Phosphate Exchange Research Articles

Assessment on the effects of aluminum-modified clay in inactivating internal phosphorus in deep eutrophic reservoirs

Aluminum-salt inactivating agents are extensively applied to the restoration of lakes polluted by internal phosphorus (hereinafter referred to as “P”). However, there is a lack of micromechanism information regarding the sediment P cycle and its interactions with aluminum salts, which has restricted the engineering applications of aluminum salts. In this study, a sediment core incubation system was used to simulate the influence of aerobic and anaerobic conditions on the effectiveness and stability of aluminum-modified clay (AMC). This study also investigated the millimeter-scale dynamics of P across the sediment-water interface (SWI) using the HR-Peeper and DGT techniques. According to the results, sediment P release mainly occurred under anaerobic conditions. When the incubation system was in an anaerobic state, AMC effectively reduced the internal-P loading. In pore water, there was a positive correlation between soluble Fe and SRP, suggesting that the reductive dissolution of Fe-P constituted the main mechanism of sediment P release. After with dosing AMC, the concentrations of SRP and labile P in the capping layer both dropped abruptly to low levels and the content of Al-P in surface sediments rose, suggesting that AMC had strongly adsorbed phosphates, formed inert Al-P and blocked the phosphate exchange between pore water and overlying water. This study elaborated on the micromechanism of the control of sediment internal P input by AMC and revealed that Al-P precipitation constituted the main mechanism of the inhibition of sediment P release by aluminum-salt inactivating agents. The research findings have a great significance for guiding field applications of aluminum-salt inactivating agents.

Metformin downregulates the mitochondrial carrier SLC25A10 in a glucose dependent manner

Metformin, a commonly used agent in the treatment of type 2 diabetes, is also associated with reduced risk of cancer development and improvement in cancer survival. Although much is known about metformin, the mechanisms behind its anti-cancer properties are not fully understood. In this study we addressed the role of a mitochondrial transporter commonly upregulated in cancer cells, SLC25A10, for cell survival and metabolism in the presence of metformin. SLC25A10 is a carrier in the mitochondrial inner membrane that transports malate and succinate out of the mitochondria, in exchange of phosphate and sulfate. We show that metformin treatment results in decreased gene expression of the SLC25A10 carrier both in lung cancer A549 mock cells and A549 SLC25A10 knockdown (siSLC25A10) cells. The decrease was even more pronounced when cells were grown at low glucose concentrations. The expression levels of key enzymes in glucose metabolism showed slightly altered mean values for all genes tested in both control cells and siSLC25A10 cells upon metformin treatment. The gene expression of the metabolic regulator glutamic-oxaloacetic transaminase 1 decreased in wild type cells upon metformin treatment whereas there was a trend of increased expression in the siSLC25A10 cells upon metformin treatment. In addition, the gene expression of the cyclin-dependent kinase inhibitor 1A was markedly increased in the siSLC25A10 compared to control A549 cells, and with even larger increases in the presence of metformin and at low glucose concentration. Our data show that in siSLC25A10 cell lines, metformin significantly alters the SLC25A10 carrier at both mRNA and protein levels and can thereby affect the supply of nutrients and the metabolic state of cancer cells.

PO-261 Subcellular localization and expression of NME6, a member of the NME/Nm23/NDPK family, in human tumour cells

