Abstract: Phosphate mobilization into the plant is a complex process requiring numerous transporters for absorption and translocation of this major nutrient. In the genome of Arabidopsis thaliana, nine closely related high affinity phosphate transporters have been identified but their specific roles remain unclear. Here we report the molecular, histological and physiological characterization of Arabidopsis pht1;4 high affinity phosphate transporter mutants. Using GUS-gene trap and in situ hybridization, Pht1;4 was found mainly expressed in inorganic phosphate (Pi) limiting medium in roots, primarily in the epidermis, the cortex and the root cap. In addition to this, expression was also observed at the lateral root branch points on the primary root and in the stele of lateral roots, suggesting a role of Pht1;4 in phosphate absorption and translocation from the growth medium to the different parts of the plant. Pi-starved pht1;4 plantlets exhibited a strong reduction of phosphate uptake capacity (40). This phenotype appears only related to the pht1;4 mutation as there were no obvious changes in the expression of other Pht1 family members in the mutants background. However, after 10 days of growth on phosphate deficient or sufficient medium, the Pi content in the mutants was not significantly different from that of the corresponding wild type controls. Furthermore, the mutants did not display any obvious growth defects or visible phenotypes when grown on a low phosphate containing medium. The work described here offers a first step in the complex genetic dissection of the phosphate transport system in planta.

Abstract: Recent studies have shown that zerovalent iron (Fe0) may potentially be used as a chemical medium in permeable reactive barriers (PRBs) for groundwater nitrate remediation; however, the effects of commonly found organic and inorganic ligands in soil and sediments on nitrate reduction by Fe0 have not been well understood. A 25.0 mL nitrate solution of 20.0 mg of N L-1 (1.43 mM nitrate) was reacted with 1.00 g of Peerless Fe0 at 200 rpm on a rotational shaker at 23 °C for up to 120 h in the presence of each of the organic acids (3.0 mM formic, 1.5 mM oxalic, and 1.0 mM citric acids) and inorganic acids (3.0 mM HCl, 1.5 mM H2SO4, 3.0 mM H3BO3, and 1.5 mM H3PO4). These acids provided an initial dissociable H+ concentration of 3.0 mM available for nitrate reduction reactions under conditions of final pH < 9.3. Nitrate reduction rates (pseudo-first-order) increased in the order: H3PO4 < citric acid < H3BO3 < oxalic acid < H2SO4 < formic acid < HCl, ranging from 0.00278 to 0.0913 h-1, corresponding to surface a...

Abstract: The corrosion protection by zinc phosphate conversion coating on magnesium alloy AM60 is studied. Three phosphatation solutions containing phosphoric acid, phosphate ions, nitrates and nitrites added with zinc and fluorides were used. Therefore, the present investigation aims to study the role of the phosphating bath components on the phosphating process and to enhance the possibility of obtaining phosphate layers on magnesium AM60 alloy by immersion in the various phosphatation solutions. The morphology and the coating composition on the electrode surface were analysed (SEM, EDX, X-ray diffraction and Raman spectroscopy). The phosphate films formed are mainly composed of tetra-hydrated zinc phosphate, otherwise known as hopeite. A mechanism is proposed to explain the germination and the growth of the phosphate crystals on AM60 alloy.

Abstract: In this paper, we report the utilization of high ionic strength (>1100 mM) calcium phosphate solutions in depositing 20–65-μm-thick, bonelike apatitic calcium phosphate on Ti6Al4V within 2–6 h, at room temperature. The super-strength solution used here multiplied the concentrations of calcium and phosphate ions in human plasma or simulated body fluid (SBF) by a factor of ten. The interesting features of the technique are given in the following. First, the solutions did not contain any buffering agents, such as Tris or Hepes. Second, during the process, homogeneous formation of calcium phosphate nano-clusters took place. However, their presence did not adversely affect the coating process. Third, other than simple surface treatments to begin with, no other additional intermediate steps were necessary. The only step needed after the preparation of the solution from reagents is the addition of proper amounts of NaHCO3 to raise the pH to 6.5 prior to the coating procedure. Fourth, there is no CO2 bubbling required, and hence, this is a robust process. Fifth, such a procedure led to a significant enhancement of coating rate enabling the formation in as little as 2–6 h. Coating proceeded with a linear rate. Sixth, the adhesion strength (12 ± 2 MPa) of the present coatings was comparable to coatings produced by soaking in 1.5× SBF solutions over a prolonged period of time, typically two to three weeks. Finally, the carbonate content (8 wt%) and Ca/P molar ratio (1.57) qualify the coating as bonelike.

