Galactolipid Synthesis in Vicia faba Leaves: IV. Site(s) of Fatty Acid Incorporation into the Major Glycerolipids

The fatty acids of the major glycerolipids of Vicia faba leaves were analyzed immediately following ¹⁴CO₂ feeding. The leaves were fractionated into chloroplast and cytoplasmic fractions and the location of radioactivity in the fatty acids determined. The results indicate that the major site of incorporation of fatty acids is in the phospholipids. Phosphatidylcholine contained the highest level of radioactivity in the cytoplasmic fraction, whereas phosphatidylglycerol contained radioactivity in both the chloroplast and cytoplasmic fractions. The galactolipids contained very little radioactivity in comparison, this radioactivity being confined to high speed centrifugal fractions believed to contain the envelopes of the chloroplast. Our results suggest that phosphatidylcholine is a major site of incorporation of fatty acids (mainly in oleic acid) in the cytoplasm, whereas phosphatidylglycerol is also a site of incorporation involving both oleic and palmitic acids, inside and outside the chloroplast.     

The attractiveness of odorous esterified fatty acids to the potential biocontrol agent,Altica cyanea

The fatty acid composition of foliar buds, young, mature, and senescent leaves, and stem parts of the rice-field weed, Ludwigia adscendens L. (Onagraceae) was analyzed by thin layer chromatography and gas chromatography flame ionization detection. The analysis of fatty acid composition revealed that saturated fatty acids (i.e., C14:0, C16:0, and C18:0) were prevailing compounds among the all weed parts except senescent leaves where C18:1 was predominant. The esterified fatty acids isolated from different weed parts over the range of 10–100 μg/ml followed by individual synthetic esterified fatty acids that were identified from the esterified extracts of different weed parts, and a mixture of synthetic esterified fatty acids except esterified eicosenoic acid and docosahexaenoic acid were applied to identify their role as a chemical cue for a potential biocontrol agent, Altica cyanea (Weber) (Coleoptera: Chrysomelidae) in a Y-tube olfactometer under laboratory conditions. In this bioassay, the esterified fatty acids from mature leaves and stem parts of this weed attracted A. cyanea at 20–100 μg/ml and at 80 μg/ml concentrations, respectively. Clear attraction was recorded by female A. cyanea insects in the mixture of synthetic esterified fatty acids at 60, 80, and 100 μg/ml concentrations. It is thus concluded that A. cyanea rely on an effective proportion of esterified fatty acids as an olfactory cue for attraction.     

Desaturation of Fatty acids associated with monogalactosyl diacylglycerol: the effects of san 6706 and san 9785

The effects of two substituted pyridazinone herbicides, San 6706 and San 9785, on photosynthesis, dark respiration, and fatty acid metabolism were studied in mature leaf tissue of Vicia faba.     

Turnover of Fatty Acids during Natural Senescence of Arabidopsis, Brachypodium, and Switchgrass and in Arabidopsis β-Oxidation Mutants

During leaf senescence, macromolecule breakdown occurs and nutrients are translocated to support growth of new vegetative tissues, seeds, or other storage organs. In this study, we determined the fatty acid levels and profiles in Arabidopsis (Arabidopsis thaliana), Brachypodium distachyon, and switchgrass (Panicum virgatum) leaves during natural senescence. In young leaves, fatty acids represent 4% to 5% of dry weight and approximately 10% of the chemical energy content of the leaf tissues. In all three species, fatty acid levels in leaves began to decline at the onset of leaf senescence and progressively decreased as senescence advanced, resulting in a greater than 80% decline in fatty acids on a dry weight basis. During senescence, Arabidopsis leaves lost 1.6% of fatty acids per day at a rate of 2.1 μg per leaf (0.6 μg mg⁻¹ dry weight). Triacylglycerol levels remained less than 1% of total lipids at all stages. In contrast to glycerolipids, aliphatic surface waxes of Arabidopsis leaves were much more stable, showing only minor reduction during senescence. We also examined three Arabidopsis mutants, acx1acx2, lacs6lacs7, and kat2, which are blocked in enzyme activities of β-oxidation and are defective in lipid mobilization during seed germination. In each case, no major differences in the fatty acid contents of leaves were observed between these mutants and the wild type, indicating that several mutations in β-oxidation that cause reduced breakdown of reserve oil in seeds do not substantially reduce the degradation of fatty acids during leaf senescence.     

