Effect of Oxidized Arachidonic Acid and Hexanal on the Mouse Taste Perception of Bitterness and Umami

The oxidization of fatty acids generates many volatile compounds forming an aroma, but little is known whether mammals use gustatory sense to detect the oxidized products as a taste or only use olfactory sense to detect as an aroma. We examined in this study the effect of aqueous extracts of the compounds from autoxidized arachidonic acid (AA) ethyl ester or hexanal which is the predominant component generated from oxidized AA by the anosmic mouse licking performance to a tastant. The addition of the water extract from oxidized AA or hexanal to a quinine hydrochloride (QHCl) solution decreased the anosmic mice licking frequency at several concentrations of QHCl. Hexanal also reduced the licking frequency of anosmic mice conditioned to avoid MSG at several concentrations of monosodium glutamate (MSG). These results suggest that hexanal would affect mouse taste perception to QHCl and MSG via the gustatory sensation.     

The carbon and energy sources of the non-photosynthetic plastid in the malaria parasite

The malaria parasite harbours an indispensable plastid known as the ‘apicoplast’. The apicoplast’s exact role remains uncertain, but it houses components involved in fatty acid, isoprenoid and haem biosyntheses. These pathways offer opportunities to develop anti-malarials. In the absence of photosynthesis, how apicoplast anabolism is fuelled is unclear. Here we investigated plant-like transporters of the apicoplast and measured their substrate preferences using a novel cell-free assay system to explore the carbon and energy sources of the apicoplast. The transporters exchange triose phosphate and phosphoenolpyruvate for inorganic phosphate, demonstrating that the apicoplast taps into host-derived glucose to fuel its metabolism.     

DNA from pre-erythrocytic stage malaria parasites is detectable by PCR in the faeces and blood of hosts

Following the bite of an infective mosquito, malaria parasites first invade the liver where they develop and replicate for a number of days before being released into the bloodstream where they invade red blood cells and cause disease. The biology of the liver stages of malaria parasites is relatively poorly understood due to the inaccessibility of the parasites to sampling during this phase of their life cycle. Here we report the detection in blood and faecal samples of malaria parasite DNA throughout their development in the livers of mice and before the parasites begin their growth in the blood circulation. It is shown that parasite DNA derived from pre-erythrocytic stage parasites reaches the faeces via the bile. We then show that different primate malaria species can be detected by PCR in blood and faecal samples from naturally infected captive macaque monkeys. These results demonstrate that pre-erythrocytic parasites can be detected and quantified in experimentally infected animals. Furthermore, these results have important implications for both molecular epidemiology and phylogenetics of malaria parasites. In the former case, individuals who are malaria parasite negative by microscopy, but PCR positive for parasite DNA in their blood, are considered to be “sub-microscopic” blood stage parasite carriers. We now propose that PCR positivity is not necessarily an indicator of the presence of blood stage parasites, as the DNA could derive from pre-erythrocytic parasites. Similarly, in the case of molecular phylogenetics based on DNA sequences alone, we argue that DNA amplified from blood or faeces does not necessarily come from a parasite species that infects the red blood cells of that particular host.     

Trypanosoma cruzi: Comparative fatty acid metabolism of the epimastigotes and trypomastigotes in vitro

In vitro studies on the fatty acid metabolism of the epimastigotes and trypomastigotes of Trypanosoma cruzi showed the following: (1) Trypomastigotes demonstrated the ability to convert labeled palmitic acid to CO₂. Epimastigotes either did not convert this fatty acid to CO₂ or did so at a very low rate. (2) Trypomastigotes incorporated palmitic acid into neutral lipids, but, at a rate less than that of the epimastigotes. (3) While epimastigotes readily incorporated palmitic acid into phospholipid lipids, trypomastigote forms seemed to lack this ability.     

