Transition of Lipid Synthesis from Chloroplasts to a Cytoplasmic System during Hardening in Chlorella ellipsoidea

Chlorella ellipsoidea Gerneck (IAM C-27) was synchronously grown and cells at an intermediate stage in the ripening phase of the cell cycle were hardened at 3 C for 48 hours. At various times of hardening, the cells were pulse-labeled for 4 minutes with [¹⁴C]NaHCO₃ in the light or with [¹⁴C]glucose in the dark, and the incorporation rate of ¹⁴C into total lipids was determined. A high incorporation rate of [¹⁴C]NaHCO₃ at zero time of hardening decreased after 6 hours. In the next 15 hours, a distinct increase was noted. This increase occurred prior to the development of frost hardiness. Cycloheximide completely inhibited both the increase and the development, and 3-(3,4-dichlorophenyl)-1,1-dimethylurea remarkably lowered the high incorporation rate at zero time. The incorporation rate of [¹⁴C]glucose increased along with hardiness in the dark. These results suggest that the major site of lipid synthesis shifts from chloroplasts to a cytoplasmic system during hardening of Chlorella.     

Metabolism of tween-Fatty Acid esters by cultured soybean cells : kinetics of incorporation into lipids, subsequent turnover, and associated changes in endogenous Fatty Acid synthesis

Uptake of Tween-fatty acid esters and incorporation of the fatty acids into lipids by soybean (Glycine max [L.] Merr.) suspension cultures was investigated, together with subsequent turnover of the incorporated fatty acids and associated changes in endogenous fatty acid synthesis. Tween uptake was saturable, and fatty acids were rapidly transferred from Tweens to all acylated lipids. Patterns of incorporation into glycerolipids were similar in cells treated with Tweens carrying [1-¹⁴C]-fatty acids and in cells treated with [1-¹⁴C]acetate, indicating that exogenous fatty acids were used for glycerolipid synthesis essentially as if they had been made by the cell. In Tween-treated cells neutral lipids (which include Tweens) initially accounted for the majority of lipid radioactivity. Radioactivity was then rapidly transferred to glycerolipids. A transient pool of free fatty acids accounting for up to 10% of lipid radioactivity was observed. This was consistent with the hypothesis that fatty acids are transferred from Tweens to lipids by deacylation of the Tweens, creating a pool of free fatty acids which are then used for lipid synthesis. Sterols were only slightly labeled in cells treated with Tweens, but accounted for nearly 50% of lipid radioactivity in cells treated with acetate. This suggested very little degradation and reutilization of the radioactive fatty acids in cells treated with Tweens. In cells treated with either [1-¹⁴C]acetate or Tween-[1-¹⁴C]-18:1, 70% of the initial fatty acid radioactivity remained in fatty acids after a 100 hour chase. By contrast, fatty acids not normally present disappeared more rapidly, suggesting differential treatment of such fatty acids compared with those normally present. Cells which had incorporated large amounts of exogenous fatty acids altered fatty acid synthesis in three distinct ways: (a) amounts of [1-¹⁴C]acetate incorporated into fatty acids were reduced; (b) cells incorporating exogenous unsaturated fatty acids increased the proportion of [1-¹⁴C]acetate partitioned into saturated fatty acids, while the converse was true of cells which had incorporated exogenous saturated fatty acids; (c) desaturation of 18:1 to 18:2 and 18:3 was reduced in cells which had incorporated unsaturated fatty acids. These results suggest that Tween-fatty acid esters will be useful for supplying fatty acids to cells for a variety of studies related to fatty acid or membrane metabolism.     

Substrate utilization for energy production and lipid synthesis in oligodendrocyte-enriched cultures prepared from rat brain

The metabolism of oligodendrocytes has been studied using cultures of oligodendrocyte-enriched glial cells isolated from cerebra of 5–8-day old rats. Cultures containing 60–80% oligodendrocytes were incubated for 16h with [3-¹⁴C]acetoacetate, d-[3-¹⁴C]3-hydroxybutyrate, [U-¹⁴C]glucose, l-[U-¹⁴C]glutamine and [1-¹⁴C]pyruvate or [2-¹⁴C]pyruvate in the presence or absence of other oxidizable substrates. Labelled CO₂ was collected as an index of oxidative metabolism and the incorporation of label into total lipids, fatty acids and cholesterol was used as an index of the de novo synthesis of lipids. Glucose, acetoacetate, D-3-hydroxybutyrate, pyruvate and l-lactate were measured to determine substrate utilization and product formation under various conditions. Our results indicate that glucose is rapidly converted to lactate and is a relatively poor substrate for oxidative metabolism and lipid synthesis. Ketone bodies were used as an energy source and as precursors for the synthesis of fatty acids and cholesterol. Preferential incorporation of acetoacetate into cholesterol was not observed. Exogenous pyruvate was incorporated into both the glycerol skeleton of complex lipids and into cholesterol and fatty acids. l-Glutamine appeared to be an important substrate for the energy metabolism of these cells.     