Abstract: Comparison of bottom-water chemistry in the marine‐limnic habitat gradient shows greater phosphorus availability in marine waters, primarily because of enhanced iron sequestration by sulfide. In the oxidative hydrolysis of iron and the concomitant precipitation of phosphate, a minimum of two iron atoms are needed to precipitate one phosphate molecule (Fe : P 5 2). However, dissolved Fe : P , 2 predominates in anoxic marine waters, therefore leaving some phosphate in solution after oxygenation because of a shortage of dissolved iron for phosphate coprecipitation by iron oxyhydroxide. In contrast, anoxic bottom waters in most freshwater lakes show Fe : P . 2, allowing almost complete phosphate removal on oxygenation. This difference is a consequence of the high sulfate content of sea salt, and a main reason why nitrogen normally limits net primary production in temperate coastal waters, in contrast to the predominant phosphorus limitation of near-neutral lakes.

Abstract: An equilibrium thermodynamic model of the interaction of calcium, phosphate and casein in milk is described in which the micellar calcium phosphate is assumed to be in the form of calcium phosphate nanoclusters. A generalized empirical formula for the nanocluster is used to define the molar ratios of small ions (Ca, Mg, Pi and citrate) to a casein phosphorylated sequence (phosphate centre, PC). From this model, a method of calculating the partition of milk salts into diffusible and non-diffusible fractions is obtained. No arbitrary assumptions are made, no fitting of adjustable parameters is done and the PCs in the caseins are defined by inspection of their primary structures. In addition to the salt partition, the mole fractions of the individual caseins not complexed to the calcium phosphate through one or more of their PCs are computed and a generic stability rule for milks is derived. The use of the model is illustrated by calculations of the partition of salts in a standard milk and by comparison with experimental data on the partition of salts in the milk of individual cows. The generic stability rule is applied to the individual milks to determine whether the micellar calcium phosphate is thermodynamically stable. According to the calculations, compositions that might lead to pathological calcification in the lumen of the mammary gland were seldom found in primiparous healthy cows in early or mid lactation but occurred more often in multiparous animals, in late lactation and during mastitic infection.

Abstract: U(VI)-phosphate interactions are important in governing the subsurface mobility of U(VI) in both natural and contaminated environments. We studied U(VI) adsorption on goethite-coated sand (to mimic natural Fe-coated subsurface materials) as a function of pH in systems closed to the atmosphere, in both the presence and the absence of phosphate. Our results indicate that phosphate strongly affects U(VI) adsorption. The effect of phosphate on U(VI) adsorption was dependent on solution pH. At low pH, the adsorption of U(VI) increased in the presence of phosphate, and higher phosphate concentration caused a larger extent of increase in U(VI) adsorption. Phosphate was strongly bound by the goethite surface in the low pH range, and the increased adsorption of U(VI) at low pH was attributed to the formation of ternary surface complexes involving both U(VI) and phosphate. In the high pH range, the adsorption of U(VI) decreased in the presence of phosphate at low total Fe concentration, and higher phosphate concentration caused a larger extent of decrease in U(VI) adsorption. This decrease in U(VI) adsorption was attributed to the formation of soluble uranium-phosphate complexes. A surface complexation model (SCM) was proposed to describe the effect of phosphate on U(VI) adsorption to goethite. This proposed model was based on previous models that predict U(VI) adsorption to iron oxides in the absence of phosphate and previous models developed to predict phosphate adsorption on goethite. A postulated ternary surface complex of the form of (>FePO4UO2) was included in our model to account for the interactions between U(VI) and phosphate. The model we established can successfully predict U(VI) adsorption in the presence of phosphate under a range of conditions (i.e., pH, total phosphate concentration, and total Fe concentration).

