Bacterial fluoride resistance,Fluc channels,and the weak acid accumulation effect

Fluoride ion (F⁻) is a ubiquitous environmental threat to microorganisms, which have evolved a family of highly selective “Fluc” F⁻ channels that export this inhibitory anion from their cytoplasm. It is unclear, however, how a thermodynamically passive mechanism like an ion channel can protect against high concentrations of external F⁻. We monitored external F⁻ concentrations in Escherichia coli suspensions and showed that, in bacteria lacking Fluc, F⁻ accumulates when the external medium is acidified, as a predicted function of the transmembrane pH gradient. This weak acid accumulation effect, which results from the high pKa (3.4) and membrane permeability of HF, is abolished by Fluc channels. We also found that, although bacterial growth is inhibited by high concentrations of F⁻, bacteria can withstand cytoplasmic F⁻ at levels a hundred times higher than those that inhibit proliferation, resuming growth when the F⁻ challenge is removed.     

Characterization of fluoride uptake by roots of tea plants (Camellia sinensis (L.) O. Kuntze)

Backgrounds and aims

Tea plants (Camellia sinensis (L.) O. Kuntze) accumulate high fluoride in the leaves whereas the mechanism on its uptake is poorly understood. The measured F^? uptake was compared to calculated uptake from transpiration rates assumuing no discrimination between F^? and water to characterize the property of F^? absorption by tea plant roots.

Methods

The F^? uptake was examined by depletion method under variable external F^? concentrations, pH, temperature, relative air humidity, anion channel blockers and metabolism inhibitors in solution experiments.

Results

Measured F^? uptake rates were significantly larger than those calculated from transpiration rates regardless of external F^? concentrations, uptake durations, relative humidity, and solution pH. The measured and net F^? uptake (subtracting that calculated from transpiration rate from the measured uptake) were reduced by low temperature and inhibited by anion channel and metabolism inhibitors anthracene-9-carboxylic acid (A-9-C), niflumic acid (NFA), and carbonylcyanide m-chlorophenylhydrazone (CCCP) but not by dihydro-4, 4′ diisothiocyanostilbene-2, 2′-disulphonic acid (DIDS). The F^? uptake showed biphasic response patterns, following saturable Michaelis–Menten kinetics in the range of low external F^? (below 100 μmol?L^?1) while increased linearly with external supply in the range of high concentrations.

Conclusion

The uptake of F^? by roots of accumulator tea plants was likely an active process and energy-dependent. This helps to explain why tea plants are able to accumulate considerably high F^?.     

Combined Impact of Exercise and Temperature in Learning and Memory Performance of Fluoride Toxicated Rats

In previous studies, we investigated a link between high fluoride exposure and functional IQ deficits in rats. This study is an extension conducted to explore the combined influence of physical exercise and temperature stress on the learning ability and memory in rats and to assess whether any positive modulation could be attenuated due to exercise regimen subjected to F-toxicated animals at different temperatures. Accumulation of ingested fluoride resulted significant inhibition in acetylcholinesterase activity (P?<?0.05), plasma cortisol levels (P?<?0.05), and impaired the acquisition, performance, latency time, and retention in fluoride-exposed animals. Fluoride-toxicated rats took more number of sessions during the learning phase [F _{5, 35}?=?19.065; P?<?0.05] and post hoc analysis on the number of correct choices revealed that there was a significant effect of treatments [F _{5, 30}?=?15.763; P?<?0.05]; sessions [F _{8, 240}?=?58.698; P?<?0.05]; and also significant difference in the interactions [F _{40, 240}?=?1.583; P?<?0.05]. The latency data also revealed a significant difference between groups [F _{5, 30}?=?28.085; P?<?0.05]; time?=?[F _{8, 240}?=?136.314; P?<?0.05]; and there was a significant difference in the interactions [F _{40, 240}?=?2.090; P?<?0.05]. In order to ascertain if interdependence between fluoride concentrations and the foregoing free radical parameters, respective correlation coefficients were calculated and results clearly emphasize the positive role of exercise in the promotion of cognitive functions by decreasing fluoride levels in rat hippocampus. A significant recovery in cognitive function was noticed in all the exercised animals due to reduced burden of brain oxidative stress. In comparison to exercise regimens performed at different temperatures, high (35?°C) and low temperatures (20?°C) led to a slower acquisition and poor retention of the task when compared to thermo neutral temperatures (25 and 30?°C). Thus exercise up-regulate antioxidant defenses and promote learning abilities in fluorotic population.     