Galactolipid Synthesis in Vicia faba Leaves: II. Formation and Desaturation of Long Chain Fatty Acids in Phosphatidylcholine, Phosphatidylglycerol, and the Galactolipids

The labeling kinetics of the fatty acids of phosphatidylcholine (PC), phosphatidylglycerol (PG), monogalactosyldiglyceride (MGDG), and digalactosyldiglyceride (DGDG) were examined after ¹⁴CO₂ feeding and incubation of leaf discs of Vicia faba over 72 hours in continuous light. The results indicate a rapid accumulation and turnover of radioactivity into PC and PG fatty acids (oleic acid in PC and oleic and palmitic acids in PG). Radioactivity accumulates in MGDG and DGDG fatty acids much more slowly and continuously over 72 hours. Most of this activity is found in linoleic and linolenic acids; very little activity is found in the more saturated fatty acids. Little or no desaturation occurs in situ in conjunction with the galactolipids. The results suggest that PC and PG may act as “carriers” for MGDG and DGDG fatty acid synthesis. Analyses of the labeling patterns of the molecular species of MGDG after ¹⁴CO₂ and ¹⁴C-acetate feeding confirm that MGDG is formed by galactosylation of a preformed diglyceride containing predominantly unsaturated fatty acids.     

Lipid Mixtures Containing a Very High Proportion of Saturated Fatty Acids Only Modestly Impair Insulin Signaling in Cultured Muscle Cells

In vitro examinations of the effect of saturated fatty acids on skeletal muscle insulin action often use only one or two different fatty acid species, which does not resemble the human plasma fatty acid profile. We compared graded concentrations (0.1-0.8mM) of 3 different lipid mixtures: 1) a physiologic fatty acid mixture (NORM; 40% saturated fatty acids), 2) a physiologic mixture high in saturated fatty acids (HSFA; 60% saturated fatty acids), and 3) 100% palmitate (PALM) on insulin signaling and fatty acid partitioning into triacylglycerol (TAG) and diacylglycerol (DAG) in cultured muscle cells. As expected, PALM readily impaired insulin-stimulated pAkt^Thr308/Akt and markedly increased intracellular DAG content. In contrast, the fatty acid mixtures only modestly impaired insulin-stimulated pAkt^Thr308M/Akt, and we found no differences between NORM and HSFA. Importantly, NORM and HSFA did not increase DAG content, but instead dose-dependently increased TAG accumulation. Therefore, the robust impairment in insulin signaling found with palmitate exposure was attenuated with physiologic mixtures of fatty acids, even with a very high proportion of saturated fatty acids. This may be explained in part by selective partitioning of fatty acids into neutral lipid (i.e., TAG) when muscle cells were exposed to physiologic lipid mixtures.     

Fatty acid concentration of plasma,muscle, adipose and liver from beef heifers fed an encapsulated n-3 polyunsaturated fatty acid supplement

Increasing the content of polyunsaturated fat in the human diet is a priority for reducing cardiovascular disease and cancer risks. Beef has the potential to contribute to the polyunsaturated fat content in the human diet; however, ruminants cannot synthesise many long-chain fatty acids de novo; they require dietary supplementation. The objectives of the current study were to evaluate (i) the effect of a partially rumen protected n-3 long-chain polyunsaturated fatty acid (LC-PUFA) dietary supplement on the fatty acid composition of muscle (Longissimus dorsi), adipose and liver tissues of beef heifers and (ii) the usefulness of blood plasma as a predictor of tissue concentrations of specific fatty acids. Charolais crossbred heifers (n = 20) were assigned to one of two isolipid dietary treatments namely palmitic acid (control) or an n-3 LC-PUFA supplement for a 91-day period. Blood plasma and adipose tissue samples were taken to determine the temporal effect of these diets on fatty acid composition (days 0, 10, 35 and 91), while liver and muscle samples were taken following slaughter. Dietary lipid source did not influence animal growth rate or body condition score. At day 91, the percentage differences between control and n-3 LC-PUFA heifers in concentrations of eicosapentaenoic acid were +61, +176 and +133 % in liver, muscle and adipose, respectively. For docosahexaenoic acid, at the same time point, the percentage differences were +57, +73 and +138 % for liver, muscle and adipose, respectively. Medium-to-strong positive correlation coefficients were evident for liver and plasma fatty acids, in particular, there were positive relationships with concentrations of total saturated fatty acid (SFA), total n-6 PUFA and total n-3 PUFA. This trend also extended to both the ratio of PUFA to SFA (slope (β₁) = 0.56 ± 0.167, intercept (β₀) = 0.56, R² = 0.61, P < 0.05) and the ratio of n-6 to n-3 PUFA (β₁ = 0.15 ± 0.054, β₀ = 0.24, R² = 0.52, P < 0.05). A strong correlation was also detected in the ratio of n-6 to n-3 in plasma and muscle tissue of heifers fed the n-3 LC-PUFA diet (β₁ = 0.53 ± 0.089, β₀ = −0.31, R² = 0.83, P < 0.001). The results of this study show that the n-3 LC-PUFA can be readily increased through targeted supplementation and that plasma concentrations of n-3 LC-PUFA are useful predictors of their concentrations in a number of economically important tissues.     