The relative hardening of roots and shoots and the influence of day-length during hardening in perennial ryegrass

The influence of long and short days during the hardening period on the cold hardiness of perennial ryegrass seedlings was studied as was the relative hardiness of roots and shoots. Hardiness was assessed by the electrolyte release method which was a measure of the amount of damage subsequent to low temperature treatment. Long days promoted hardiness in shoots of Pax 0tofte plants and in one case under short days the roots were found to be hardy. Generally roots were less hardy than shoots in Pax 0tofte and S23 plants hardened under long days for 2 wk. When hardened at the fourth leaf stage for 2 wk at + 5 ^oC under long day conditions, Pax 0tofte plants were more hardy than those of S23. The long day effect on hardiness was arrived at more rapidly, there being no difference in hardiness after 3 wk in Pax 0tofte hardened under long or short days, whereas a significant degree of hardening was observed after 1 wk of hardening under long days at – 4 ^oC. The results obtained are discussed in relation to winter kill of grasses in the West of Scotland, and it is considered that root damage is not an important factor in causing winter kill. The promotive effect of long days on hardiness when hardening commences in late autumn is considered an advantage in temperate regions as it may also allow early frosts to be withstood.     

Assimilation and biosynthesis of lipids in Arctic Calanus species based on feeding experiments with a C labelled diatom

The dominant Arctic Ocean and North Atlantic copepods Calanus hyperboreus, Calanus glacialis, and Calanus finmarchicus were collected in the Greenland Sea and fed ¹³C labelled diatom Thalassiosira weissflogii to follow the transfer and assimilation of carbon, lipid, and individual fatty acids and alcohols. The diatom was grown with ¹³C for 3 to 5 days and fed then to the copepods. During the feeding period of 14 days, total carbon increased in the copepodite stages V of C. hyperboreus and C. finmarchicus, whereas carbon remained almost constant in C. glacialis females. However, total lipid increased in all species and stages. Highest lipid accumulation occurred in C. hyperboreus in which nearly all lipids were exchanged already after 11 days of feeding. In the other species lipid accumulation made up between 22% (C. finmarchicus) and 45% of total lipid (C. glacialis). The proportion of wax esters was high ranging from 76% of total lipid in C. glacialis to 92% in C. finmarchicus. The fatty acid composition of the alga was dominated by 16:1(n-7), 16:0, 20:5(n-3), and 22:6(n-3). The composition of the copepods was similar because of feeding already on diatoms in the field. In addition, the monounsaturated fatty acids and alcohols, 20:1(n-9) and 22:1(n-11), were major components of the copepod lipids. During the feeding period the highest ¹³C labelling was always found in the C₁₆ polyunsaturated fatty acids and in the 16:1(n-7) alcohol. Because these components occurred only in trace amounts in the copepods they totally originated from the diet explaining the high labelling. It is noteworthy that the 16:1(n-7) alcohol originated only from the corresponding dietary and not from the abundant internal fatty acid. The long-chain monounsaturated fatty acids and alcohols, 20:1(n-9) and 22:1(n-11), are not existent in phytoplankton and have to be produced de novo. They were less labelled in the smaller species but highly ¹³C enriched in C. hyperboreus. Although dietary fatty acids were generally retained by the copepods it seems that fatty acids or even lipids were selectively accumulated and turned over due to bodily requirements, and thus, essential polyunsaturated fatty acids were preferentially retained. During feeding mixing, accumulation, and exchange of internal and dietary fatty acids and alcohols occurred as well as utilisation of lipids from both sources for metabolic requirements. The differences in lipid assimilation fit to the different life strategies of the copepods.     