Molecular dynamics investigation of nitric oxide (II) interaction with a model biological membrane

Nitric oxide (II) diffusion through a model two-component (phosphatidylcholine and phosphatidylethanolamine molecules) biological membrane is investigated using the molecular dynamics method. It is shown that NO molecules are rotating in the process of diffusion into the phospholipid bilayer. The calculated diffusion coefficient D[NO] = 0.35 (±0.23) × 10^?5 (cm²/s) is in a good agreement with literature data. This testifies that free diffusion of NO molecules may be a plausible mechanism of the NO permeation through the membranes.     

Fluoride inhibition of yeast enolase: Crystal structure of the enolase–Mg2+–F−–Pi complex at 2.6 Å resolution

Enolase in the presence of its physiological cofactor Mg²⁺ is inhibited by fluoride and phosphate ions in a strongly cooperative manner (Nowak, T, Maurer, P. Biochemistry 20:6901, 1981). The structure of the quaternary complex yeast enolase–Mg²⁺–F^?–P_i has been determined by X-ray diffraction and refined to an R = 16.9% for those data with F/σ(F) ≥ 3 to 2.6 Å resolution with a good geometry of the model. The movable loops of Pro-35-Ala-45, Val-153-Phe-lo9, and Asp-255-Asn-266 are in the closed conformation found previously in the precatalytic substrate–enzyme complex. Calculations of molecular electrostatic potential show that this conformation stabilizes binding of negatively charged ligands at the Mg²⁺ ion more strongly than the open conformation observed in the native enolase. This closed conformation is complementary to the transition state, which also has a negatively charged ion, hydroxide, at Mg²⁺. The synergism of inhibition by F^? and P_i most probably is due to the requirement of P_i, for the closed conformation. It is possible that other Mg²⁺-dependent enzymes that have OH^? ions bound to the metalion in the transition state also will be inhibited by fluoride ions. © Wiley-Liss, Inc.     

Fluoride in the Bones of Foxes (Vulpes vulpes Linneaus, 1758) and Raccoon Dogs (Nyctereutes procyonoides Gray, 1834) from North-Western Poland

Assessment of exposure to fluoride (F^?) is increasingly focused on mineralized tissues, mainly bones. Their periodic growth and continuous reconstruction make them a good material for studying long-term F^? accumulation. In this study, F^?concentrations were determined in the bones of foxes and raccoon dogs from north-western Poland and relationships between bone F^? and the age categories of the animals were attempted to be identified. Bone samples were collected from femurs of 32 foxes (15 males and 17 females) and 18 raccoon dogs (10 males and 8 females) from polluted, medium-polluted, and unpolluted by F^? areas. Bone F^? was determined by potentiometric method, and results were expressed per dry weight (dw); they ranged from 176 to 3,668 mg/kg dw in foxes and from 84 to 1,190 mg/kg dw in raccoon dogs. Foxes from north-western Poland accumulated much more F^? in their bones than raccoon dogs. Our study shows that the assessment of hazards created by industrial emitters can be conducted conveniently by the measurements of fluorine content in hard tissues of wild animals. Due to availability of such type of material for studies, it seems that the analysis of fluoride content in bones can be a good tool in the development of ecotoxicology.     

