Fatty Acid Unsaturation Index Research Articles

Seasonal acclimation of superoxide anion production, antioxidants, IUFA, and electron transport rates in chloroplasts of two Sabina species

Chloroplasts are the main source of reactive oxygen species (ROS) production in plant, better balance between productions and scavenging of ROS in chloroplasts plays an important role in development of freezing tolerance. In the present study, two evergreen woody plants, Sabina przewalskii Kom. scattered at higher altitudes, Sabina chinensis (Lin.) Ant. distributed at lower altitudes, were used to investigate seasonal variation patterns in superoxide anion production, antioxidants, and index of unsaturated fatty acid (IFUA) during the natural temperature variations. IFUA, GSH, AsA and Car content in chloroplasts were all negatively correlated mean air temperature in both Sabina species, which were regarded to be useful to maintenance of membrane fluidity and function and improvement of antioxidative ability during cold stress. However, positive correlation of air temperature with superoxide anion generation was also found in two Sabina trees, which also suggested that decreased superoxide anion generation was related to increased antioxidants in winter. Compared with S. chinensis (Lin.) Ant., there were significantly higher antioxidants and lower quantity of superoxide anion in S. przewalskii Kom., however, there was higher unsaturated fatty acids ratio in S. chinensis (Lin.) Ant. than S. przewalskii Kom. These results together suggested that the regulations of superoxide anion production and antioxidants in chloroplasts are critical to increase in cold-tolerance between two Sabina evergreen trees; however, high unsaturation lipid level is only one of the factors that maintain the membrane function of chloroplasts for cold-tolerance during decreasing temperature.

Protective Effect of Rare Earth Against Oxidative Stress Under Ultraviolet-B Radiation

The effects of lanthanum (III) (La(III)) in protecting soybean leaves against oxidative stress induced by ultraviolet-B (UV-B) radiation were investigated. The increase in contents of hydrogen peroxide (H(2)O(2)) and superoxide (O2*-) due to UV-B radiation suggested oxidative stress. The increase in the content of malondialdehyde (MDA) and the decrease in the index of unsaturated fatty acid (IUFA) indicated oxidative damage on cell membrane induced by UV-B radiation. La(III) partially reversed UV-B-radiation-induced damage of plant growth. The reduction in the contents of H(2)O(2), O2*-, and MDA and increase in the content of IUFA, compared with UV-B treatment, also indicated that La(III) alleviated the oxidative damage induced by UV-B radiation. The increase in the activities of superoxide dismutase and peroxidase and the contents of ascorbate, carotenoids, and flavonoids were observed in soybean leaves with La(III) + UV-B treatment, compared with UV-B treatment. Our data suggested that La(III) could protect soybean plants from UV-B-radiation-induced oxidative stress by reacting with reactive oxygen species directly or by improving the defense system of plants.

Fatty acid analyses may provide insight into the progression of starvation among squamate reptiles

Fasting-induced changes in fatty acid composition have been reported to occur within the body lipids of several types of animals; however, little is known about the changes in fatty acid profiles exhibited by reptiles subjected to prolonged fasting. This study characterizes the fatty acid profiles of six reptile species subjected to sublethal periods of fasting lasting 0, 56, 112, and 168 days. Analyses of fatty acid methyl esters (FAMEs) conducted on the total body lipids of rattlesnakes ( Crotalus atrox), ratsnakes ( Elaphe obsoleta), pythons ( Python regius), boas ( Boa constrictor), true vipers ( Bitis gabonica), and monitor lizards ( Varanus exanthematicus) revealed that all of the species exhibited similar characteristic changes in their fatty acid profiles during starvation stress. According to ANOVAs, the four most effective indicators of the onset of starvation were significant increases in the [1] fatty acid unsaturation index as well as ratios of [2] linoleic to palmitoleic acid, [3] oleic to palmitic, and [4] arachidonic to total fatty acid concentrations. The results of this study suggest that FAME analyses might be useful for identifying nutritional stress and/or starvation among squamate reptiles; however, forthcoming studies will be required to validate the generality of these responses. I also review the potential limitations of this approach, and suggest experiments that will be important for future applications of FAME analyses. Ultimately, it is hoped that FAME analyses can be used in conjunction with current practices as an additional tool to characterize the prevalence of starvation experienced by free-living reptiles.

