Evaluation of different protocols for the analysis of lipophilic plant metabolites by gas chromatography–mass spectrometry using potato as a model

In the analysis of lipophilic plant metabolites by gas chromatography?Cmass spectrometry a step is required to release fatty acids and other analytes from complex molecules. Seven alternative methods were compared to the standard method of 1% H₂SO₄/50°C/16?h using Desirée and Phureja potato tubers as models. With two sodium methoxide alkali-catalysed methods (0.5?M NaOCH₃/50°C/1 and 16?h) recoveries of ferulic acids increased, long chain fatty acids and sterols decreased, 2-hydroxy acids were negligible, solanidine was absent and ??5-avenasterol isomerisation was minimal. Using a harsh alkali hydrolysis (1.0?M KOH/120°C/24?h) followed by a mild methylation (1% H₂SO₄/50°C/1.5?h), recoveries of polyunsaturated fatty acids were poor, sterols decreased but ??5-avenasterol isomerisation was minimal. With a mild alkali hydrolysis (0.5?M NaOH/100°C/5?min) followed by methylation with boron trifluoride (14%BF₃/100°C/30?min) recoveries of sterols and 2-hydroxy fatty acids were similar to the standard method and ??5-avenasterol isomerisation was high. Lower ferulic acid recoveries, absence of solanidine and overestimation of fatty alcohols were evident in both methods involving alkali hydrolysis. Three different methods using hydrochloric acid (1.00?M HCl/70°C/5?h, 0.63?M HCl/110°C/2?h and 2.00?M HCl/50°C/24?h) all gave increased recoveries of 2-hydroxy acids, ferulic acids, solanidine and sterols, although ??5-avenasterol isomerisation increased. Hydrochloric acid methods are recommended for studies requiring quantitative determinations (i.e. concentration of metabolite in sample). Either the hydrochloric acid methods or the standard sulphuric acid method are suggested for determining relative concentrations between samples, although there is a requirement for further studies.     

Regulation of the synthesis of unsaturated fatty acids by growth temperature in Bacillus subtilis

Bacillus subtilis synthesizes, almost exclusively, saturated fatty acids, when grown at 37° C. When cultures were transferred from 37° C to 20° C, a chloramphenicol- and rifampicin-sensitive synthesis of a C-16 unsaturated fatty acid was observed. Synthesis of this compound reached a plateau after 5 h at 20° C, reaching levels of 20% of the total fatty acid content. [¹⁴C]-labelled fatty acids attached as thioesters to acyl-carriers compounds, such as coenzyme A (CoA) or acyl-carrier protein (ACP) synthesized de novo by glycerol-requiring auxotrophs deprived of glycerol to arrest phospholipid synthesis, could not be desaturated at 20° C. Desaturation of these fatty acids was readily observed when glycerol was restored to the cultures allowing resumption of transfer of acyl-moieties from acyl-thioesters to phospholipid. It was also observed that depletion of the pools of CoA and ACP by starvation of pantothenate auxotrophs had no effect on the observed synthesis of unsaturated fatty acid at 20° C. The overall results indicate that synthesis of unsaturated fatty acids in B. subtilis is a cold-inducible process and that phospholipids are obligate intermediates in this fatty acid desaturation pathway.     

Synthesis of structured lipid with balanced omega-3: Omega-6 ratio by lipase-catalyzed acidolysis reaction: Optimization of reaction using response surface methodology

The present study deals with the production of structured lipid containing omega-3 and omega-6 fatty acids in the ratio of 1:1 by incorporating omega-3 fatty acids (α-linolenic acid) from linseed oil into groundnut oil using lipase (Lipozyme IM from Rhizomucor miehei) catalyzed acidolysis reaction in hexane. The reaction conditions were optimized by response surface methodology with a four-variable five-level central composite rotatable experimental design. The influence of four independent parameters, namely ratio of fatty acid concentrate from linseed to groundnut oil (0.66–1.98, w/w), reaction temperature (30–60 °C), enzyme concentration (1–5%) and reaction time (2–54 h) on omega-3 fatty acids incorporation into groundnut oil were optimized. Optimal conditions for the structured lipid containing omega-3 to omega-6 fatty acids in the ratio of 1:1 were determined to be; enzyme concentration 3.75% (w/w), temperature 37.5 °C, incubation time 30.81 h and ratio of free fatty acid concentrate from linseed oil to groundnut oil 1.16 (w/w).     