The effects of external electric field: creating non-zero first hyperpolarizability for centrosymmetric benzene and strongly enhancing first hyperpolarizability for non-centrosymmetric edge-modified graphene ribbon H2N-(3,3)ZGNR-NO2

How to generate a non-zero first hyperpolarizability for a centrosymmetric molecule is a challenging question. In this paper, an external (pump) electric field is used to make a centrosymmetric benzene molecule generate a non-zero value of the electric field induced first hyperpolarizability (β ^F ). This comes from the centrosymmetry breaking of electron cloud. Two interesting rules are exhibited. (1) β ^F is anisotropic for different directional fields (F _i, i?=?X, Y, Z). (2) The field dependence of β ^F is a non-monotonic function, and an optimum external electric field causes the maximum value of β ^F . The largest first hyperpolarizability β ^F reaches the considerable level of 3.9?×?10⁵ a.u. under F _Y?=?330?×?10^?4 a.u. for benzene. The external electric field effects on non-centrosymmetric edge-modified graphene ribbon H₂N-(3,3)ZGNR-NO₂ was also studied in this work. The first hyperpolarizability reaches as much as 2.1?×?10⁷ a.u. under F _X?=?600?×?10^?4 a.u. for H₂N-(3,3)ZGNR-NO₂. We show that the external electric field can not only create a non-zero first hyperpolarizability for centrosymmetric molecule, but also remarkably enhance the first hyperpolarizability for a non-centrosymmetric molecule.     

Fluorescence spectrometric study on the interaction of tamibarotene with bovine serum albumin

The interaction between tamibarotene and bovine serum albumin (BSA) was studied using fluorescence quenching technique and ultraviolet–visible spectrophotometry. The results of experiments showed that tamibarotene could strongly quench the intrinsic fluorescence of BSA by a dynamic quenching mechanism. The apparent binding constant, number of binding site and corresponding thermodynamic parameters at different temperatures were calculated respectively, and the main interaction force between tamibarotene and BSA was proved to be hydrophobic force. Synchronous fluorescence spectra showed that tamibarotene changed the molecular conformation of BSA. When BSA concentration was 1.00 × 10^?6 mol L^?1, the quenched fluorescence ΔF had a good linear relationship with the concentration of tamibarotene in the range 1.00 × 10^?6 to 12.00 × 10^?6 mol L^?1 with the detection limit of 6.52 × 10^?7 mol L^?1. Copyright © 2010 John Wiley & Sons, Ltd.     

One-electron reduction of halothane and formation of halide ions in aqueous solutions

Formation of Br^? and, under certain conditions also F^? ions has been observed in the radiation chemically induced one-electron reduction of the anesthetic halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) in aqueous solutions. The initial step is the release of Br^? and formation of the 2-chloro-1,1,1-trifluoroethyl radical. The latter can react via competing pathways including H-atom abstraction, addition of molecular oxygen and further reduction by an antioxidant. All of these three competitive routes lead to different product patterns. High yields of F^? ions are observed under anaerobic conditions in the presence of antioxidants such as ascorbate, propylgallate, etc. The fluoride elimination is strongly pH-dependent and seems to occur in various steps after initiation through reduction of the (CF₃CHCl) radical. The implication for biochemical studies on the metabolism of halothane under different oxygen concentrations is discussed.     

Proteomic analysis of urine in rats chronically exposed to fluoride

Urine is an ideal source of materials to search for potential disease‐related biomarkers as it is produced by the affected tissues and can be easily obtained by noninvasive methods. 2‐DE‐based proteomic approach was used to better understand the molecular mechanisms of injury induced by fluoride (F^?) and define potential biomarkers of dental fluorosis. Three groups of weanling male Wistar rats were treated with drinking water containing 0 (control), 5, or 50 ppm F^? for 60 days (n = 15/group). During the experimental period, the animals were kept individually in metabolic cages, to analyze the water and food consumption, as well as fecal and urinary F^? excretion. Urinary proteome profiles were examined using 2‐DE and Colloidal Coomassie Brilliant Blue staining. A dose‐response regarding F^? intake and excretion was detected. Quantitative intensity analysis revealed 8, 11, and 8 significantly altered proteins between control vs. 5 ppm F^?, control vs. 50 ppm F^? and 5 ppm F^? vs. 50 ppm F^? groups, respectively. Two proteins regulated by androgens (androgen‐regulated 20‐KDa protein and α‐2μ‐globulin) and one related to detoxification (aflatoxin‐B1‐aldehyde‐reductase) were identified by MALDI‐TOF‐TOF MS/MS. Thus, proteomic analysis can help to better understand the mechanisms underlying F^? toxicity, even in low doses. © 2010 Wiley Periodicals, Inc. J Biochem Mol Toxicol 25:8–14 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/jbt.20353     