Metabolomic assays of the concentration and mass isotopomer distribution of gluconeogenic and citric acid cycle intermediates

We developed gas chromatography-mass spectrometry assays for the relative concentration and for the mass isotopomer distribution of gluconeogenic and citric acid cycle intermediates in tissues. The assay involves (i) spiking the sample with one or more internal standards, (ii) chloroform–methanol extraction at −25 °C, (iii) Folch wash of the extract, (iv) treatment of the water-methanol phase with methoxylamine, (v) evaporation and trimethylsilyl derivatization, and (vi) ammonia positive chemical ionization gas chromatography-mass spectrometry. For metabolomic computations, indices of concentrations for all compounds assayed are calculated as (Area of analyte)/(Area of reference compound). The assay was applied to a study of the effect of mercaptopicolinate, an inhibitor of phosphoenolpyruvate carboxykinase, on the profile of gluconeogenic intermediates in rat livers perfused with pyruvate. Crossover analysis of concentrations indices, compared to a control group, yielded very similar profiles as previous enzymatic assays, and correctly identified the site of action of mercaptopicolinate. Principal component analysis distinguished between control and drug treated samples. A loadings plot was used to identify the site of action of the drug in the metabolic pathway. Since metabolite concentrations do not address the flux through a pathway, perfusions with [1,4-¹³C₂] succinate dimethylester were conducted to assess fluxes around PEPCK. This allowed a dynamic metabolomics analysis which indicated that considerable flux through the pathway remained in the presence of mercaptopicolinate. This study illustrates the power of dynamic metabolomics to complement concentration based metabolomic studies.

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Salicylic acid mitigates salt induced toxicity through the modifications of biochemical attributes and some key antioxidants in capsicum annuum

Abiotic stress causes extensive loss to agricultural yield production worldwide. Salt stress is one of them crucial factor which leads to decreased the agricultural production through detrimental effect on growth and development of crops. In our study, we examined the effect of a defense growth substance, salicylic acid (SA 1 mM) on mature vegetative (60 Days after sowing) and flowering (80 DAS) stage of Pusa Sadabahar (PS) variety of Capsicum annuum L. plants gown under different concentrations of NaCl (25, 50, 75, 100 and 150 mM) and maintained in identical sets in pots during the whole experiment. Physiological studies indicated that increase in root & shoot length, fresh & dry weight, number of branches per plant, and yield (number of fruits per plant) under salt + SA treatment. Biochemical studies, enzymatic antioxidants like CAT, POX, and non-enzymatic antioxidant such as ascorbic acid (AsA content), carotenoids, phenolics, besides other defense compounds like proline, protein, chlorophyll contents were studied at 10 days after treatment at the mature vegetative and flowering stage. The addition of SA led to lowering of in general, all studied parameters in the mature vegetative stage but increased the same during the flowering stage, especially in the presence of NaCl; although the control I (without SA and NaCl) remained lower in value than control II (with SA, without NaCl). Interestingly, total phenolics were higher in control I (without SA or NaCl) whereas chlorophylls were higher in treatments with SA and NaCl. Thus, physiological concentration of SA (1 mM) appears to be significantly effective against salt stress during the flowering stage. In addition, during the mature vegetative stage, however, proline accumulates in SA treated sets, to help in developing NaCl-induced drought stress tolerance.     

Carbon and nitrogen dynamics in acid detergent fibre lignins of beech (Fagus sylvatica L.) during the growth phase