Lipids in plant tissue cultures. VI. Effect of temperature on the lipids of Brassica napus and Tropaeolum majus cultures

The lipid contents of callus cultures of rape (Brassica napus) and nasturtium (Tropaeolum majus) increase in response to decreasing the temperature, though to different degree. Irrespective of the incubation temperature the lipids in cultures of both plants contain as predominant classes steryl glycosides, esterified steryl glycosides, sterols, steryl esters and fatty acids and, as minor constituents, various proportions of triacylglycerols, phospholipids and several unidentified fractions.The ratio of phospholipids to triacylglycerols as well as the ratio of diacylglycerophosphorylethanolamines to dicylglycerophosphorylcholines increase with time both in rape cultures incubated at 30°C and in those kept at 5°C.The lipids in rape and nasturtium cultures grown at 30°C contain smaller proportions of polyunsaturated fatty acids than the lipids in cultures incubated at 5°C. Erucic acid, the major constituent fatty acid of the seed lipids, in both plants, occurs only in trace amounts in the lipids of callus cultures. In contrast, linoleic and linolenic acids, which occur only in traces in the seed lipids of nasturtium, are major constituent fatty acids in the lipids of callus cultures derived from seedlings of this plant.The levels of constituent polyunsaturated fatty acids in the diacylglycerophosphorylethanolamines and the diacylglycerophosphorylcholines increase with time whereas in the triacylglycerols only linolenic acid is slightly increased.     

Membranes of Tetrahymena: III. The effect of temperature on membrane core structures and fatty acid composition of Tetrahymena cells

Membrane core structures as revealed by the freeze-etch electron microscopy and the fatty acid composition measured by gas-liquid chromatography have been analyzed in Tetrahymena cells exposed to low temperature for varying periods.When cells were grown to mid-log phase at the optimal growth temperature of 28 °C and then chilled to 10 °C, cell division was inhibited. However, within 16 h the cells adapted to the low temperature.Chilling effected drastic structural alterations in the cores of different membrane types (membranes of the pellicula, the alveolar sacs, the endoplasmic reticulum and the nuclei). In all cases, there was a segregation of smooth faces from particle-rich faces in the fracture planes. However, the native membrane state, i.e. like that of cells grown at 28 °C, reappeared when the cells adapted to the low temperature.The total lipids of Tetrahymena cells contained primarily even-numbered fatty acids ranging from C₁₂ to C₁₈, but we also detected appreciable amounts of C₂₀ acids; this has not been reported before. During the initial phase of chilling, when cell division is inhibited, about 50% of the saturated fatty acids were replaced by unsaturated fatty acids, primarily monoenoic, dienoic and trienoic acids.We conclude that the structural recovery of the membranes in chilled Tetrahymena cells is accomplished by a desaturation of membrane fatty acids. This is discussed with respect to membrane “fluidity”.     

Fatty acids profile and temperature in the cultured marine diatom Odontella aurita

The diatom Odontella aurita has now been industrially cultured and commercialized as a dietary supplement rich in omega-3 fatty acids for several years. In this study, we investigated the effect of three temperatures (8, 16, and 24 °C) on the growth and fatty acid composition of cells harvested during the exponential and stationary growth phases. These temperatures were selected on the basis of photosynthesis responses previously obtained at different temperatures using a modulated fluorometer. Our results confirm that both growth and lipid composition were sensitive to culture temperature. Growth was reduced when O. aurita was cultured at low temperature (8 °C) compared to when it was cultured at high temperatures (16 and 24 °C), but the proportion of polyunsaturated fatty acids (PUFAs, 20:5 n-3 and 22:6 n-3) increased while the level of saturated fatty acids (SFAs, 14:0 and 16:0) decreased in the cells harvested during both the exponential and stationary growth phases. On the other hand, the cells grown at 24 °C displayed a marked decrease in PUFA and an increase in SFA levels. Harvesting time is also a critical parameter in achieving optimum n-3 PUFA productivity during batch cultivation. Indeed, changes in fatty acid composition with growth phase seem to be dependent on the culture temperature, with the most marked effects being observed at 24 °C. PUFA levels (i.e., levels of 20:5 n-3 and 22:6 n-3) increased during the stationary growth phase, while the proportion of SFAs and monounsaturated fatty acids (MUFAs) fell with time. As this species is currently grown in outdoor ponds with seasonal temperature variations (minimal and maximal average temperatures in winter and summer, from 3 to 9 °C and from 13 to 26 °C, respectively), this factor can be expected to have a strong influence on the fatty acid content and composition of the algal biomass harvested and commercialized.     