Sub-microsecond chlorophyll A delayed fluorescence from Photosystem I Magnetic field-induced increase of the emission yield

(1) In photosystem I (PS I) particles in the presence of dithionite and intense background illumination at 290 K, an external magnetic field (0–0.22 T) induced an increase, ΔF, of the low chlorophyll a emission yield, F ($\text{ΔF}\text{F}\text{? 1–1.5\%}$). Half the effect was obtained at about 35–60 mT and saturation occurred for magnetic fields higher than about 0.15 T. In the absence of dithionite, no field-induced increase was observed. Cooling to 77 K decreased ΔF at 685 nm, but not at 735 nm, to zero. Measuring the emission spectra of F and ΔF, using continuous excitation light, at 82, 167 and 278 K indicated that the spectra of F and ΔF have about the same maximum at about 730, 725 and 700 nm, respectively. However, the spectra of ΔF show more long-wavelength emission than the corresponding spectra of F. (2) Only in the presence of dithionite and with (or after) background illumination, was a luminescence (delayed fluorescence) component observed at 735 nm, after a 15 ns laser flash (530 nm), that decayed in about 0.1 μs at room temperature and in approx. 0.2 μs at 77 K. A magnetic field of 0.22 T caused an appreciable increase in luminescence intensity after 250 ns, probably mainly caused by an increase in decay time. The emission spectra of the magnetic field-induced increase of luminescence, ΔL, at 82, 167 and 278 K coincided within experimental error with those of ΔF mentioned above. The temperature dependence of ΔF and ΔL was found to be nearly the same, both at 685 and at 735 nm. (3) Analogously to the proposal concerning the 0.15 μs luminescence in photosystem II (Sonneveld, A., Duysens, L.N.M. and Moerdijk, A. (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 5889–5893), we propose that recombination of the oxidized primary donor P-700⁺ and the reduced acceptor A^?, probably A^?₁, of PS I causes the observed fast luminescence. The effect of an external magnetic field on this emission may be explained by the radical pair mechanism. The field-induced increase of the 0.1–0.2 μs luminescence seems to be at least in large part responsible for the observed increase of the total (prompt + delayed) emission measured during continuous illumination in the presence of a magnetic field.     

The fluoride transporter FLUORIDE EXPORTER (FEX) is the major mechanism of tolerance to fluoride toxicity in plants1

Fluoride is everywhere in the environment, yet it is toxic to living things. How biological organisms detoxify fluoride has been unknown until recently. Fluoride-specific ion transporters in both prokaryotes (Fluoride channel; Fluc) and fungi (Fluoride Exporter; FEX) efficiently export fluoride to the extracellular environment. FEX homologs have been identified throughout the plant kingdom. Understanding the function of FEX in a multicellular organism will reveal valuable knowledge about reducing toxic effects caused by fluoride. Here, we demonstrate the conserved role of plant FEX (FLUORIDE EXPORTER) in conferring fluoride tolerance. Plant FEX facilitates the efflux of toxic fluoride ions from yeast cells and is required for fluoride tolerance in plants. A CRISPR/Cas9-generated mutation in Arabidopsis thaliana FEX renders the plant vulnerable to low concentrations (100-µM) of fluoride at every stage of development. Pollen is particularly affected, failing to develop even at extremely low levels of fluoride in the growth medium. The action of the FEX membrane transport protein is the major fluoride defense mechanism in plants.