The ectomycorrhizal fungus (Paxillus involutus) modulates leaf physiology of poplar towards improved salt tolerance

Ectomycorrhizas (EMs) are mutualistic associations between soil fungi and plant roots. Although the physical interaction occurs only in roots, mycorrhizas may alter the physiology of the whole plant, resulting in changes in host responses to abiotic stress. To elucidate the influence of an ectomycorrhizal fungus on leaf physiology and performance under salt stress, we analysed the levels of nutrient elements, phytohormones, carbohydrates, amino compounds and fatty acids in leaves of Populus × canescens. The poplars were cultivated either in the presence or absence of Paxillus involutus and either with or without salt stress imposed by 150 mM NaCl. Leaves of ectomycorrhizal plants displayed higher quantum yield of photochemistry (Φ_PSII), increased concentrations of phosphorus and potassium, decreased concentrations of galactose, increased concentrations of the stress metabolite γ-amino butyric acid and a lower unsaturated-to-saturated fatty acid ratios than those of non-ectomycorrhizal plants. Salt exposure of P. × canescens led to leaf chlorosis and shedding, decreases in Φ_PSII, K⁺-to-Na⁺ ratio, 9Z-hexadecenoic acid, 9Z-octadecenoic acid and unsaturated-to-saturated fatty acid ratio, and increases in ABA, glucose, fructose and some amino compounds. Under salinity leaves of ectomycorrhizal plants showed an alleviation of leaf chlorosis, improved water status, higher Φ_PSII and K⁺-to-Na⁺ ratio, less accumulation of major amino compounds and lower unsaturated-to-saturated fatty acid ratios than those of non-mycorrhizal plants. These results indicate that ectomycorrhizas attenuate salinity induced injury in leaves of P. × canescens, which may be ascribed to the improved nutrient status, osmo-regulation and changes in fatty acid composition in leaves of ectomycorrhizal plants.     

Light,temperature and nitrogen starvation effects on the total lipid and fatty acid content and composition ofSpirulina platensis UTEX 1928

The total lipid and fatty acid content ofSpirulina platensis UTEX 1928 was 7.2 and 2.2% respectively of cellular dry weight under controlled conditions supporting high growth rates. With increases in irradiance from 170 to 870 μmol photon m^?2 s^?1, growth rate increased, total lipid decreased, and fatty acid composition was unaffected. At 1411 μmol photon m^?2 s^?1, total lipid increased slightly and percent composition of the fatty acid gamma linolenic acid increased. Growth and total lipid content ofS. platensis were affected by changes in growth temperature from 25 to 38 °C. With increased growth rate, total lipid content increased. This suggests that the storage of carbon increases at temperatures supporting high growth rates. The degree of saturation increased with temperature. Although the percent composition of gamma linolenic acid was higher at lower growth temperature, production was still primarily a function of growth rate. The effect of temperature on fatty acid content and degree of saturation was of secondary importance. Nitrogen starvation increased total lipid content but decreased fatty acid content as a percentage of dry weight; composition of the fatty acids was unaffected. N-starvation appeared to suspend synthesis of long chain fatty acids inS. platensis, suggesting that some other compound stores fixed carbon when nitrogen is limiting. It was concluded that fatty acid production inS. platensis is maximized by optimizing culture conditions for growth.     