Phase transitions of phospholipid bilayers from an unsaturated fatty acid auxotroph of Escherichia coli

Total phospholipids were extracted from cells of temperature sensitive unsaturated fatty acid auxotrophs of Escherichia coli (K-12 UFA^ts) grown at 28°C (PL28), and at 42°C in the presence of 2% KCl as an osmotic stabilizer (PL42 (KCl)). From the analysis of fatty acids, it was shown that the content of unsaturated fatty acids of PL42 (KCl) is only 9% of the total fatty acids, while that of PL28 is 54%. The thermal phase transitions of the bilayers prepared from the phospholipid fractions were studied by proton magnetic resonance. The line widths of the methylene signals and the sums of the methylene and methyl signal intensities were plotted against reciprocal values of absolute temperature 1/T or temperature itself. From the plots phase transitions were detected at about 19°C for PL28 and at 43°C for PL42 (KCl). In spite of its complex composition of fatty acids a highly cooperative transition was observed in the case of PL42 (KCl). It was also suggested that the phospholipids bilayers in the biomembranes of this strain at the growth temperature (42°C) are in the state where the gel and liquid crystalline phases coexist.     

Separation of some mono-, di- and tri-unsaturated fatty acids containing 18 carbon atoms by high-performance liquid chromatography and photodiode array detection

Positional and geometric isomers of mono-, di- and tri-unsaturated fatty acids containing 18 carbon atoms were separated on commercially available reversed-phase columns in gradient systems composed of acetonitrile and water, utilizing photodiode array detection. The biological samples were hydrolyzed with 2 M NaOH for 35–40 min at 85–90°C. After cooling, the hydrolysates were acidified with 4 M HCl and the free fatty acids were extracted with dichloromethane. The organic solvent was removed in a gentle stream of argon. The fatty acids were determined after pre-column derivatization with dibromacetophenone in the presence of triethylamine. The reaction components were mixed and reacted for 2 h at 50°C. Separations of derivatized fatty acids were performed on two C₁₈ columns (Nova Pak C₁₈, 4 μm, 250×4.6 mm, Waters) by binary or ternate gradient programs and UV detection at 254 and 235 nm. The geometric and positional isomers of some unsaturated fatty acids were substantially retained on the C₁₈ columns and were distinct from some saturated fatty acids, endogenous substances in biological samples or background interference. Only slight separation of critical pairs of cis-9 C_18:1/cis-11 C_18:1 and cis-6 C_18:1/trans-11 C_18:1 was obtained. A ternate gradient program can be used for complete fractionation of a mixture of conjugated linoleic acid isomers (CLA) from cis-9, cis-12 and trans-9, trans-12 isomers of C_18:2. The CLA isomers in the effluent were monitored at 235 nm. The CLA isomers were differentiated from saturated and unsaturated fatty acids using a photodiode array detector. The utility of the method was demonstrated by evaluating the fatty acid composition of duodenal digesta, rapeseed and maize oils.     