Plants rely on a fluoride transporter to tolerate toxic fluoride ions.     

Efficient microwave-assisted direct radiosynthesis of [18F]PR04.MZ and [18F]LBT999: Selective dopamine transporter ligands for quantitative molecular imaging by means of PET

PR04.MZ 8-(4-fluoro-but-2-ynyl)-3-p-tolyl-8-aza-bicyclo[3.2.1]octane-2-carboxylic acid methyl ester (1) and LBT999 8-((E)-4-fluoro-but-2-enyl)-3b-p-tolyl-8-aza-bicyclo[3.2.1]octane-2β-carboxylic acid methyl ester (2) are selective dopamine reuptake inhibitors, derived from cocaine. Compounds 1 and 2 were labelled with fluorine-18 at their terminally fluorinated N-substituents employing microwave enhanced direct nucleophilic fluorination. K[¹⁸F]F^? Kryptofix^®222 cryptate, tetrabutyl ammonium [¹⁸F]fluoride and caesium [¹⁸F]fluoride were compared as fluoride sources under conventional and microwave enhanced conditions. Fluorination yields were remarkably increased under microwave irradiation for all three fluoride salts. Radiochemically pure (>98%) [¹⁸F]PR04.MZ (0.95–1.09 GBq, 42–135 GBq/μmol) was obtained within 34–40 min starting from 3.0 GBq [¹⁸F]fluoride ion in 32–36% non-decay-corrected overall yield using K[¹⁸F]F^?Kryptofix^®222 cryptate in MeCN.     

Barrier potentials,molecular structure,force filed calculations and quantum chemical studies of some bipyridine di-carboxylic acids using the experimental and theoretical using (DFT,IVP) approach

ABSTRACT

FT-IR and FT-Raman spectra of 2,2′-bipyridine-3,3′-dicarboxylic acid (B3DA), 2,2′-bipyridine-4,4′-dicarboxylic acid (B4DA) and 2,2′-bipyridine-5,5′-dicarboxylic acid (B5DA) were recorded and analysed. The quantum chemical calculations of the title compounds begin with barrier potentials at different rotation angles around the C–C′ and C–Cα bonds in order to arrive conformation of lowest energy using DFT employing B3LYP functional with 6-311++G(d,p) basis set. This confirmation was further optimised to get the global minimum geometry. The vibrational frequencies along with IR, Raman intensities were computed, the rms error between observed and calculated frequencies were 11.2 cm^?1, 10.2 cm^?1 and 12.2 cm^?1 for B3DA, B4DA, and B5DA. An 87-element modified valence force field is derived by solving the inverse vibrational problem using Wilson’s GF matrix method. This force field is refined using 163 observed fundamentals employing in overlay least-squares technique. The average error between computed and experimental frequencies was found as 12.85 cm^?1 using potential energy distribution (PED) and eigenvectors. By using the gauge-independent atomic orbital (GIAO) method calculate the ¹H and ¹³C NMR chemical shifts of the molecules and compared with experimental results. The first-order hyperpolarisability, HOMO and LUMO energies, molecular electrostatic potential (MESP) and natural orbital analysis (NBO) of titled compounds were evaluated using DFT.     

Propensity to Form Amyloid Fibrils Is Encoded as Excitations in the Free Energy Landscape of Monomeric Proteins