Milk Fatty Acid Unsaturation: Genetic Parameters and Effects of Stearoyl-CoA Desaturase (SCD1) and Acyl CoA: Diacylglycerol Acyltransferase 1 (DGAT1)

With regard to human health aspects of milk fat, increasing the amount of unsaturated fatty acids in milk is an important selection objective. The cow's diet has an influence on the degree of unsaturation, but literature suggests that genetics also plays a role. To estimate genetic variation in milk fatty acid unsaturation indices, milk fatty acid composition of 1,933 Dutch Holstein Friesian heifers was measured and unsaturation indices were calculated. An unsaturation index represents the concentration of the unsaturated product proportional to the sum of the unsaturated product and the saturated substrate. Intraherd heritabilities were moderate, ranging from 0.23±0.07 for conjugated linoleic acid (CLA) index to 0.46±0.09 for C16 index. We genotyped the cows for the SCD1 A293V and DGAT1 K232A polymorphisms, which are known to alter milk fatty acid composition. Both genes explain part of the genetic variation in unsaturation indices. The SCD1V allele is associated with lower C10, C12, and C14 indices, and with higher C16, C18, and CLA indices in comparison to the SCD1 A allele, with no differences in total unsaturation index. In comparison to the DGAT1K allele, the DGAT1 A allele is associated with lower C10, C12, C14, and C16 indices and with higher C18, CLA, and total indices. We conclude that selective breeding can contribute to higher unsaturation indices, and that selective breeding can capitalize on genotypic information of both the SCD1 A293V and the DGAT1 K232A polymorphism.

Neutrophil fatty acid composition: effect of a single session of exercise and glutamine supplementation

The fatty acid composition of immune cells appears to contribute to variations of cell function. The independent and combined effects of a single session of exercise (SSE) and glutamine supplementation (GS) on neutrophil fatty acid composition were investigated. Compared to control (no treatment given--i.e. neither SSE or GS), single session of exercise decreased myristic, palmitic and eicosapentaenoic (EPA) acids, and increased lauric, oleic, linoleic, arachidonic (AA) and docosahexaenoic (DHA) acids whereas glutamine supplementation combined with SSE (GS+SSE) increased oleic acid. Polyunsaturated/saturated fatty acid ratio and Unsaturation index were higher in neutrophils from the SSE and GS groups as compared with control. These findings support the proposition that SSE and GS may modulate neutrophil function through alterations in fatty acid composition.

Tributyltin chloride interactions with fatty acids composition and degradation ability of the filamentous fungus Cunninghamella elegans

Abstract Toxic organotin compounds are widely present in the environment. Tributyltin chloride (TBT), an organotin, is degraded by a filamentous fungus Cunninghamella elegans. The major fatty acids of this fungus were: palmitate (16:0), stearate (18:0), oleate (18:1n9), linoleate (18:2n6) and γ-linolenate (18:3n6). We show that the fatty acid unsaturation index was decreased and the conversion of stearic acid (18:0) in oleic acid (18:1n9) was significantly inhibited in the presence of TBT. Changes in fatty acid compositions during TBT degradation at 10 mg l−1 in C. elegans revealed that the degree of saturation was correlated with biotransformation of the xenobiotic to less toxic compounds: dibutyltin and monobutyltin. Our results suggest that the high TBT resistance in C. elegans is associated with the modulation of the fatty acids composition and the biocide degradation.

Western Diamondback Rattlesnakes Demonstrate Physiological and Biochemical Strategies for Tolerating Prolonged Starvation

Because of the uncertainty in food resources in nature, all animals face the possibility of imposed periods of fasting (i.e., starvation) at some point in their lives. I investigated physiological and biochemical responses to starvation that occur in a species of rattlesnake known to tolerate successfully prolonged periods of starvation in the wild. Sixteen subadult Crotalus atrox were fasted for up to 24 wk under controlled conditions simulating their active season. Snakes exhibited significant reductions in plasma glucose but increased circulating ketone bodies. Fasting snakes lost mass at a linear rate and increased their relative moisture content during the experiment. The bodies of fasting snakes demonstrated an increase in their fatty acid (FA) unsaturation index and were apparently able to "spare" essential FAs effectively from beta -oxidation. Endogenous essential and nonessential amino acids were used indiscriminately to fuel energetic requirements, suggesting that essential amino acids are not preferentially spared during starvation. The (15)N signature of excreted nitrogenous waste increased significantly, presumably as a result of shifting amino acid source pools during starvation. Because our comparative knowledge of starvation physiology contains large taxonomic gaps, particularly with respect to amphibians and reptiles, an understanding of the biological responses exhibited by these animals may offer insight into the evolution of physiological strategies animals employ to cope with the pressures of starvation.