Ketone-body utilization and lipid synthesis by developing rat brain—a comparison between in vivo and in vitro experiments

The distribution of ketone bodies between oxidation and lipid synthesis was analysed in homogenates of developing rat brain. The capacity for lipid synthesis of homogenized or minced brain preparations was compared with rates of lipid synthesis in vivo, assessed by incorporation of ³H from ³H₂O into fatty acids and cholesterol. Brain homogenates of suckling rats (but not those of adults) incorporated label from [3-¹⁴C]ketone bodies into lipids, but this process was slow as compared to ¹⁴CO₂ production (< 5%) and much slower than the total rate of ketone-body utilization (< 0.5%). Study of ³H₂O incorporation demonstrated that the rates of lipogenesis and cholesterogenesis are at least one order of magnitude higher in vivo than in vitro. Maximal rates of ³H incorporation into fatty acids (3 μmol/g brain . h) and into cholesterol (0.6 μmol/g brain . h) were found during the third postnatal week. Adult rats still incorporated ³H into brain fatty acids at an appreciable rate (1 μmol/g brain . h), whereas cholesterogenesis was very low. It is concluded that in vitro measurements of lipid synthesis severely underestimate the rates that occur in developing rat brain in vivo. The high rate of ³H incorporation into lipids by developing and adult rat brain as compared to the amounts of these lipids present in the brain suggests an important contribution of endogenous lipid synthesis during brain development and an appreciable rate of fatty acid turnover during brain growth, but also in the adult brain.     

Percentage recovery of free fatty acids from bovine muscle lipids by nonchromatographic techniques

The inability of silicic acid to completely separate the neutral lipids from phospholipids has been reported by several investigators (1,2). Hornstein et al. (3) increased the polarity of the solvent system and reported a clean separation of the phospholipid fraction by adsorption on activated silicic acid. Studies on bovine lipids by Hood and Allen (2) utilized acid-washed Florisil to separate the lipid fractions claiming that silicic acid incompletely separates the free fatty acids from the phospholipids. Work performed in this laboratory (4) on bovine lipids confirmed that phospholipids could be effectively separated from free fatty acids by adsorption on silicic acid by incorporating the solvent system described by Hornstein et al. (3). The liquid-liquid partition procedure of Hamilton and McDonald (5) was also found to be sensitive enough to partition the extremely small amount of free fatty acids from the esterified fatty acids. This paper provides evidence for the effectiveness of these methods in separating the frec fatty acids by incorporating an internal standard [1-¹⁴C]palmitic acid.     

Relationships of leaf Fatty acids to cold hardening of citrus seedlings

Three cultivars of citrus with different sensitivities to freezing temperatures (citron, Citrus medica L.; rough lemon, C. limon Burm. F; sour orange, C. aurantium L.) were cold hardened for 4 weeks. Lipids from leaves of hardened and control seedlings were fractionated and analyzed for fatty acids. The absolute amount of triglycerides and phospholipids increased in the leaves upon hardening. With hardening, total linoleic acid also increased 141% in citron, 210% in rough lemon, and 233% in sour orange. Specific increases in linoleic acid were found in triglycerides, in the four phospholipids (phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylglycerol), and in neutral lipids more polar than triglycerides. Trans-3-hexadecenoic acid was found only in phosphatidylglycerol.     

Incorporation of 2-14C-acetate into isolated nuclei and cytosolic lipids of rat thymus cells

It is generally recognized nowadays that active lipid metabolism takes place in the nucleus of a mammalian cell. Experimental data testify to the biosynthesis of polyphosphoinositides and phosphatidylcholine and reveal corresponding enzymes within nuclei of mammalian cells. These findings suggest that lipidmediated signaling pathways in nuclei operate independently of lipid-mediated regulatory mechanisms functioning in membranes and cytosol. To explore the pathways of intranuclear lipid biosynthesis, we studied incorporation of 2-¹⁴C-acetate into lipids of cytosol and isolated nuclei of rat thymus cells after separate and combined incubation with the labeled precursor. The most efficient incorporation of 2-¹⁴C-acetate into lipids (cholesterol, free fatty acids, and phospholipids) was observed in a reaction mixture containing cytosol. When the reaction mixture contained only nuclei, incorporation of the radioactive precursor into lipids also took place, but specific radioactivity of the lipids was essentially lower than in the cytosol. In both cases, 2-¹⁴C-acetate incorporated into phosphatidylethanolamine, sphingomyelin, phosphatidylserine, phosphatidylinositol, and cardiolipin. Phosphatidylcholine, the most abundant membrane phospholipid, demonstrated the lowest radioactivity, which was significantly lower than that of phosphatidylethanolamine. Incorporation of newly synthesized free fatty acids in nuclear phospholipids was inhibited, if nuclei were incubated with cytosol. As a result, radioactive free fatty acids were accumulated in nuclei, while in cytosol they were efficiently incorporated into phospholipids. The levels of phospholipids and cholesterol remained constant regardless of incubation protocol, while the overall yield of free fatty acids decreased after combined incubation of nuclear and cytosolic fractions or after incubation of cytosol without nuclei. Putative mechanisms underlying the appearance of radioactive lipids in isolated nuclei of thymus cells are discussed.     