Abstract: Recently, molecular studies have determined that the SLC17/type I phosphate transporters, a family of proteins initially characterized as phosphate carriers, mediate the transport of organic anions. While their role in phosphate transport remains uncertain, it is now clear that the transport of organic anions facilitated by this family of proteins is involved in diverse processes ranging from the vesicular storage of the neurotransmitter glutamate to the degradation and metabolism of glycoproteins.

Abstract: The possibility of increasing the arsenate adsorption capacity of seawater-neutralized red mud (Bauxsol) through acid treatment, combined acid and heat treatment, and the addition of ferric sulfate (Fe 2 (SO 4 ) 3 ·7H 2 O) or aluminum sulfate (Al 2 (SO 4 ) 3 ·18H 2 O) is investigated. The results show that acid treatment alone, as well as in combination with heat treatment increases the removal efficiency, with the combination providing the best removal. Adding ferric sulfate or aluminum sulfate, however, suppress the removal. The results also show that activated Bauxsol (AB) produced using combined acid and heat treatment can remove roughly 100% arsenate (at pH 4.5) with or without competing anions (i.e., phosphate, bicarbonate, and sulfate) when the initial arsenate concentration is ⩽2 mg l −1 . Furthermore, it is found that the adsorption process using AB is not accompanied by the release of unwanted contaminants, and TCLP results indicate that the spent AB is not hazardous. It is believed that the AB produced here has good potential as an alternative adsorbent to conventional methods for removing arsenate from water.

Abstract: The extraordinary capacity of isolated mitochondria to accumulate Ca2+ has been established for more than 40 years. The distinct kinetics of the independent uptake and efflux pathways accounts for the dual functionality of the transport process to either modulate matrix free Ca2+ concentrations or to act as temporary stores of large amounts of Ca2+ in the presence of phosphate. One puzzle has been the nature of the matrix calcium phosphate complex, since matrix free Ca2+ seems to be buffered in the region of 1–5 μM in the presence of phosphate while millimolar Ca2+ remains soluble in in vitro media. The key seems to be the elevated matrix pH and the third-power relationship of the PO4 3− concentration with pH. Taking this into account we may now finally have a model that explains the major features of physiological mitochondrial Ca2+ transport.

Abstract: Summary The herbicide glyphosate and inorganic phosphate are strongly adsorbed by inorganic soil components, especially aluminium and iron oxides, where they seem to compete for the same adsorption sites. Consequently, heavy phosphate application may exhaust soil's capacity to bind glyphosate, which may lead to pollution of drain- and groundwater. Adsorption of phosphate and glyphosate to five contrasting Danish surface soils was investigated by batch adsorption experiments. The different soils adsorbed different amounts of glyphosate and phosphate, and there was some competition between glyphosate and phosphate for adsorption sites, but the adsorption of glyphosate and phosphate seemed to be both competitive and additive. The competition was, however, less pronounced than found for goethite and gibbsite in an earlier study. The soil's pH seemed to be the only important factor in determining the amount of glyphosate and phosphate that could be adsorbed by the soils; consequently, glyphosate and phosphate adsorption by the soils was well predicted by pH, though predictions were somewhat improved by incorporation of oxalate-extractable iron. Other soil factors such as organic carbon, the clay content and the mineralogy of the clay fraction had no effect on glyphosate and phosphate adsorption. The effect of pH on the adsorption of glyphosate and phosphate in one of the soils was further investigated by batch experiments with pH adjusted to 6, 7 and 8. These experiments showed that pH strongly influenced the adsorption of glyphosate. A decrease in pH resulted in increasing glyphosate adsorption, while pH had only a small effect on phosphate adsorption.