To study the incorporation of carbon and nitrogen in different plant fractions, 3‐year‐old‐beech (Fagus sylvatica L.) seedlings were exposed in microcosms to a dual‐labelling experiment employing ¹³C and ¹⁵N throughout one season. Leaves, stems, coarse and fine roots were harvested 6, 12 and 18 weeks after bud break (June to September) and used to isolate acid‐detergent fibre lignins (ADF lignin) for the determination of carbon and nitrogen and their isotope ratios. Lignin concentrations were also determined with the thioglycolic acid method. The highest lignin concentrations were found in fine roots. ADF lignins of all tissues analysed, especially those of leaves, also contained significant concentrations of nitrogen. This suggests that lignin‐bound proteins constitute an important cell wall fraction and shows that the ADF method is not suitable to determine genuine lignin. ADF lignin should be re‐named as ligno‐protein fraction. Whole‐leaf biomass was composed of 50 to 70% newly assimilated carbon and about 7% newly assimilated nitrogen; net changes in the isotope ratios were not observed during the experimental period. In the other tissues analysed, the fraction of new carbon and nitrogen was initially low and increased significantly during the time‐course of the experiment, whereas the total tissue concentrations of carbon remained almost unaffected and nitrogen declined. At the end of the experiment, the whole‐tissue biomass and ADF lignins of fine roots contained about 65 and 50% new carbon and about 50 and 40% new nitrogen, respectively. These results indicate that significant metabolic activity was related to the formation of structural biopolymers after leaf growth, especially below‐ground and that this activity also led to a substantial binding of nitrogen to structural compounds.     

Abscisic acid inhibits germination of mature Arabidopsis seeds by limiting the availability of energy and nutrients

The addition of abscisic acid (ABA) to mature non-dormant seeds inhibits their germination. This effect of ABA might be related to its natural function as an endogenous inhibitor of precocious germination during seed formation. In this work, we studied how ABA affects the germination of mature seeds and the growth of nascent seedlings of Arabidopsisthaliana (L.) Heynh. Our findings were as follows: (i) inhibition by ABA was gradual, dose-dependent, and did not disappear after germination; (ii) inhibition of germination was relieved by the addition of metabolizable sugars or amino acids to the plating media; (iii) the effect of sugars and amino acids was cooperative, indicating that these two groups of metabolites relieve different deficiencies; (iv) ABA caused appreciable alterations in energy and nitrogen metabolism; and (v) ABA prevented the degradation of the seed storage proteins. In summary, ABA appears to inhibit seed germination by restricting the availability of energy and metabolites. This mechanism seems consistent with other known effects of ABA. Received: 3 February 1997 / Accepted: 10 March 1997     

The effects of blood feeding and exogenous supply of tryptophan on the quantities of xanthurenic acid in the salivary glands of Anopheles stephensi (Diptera: Culicidae)

Xanthurenic acid (XA), produced as a byproduct during the biosynthesis of insect eye pigment (ommochromes), is a strong inducer of Plasmodium gametogenesis at very low concentrations. In previous studies, it was shown that XA is present in Anopheles stephensi (Diptera: Culicidae) mosquito salivary glands and that during blood feeding the mosquitoes ingested their own saliva into the midgut. Considering these two facts together, it is therefore likely that XA is discharged with saliva during blood feeding and is swallowed into the midgut where it exerts its effect on Plasmodium gametocytes. However, the quantities of XA in the salivary glands and midgut are unknown. In this study, we used high performance liquid chromatography with electrochemical detection to detect and quantify XA in the salivary glands and midgut. Based on the results of this study, we found 0.28+/-0.05 ng of XA in the salivary glands of the mosquitoes, accounting for 10% of the total XA content in the mosquito whole body. The amounts of XA in the salivary glands reduced to 0.13+/-0.06 ng after mosquitoes ingested a blood meal. Approximately 0.05+/-0.01 ng of XA was detected in the midgut of nonblood fed An. stephensi mosquitoes. By adding synthetic tryptophan as a source of XA into larval rearing water (2 mM) or in sugar meals (10 mM), we evaluated whether XA levels in the mosquito (salivary glands, midgut, and whole body) were boosted and the subsequent effect on infectivity of Plasmodium berghei in the treated mosquito groups. A female specific increase in XA content was observed in the whole body and in the midgut of mosquito groups where tryptophan was added either in the larval water or sugar meals. However, XA in the salivary glands was not affected by tryptophan addition to larval water, and surprisingly it reduced when tryptophan was added to sugar meals. The P. berghei oocyst loads in the mosquito midguts were lower in mosquitoes fed tryptophan treated sugar meals than in mosquitoes reared on tryptophan treated larval water. Our results suggest that mosquito nutrition may have a significant impact on whole body and midgut XA levels in mosquitoes. We discuss the observed parasite infectivity results in relation to XA's relationship with malaria parasite development in mosquitoes.     