Free Sugars and Organic Acids in the Leaves of Various Plant Species and their Compartmentation Between the Tissues4

The distribution of free sugars and organic acids between theepidermis and mesophyll of Tulipa gesneriana L., Vicia fabaL., and Commelina communis L. leaves was studied using mainlygas-liquid chromatography. Fructose, glucose, sucrose, and myo-inositol were found in theepidermis and mesophyll of all three species. In T. geenerianaleaf tissues arabinose (trace levels), stachyose, tuliposidesA and B (mainly in the mesophyll), and xylose (trace levelsalso in V. faba tissues) were also detected. The acids were more difficult to detect and identify, beingat considerably lower concentrations than the sugars in bothtissues. Fumaric, citric, malic, ascorbic (trace levels), andan unidentified acid were common to the epidermis and mesophyllof all three species. Of special interest was the detectionof large amounts of glyceric acid in the epidermis and mesophyllof V. faba; this acid was not detected in the tissues from theother species. Fumaric acid was also very abundant in the epidermisof V.faba. A special study was made of the compartmentation of acids andsugars between the epidermis and mesophyll of T. geenerianaleaves after light and dark treatments. No changes in free acidor sugar levels were detected in the epidermis or mesophyllafter these treatments. Except for suceinic acid (P < 0·05),there were no statistically significant differences in acidlevels between the epidermis and mesophyll but for most of thesugars (myo-inositol, arabinose, and xylose being exceptions)differences were highly significant (P < 0·001), highestlevels occurring in the mesophyll. The differences in sugarlevels and the similarity in acid levels between epidermis andmesophyll of tulip leaves were considered to be essentiallydue to the different CO₂ fixing mechanisms and capacities ofthe two tissues. The energy source for the essentially non-greenepidermal tissue was discussed.     

Red cabbage extract limits copper stress injury in meristematic cells of <Emphasis Type="Italic">Vicia faba</Emphasis>

Natural phenolic compounds (phenolic acids, flavonoids, tannins, lignans) present in food of plant origin are in the focus of interest due to their prevalence, properties and biological activity. The aim of the presented work was to investigate antioxidant and antigenotoxic effects of the anthocyanin-rich extract from red cabbage leaves (Brassica oleracea rubrum) on the changes induced by toxic Cu²⁺ concentrations. MeOH extract from red cabbage containing anthocyanin (ATH) and phenolic acid derivatives exhibited strong antioxidant properties. Cu²⁺ decreased mitotic index (MI) and inhibited proliferative activity of Vicia faba root meristematic cells. The morphology of mitotic chromosomes was changed; “erosion” and pulverization might result from Cu²⁺ high-cytotoxicity. Numerous micronuclei, chromatid bridges and lagging/lost chromosomes were found in the meristematic cells of V. faba, which indicate the clastogenic effect of Cu²⁺. The application of the ATH-rich extract lowered the number of disturbances induced by Cu²⁺. The positive role of the ATH-rich red cabbage extract will be discussed.     

Levels of short-chain fatty acids and of abscisic acid in water-stressed and non-stressed leaves and their effects on stomata in epidermal strips and excised leaves

Straight-chain saturated fatty acids (C6-C11) and abscisic acid (ABA) accumulate in the leaves of Phaseolus vulgaris L. and Hordeum vulgare L. under water stress. ABA and certain of the fatty acids, particularly decanoic and undecanoic acid, can inhibit stomatal opening and cause stomatal closure in epidermal strips of Commelina communis L. depending on the incubating medium used. 10^-4 M (±)-ABA inhibits opening in media containing either high or relatively low concentrations of KCl but causes closure only in the latter medium. The fatty acids (at 10^-4 M) prevent opening in both media while significant closure of open stomata was caused only by undecanoic acid in both media and, additionally, by decanoic acid in the low-KCl medium. 10^-4 M formic acid also caused stomatal closure and prevented opening to significant extents in the low-KCl medium (it was not tested in the high-KCl medium). The efficacy of undecanoic acid in causing 50% inhibition of opening is about three orders of magnitude lower than that of ABA. At a concentration of 10^-3 M, nonanoic, decanoic and particularly undecanoic acid and all-trans-farnesol cause increased cell leakage in Beta vulgaris L. root tissue. Undecanoic acid (10^-4 M) also causes some loss of guard cell integrity in C. communis within 1.5 h of treatment. ABA (10^-4 M) reduces transpiration rates in barley and C. communis leaves when applied via the transpiration stream but decanoic and undecanoic acids did not have this effect. Transpiration was not affected when ABA or the fatty acids were applied to the leaf surfaces.Abbreviations ABA abscisic acid - RWC relative water content - SCFA short-chain fatty acids Deceased May 1977     

The effects of pro- and anti-atherosclerotic factors on intracellular nucleotide concentration in murine endothelial cells