Effects of molten-salt/ionic-liquid mixture on extraction of docosahexaenoic acid (DHA)-rich lipids from Aurantiochytrium sp. KRS101

In this study, lipid extraction from Aurantiochytrium sp. was performed using a molten-salt/ionic-liquid mixture. The total fatty acid content of Aurantiochytrium sp. was 478.8 mg/g cell, from which 145 mg/g cell (30.3 % of total fatty acids) of docosahexaenoic acid (DHA) was obtained. FeCl₃·6H₂O showed a high lipid extraction yield (207.9 mg/g cell), when compared with that of [Emim]OAc, which was only 118.1 mg/g cell; notably however, when FeCl₃·6H₂O was mixed with [Emim]OAc (5:1, w/w), the yield was increased to 478.6 mg/g cell. When lipid was extracted by the FeCl₃·6H₂O/[Emim]OAc mixture at a 5:1 (w/w) blending ratio under 90 °C, 30 min reaction conditions, the fatty acid content of the extracted lipid was a high purity 997.7 mg/g lipid, with most of the DHA having been extracted (30.2 % of total fatty acids). Overall, lipid extraction from Aurantiochytrium sp. was enhanced by the synergistic effects of the molten-salt/ionic-liquid mixture with different ions.     

Fatty Acid Synthesis in Leucoplasts Isolated from Developing Seeds of Brassica campestris

Fatty acid synthesis from Na (1-¹⁴C) acetate in leucoplasts isolated from developing seeds of Brassica compestris was found to be maximum when leucoplasts were supplied with 0.8 mM acetate, 20 mM NaHCO₃, 8 mM ATP, 8 mM MgCl₂, 4 mM MnCl₂, 0.6 mM CoA, 1 mM NADH, 1 mM NADPH and 0.2 M sorbitol and incubated at 30°C for 2 h. The rate of fatty acid synthesis was highest at pH 8.5 In presence of 0.4 M Bistris-propane buffer and linear for upto 4 h at 30°C with 80–110 μg plastid protein. Sorbitol was an essential requirement as it prevented the rupturing of leucoplasts by osmosis. ATP and divalent cations were almost absolute requirements, whereas nucleotides, CoA and bicarbonate improved the rate of fatty acid synthesis by two to ten folds. Mg²⁺ and NADH were the preferred cation and nucleotide, respectively. High concentration of dithiothreltol inhibited the incorporation of (¹⁴C) acetate Into fatty acids. The system developed as above could be used for in vitro studies.     

Temperature-sensitive mutants of a thermotolerant yeast,Hansenula polymorpha

Temperature-sensitive mutants (TS-1 and TS-7) of a thermotolerant yeast, Hansemula polymorpha CK-1, were isolated. The mutants were unable to grow at 50°C, the maximum growth temperature of the wild type. Mutants TS-1 and TS-7 grown at 20°C showed 33 and 50% viabilities after 6 h of incubation of 50°C, respectively. Mutant TS-1 showed little variation of the degree of fatty acid unsaturation (1.26–1.28/mol) and mutant TS-7 had an almost constant sterol/phospholipid molar ratio (0.31–0.34) at 20, 30 and 40°C, although the wild type had a decrease of the degree of fatty acid unsaturation from 1.56 at 20°C to 1.30 at 40°C and an increase of the sterol/phospholipid molar ratio from 0.26 at 20°C to 0.54 at 40°C.     

Correlations between the thermal stability of chloroplast (thylakoid) membranes and the composition and fluidity of their polar lipids upon acclimation of the higher plant,Nerium oleander,to growth temperature

The thermal stability of excitation transfer from pigment proteins to the Photosystem II reaction center of Nerium oleander adjusts by 10 Celsius degrees when cloned plants grown at 20°C/15°C, day/night growth temperatures are shifted to 45°C/32°C growth temperature or vice versa. Concomitant with this adjustment is a decrease in the fluidity of thylakoid membrane polar lipids as determined by spin labeling. The results are consistent with the hypothesis that there is a limiting maximum fluidity compatible with maintenance of native membrane structure and function. This limiting fluidity was about the same as for a number of other species which exhibit a range of thermal stabilities. Inversely correlated shifts in lipid fluidity and thermal stability occurred during the time course of acclimation of N. oleander to new growth temperatures. Thus, the temperature at which the limiting fluidity was reached changed during acclimation while the limiting fluidity remained constant. Although the relative proportion of the major classes of membrane polar lipids remained constant during adjustments in fluidity, large changes occured in the abundance of specific fatty acids. These changes were different for the phospho- and galacto-lipids suggesting that the fatty acid composition of these two lipid classes is regulated by different mechanisms. Comparisons between membrane lipid fluidity and fatty acid composition indicate that fluidity is not a simple linear function of fatty acid composition.     