Carbon isotope variations in a plantation of Sitka spruce,and the effect of acid mist

Intra- and inter-tree variations in ¹³C/¹²C ratios were studied within a single clone plantation of 20-year-old Sitka spruce, some of which were treated with mist simulating acidic cloud water. For groups of trees of similar height and the same treatment, sampled at the same whorl height, ¹³C values for current year needles showed variations (1 SD) of between 0.2 and 0.7. The variations reflect the seasonally averaged influences, on intercellular CO₂ concentrations, of slight variations in the microhabitat within a group. For a typical intra-group variation of 0.4 one may be able to distinguish between groups whose mean intercellular CO₂ concentrations differ by only 8 ppm. Acid misting resulted in a lowering of ¹³C values by c. 0.7 (significant at the P0.05 level). This reflects higher intercellular CO₂ concentrations for acid misted trees, which can be interpreted in terms of their having assimilation rates c. 10% lower than those of control trees, and might explain the observed reduction in stem growth for acid-misted trees. Without careful attention to sampling strategy, however, these small inter-tree ¹³C variations can be easily masked by the much larger intra-tree variations with height. Large gradients of increasing needle ¹³C with height, of c. 0.5 m^-1, were observed in two untreated trees of different total height. The gradient was similar for both trees so, though ¹³C values of both trees were identical close to their leaders (–27), the taller tree displayed much lower values close to the ground (–31). The gradients are believed to reflect lower light levels close to the ground, rather than the accumulation of respired CO₂ in the atmosphere. The different height response of stems versus needles, reflected by an increase in ¹³C_stems–¹³C_needles with height (for cellulose), is discussed in terms of stem photosynthetic recapture of internally respired CO₂.     

Ecophysiological studies on orchids of Madagascar: incidence and plasticity of crassulacean acid metabolism in species of the genus Angraecum Bory

The present study is an investigation on photosynthetic options in an orchid taxon and deals with the mainly epiphytes comprising genus Angraecum Bory. The incidence of crassulacean acid metabolism (CAM) in Angraecum species collected at various habitats in Madagascar was surveyed by analysis of stable carbon isotope composition (¹³C values). The values showed both inter- and intraspecific variability and suggest that in situ about 50% of the analysed species perform C3 photosynthesis, 20% moderate CAM (fixation of external CO₂ during day-and night-time) and 30% pronounced CAM (CO₂ uptake entirely during the night). The photosynthetic behaviour of the species indicated by the ¹³C values was clearly related to the habitat from where the samples derived. In A. eburneum, A. sororium and particularly in A. sesquipedale the stable carbon isotope analysis was complemented by measurements of CAM performance under controlled conditions. The experiments with A. sesquipedale revealed that drought and temperature are important factors modulating CAM, whereas variation of the leaf-to-air water vapor pressure difference was less effective. Altogether, the results of the study support the view that the high biological adaptability and thus the ecological success of the genus Angraecum is largely based on genotypic diversity and intraspecific plasticity of the photosynthetic behaviour.     

Interactions and space requirement of the phosphate head group of membrane lipids: The single crystal structures of a triclinic and a monoclinic form of hexadecyl-2-deoxyglycerophosphoric acid monohydrate