Direct Evidence That Maltose Transport Activity Is Affected by the Lipid Composition of Brewer's Yeast

A brewer's yeast strain was grown with maltose as sole carbon source under strictly anaerobic conditions with and without ergosterol and/or unsaturated fatty acid (Tween 80) supplements. Under all these conditions the MALx1 genes for maltose transporters were strongly expressed during growth. The fatty acid unsaturation indices of growing and stationary phase yeast were increased from about 20% to 56–69% by supplementation with Tween 80. Ergosterol contents were increased up to at least 4-fold by supplementation with ergosterol and Tween 80. Maltose transport activity measured at 20°C was not increased by supplementation with Tween 80 alone, but was increased 2-fold and 3-fold, respectively, in growing and stationary phase yeast by supplementation with ergosterol together with Tween 80. The stimulation of maltose transport by ergosterol was greater when the transport was measured at temperatures (10°C and 0°C) lower than 20°C. The results show that proper function of maltose transporters requires adequate amounts of ergosterol in the yeast. This effect may partly explain the low maltose (and maltotriose) uptake rates both in the second half of brewery fermentations, when the sterol content of yeast has fallen, and when fresh wort is pitched with sterol-deficient cropped yeast.

Vitamin B6 supplementation increases the docosahexaenoic acid concentration of muscle lipids of rainbow trout (Oncorhynchus mykiss)

Fish fillet quality is influenced by feed quality. In particular, vitamin B6 availability improves growth rate and nutritional value, because it is related to protein and lipid metabolism. The present study investigates the effect of increasing amounts of vitamin B6 on growth, fatty acid composition and lipid peroxidation of muscle tissue of rainbow trout (Oncorhynchus mykiss). Quadruplicate groups of trout of a mean initial weight of 110 g were fed commercial diets supplemented with four different quantities of vitamin B6 (0, 10, 25 and 50 mg kg−1 diet). Over the experimental period, there were no significant differences in weight gain and feed intake, while vitamin B6 concentration of muscle was affected by dietary intake, even though its increase was not proportional to the concentrations in the feed. The fatty acid composition of muscle lipid showed differences between the four groups. The percentage of long-chain unsaturated fatty acids, in particular docosahexaenoic acid, increased significantly in vitamin B6-supplemented groups. However, despite the increased fatty acid unsaturation index, lipid peroxidation parameters such as vitamin E content, malondialdehyde production, glutathione reductase and glutathione peroxidase activities did not show significant differences, meaning that the higher level of long-chain unsaturated fatty acid did not increase the muscle susceptibility to oxidative stress.

Calcium Influence on Chilling Resistance of Grafting Eggplant Seedlings

Calcium (Ca) influence on chilling resistance of grafting eggplant seedlings were studied in a hydroponic system. Under the calcium sufficient treatment, the activities of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) in grafting seedlings at 5°C were all obviously higher than those of calcium deficiency, peaking at 36 h, 24 h, and 24 h chilling stress, respectively. Several parameters of cellular membrane fluidity, such as content of unsaturated fatty acid (UFA), the ratio of UFA to SFA (U/S), index of UFA (IUFA) also distinctively increased. The contents of malondialdehyde (MDA) and saturated fatty acid (SFA) were lower than those of calcium deficiency. This study suggests that the variation of parameters mentioned above might be caused by cellular calcium levels. Calcium content was potentially the main reason that grafting seedlings had higher chilling resistance than own-root seedlings. Calcium appears to play an important role in increasing chilling resistance of grafting eggplant seedlings.

Morphological and immunological characterization of immunostimulatory complexes based on glycoglycerolipids from Laminaria japonica.

Some physicochemical properties of glycoglycerolipids (monogalactosyldiacylglycerol, digalactosyldiacylglycerol and sulfoquinovosyldiacylglycerol) from the sea algae Laminaria japonica, as well as their ability to become incorporate into immunostimulating complexes (ISCOMs), used as a delivery system of microbial and tumor antigens in vesicular form, were studied. These glycolipids were found to differ essentially in fatty acid composition, unsaturation index and thermotropic behavior. The possibility of ISCOM modification by embedding the glycolipids studied instead of a phospholipid component in vesicles was shown. A preliminary research of the immunogenicity of the pore-forming protein from Yersinia pseudotuberculosis in modified (by monogalactosyldiacylglycerol) and typical (egg phosphatidylcholine) ISCOMs did not reveal a significant enhancement of immune response in comparison with that of isolated protein.

