markedly increased and, correspondingly, the content of linoleic acid (18:2) decreased. Similar changes were found after 6 h under LT (4°C) treatment. Under LT stress, wild type (WT) tomato plants showed a much greater increase in relative electrolyte leakage and malondialdehyde (MDA) contents compared with transgenic plants. Transgenic plants exhibited higher activities of antioxidative enzymes and a lower content of reactive oxygen species (ROS). Transgenic plants maintained a relatively higher level of the net photosynthetic rate (P _N) and chlorophyll (Chl) content than WT plants under LT stress. Taken together, we suggested that overexpression of Lefad7 enhanced LT tolerance by changing the composition of membrane lipids in tomato plants, with the increased content of trienoic fatty acids and reduced content of dienoic fatty acids that led to series of physiological alterations.     

Fatty acids as organic markers for the study of trophic relationships in littoral cladoceran communities of a pond

The fatty acid (FA) composition of zooplankton and paniculatematter (including phytoplankton) associated with the submergedvegetation of a pond shoreline was analysed by gas chromatography.The FA of paniculate matter was characterized by fluctuatingproportions of polyunsaturated FA (PUFA), comprising between31.7 and 51.1% of total FA and originating from phytoplankton.Important levels of bacterial FA (branched 15:0 and 17:0) anddetrital FA (17:0, 17:1) were also detected. Littoral zooplanktonwas dominated by two cladocerans: Eurycercus lametlatus andSimocephalus velulus. Their triacyglycerol fatty acids (TAG-FA)were characterized by PUFA (18:2(n-6), 18:3(n-3). 20:5(n-3))originating in phytoplankton and periphytic algae, and alsoby bacterial and detrital odd-numbered FA. An unusual unsaturatedFA (22:2(n-6)) was detected in the trophic web. It was incorporatedinto cladoceran polar lipids, together with long 22-carbon FAof (n-6) series. Unsaturation of polar lipids was inverselycorrelated with water temperature in both cladocerans. The influenceof dietary FA on the composition of polar lipid FA is also considered.