Competition between cis,trans and Cyclopropane Fatty Acid Formation and its Impact on Membrane Fluidity

The impact of cis, trans and cyclopropane fatty acids on membrane fluidity was investigated using batch‐grown Pseudomonas putida P8 and Comamonas testosteroni ATCC 17454. A major difference observed between the two investigated strains is the absence of the ability to synthesize trans‐unsaturated fatty acids in Comamonas. When grown exponentially at 30 °C, a shift to 35 °C increased the trans/cis ratios of the fatty acids of P. putida P8 from 0 to 0.81 and 0 to 1.07, in lipid extracts and cell hydrolyzates, respectively. After prolonged growth followed by nutrient deprivation for 48 h, both at 30 °C, trans fatty acids were absent, but the cyclo/cis ratios rose from 0.1 to 1.55 in lipid extracts, and from 0.1 to 1.54 in cell hydrolyzates. C. testosteroni ATCC 17454 contained no cyclo fatty acids when harvested in the exponential phase after 6 h, whereas after 72 h cultivation, the cyclo/cis ratios rose to 0.49 and 0.47, in lipid extracts and cell hydrolyzates, respectively. Trans fatty acids were never observed in this strain. Increased cyclo/cis and trans/cis ratios correlated with decreased fluidity measured by the fluorescence anisotropy of 1,6‐diphenyl‐1,3,5‐hexatriene (DPH) intercalated in the bilayers of liposomes and by Fourier Transform Infrared (FTIR) spectroscopy of lipids prepared from the cells. The specific effect of cyclopropane fatty acids on membrane fluidity was much smaller than that of trans fatty acids. FTIR‐measurements of intact cells of P. putida P8 confirmed the high potency of trans fatty acids to decrease the fluidity. In cells with induced cyclopropane fatty acid synthesis, the membranes remained more fluidized, indicating the lower importance of these fatty acids for homeoviscosis.     

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.     

Low-temperature-induced desaturation of fatty acids and expression of desaturase genes in the cyanobacterium Synechococcus sp. PCC 7002

Changes in response to temperature of lipid classes, fatty acid composition and mRNA levels for acyl-lipid desaturase genes were studied in the marine unicellular cyanobacterium, Synechococcus sp. PCC 7002. The degree of unsaturation of C₁₈ fatty acids increased in cells grown at lower temperature for all lipid classes, and ω3 desaturation occurred specifically in cells grown at low temperature. While the level of 18:1(9) fatty acids declined, desaturation at the ω3 position of C₁₈ fatty acids increased gradually during a 12-h period after a temperature shift-down to 22°C. However, the mRNA levels of the desA (Δ12 desaturase), desB (ω3 desaturase) and desC (Δ9 desaturase) genes increased within 15 min after a temperature shift-down to 22°C; the desaturase gene mRNA levels also rapidly declined within 15 min after a temperature shift-up to 38°C. Therefore, the elevation of mRNA levels for the desaturase genes is not the rate-limiting event for the increased desaturation of membrane lipids after a temperature shift-down. The rapid, low-temperature-induced changes in mRNA levels occurred even when cells were grown under light-limiting conditions for which the growth rates at 22°C and 38°C were identical. These studies indicate that the ambient growth temperature, and not some other growth rate-related process, regulates the expression of acyl lipid desaturation in this cyanobacterium.     

Seasonal Changes of Fatty Acid Compositions in Overwintering Larvae of Rice Stem Borer,Chilo suppressalis (Lepidoptera: Pyralidae)

Cold acclimation and overwintering state can affect fatty acid compositions of insects. To determine compositional change of fatty acids during nondiapause and diapause stages, an experiment was conducted to investigate fatty acid constituents from whole body of C. suppressalis larvae. Five most abundant fatty acids were found to be palmitoleic (35–58%), palmitic (18–44%), oleic (14–23%), stearic (0.5–2.5%) and linoleic acid (0.4–2%). However, linolenic, erucic, lauric and myristic acid were found at lower level. Saturated fatty acids significantly decreased and conversely unsaturated fatty acids increased from August (pre-diapause) to October (initiation of diapause). The increase in seasonal cold hardiness during cold acclimation, exposed at −15°C for 24 h, was related to degree of fatty acid unsaturation. The elevation of palmitoleic acid content at low temperature resulted in an increase in the overall degree of unsaturation in the whole body. These results indicated the importance of unsaturated fatty acids composition to prepare larvae entering diapause phase.     