Morphological and immunological characterization of immunostimulatory complexes based on glycoglycerolipids from Laminaria japonica.

Some physicochemical properties of glycoglycerolipids (monogalactosyldiacylglycerol, digalactosyldiacylglycerol and sulfoquinovosyldiacylglycerol) from the sea algae Laminaria japonica, as well as their ability to become incorporate into immunostimulating complexes (ISCOMs), used as a delivery system of microbial and tumor antigens in vesicular form, were studied. These glycolipids were found to differ essentially in fatty acid composition, unsaturation index and thermotropic behavior. The possibility of ISCOM modification by embedding the glycolipids studied instead of a phospholipid component in vesicles was shown. A preliminary research of the immunogenicity of the pore-forming protein from Yersinia pseudotuberculosis in modified (by monogalactosyldiacylglycerol) and typical (egg phosphatidylcholine) ISCOMs did not reveal a significant enhancement of immune response in comparison with that of isolated protein.

Effects of culture method and growth phase on free lipid composition of Yersinia pseudotuberculosis.

The influence of culture method (free-floating cells in liquid nutrient broth or bacteria attached to agar surface on solid agarized medium of the same formulation) and bacterial age on the composition of free lipids in Yersinia pseudotuberculosis (O:Ib serovar, strain KS 3058) grown in the cold (5 degrees C) has been investigated. The specific growth rate of the bacteria on solid medium was about threefold less than that in liquid medium. The qualitative composition of phospholipids and fatty acids only slightly depended on the bacterial culture method. At the same time, the colonially growing cultures contained somewhat more total lipids, they synthesized more phospholipids, in the linear growth phase they contained more lysophosphatides, and they had higher fatty acid unsaturation index and higher pathogenic potential than their "planktonic" counterparts grown in otherwise identical conditions. The bacterial growth phase influenced the amount of 3-hydroxytetradecanoic acid and, indirectly, that of lipopolysaccharide. The dynamics of changes in the amount of this acid with bacterial age was opposite in the surface and broth cultures.

Changes of microsomal membrane properties in spring wheat leaves ( Triticum aestivum L.) exposed to enhanced ultraviolet-B radiation

The properties of microsomal membranes in spring wheat leaves ( Triticum aestivum L. cv. Ganlong No. 92-005) exposed to (0) control, 8.64 (T 1) and 11.2 kJ m −2 day −1 (T 2) biologically effective UV-B irradiation (UV-B BE) were studied under greenhouse conditions. These irradiance levels correspond to a decrease in the stratospheric ozone of ≈12.5 and 20%, respectively, for a clear solstice day at Lanzhou (36.04°N, 1550 m), China. Compared with controls, the content of malondialdehyde (MDA) increased by 70.8% in T 1 and 83.8% in T 2 on the 7th day of the radiation, and the IUFA (index of unsaturated fatty acids) decreased, indicating peroxidation of lipid acids. Simultaneously, a drastic decrease of phospholipid content after 21 days and an increase of membrane lipid microviscosity on UV-B irradiation were also found, suggesting a reduction in the fluidity of membrane lipids. Ethylene emission by the microsomal membrane, in the presence of exogenous 1-aminocyclopropane-1-carboxylic acid was higher in the wheat seedlings after 7, 14 and 21 days’ irradiation than in the controls. These changes were correlated with a rise in lipoxygenase activity. Membrane-bound enzymes (Ca 2+-ATPase and Mg 2+-ATPase) were promoted by UV radiation in the first 7 days and significantly decreased after 14 and 21 days’ treatment in comparison to control. Our results suggest that UV-B radiation may cause changes in structural complexity and function of microsomal membranes in spring wheat leaves.