Effects of hardening and freezing stress on membrane lipids and CO2 fixation of Ceratodon purpureus protonemata

Membrane lipids and steady-state CO₂ fixation rates were studied in moss protonemata in order to evaluate separately the effects of growth temperature, freezing stress and the achievement of frost hardiness. Protonemata of Ceratodon purpureus (Hedw.) Brid, were grown at 20 and 4°C and parts of both materials were then hardened. The low growth temperature increased the content and unsaturation level of membrane lipids significantly. This did not, however, cause a noticeable increase in the frost hardiness. Nor was the achievement of frost hardiness in this material accompanied by further changes in the amount or unsaturtion level of any membrane lipid class. Cytoplasmic membranes were abundant in both unhardened and hardened materials grown at 4°C, which agreed with the high phospholipid content of these protonemata. The only significant difference in membrane lipids between unhardened and hardened materials was a 50% lower level of trans 16:1 fatty acid in the phosphatidylglycerol fraction of hardened protonemata.
In hardened protonemata monogalactosyldiacylglycerol (MGDG) was the membrane lipid most liable to decrease during the freeze-thaw cycle. The loss of MGDG was accompanied by partial inhibition of CO₂ fixation. Provided the content of phospholipids remained unchanged (freeze-thaw cycle with – 10°C in hardened protonemata), this inhibition was mostly reversible. If loss of the phospholipids also had occurred during the freeze-thaw cycle, as was the case in unhardened material at or below -10°C, CO₂ fixation was severely and nearly irreversibly inhibited after thawing.     

Changes in fatty acid composition of lipids in chloroplast membranes of tobacco plants during cold hardening

Changes in fatty acid composition of chloroplast membrane lipids were investigated using tobacco (Nicotiana tabacum L., cv. Samsun) plants subjected to cold hardening for 6 days at 8°C. Under optimal growing temperature (22°C), the lipids of thylakoid membranes were characterized by elevated content of 16:3n-3 and 18:3n-3 fatty acids (FA). Compared to the lipids of chloroplast envelope membranes, the thylakoid lipids were less rich in the content of saturated, mono- and diunsaturated FA. The relative content of unsaturated FA in chloroplast membranes increased substantially during cold hardening, which was mainly due to the accumulation of 18:3n-3 FA. It is concluded that the observed changes in FA composition of chloroplast lipids during cold hardening adjust the fluidity of these membranes to the level sufficient for functioning of tobacco photosynthetic apparatus, which is a prerequisite for accumulation of assimilates and allows the hardened tobacco plants to survive under conditions of hypothermia.     

Intracellular resistance correlates with initial stage of frost hardening in willow (Salix viminalis)

Distributed model parameters of shoots of five clones of willow ( Salix viminalis ) were examined with electrical impedance analysis at the end of the growing season and with cold acclimation. The parameters were compared with regard to frost hardiness, linoleic (18:2) and linolenic (18:3) fatty acids, unsaturation/saturation ratio of fatty acids and dry weight content. The intracellular resistance (r_i) correlated best with changes in frost hardiness. The value of r_i rose from 1–2 Ω m in non-hardened to about 12 Ω m in hardened samples. In the initial stages of frost hardening, a linear relationship was found between r_i and frost hardiness and levels of 18:2 fatty acid, and an inverse relationship between r_i and levels of 18:3 fatty acid. The unsaturation/saturation ratio of fatty acids rose fairly rapidly in the initial stage of hardening. The dry weight content increased stepwise during the experimental period, and less steadily than r_i. In addition, equivalent circuit parameters changed in the prehardening phase, and were probably connected with cell differentiation and lignification. Frost hardiness by the visual method and by extracellular resistance, determined after controlled freezing tests, correlated well in the initial stages of hardening until about − 10°C but deviated upon further hardening.     