The crystal structures of a triclinic form (HPA1) and a monoclinic form (HPA2) of hexadecyl-2-deoxyglycerophosphoric acid monohydrate were determined by single crystal analysis. The unit cell dimensions for HPA1 are $\text{a = 4.75, b = 5.72, c = 44.36}\text{A}\text{?}$ and α = 91.0, β = 101.5, γ = 100.5° (P$\text{1}$) and for HPA2, $\text{a = 4.75, b = 5.72, c = 88.72}\text{A}\text{?}$ and γ = 100.8° (P2₁). In both structures the molecules are fully extended and pack tail-to-tail in bilayers with tilting (47°) hydrocarbon chains. In HPA2, however, the chain tilt alternatingly changes direction in adjacent bilayers, giving rise to a doubled unit cell which spans two bilayers. The dihydrogen phosphate groups interact by hydrogen bonds and are arranged in rows. Laterally between these phosphate rows the water molecules are accommodated producing a compact two-dimensional network of hydrogen bonds. The packing cross-section in the layer plane of the dihydrogen phosphate monohydrate group is 26.7 Ų in both structures. The hydrocarbon chains pack according to the triclinic (T|) chain packing mode. In HPA2, however, the chain packing is somewhat less compact with accounts for a 2% increase in the molecular volume. In both structures the ether oxygen is accommodated into the hydrocarbon matrix without distortion of the chain packing.     

The response of the malaria mosquito, Anopheles gambiae, to two components of human sweat, ammonia and l-lactic acid, in an olfactometer

In an olfactometer study on the response of the anthropophilic malaria mosquito Anopheles gambiae s.s. (Diptera, Culicidae) to human sweat it was found that freshly collected sweat, mostly of eccrine origin, was attractive, but that incubated sweat was significantly more attractive than fresh sweat. The behavioural response to l ‐lactic acid and ammonia, the main constituents of sweat, was investigated. l ‐lactic acid was attractive at one concentration only (11.11 mm ) and removal of the l ‐lactic acid from the sweat by enzymatic decomposition did not affect the attractiveness of sweat. Ammonia caused attraction over a range of 0.1–13.4 m on glass slides and at 0.84–8.40 μmol/min in an air stream. It is concluded that: human sweat contains kairomones for host‐seeking An. gambiae; ammonia is an important kairomone for this mosquito; and that l ‐lactic acid is not a prerequisite in the attraction of An. gambiae to sweat.     

Simultaneous and independent effects of abscisic acid on stomata and the photosynthetic apparatus in whole leaves

(±)-Abscisic acid (ABA) at 10^-5 M was added to the transpiration stream of leaves of 16 species (C₃ and C₄, monocotyledons and dicotyledons). Stomatal responses followed one of three patterns: i) stomata that were wide and insensitive to CO₂ initially, closed partially and became sensitive to CO₂; ii) for stomata that were sensitive to CO₂ before the application of ABA, the range of highest sensitivity to CO₂ shifted from high to low intercellular partial pressures of CO₂, for instance in leaves of Zea mays from 170–350 to 70–140 bar; iii) when stomata responded strongly to ABA, their conductance was reduced to a small fraction of the initial conductance, and sensitivity to CO₂ was lost. The photosynthetic apparatus was affected by applications of ABA to various degrees, from no response at all (in agreement with several previous reports on the absence of effects of ABA on photosynthesis) through a temporary decrease of its activity to a lasting reduction. Saturation curves of photosynthesis with respect to the partial pressure of CO₂ in the intercellular spaces indicated that application of ABA could produce three phenomena: i) a reduction of the initial slope of the saturation curve (which indicates a diminished carboxylation efficiency); ii) a reduction of the level of the CO₂-saturated rate of assimilation (which indicates a reduction of the ribulose-1,5-bisphosphate regeneration capacity); and iii) an increase of the CO₂ compensation point. Photosynthesis of isolated mesophyll cells was not affected by ABA treatments. Responses of the stomatal and photosynthetic apparatus were usually synchronous and often proportional to each other, with the result that the partial pressure of CO₂ in the intercellular spaces frequently remained constant in spite of large changes in conductance and assimilation rate. Guard cells and the photosynthetic apparatus were able to recover from effects of ABA applications while the ABA supply continued. Recovery was usually partial, in the case of the photosynthetic apparatus occasionally complete. Abscisic acid did not cause stomatal closure or decreases in the rate of photosynthesis when it was applied during a phase of stomatal opening and induction of photosynthesis that followed a transition from darkness to light.Abbreviations and symbols A rate of CO₂ assimilation - ABA (±)-abscisic acid - c _a partial pressure of CO₂ in the ambient air or in the gas supplied to the leaf chambers - c _i partial pressure of CO₂ in the intercellular spaces of a leaf - e _a partial pressure of H₂O in the air - g conductance for water vapor - J quantum flux - T ₁ leaf temperature     