IntroductionNucleoside diphosphate kinases (NDPKs) catalyse the exchange of the terminal phosphate from trinucleotides to dinucleotides through a high-energy phosphohistidine intermedier. They are encoded by NME genes and have been found, with a few exceptions, in all living beings. Besides their well-known function as key regulators of the cellular nucleotide homeostasis, they have been appointed numerous additional biochemical and biological functions. The family consists of ten members. NME1-NME4, have been extensively studied, especially NME1 in the context of metastasis formation. The NME1-NME4 are highly homologous among themselves and they all possess the NDP kinase activity in their hexameric form. The information on NME5-NME9 members is rather scarce but it is known that they display a lower level of mutual homology and apparently do not possess the NDP kinase activity. Their multimeric structure has not yet been revealed. The goal of our recent studies is revealing the subcelullar localization, structure and function of NME6.Material and methodsSubcellular localization has been approached by using a specific anti-NME6 antibody and transfection of an NME6-GFP vector followed by confocal microscopy. The results have been confirmed by cellular fractionation. The expression of NME6 in human tumour cells was revealed by Western blotting with specific anti-NME6 antibodies.Results and discussionsThe results of immunofluorescent techniques revealed that NME6 colocalizes with mitochondria. The cellular fractioning confirmed these results. The endogenous NME6 was not detected in the nuclear or cytoplasmic fraction. NME6 has a fairly strong expression in a panel of human melanoma cell lines and is HeLa cells, as well.ConclusionThe mitochondrial localization of NME6 has been confirmed by three different methods although it is known that it does not possess the mitochondrial signalling sequence. The expression of NME6 has been proven to be quite prominent. Since it has been shown that NME6 is an evolutionary very old gene it is obvious it has an important role in homeostasis of every living cell. Our future studies will be focused on revealing the precise localization of NME6 in the mitochondria and its role in cellular bioenergetics, the quaternary structure of the protein, its potential NDPK activity, its function in basic cellular processes and potential role in cancer onset and progression.

A young researcher’s guide to NME/Nm23/NDP Kinase

Nucleoside diphosphate kinases (NDPKs) catalyze the exchange of the terminal phosphate from trinucleotides to dinucleotides through a high- energy phosphohistidine intermedier. They are encoded by NME genes and have been found, with a few exceptions, in all living beings. Besides their well-known function as key regulators of the cellular nucleotide homeostasis, they have been appointed numerous additional biochemical and biological functions. The discovery of NME1/NDPK A as the first metastasis suppressor opened new avenues in cancer research. Although the precise role of NME genes/proteins in cancer dissemination is not yet revealed, it seems that further intensive research in this field may lead to new advances in cancer diagnosis and prognosis, as well as encourage new therapeutic strategies.

Hierarchically Structured FeNiOx Hy Electrocatalyst Formed by In Situ Transformation of Metal Phosphate for Efficient Oxygen Evolution Reaction.

A simple and low-cost fabrication method is needed to obtain effective and robust heterogeneous catalysts for the oxygen evolution reaction (OER). In this study, an electrocatalyst FeNiOx Hy with a hierarchical structure is synthesized on nickel foam by a simple fabrication method through anion exchange from a metal phosphate to a metal hydroxide. The as-fabricated FeNiOx Hy electrode requires overpotentials of 206 and 234 mV to deliver current densities of 10 and 50 mA cm-2 , respectively. The catalytic performance of FeNiOx Hy is superior to that of most previously reported FeNi-based catalysts, including NiFe layered double hydroxide. The catalyst also shows good long-term durability at a current density of 50 mA cm-2 over 50 h with no activity decay under 1 m KOH. By comparison to the directly electrodeposited FeNi hydroxide in morphology and electrochemical properties, the improved activity of the catalyst could be mainly attributed to an enhancement of its intrinsic activity, which was caused by the anion exchange of phosphate to (oxy)hydroxide. Further studies by cyclic voltammetry indicated a stronger interaction between Ni and Fe from the negative shift of the oxidation peak of Ni2+ /Ni3+ in comparison with reported FeNiOx Hy , which promoted the generation of active Ni3+ species more easily. This work may provide a new approach to the simple preparation of effective and robust OER catalysts by anion exchange.