Composition and positional distribution of fatty acids in polar lipids from Chlorella ellipsoidea differing in chilling susceptibility and frost hardiness

The composition and positional distribution of fatty acids in the polar lipids from 4 strains of Chlorella differing in chilling susceptibility and frost hardiness were analyzed by enzymatic hydrolysis and gas-liquid chromatography. Analysis of the polar lipids from chilling-sensitive, chilling-resistant and chilling-sensitive revertant strains of Chlorella ellipsoidea IAM C-102 showed that the sum of palmitic and trans -3-hexadecenoic acid in phosphatidylglycerol (PG) is about 60% for the sensitive strains and 53% for the resistant strain. The sum of dipalmitoyl and 1-palmitoyl-2-( trans -3-hexadecenoyl) PG as estimated from the positional distribution of their fatty acids, is about 10% in the case of each of the three strains. The contents of unsaturated fatty acids in phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were higher in the resistant than in the sensitive strain. This suggests that unsaturation of fatty acids in not only PG but also PC and PE is involved in chilling sensitivity of Chlorella . On the other hand, lipid changes during the development of frost hardiness of C. ellipsoidea IAM C-27, a frost hardy strain, were examined. The results showed that fatty acids in most lipid classes are unsaturated in the hardening process but their degree of unsaturation is not greatly different from that of the chilling-resistant strain, suggesting that not only unsaturation of fatty acids in lipids but also other factors are necessary for the development of frost hardiness.     

Lipids,amino acids,sugars, hardiness and growth of Festuca arundinacea

Tall fescue (Festuca arundinacea Schreb. cv S.170) plants were grown in environments differing only in temperature: 6/4, 16/14 or 21/19°. The content of total and individual sugars and amino acids in leaf laminae and roots did not relate closely to the hardiness of the organ. The unsaturation of lipid fatty acids alone was clearly unrelated to hardiness because the difference in unsaturation was greater in the neutral lipids, glycolipids and phospholipids from roots than from leaves but only the latter differed in hardiness. Total amounts of lipids could have been related to hardiness but phospholipids and glycolipids in the roots were not. At least some of these changes may be related to adaptation of growth to temperature.     

Plasmodium lophurae: Quantitative in vitro incorporation of 14C-1-acetate into lipids

Blood from ducks parasitized with Plasmodium lophurae and normal duck blood were incubated with sodium ¹⁴C-1-acetate. After release of the parasites from infected red blood cells (RBC) and concurrent treatment of normal blood, lipids were extracted from cellular material and plasma and lipid classes separated by thin-layer chromatography. Specific activity (dpm/mg lipid) of lipid classes was measured quantitatively by liquid scintillation radioassay and gravimetric analysis. The data indicated that the parasite within the RBC incorporated ¹⁴C-labeled lipid precursors.Experiments employing sodium ¹⁴C-1-acetate in two concentrations, 50 μCi ¹⁴C in 0.91 μmole sodium acetate/50 ml blood and 500 μCi ¹⁴C in 9.1 μmole sodium acetate/50 ml blood (1.82 × 10^?5M and 1.82 × 10^?4M), showed higher ¹⁴C incorporation into parasitized blood than normal blood preparations at the higher substrate concentration at 5 hr of incubation. At $\text{1.82 × 10}{}^{\mathrm{?5}}\text{M}{}^{14}$C-1-acetate, the highest specific activity in P. lophurae was associated with lipid alcohols. Monoglycerides and diglycerides were significantly labeled. At the higher acetate concentration (1.82 × 10^?4M), monoglyceride and diglyceride lipid classes had the highest specific activity in preparations of partially purified P. lophurae.Lipids of plasma from parasitized blood incubated for 5 hr with both concentrations of labeled acetate exhibited the highest specific activity in the free fatty acid class and sterols.At 24 hr of incubation, the lipids of partially purified P. lophurae had increased specific activity in free fatty acids, diglycerides, monoglycerides, phospholipids, and triglycerides.In plasma from parasitized blood incubated 24 hr with ¹⁴C-1-acetate, the highest specific activity and greatest percent of ¹⁴C incorporation was found in free fatty acids.     

Photosynthesis of Lipids from CO(2) in Spinacia oleracea

Young expanding spinach leaves exposed to ¹⁴CO₂ under physiological conditions for up to 20 minutes assimilated CO₂ into lipids at a mean rate of 7.6 micromoles per milligram chlorophyll per hour following a lag period of 5 minutes. Label entered into all parts of the lipid molecule and only 28% of the ¹⁴C fixed into lipids was found in the fatty acid moieties, i.e. fatty acids were synthesized from CO₂in vivo at a mean rate of 2.1 micromoles per milligram chlorophyll per hour. Intact spinach chloroplasts isolated from these leaves incorporated H¹⁴CO₃ into fatty acids at a maximal rate of 0.6 micromole per milligram chlorophyll per hour, but were unable to synthesize either the polar moieties of their lipids or polyunsaturated fatty acids. Since isolated chloroplasts will only synthesize fatty acids at rates similar to the one obtained with intact leaves in vivo if acetate is used as a precursor, it is suggested that acetate derived from leaf mitochondria is the physiological fatty acid precursor.     