Protein aggregation, linked to many of diseases, is initiated when monomers access rogue conformations that are poised to form amyloid fibrils. We show, using simulations of src SH3 domain, that mechanical force enhances the population of the aggregation-prone (N^?) states, which are rarely populated under force free native conditions but are encoded in the spectrum of native fluctuations. The folding phase diagrams of SH3 as a function of denaturant concentration ([C]), mechanical force (f), and temperature exhibit an apparent two-state behavior, without revealing the presence of the elusive N^? states. Interestingly, the phase boundaries separating the folded and unfolded states at all [C] and f fall on a master curve, which can be quantitatively described using an analogy to superconductors in a magnetic field. The free energy profiles as a function of the molecular extension (R), which are accessible in pulling experiments, (R), reveal the presence of a native-like N^? with a disordered solvent-exposed amino-terminal β-strand. The structure of the N^? state is identical with that found in Fyn SH3 by NMR dispersion experiments. We show that the timescale for fibril formation can be estimated from the population of the N^? state, determined by the free energy gap separating the native structure and the N^? state, a finding that can be used to assess fibril forming tendencies of proteins. The structures of the N^? state are used to show that oligomer formation and likely route to fibrils occur by a domain-swap mechanism in SH3 domain.     

Assessment of Fluoride in Three Selected Polluted Environments along the Egyptian Mediterranean Sea: Effects on Local Populations

Fluoride ion (F^?) is a relevant component of concern due to its potential toxicity for humankind. This study clarifies the status of F^? for human health in three polluted regions along the Egyptian Mediterranean Sea coast, and determining its contents in seawater and different fish tissues (muscle, skin, brain, and bone). Fluoride ion concentrations in different fish tissues had a descending trend of brain > skin > muscle > bone with averages of 26.8 ± 26.0, 24.8 ± 6.5, 12.7 ± 2.3, and 9.0 ± 1.6 μg F^?/g wet wt, respectively. The bioconcentration factor for fluoride ion in different fish tissues was determined and multivariate analyses were conducted. The human health hazard assessment from fish consumption and seawater contact using hazard quotient (HQ) and ingestion and dermal absorption dose of whole body for different ages of females and males as well as the specified body parts (legs, arms, and hands) were calculated. Although the calculated daily intake values for ingestion of fish in the present study were lower than some established tolerable daily intake values, their hazard quotients were within 1 ≥ HQ < 10 and may reflect a possible fluoride adverse effect on human health from the consumption of the gathered fish species.     

Photosynthetic characteristics of female vegetative tissues of Porphyra katadai var. hemiphylla (Bangiales, Rhodophyta) in culture

In this study, chlorophyll fluorescence parameters (?F/F _m′, F _v/F _m) and oxygen evolution of female vegetative tissues of Porphyra katadai var. hemiphylla in unisexual culture (FV) and in mixed culture with male vegetative tissues (FV-M) were followed at 5–20 °C, 10 and 80 μmol photons m^?2 s^?1. The formation of reproductive tissues was closely correlated with decreasing photosynthetic activities. At the same temperature the tissues cultured under 80 μmol photons m^?2 s^?1 showed a greater extent of maturation than those under 10 μmol photons m^?2 s^?1, and their decrease in photosynthesis was also larger. Under the same light intensity the extent of maturation increased with increasing temperature, and both cultures showed higher values of ?F/F _m′ and F _v/F _m at 10 and 15 °C, while their oxygen evolution became negative at 15–20 °C during the later period. Under the same culture condition the maturation of FV-M culture was relatively faster than that of FV culture, while their photosynthetic activity, especially ?F/F _m′, was lower.     

Effect of Fluoride on Arsenic Uptake from Arsenic-Contaminated Groundwater using Pteris vittata L.

High-arsenic groundwater in inland basins usually contains high concentrations of fluoride. In the present study, the effects of fluoride on arsenic uptake by Pteris vittata and on arsenic transformation in growth media were investigated under greenhouse conditions. After P. vittata was hydroponically exposed to 66.8 μM As (V) in the presence of 1.05 mM F^? in the form of NaF, KF, or NaF+KF for 10 d, no visible toxicity symptoms were observed, and there were not significant differences in the dry biomass among the four treatments. The results showed that P. vittata tolerated F^? concentrations as high as 1.05 mM but did not accumulate fluoride in their own tissues. Arsenic uptake was inhibited in the presence of 1.05 mM F^?. However, in hydroponic batches with 60 μM As (III) or 65 μM As (V), it was found that 210.6 and 316.0 μM F^? promoted arsenic uptake. As(III) was oxidized to As(V) in the growth media in the presence and absence of plants, and F^? had no effect on the rate of As(III) transformation. These experiments demonstrated that P. vittata was a good candidate to remediate arsenic-contaminated groundwater in the presence of fluoride. Our results can be used to develop strategies to remediate As-F-contaminated water using P. vittata.     