Effects of Exogenous Fatty Acids on H +-ATPase Activity and Lipid Composition of Plasma Membrane Vesicles Isolated from Roots of Barley Seedlings under Salt Stress

Summary The effects of exogenous fatty acids of different saturaturation degrees on the H+-ATPase activity and lipid composition of the plasma membrane (PM) vesicles isolated from the roots of two barley cultivars differing in salt-sensitivity (Jian 4, salt-tolerant; Kepin 7, salt-sensitive) were investigated under 100 mmol L−1 NaCl stress for 2 days. The PM vesicles with high purity were prepared by discontinuous sucrose density gradient centrifugation. The H+-ATPase activities, phospholipid contents and the index of unsaturated fatty acids (IUFA) increased in the PM vesicles isolated from the roots of seedlings of two barley cultivars under NaCl stress. However, there was no obvious change in the IUFA value with exogenous fatty acids of different saturation degrees. Exogenous stearic acid and linoleic acid increased the H+-ATPase activities and phospholipid contents, but their effects on galactolipid contents of the PM of Kepin 7 were different. For Jian 4, treated with linoleic acid, the galactolipid content increased by 115.85 %; the PM H+-ATPase activity and phospholipid contents increased slightly. This is consistent with the lower Na+ content and Na+/K+ ratio in leaves of salt-tolerant Jian 4 under salt stress.

Pregnancy-induced hypertension: maternal and neonatal plasma lipid-soluble antioxidant levels and its relationship with fatty acid unsaturation

Our purpose was to investigate whether plasma lipid-soluble antioxidant levels during the third trimester of pregnancy and immediately after birth are altered in women with pregnancy-induced hypertension. Nested case-control study of women with pregnancy-induced hypertension. A group of 23 women with (mild) pregnancy-induced hypertension and their neonates, were compared with 23 matched controls with uncomplicated pregnancies. Concentrations of vitamin E isomers, several carotenoids, and retinol were determined by HPLC in venous plasma which had been stored for 2-5 y. Antioxidant levels were adjusted for the degree of fatty acid unsaturation in plasma phospholipids as analysed 2-5 y before. In the third trimester of pregnancy, lipid-soluble antioxidant levels were similar in women with pregnancy-induced hypertension and controls. From the third trimester to postpartum, mean (+/- s.e.m.) beta + gamma-tocopherol levels decreased by 0.38 +/- 0.17 mumol/l or 5% (P = 0.038) in the control group. In the pregnancy-induced hypertension group, however, plasma levels of most antioxidants decreased from the third trimester to postpartum, but only the decreases in plasma levels of beta + gamma-tocopherol of 1.08 +/- 0.27 mumol/l or 26% (P = 0.042), of alpha-tocopherol of 2.51 +/- 1.58 mumol/l or 6% (P = 0.024), and of lutein of 0.13 +/- 0.04 mumol/l or 15% (P = 0.013) reached statistical significance as compared with the changes in the control group. At the same time, the polyunsaturated fatty acid unsaturation index of plasma phospholipids (UI) decreased in the pregnancy-induced hypertension group as well. Consequently, antioxidant levels, adjusted for UI, changed similarly in both groups. Umbilical vein plasma antioxidant levels were also similar after complicated and uncomplicated pregnancies. Plasma lipid-soluble antioxidant levels in mother and child are affected by mild pregnancy-induced hypertension, but this effect disappears after adjustment for fatty acid unsaturation.

Effects of calcium on lipid composition and function of plasma membrane and tonoplast vesicles isolated from roots of barley seedlings under salt stress

The effects of salt stress(200 mmol L‐1) and calcium (Ca) on the lipid composition and function of plasma membrane and tonoplast vesicles isolated from the roots of barley seedlings (Hordeum vulgare L. Jian 4) have been investigated. Nine days of exposure to 200 mmol L‐1 NaCl resulted in a significant increase in the electrolyte leakage and Na+/K+ ratio in the roots, sheaths, and leaves of barley. The index ofunsaturated fatty acids (IUFA) in plasma membrane (PM) and tonoplast (TP) vesicles, and the levels of galactolipid in TP increased (p<0.01). The contents of phospholipids in PM decreased (p<0.05). In contrast to salt treatment, supplement of Ca2+(17.5 mmol L‐1) obviously increased the phospholipids content, and significantly decreased the levels of galactolipids and IUFA in PM and TP vesicles. The results showed that the alleviating effect of Ca2+ on NaCl induced injury in barley seedlings may be related to the changes of membrane lipid composition including phospholipids, galactolipids, and their fatty acids.