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.     

Differential lipid and fatty acid profiles of photoautotrophic and heterotrophic Chlorella zofingiensis: Assessment of algal oils for biodiesel production

The objective of this study was to document and compare the lipid class and fatty acid composition of the green microalga Chlorella zofingiensis cultivated under photoautotrophic and heterotrophic conditions. Compared with photoautotrophic cells, a 900% increase in lipid yield was achieved in heterotrophic cells fed with 30 g L⁻¹ of glucose. Furthermore heterotrophic cells accumulated predominantly neutral lipids (NL) that accounted for 79.5% of total lipids with 88.7% being triacylglycerol (TAG); whereas photoautotrophic cells contained mainly the membrane lipids glycolipids (GL) and phospholipids (PL). Together with the much higher content of oleic acid (C18:1) (35.2% of total fatty acids), oils from heterotrophic C. zofingiensis appear to be more feasible for biodiesel production. Our study highlights the possibility of using heterotrophic algae for producing high quality biodiesel.     

Free and Bound Gibberellin Activities and Ent-kaurene Synthesis during Induction of Cold Hardiness in Black Locust Seedlings

The role of gibberellin in the development of cold hardiness in black locust (Robinia pseudoacacia L.) seedlings was investigated. Free and bound gibberellin activities were followed during induction of cold hardiness using ethyl acetate partitioning and pH variation, with subsequent paper chromatographic fractionation and gibberellin bioassay. While total gibberellin activity decreased during the induction of cold hardiness in black locust seedlings, no convincing evidence was found to support conversion of free gibberellin to a bound form. However, bound gibberellin activity did appear to be more stable than did free gibberellin activity during the final stages of cold hardening at freezing temperatures. Gibberellin synthesis was followed using ¹⁴C-mevalonate conversion to ent-kaurene in a cell-free extract of the tissue. Ent-kaurene synthesis decreased during cold hardening with no detectable synthesis in fully hardened seedlings. However, since growth cessation precedes development of cold hardiness, decreased gibberellin synthesis and corresponding trends in free and bound fractions might have been expected, and a cause and effect relationship is difficult to establish. Even so, a decline in one step in gibberellin synthesis and a greater stability of bound than free gibberelin activity are associated with induction of cold hardiness in black locust seedlings.     

A COMPARATIVE STUDY OF THE METABOLISM OF DE NOVO SYNTHESIZED FATTY ACIDS FROM ACETATE AND GLUCOSE, AND EXOGENOUS FATTY ACIDS, IN SLICES OF RABBIT CEREBRAL CORTEX DURING DEVELOPMENT

Slices of rabbit cerebral cortex, from the foetal stage to the adult have been used to compare lipid synthesis from fatty acids synthesized de novo from [U-¹⁴C]glucose and [1-¹⁴C]acetate, with lipid synthesis from exogenous albumin-bound [1-¹⁴C]palmitate. Incorporation into cellular lipid has been determined in terms of DNA, protein, wet wt. of tissue and wet weight of whole brain. On a wet wt. basis, maximum incorporation of glucose carbon into lipid occurred in the foetal brain while lipid synthesis from acetate and palmitate was maximum at 4–14 days after birth. Glucose and acetate were incorporated into a diversity of lipids (with increasing amounts of phosphatidylcholine synthesized during maturation), while palmitate was incorporated into the free fatty acid and triglyceride fractions. A greater proportion of acetate was incorporated into fatty acids of chain-length longer than C16 compared with the incorporation of palmitate. However, on a molar basis de novo synthesized and exogenous palmitate were elongated, desaturated and incorporated into phospholipids at a similar rate, while exogenous palmitate was incorporated to a greater extent than de nova synthesized fatty acid into the triglyceride fraction. This difference in metabolism may be due to the different size of the non-esterified fatty acid pool in the two situations. At the period of their most active formation, the very long-chain fatty acids may be synthesized from a pool of the C18 series of fatty acids (saturated and monoenoic) not in equilibrium with the bulk of C₁₈ acids in cerebral lipids. This could be a pool of acyl groups derived from ethanolamine phospholipids.