Investigations of molecular recognition aspects related to the enantiomer separation of 2-methoxy-2-(1-naphthyl)propionic acid using quinine carbamate as chiral selector: An NMR and FT-IR spectroscopic as well as X-ray crystallographic study

The chiral recognition mechanism of a cinchona alkaloid-based chiral stationary phase (CSP) showing high enantiomer discrimination potential for 2-methoxy-2-(1-naphthyl)propionic acid (MalphaNP acid) was investigated. Conformational and structural analyses of the 1:1 complexes of 9-O-(tert-butylcarbamoyl) quinine selector (SO) and MalphaNP acid (selectand, SA) were carried out employing NMR spectroscopy in solution, Fourier-transform infrared (FT-IR) spectroscopy, and solid-state X-ray diffraction analysis. Intramolecular NOEs of a soluble analogue of the CSP afforded the conformational states of the free and complexed form of the selector. The (1)H-NMR spectra revealed that the free form of the SO constitutes anti-open as well as anti-closed and/or syn-closed conformers. Upon complexation with the (S)-MalphaNP acid enantiomer to form the more stable diastereomeric associate, a conformational transition of the selector takes place, resulting in the synthesis of the anti-open conformer nearly exclusively. FT-IR spectra reveal that, besides the primary ion-pairing interaction, stereoselective hydrogen bonding stabilizes the more stable complex via the amide hydrogen of the SO. X-ray diffraction analysis of 9-O-(tert-butylcarbamoyl)quinine and (S)-MalphaNP acid complex further revealed the occurrence of a bidentate H-bond-mediated ionic interaction between SO and SA as well as the lack of pi-pi interaction in the 1:1 complex, and corroborated the conclusions derived from spectroscopic and chromatographic studies.     

The effects of salinity,crassulacean acid metabolism and plant age on the carbon isotope composition of <Emphasis Type="Italic">Mesembryanthemum crystallinum</Emphasis> L., a halophytic C<Subscript>3</Subscript>-CAM species

The carbon isotope composition of the halophyte Mesembryanthemum crystallinum L. (Aizoaceae) changes when plants are exposed to environmental stress and when they shift from C₃ to crassulacean acid metabolism (CAM). We examined the coupling between carbon isotope composition and photosynthetic pathway by subjecting plants of different ages to salinity and humidity treatments. Whole shoot ¹³C values became less negative in plants that were exposed to 400 mM NaCl in the hydroponic solution. The isotopic change had two components: a direct NaCl effect that was greatest in plants still operating in the C₃ mode and decreased proportionally with increasing levels of dark fixation, and a second component related to the degree of CAM expression. Ignoring the presumably diffusion-related NaCl effect on carbon isotope ratios results in an overestimation of nocturnal CO₂ gain in comparison to an isotope versus nocturnal CO₂ gain calibration established previously for C₃ and CAM species grown under well-watered conditions. It is widely taken for granted that the shift to CAM in M. crystallinum is partially under developmental control and that CAM is inevitably expressed in mature plants. Plants, cultivated under non-saline conditions and high relative humidity (RH) for up to 63 days, maintained diel CO₂ gas-exchange patterns and ¹³C values typical of C₃ plants. However, a weak CAM gas-exchange pattern and an increase in ¹³C value were observed in non-salt-treated plants grown at reduced RH. These observations are consistent with environmental control rather than developmental control of the induction of CAM in mature M. crystallinum under non-saline conditions.