Thryoid control over biomembranes. Rat liver mitochondrial inner membranes.

The effects of hypothyroidism and one injection of l-thyroxine on oxidative phosphorylation and the composition of proteins and phospholipids were examined in vesicles prepared from rat liver mitochondria by digitonin extractions. At 30 °C, the rates of ADP phosphorylation in sites I and II were below normal, and Mg²⁺-ATPase activity was greater than normal in vesicles from hypothyroid rats. At temperatures below 20 °C and above 30 °C, the Mg²⁺-ATPase was not accelerated above normal rates, a feature of temperature dependence shared by ADP phosphorylation (Chen, Y.-D. I., and Hoch, F. L., 1976, Arch. Biochem. Biophys.172, 741–744). Respiration at 30 °C was undiminished in hypothyroid vesicles, as were the flavin and cytochrome contents, and thyroxine administration corrected the phosphorylation rate at 30 °C in 3 days without changing either respiration or electron-carrier contents. The 30 °C phosphorylation defect comprised a decreased V and K_m for ADP and a decrease in the number of phosphorylating sites (measured with oligomycin) that accounted for most of the decreased phosphorylation rates, either dependent on or independent of the adenine nucleotide carrier. Vesicles from hypothyroid rats were not detectably depleted in major protein subunits, but were abnormal in phospholipid fatty acid contents. Thyroxine injection corrected the low unsaturation index of the fatty acids and the membrane contents of linoleic acid and its fatty acyl metabolites. Hypothyroidism appears to affect oxidative phosphorylation through the altered inner membrane lipid environment, which implies that previously reported direct, reversible effects of thyroxine may mimic repletion of the membranes with unsaturated fatty acyl groups.     

Oxidation of Fatty Acids by Leishmania braziliensis panamensis1

Heating cultures of Leishmania braziliensis panamensis (grown at 26°C) to 34°C for 1.5–12 h transformed the cells to an ellipsoidally shaped form. The heat treatment caused an increase in the rate of oxidation of both medium and long chain fatty acids but decreased the rate of oxidation of [1-¹⁴C]glucose. The rate of fatty acid oxidation continued to increase for times as long as 20 h after returning the cultures to 26°C. In both the promastigote and heat-induced ellipsoidal forms, the ratio of ¹⁴CO₂ release from [1-¹⁴C]laurate to that from [12-¹⁴C]laurate was generally larger than four, whereas this ratio from [1-¹⁴C]oleate relative to [10-¹⁴C]oleate was approximately two. These data show that metabolic and morphological differentiation begin after a short heat treatment and that some metabolic changes may continue even after the reverse transformation is initiated. The data also suggest that either the ω-terminal portion of the fatty acids is not completely oxidized to acetyl CoA and/or that there are two functional fatty acid oxidation pathways in Leishmania.     

Population responses and fatty acid profiles of Brachionus calyciflorus (Rotifera) in relation to different thermal regimes

Diurnal temperature fluctuations affect ectothermic species more than endothermic taxa. We tested the effect of three fixed temperatures (20, 25 and 30 °C) and a 24 h variable (20–30 °C) on the population growth and fatty acid profiles of the common rotifer Brachionus calyciflorus. Depending on the temperature treatment, the peak population abundances of B. calyciflorus varied from 65 to 80 ind./ml, the lowest being on variable temperature range. The rate of population increase varied from 0.31 to 0.52 per day, highest being at 30 °C. There was a curvilinear relationship between the population density and the egg ratio (number of eggs/female) in all the tested temperature regimes. The egg ratio was higher (>0.6) for treatments involving fixed temperatures, but for variable temperature regime, the egg ratios were lower (<0.5). Temperature also induced changes in the fatty acid content of B. calyciflorus. While the total saturated fatty acids increased, both mono-unsaturated and poly-unsaturated fatty acids decreased with increasing temperature regime. These results have been interpreted in relation to the role of temperature (both intensity and mode of exposure) on the population growth characteristics of rotifers.