Bone Strength in Growing Rats Treated with Fluoride: a Multi-dose Histomorphometric,Biomechanical and Densitometric Study

Bone deformation and fragility are common signs of skeletal fluorosis. Disorganisation of bone tissue and presence of inflammatory foci were observed after fluoride (F^?) administration. Most information about F^? effects on bone has been obtained in adult individuals. However, in fluorosis areas, children are a population very exposed to F^? and prone to develop not only dental but also skeletal fluoroses. The aim of this work was to evaluate the bone parameters responsible for the effect of different doses of F^? on fracture load of the trabecular and cortical bones using multivariate analysis in growing rats. Twenty-four 21-day-old Sprague-Dawley rats were divided into four groups: F0, F20, F40 and F80, which received orally 0, 20, 40 or 80 μmol F^?/100 g bw/day, respectively, for 30 days. After treatment, tibiae were used for measuring bone histomorphometric and connectivity parameters, bone mineral density (BMD) and bone cortical parameters. The femurs were used for biomechanical tests and bone F^? content. Trabecular bone volume was significantly decreased by F^?. Consistently, we observed a significant decrease in fracture load and Young’s modulus (YM) of the trabecular bone in F^?-treated groups. However, cortical bone parameters were not significantly affected by F^?. Moreover, there were no significant differences in cortical nor trabecular BMD. Multivariate analysis revealed a significant correlation between the trabecular fracture load and YM but not with bone volume or BMD. It is concluded that when F^? is administered as a single daily dose, it produces significant decrease in trabecular bone strength by changing the elasticity of the trabecular bone.     

RESPONSES OF CERTAIN FRESHWATER PLANKTONIC ALGAE TO FLUORIDE1

The effects of dissolved fluoride supplied as NaF at up to 150 p.p.m. F^? (7.9 mM) on growth, photosynthesis, dark respiration, enolase activity and fluoride uptake were determined for six phytoplankters: Synechococcus leopoliensis (Racib.) Komarek (Cyanophyta), Oscillatoria limnetica Lemmermann (Cyanophyta), Ankistrodesmus braunii Brun (Chlorophyta), Scenedesmus quadricauda (Turp.) Bréb. (Chlorophyta), Cyclotella meneghiniana Kützing (Bacillariophyta) and Stephanodiscus minutus Grun. ex Cleve et Moll (Bacillariophyta). Growth (determined by absorbance at 660 nm or by cell-numbers) was unaffected by fluoride at up to 50 p.p.m. (2.6 mM) in all algae except S. leopoliensis, in which growth ceased transiently followed by resumption of growth at reduced rate. These effects showed a threshold at ca. 25 p.p.m. (1.3 mM) F^? and increased with increasing F^? concentration above this threshold. Photosynthetic O₂ evolution in the chlorophytes was unaffected by F^? at up to 50 p.p.m., whereas in S. leopoliensis F^? above ca. 25 p.p.m. caused a concentration-dependent inhibition of photosynthesis which was most pronounced at saturating irradiance. Dark O₂ uptake was unaffected at up to 50 p.p.m. in chlorophytes but was stimulated in S. leopoliensis. Enolase in clarified cell-extracts of all six algae was inhibited by F^?, with K_i values ranging from 27 to 319 μM. Fluorine (measured by proton-induced gamma-ray emission) could not be detected in chlorophytes exposed during growth to up to 50 p.p. m. F^?, but was detected in S. leopoliensis, O. limnetica and C. meneghiniana. Fluorine associated with cells of these algae increased as the external F^? concentration increased.