Abstract: For some bacteria and algae, it has been proposed that inorganic polyphosphates and transport of metal-phosphate complexes could participate in heavy metal tolerance. To test for this possibility in Acidithiobacillus ferrooxidans, a microorganism with a high level of resistance to heavy metals, the polyphosphate levels were determined when the bacterium was grown in or shifted to the presence of a high copper concentration (100 mM). Under these conditions, cells showed a rapid decrease in polyphosphate levels with a concomitant increase in exopolyphosphatase activity and a stimulation of phosphate efflux. Copper in the range of 1 to 2 μM greatly stimulated exopolyphosphatase activity in cell extracts from A. ferrooxidans. The same was seen to a lesser extent with cadmium and zinc. Bioinformatic analysis of the available A. ferrooxidans ATCC 23270 genomic sequence did not show a putative pit gene for phosphate efflux but rather an open reading frame similar in primary and secondary structure to that of the Saccharomyces cerevisiae phosphate transporter that is functional at acidic pH (Pho84). Our results support a model for metal detoxification in which heavy metals stimulate polyphosphate hydrolysis and the metal-phosphate complexes formed are transported out of the cell as part of a possibly functional heavy metal tolerance mechanism in A. ferrooxidans.

Abstract: Pseudo-nitzschia seriata (Cleve) H. Peragallo isolated from Scottish west coast waters was studied in batch culture with phosphate (P) or silicate (Si) as the yield-limiting nutrient at 15° C. This species produced the neurotoxin domoic acid (DA) when either nutrient was limiting but produced more when stressed by Si limitation during the stationary phase. Under P-limiting conditions, exponential growth stopped after P was reduced to a low threshold concentration. Under Si-limiting conditions, fast exponential growth was followed by a period of slower exponential growth, until Si became exhausted. A stationary phase was observed in the P-limited but not the Si-limited cultures, the latter showing a rapid decrease in cell density after the second exponential growth phase. Si-limited cultures exhibited a further period of active metabolism (as indicated by increases in chl and carbon per cell) late in the experiment, presumably fueled by regenerated Si. DA production was low in exponential phase under both conditions. In P-limited cultures, most DA was produced during the immediate postexponential phase, with little or no new DA produced during later cell senescence. In contrast, although a substantial amount of DA was produced during the slower exponential phase of the Si-limited cultures, DA production was even greater near the end of the experiment, coincident with the period of chl synthesis and increase in carbon biomass. Comparison of the magnitude of toxin production in the two nutrient regimes indicated a greater threat of P. seriata-generated amnesic shellfish poisoning events under Si rather than P nutrient limitation.

Abstract: Summary The herbicide glyphosate and inorganic phosphate are strongly adsorbed by inorganic soil components, especially aluminium and iron oxides, where they seem to compete for the same adsorption sites. Consequently, heavy phosphate application may exhaust soil’s capacity to bind glyphosate, which may lead to pollution of drain- and groundwater. Adsorption of phosphate and glyphosate to five contrasting Danish surface soils was investigated by batch adsorption experiments. The different soils adsorbed different amounts of glyphosate and phosphate, and there was some competition between glyphosate and phosphate for adsorption sites, but the adsorption of glyphosate and phosphate seemed to be both competitive and additive. The competition was, however, less pronounced than found for goethite and gibbsite in an earlier study. The soil’s pH seemed to be the only important factor in determining the amount of glyphosate and phosphate that could be adsorbed by the soils; consequently, glyphosate and phosphate adsorption by the soils was well predicted by pH, though predictions were somewhat improved by incorporation of oxalate-extractable iron. Other soil factors such as organic carbon, the clay content and the mineralogy of the clay fraction had no effect on glyphosate and phosphate adsorption. The effect of pH on the adsorption of glyphosate and phosphate in one of the soils was further investigated by batch experiments with pH adjusted to 6, 7 and 8. These experiments showed that pH strongly influenced the adsorption of glyphosate. A decrease in pH resulted in increasing glyphosate adsorption, while pH had only a small effect on phosphate adsorption.

Abstract: Some of the formulations of apatitic calcium phosphate bone cements are based on the hydrolysis of α-tricalcium phosphate (α-Ca 3 (PO 4 ) 2 , α-TCP). In this work the hydrolysis kinetics of α-TCP are studied, taking into account the particle-size distribution of the initial powder, to identify the mechanisms that control the reaction in its successive stages. The temporal evolution of the depth of reaction is calculated from the degree of reaction data, measured by X-ray diffractometry. A kinetic model is proposed, which suggests the existence of two rate-limiting mechanisms: initially, the surface area of the reactants and, subsequently, the diffusion through the hydrated layer formed around the reactants. For the specific particle size and preparation used, the controlling mechanism changeover takes place after 16 h of reaction.