The isotopic exchangeability of phosphate in Mg-Al layered double hydroxides

Layered double hydroxides (LDH) of Mg/Al are anion exchangers that are candidate materials for phosphate (PO4) recovery and recycling from waste streams. However, PO4 recycling in agriculture might be limited by incomplete desorption of PO4 from the minerals. This study was set up to identify the factors explaining irreversible PO4 sorption (“fixation”) on LDHs by comparing the isotopic exchangeability (33PO4) with the PO4 desorption from LDH materials and from boehmite as a P fixing reference mineral. Six different Mg-Al LDH materials were synthesized, by varying the synthesis pH and exposing obtained materials to hydrothermal (HT) treatment. Phase pure LDH materials were obtained from syntheses at pH 10 and 12, while at pH 8 Al-rich phase impurities such as a boehmite or gibbsite were formed. Crystallite size increased significantly during HT treatment. The LDHs were first loaded with PO4 prior to 33PO4 isotopic exchange (0–20 days, 1 mM NaHCO3) or PO4 desorption (0–20 days, NaHCO3 concentrations increasing from 0 to 20 mM). The isotopic PO4 exchangeability was 85–95% of total PO4 after 72 h in the phase pure LDHs with intercalated PO4 whereas this value was 40–54% in the presence of Al-rich phase impurities in non-HT treated materials and in boehmite. In contrast, the maximally desorbed PO4 fractions were only 55–63% for the phase pure LDHs, indicating that not all of the isotopically exchangeable PO4 can be desorbed. Samples at different stages of desorption (different initial NaHCO3 concentrations) were subjected to isotopic exchange after desorption. In the LDHs with PO4 intercalation, PO4 was increasingly less isotopically exchangeable as the initial NaHCO3 concentrations increased, while this trend was not observed for samples without intercalated PO4. This suggests that PO4 becomes increasingly less accessible for isotopic exchange as the fraction binding sites occupied with HCO3− increases. The interlayer outward diffusion of PO4 might be increasingly rate limited upon H2PO4−/HCO3− exchange, which explains the PO4 fixation in LDHs.

A climosequence of chronosequences in southwestern Australia

SummaryTo examine how climate affects soil development and nutrient availability over long timescales, we studied a series of four long‐term chronosequences along a climate gradient in southwestern Australia. Annual rainfall ranged from 533 to 1185 mm (water balance from −900 to +52 mm) and each chronosequence included Holocene (≤ 6.5 ka), Middle Pleistocene (120–500 ka) and Early Pleistocene (∼2000 ka) dunes. Vegetation changed markedly along the climosequence, from shrubland at the driest site to Eucalyptus forest at the wettest. Soil pH was similar in the youngest soil of each chronosequence, although the carbonate and P contents of the parent sand declined from dry to wet along the climosequence, presumably linked to variation in offshore productivity. Despite this, soil development and associated nutrient status followed remarkably consistent patterns along the four chronosequences. Pedogenesis involved decalcification and secondary carbonate precipitation in Holocene soils and leaching of iron oxides from Middle Pleistocene soils, leading ultimately to bleached quartz sands in the oldest soils. Along all chronosequences soil pH and total P declined, whereas C:P and N:P ratios increased, which is consistent with the predicted change from N to P limitation of vegetation during ecosystem development. The expected unimodal pattern of leaf area index was most pronounced along wetter chronosequences, suggesting an effect of climate on the expression of retrogression. The four chronosequences do not appear to span a pedogenic climate threshold, defined as an abrupt change in soil properties across a relatively small change in climate, because exchangeable phosphate and base cations declined consistently during long‐term pedogenesis. However, the proportion of total P in organic form was greater along wetter chronosequences. We conclude that soil and nutrient availability on the coastal sand plains of southwestern Australia change consistently during long‐term pedogenesis, despite marked variation in modern vegetation and climate. The four chronosequences provide a rare soil‐age × climate framework within which to study long‐term ecosystem development.Highlights We describe four long‐term coastal dune chronosequences spanning a climate gradient in a global biodiversity hotspot. Pedogenesis involves depletion of phosphorus and cations linked to decalcification and subsequent podsolization. Climate has relatively little effect on patterns of nutrient availability during ecosystem development along the climosequence. The age by climate framework enables study of effect of edaphic change on above‐ and below‐ground communities.