Mutual influence of plasmid profile and growth temperature on the lipid composition of Yersinia pseudotuberculosis bacteria

The effect of a 82 MDa plasmid or its 25 MDa DNA fragment and growth temperature on the qualitative and the quantitative fatty acid and phospholipid composition of Yersinia pseudotuberculosis cells has been examined. In the cold, plasmid-containing and plasmid-free strains failed to differ appreciably in the contents of phospholipid and fatty acid. The exceptions were an elevated proportion of diphosphatidylglycerine and a decreased fatty acid unsaturation index in the plasmidless cells and those harbouring an incomplete 57 MDa plasmid in comparison with the strain containing the 82 MDa plasmid. At 37°C, the lack of the 82 MDa plasmid or its 25 MDa fragment gave rise to a phospholipid of unknown structure, led to a sharp decrease in phospholipid content, in PE amount in particular, with a concurrent increase in the quantities of CL and LPE, and with a reduction in index of fatty acid unsaturation. The 82 MDa plasmid seems to be associated with a cancelling a temperature-dependent regulation of lipid synthesis and as a result, both the ‘cold’ and the ‘warm’ variants of the plasmid-containing strain possessed basically the close related lipid contents. Changes in composition of the polar head groups of the membrane phospholipids and in the extent of fatty acid unsaturation were suggested to be connected with an antibiotic hypersensitivity revealed earlier in plasmid-free Y. pseudotuberculosis.

Red blood cell membrane dynamics in schizophrenia. III. Correlation of fatty acid abnormalities with clinical measures

Fatty acid composition was quantitatively analyzed in RBC ghost membranes of 20 schizophrenic patients stabilized with haloperidol (5–20 mg/day) and of the same individuals after haloperidol (HD) withdrawal. The average days on medication and drug-free period were 52 and 40 days, respectively. No significant differences were demonstrated in levels (% or nmol/ml packed RBC) of polyunsaturated fatty acids (PUFAs) between HD-treated and drug-free patients. Similarly, no significant difference was found between relapsed and nonrelapsed schizophrenic patients, although the mean levels of 20:4( n−6), total PUFAs or fatty acid unsaturation index (FAUI) were consistently higher in nonrelapsers than in relapsers. On the other hand, the decreases in FAUI were significantly ( r = -0.46, p = 0.04) correlated to the increases in psychosis rating which is consistent with our previous reported correlation between altered membrane fluidity and the severity of symptomatology. In addition, decreases in 18:2( n−6) but not 20:4( n−6) was significantly correlated to the increases in psychosis rating. The present results lend further support that decreased levels of RBC PUFAs in schizophrenic patients lie in an initial stage of PUFAs pathway, possibly a defective uptake of 18:2( n−6) into RBC membranes.

Low-temperature-induced adaptations in fatty acid metabolism of Acanthamoeba castellanii cultures of different ages: relationship to changes in cell division, oxygen uptake and phagocytotic activity

The degree of unsaturation of membrane lipids of Acanthamoeba castellanii at 30 °C decreased with batch-culture age. These changes were primarily attributable to a decline in microsomal Δ12-desaturase activity and in the relative proportion of linoleate. No change in the fatty acid composition, Δ12-desaturase activity or any increased incorporation of [1-14C]acetate into polyunsaturated fatty acids was observed following chilling of early- and mid-exponential-phase cultures to 15 °C. In contrast, chilling of late-exponential and stationary-phase cultures resulted in a rapid and marked increase in the synthesis of polyunsaturated fatty acids. Thus, after 12 h incubation at 15 °C, the relative proportions of oleate and linoleate in these older cultures were similar to those of early- and mid-exponential-phase cultures at 30 °C. Despite these differences, an approximately 9.5 h lag in cell division was evident following chilling of both mid-exponential and late-exponential/early-stationary-phase cultures, and the subsequent pattern of cell division over 60 h incubation was similar in both cases. Oxygen uptake rates in cultures of either age were also decreased approximately equally at 15 °C. In contrast, chilling of mid-exponential-phase cells resulted in only an approximately 44% reduction in the rate of phagocytosis of fluorescently-labelled latex beads, whereas an approximately 98% inhibition of phagocytosis by late-exponential/early-stationary-phase cells resulted at 15 °C. Furthermore, a gradual subsequent increase in the rate of phagocytosis at 15 °C was only observed in the older cultures and was correlated with increases in the fatty acid unsaturation index of these cells. Thus, 12 h after chilling, the cells from late-exponential/early-stationary-phase cultures had achieved rates of phagocytosis similar to those of chilled cells from mid-exponential growth and their fatty acid compositions were now similar. The results suggest a role of membrane lipid unsaturation in the control of phagocytotic activity of A. castellanii.