Abstract

Endothelial cell activation and dysfunction could lead to endothelial injury that is an important factor in the development of vascular diseases. Vascular injury is strongly associated with disturbed endothelial cell energetics and pyridine nucleotide pool. This study aimed to evaluate the effects of inflammatory stimuli (IL-6, LPS), uric acid, hyperglycemia, fatty acids, flavonoids, statins and nonsteroidal anti-inflammatory drugs on cellular concentration of adenosine triphosphate (ATP), adenosine diphosphate (ADP) and nicotinamide adenine dinucleotide (NAD⁺) in cultured endothelial cells. Murine-immortalized heart endothelial cells (H5V cells) were treated with different concentrations of pro- and anti-atherosclerotic factors and intracellular concentration of nucleotides were measured using high performance liquid chromatography. Intracellular ATP concentration in H5V cells was not changed by inflammatory stimuli (IL-6 and LPS), uric acid, glucose, atorvastatin, acetylsalicylic acid, monounsaturated and polyunsaturated fatty acids. Only high concentration of palmitic acid (1?mM) and kaempferol (>0.1?mM) decreased intracellular ATP concentration. The concentration of intracellular ADP has not been altered by any of tested compounds. In turn, intracellular NAD⁺ pool was modified only by polyunsaturated fatty acids and atorvastatin. Linoleic acid, docosahexaenoic acid and atorvastatin increased cellular NAD⁺ concentration. Tested compounds have a small influence on murine endothelial cell energetics, but polyunsaturated fatty acids and atorvastatin increased intracellular NAD⁺ concentration that could be an important protective mechanism against endothelial cell injury.     

Variation of the legumin seed storage protein amongst Vicia species

Variation in legumin, the major seed storage protein of Vicia faba was investigated in different (primitive and cultivated) varieties of V. faba and in other primitive Vicia species. Qualitative variation in legumin subunit patterns on gel electrophoresis was less within the species V. faba than the variation between Vicia species. However, the large seeded modern V. faba cultivars showed much increased levels of the ‘main’ legumin subunit pairs. Analyses of amino acid composition, and nitrogen and sulphur content did not show systematic variation between the samples tested, and suggested that breeding and selection had not decreased protein content or nutritional quality. It was concluded that the heterogeneities of legumin genes in the Vicia species examined are comparable, and that selection for a large-seeded phenotype in V. faba has had the effect of increasing the expression of a subset of legumin genes, those encoding the ‘main’ subunit pairs.     

On the Specificity of a Fatty Acid Epoxygenase in Broad Bean (Vicia faba L.)

Seeds of broad bean (Vicia faba L.) contain a hydroperoxide-dependent fatty acid epoxygenase. Hydrogen peroxide served as an effective oxygen donor in the epoxygenase reaction. Fifteen unsaturated fatty acids were incubated with V. faba epoxygenase in the presence of hydrogen peroxide and the epoxy fatty acids produced were identified. Examination of the substrate specificity of the epoxygenase using a series of monounsaturated fatty acids demonstrated that (Z)-fatty acids were rapidly epoxidized into the corresponding cis-epoxy acids, whereas (E)-fatty acids were converted into their trans-epoxides at a very slow rate. In the series of (Z)-monoenoic acids, the double bond position as well as the chain length influenced the rate of epoxidation. The best substrates were found to be palmitoleic, oleic, and myristoleic acids. Steric analysis showed that most of the epoxy acids produced from monounsaturated fatty acids as well as from linoleic and α-linolenic acids had mainly the (R),(S) configuration. Exceptions were C₁₈ acids having the epoxide group located at C-12/13, in which cases the (S),(R) enantiomers dominated. 13(S)-Hydroxy-9(Z),11(E)-octadecadienoic acid incubated with epoxygenase afforded the epoxy alcohol 9(S),10(R)-epoxy-13(S)-hydroxy-11(E)-octadecenoic acid as the major product. Smaller amounts of the diastereomeric epoxy alcohol 9(R),10(S)-epoxy-13(S)-hydroxy-11(E)-octadecenoic acid as well as the α,β-epoxy alcohol 11(R),12(R)-epoxy-13(S)-hydroxy-9(Z)-octadecenoic acid were also obtained. The soluble fraction of homogenate of V. faba seeds contained an epoxide hydrolase activity that catalyzed the conversion of cis-9,10-epoxyoctadecanoic acid into threo-9,10-dihydroxyoctadecanoic acid.     