De Novo Mutations in SLC25A24 Cause a Disorder Characterized by Early Aging, Bone Dysplasia, Characteristic Face, and Early Demise

A series of simplex cases have been reported under various diagnoses sharing early aging, especially evident in congenitally decreased subcutaneous fat tissue and sparse hair, bone dysplasia of the skull and fingers, a distinctive facial gestalt, and prenatal and postnatal growth retardation. For historical reasons, we suggest naming the entity Fontaine syndrome. Exome sequencing of four unrelated affected individuals showed that all carried the de novo missense variant c.649C>T (p.Arg217Cys) or c.650G>A (p.Arg217His) in SLC25A24, a solute carrier 25 family member coding for calcium-binding mitochondrial carrier protein (SCaMC-1, also known as SLC25A24). SLC25A24 allows an electro-neutral and reversible exchange of ATP-Mg and phosphate between the cytosol and mitochondria, which is required for maintaining optimal adenine nucleotide levels in the mitochondrial matrix. Molecular dynamic simulation studies predict that p.Arg217Cys and p.Arg217His narrow the substrate cavity of the protein and disrupt transporter dynamics. SLC25A24-mutant fibroblasts and cells expressing p.Arg217Cys or p.Arg217His variants showed altered mitochondrial morphology, a decreased proliferation rate, increased mitochondrial membrane potential, and decreased ATP-linked mitochondrial oxygen consumption. The results suggest that the SLC25A24 mutations lead to impaired mitochondrial ATP synthesis and cause hyperpolarization and increased proton leak in association with an impaired energy metabolism. Our findings identify SLC25A24 mutations affecting codon 217 as the underlying genetic cause of human progeroid Fontaine syndrome.

Structure of the triose-phosphate/phosphate translocator reveals the basis of substrate specificity.

The triose-phosphate/phosphate translocator (TPT) catalyses the strict 1:1 exchange of triose-phosphate, 3-phosphoglycerate and inorganic phosphate across the chloroplast envelope, and plays crucial roles in photosynthesis. Despite rigorous study for more than 40 years, the molecular mechanism of TPT is poorly understood because of the lack of structural information. Here we report crystal structures of TPT bound to two different substrates, 3-phosphoglycerate and inorganic phosphate, in occluded conformations. The structures reveal that TPT adopts a 10-transmembrane drug/metabolite transporter fold. Both substrates are bound within the same central pocket, where conserved lysine, arginine and tyrosine residues recognize the shared phosphate group. A structural comparison with the outward-open conformation of the bacterial drug/metabolite transporter suggests a rocker-switch motion of helix bundles, and molecular dynamics simulations support a model in which this rocker-switch motion is tightly coupled to the substrate binding, to ensure strict 1:1 exchange. These results reveal the unique mechanism of sugar phosphate/phosphate exchange by TPT.

Fractionation and availability of phosphorus in acid soils of Hagereselam, Southern Ethiopia under different rates of lime

BackgroundPhosphorus (P) availability is commonly assumed to limit productivity in many tropical soils, yet there is relatively little information on the phosphorus chemical forms, distribution, and transformations that P undergoes in Ethiopian soils. We used a sequential fractionation scheme to assess phosphorus fractions of acid soils of Southern Ethiopia. The study area called Hagereselam is characterized by high soil acidity, and the availability of P in the study area is relatively low. As crop production in Ethiopia is dominated by low external input practices, native P remains the main contributor to plant P nutrition in many locations.ResultAlthough the total P concentration is 829.7 mg kg−1, the organic P content was relatively low (58 mg kg−1) and constituted on average less than 7% of the total P. The ratio of organic carbon to organic P was generally greater than 240, suggesting the potential for immobilization of P. The Al + Fe-associated P was the dominant inorganic P pool. The majority of the P occurred in recalcitrant form (568.3 mg kg−1). Readily available, exchangeable phosphate, as extracted by anion-exchange resin membranes, was present in very low concentrations (3.3 mg kg−1); moreover, labile P accounted for less than 2% (9.9 mg kg−1) of the total soil P.ConclusionLime was used as a reclamation material for acid soils, and the application of lime significantly affected the different P fractions and was involved in the transformation of P fraction. Organic P forms were significantly lower for higher levels of lime application, suggesting that lime amendment enhanced organic P decomposition. Moreover, application of lime increased Ca-P and decreased Al + Fe–P for acid soils.Graphical abstractEffect of lime of phosphorus pools