Reversal of Abscisic Acid-Induced Stomatal Closure by trans-Cinnamic and p-Coumaric Acid

Abscisic acid (ABA)-induced increase in stomatal diffusive resistance (SDR) in excised leaves of bean (Phaseolus vulgaris L. cv Pencil Pod) and maize (Zea mays L. cv Golden Bantam) is inhibited by low concentrations of trans-cinnamic acid (TCA) (1 micromolar) and p-coumaric acid (PCA) (10 micromolar) when given together with ABA (10 micromolar) in the transpiration stream through the cut end of the petiole or leaf blade. A concentration effect is observed both in the ABA action and its reversal by phenolic acids. Leaves having attained a high diffusive resistance in ABA solution recover rapidly when transferred to water. ABA (10 micromolar) induced closure of the stomata in onion, Allium cepa L. and Vicia faba epidermal peels. This is associated with loss of K⁺ from guard cells. In the presence of TCA (10 micromolar) and PCA (10 micromolar) K⁺ is retained in the guard cells with open stomata. The dark closure of stomata is also inhibited by TCA and PCA. It is suggested that these phenolic acids may inhibit the ABA effect by competing with or acting on some ABA-specific site, probably located on the plasma membrane, regulating flux of K⁺ ions. A weak association of ABA with the plasma membrane is envisaged because of the rapid recovery obtained upon transferral of the leaves to water.     

Optimization of biomass and fatty acid productivity of Scenedesmus obliquus as a promising microalga for biodiesel production

Nowadays, microalgae are discussed as a promising feedstock for biodiesel production. The present study examines the possibility of enhancement of fatty acid productivity of Scenedesmus obliquus by modifications of the culture medium composition. The effect of different concentrations of sodium bicarbonate, salinity, potassium nitrate, glycerol and sugarcane molasses on the enhancement of biomass and esterified fatty acids production was studied. NaHCO₃ caused an increase in the biomass productivity at low concentrations (0.5 g L^?1), while negatively affected fatty acid productivity at all tested concentrations. Increase of salinity enhanced both biomass and fatty acid productivity. The optimum NaCl concentration and sea water ratio were 0.94 g L^?1 and 25 % which resulted in 56 and 39 % increase in fatty acid productivity, respectively. Nitrogen deficiency showed increase in fatty acid content by 54 % over control but fatty acid productivity was decreased as a result of growth inhibition. Nitrogen-free cultures and cultures treated with ?50 % concentrations of KNO₃ showed 96 and 42 % decrease in EFA productivity, respectively, as compared with the control. Addition of 0.05 and 0.1 M of glycerol increased the biomass productivity by 6 and 5 %, respectively but showed no significant effect on fatty acid productivity as a result of decrease in fatty acid content. Finally, usage of sugarcane molasses stimulated both biomass and fatty acid content. The increase in fatty acid productivity was 32, 65 and 73 % above the control level at 1, 3 and 5 g L^?1 of sugarcane molasses, respectively.     

Abscisic Acid Accumulation by in Situ and Isolated Guard Cells of Pisum sativum L. and Vicia faba L. in Relation to Water Stress

Isolated guard cells, prepared by sonication of epidermal peels, were used to investigate the endogenous level of abscisic acid (ABA) in the guard cells of turgid and stressed leaves of Vicia faba L. and the argenteum (arg) mutant of Pisum sativum L. The guard cells of V. faba and arg were found to contain 18 and 8 times more ABA, respectively, when isolated from stressed leaves than from turgid leaves. Isolated guard cells of V. faba were also directly stressed with the osmoticum Aquacide III. These guard cells were capable of producing stress-induced ABA to at least 3 times their ABA level when non-stressed.     

Galactolipid Synthesis in Vicia faba Leaves: I. Galactose, Glycerol, and Fatty Acid Labeling after CO(2) Feeding

The galactose, glycerol, and fatty acids of mono- and digalactosyl diglycerides (MGDG and DGDG) have been separated and analyzed for ¹⁴C activity after ¹⁴CO₂ feeding of Vicia faba leaf discs. Fully expanded and developing leaves were analyzed at time intervals following feeding during continuous illumination. In addition, fully expanded leaves were analyzed after similar times in complete darkness. In all cases, ¹⁴C was incorporated very rapidly into galactose, whereas glycerol and fatty acids were labeled much more slowly and over a longer period of time. The data are consistent with the galactosylation of a diglyceride to MGDG which is in turn galactosylated to DGDG. The data suggest that the formation of diglycerides suitable for galactosylation to MGDG is slow in comparison to the galactosylation process. It is also suggested that DGDG may be formed from more than one pool of MGDG. The complete analysis of the ¹⁴C incorporation into galactose appears to represent the only satisfactory method of comparing galactolipid synthesis by ¹⁴C incorporation. Estimates of comparative rates of synthesis of MGDG and DGDG have been made on this basis.