Co-effect of phosphorus and cadmium interaction on fraction distribution and accumulation of phosphorus in mangrove-sediment system

ABSTRACTMangrove [Kandelia obovata (S. L.)] seedlings were cultivated in rhizoboxes under different rates of phosphorus (P) and cadmium (Cd) level. The speciation distributions of P both in the rhizosphere and non-rhizosphere sediments were examined using sequential extraction procedures. P contents in different K. obovata (S.L.) tissues were also determined. Results showed that considerable differences existed in P speciation distribution between rhizosphere and bulk sediments. A higher proportion of iron-bound phosphate (Fe-P) was found in the rhizosphere sediments, while a relatively higher concentration of exchangeable phosphate (Ex-P) and Aluminum-bound phosphate was found in the bulk sediments. P accumulation in plant tissues was significantly positively correlated to Ex-P and Fe-P. Results indicated that root activities play an important role in the P cycling. And the coexistence of P and Cd induced higher P accumulation in mangrove plants. It is suggested that the root-induced chemical and biological changes in the rhizosphere environment play an important role in enhancing the bioavailability of soil P.

A phosphorus threshold for mycoheterotrophic plants in tropical forests.

The majority of terrestrial plants associate with arbuscular mycorrhizal (AM) fungi, which typically facilitate the uptake of limiting mineral nutrients by plants in exchange for plant carbon. However, hundreds of non-photosynthetic plant species-mycoheterotrophs-depend entirely on AM fungi for carbon as well as mineral nutrition. Mycoheterotrophs can provide insight into the operation and regulation of AM fungal relationships, but little is known about the factors, fungal or otherwise, that affect mycoheterotroph abundance and distribution. In a lowland tropical forest in Panama, we conducted the first systematic investigation into the influence of abiotic factors on the abundance and distribution of mycoheterotrophs, to ask whether the availability of nitrogen and phosphorus altered the occurrence of mycoheterotrophs and their AM fungal partners. Across a natural fertility gradient spanning the isthmus of Panama, and also in a long-term nutrient-addition experiment, mycoheterotrophs were entirely absent when soil exchangeable phosphate concentrations exceeded 2 mg P kg-1 Experimental phosphorus addition reduced the abundance of AM fungi, and also reduced the abundance of the specific AM fungal taxa required by the mycoheterotrophs, suggesting that the phosphorus sensitivity of mycoheterotrophs is underpinned by the phosphorus sensitivity of their AM fungal hosts. The soil phosphorus concentration of 2 mg P kg-1 also corresponds to a marked shift in tree community composition and soil phosphatase activity across the fertility gradient, suggesting that our findings have broad ecological significance.

The effects of sulfur amendments on the geochemistry of sulfur, phosphorus and iron in the mangrove plant (Kandelia obovata (S. L.)) rhizosphere

P (phosphorus) and Fe (iron) are limiting elements and S (sulfur) is an important element of the biogeochemical cycle in the mangrove environment. To assess the effects of sulfur on the geochemical cycling of Fe and P at the sediment-plant interface, the speciation distributions of Fe, P and S in sediments were examined. The data showed that higher proportions of amorphous Fe, Fe-bound phosphate, chromium reducible sulfur and elemental sulfur were found in the rhizosphere, while more crystalline Fe, exchangeable phosphate and acid-volatile sulfide were determined in the non-rhizosphere. Sulfate application induced an increase in the Ex-P concentration, high P accumulation and high iron plaque deposition in the roots. In conclusion, sulfate applications had a significant influence on the geochemical cycling of Fe and P in the sediments. It significantly curtailed the Fe and P limit to plant growth and enhanced plant resistance to the rugged surroundings in mangrove.

Take a Trip Through the Plant and Fungal Transportome of Mycorrhiza.

Soil nutrient acquisition and exchanges through symbiotic plant-fungus interactions in the rhizosphere are key features for the current agricultural and environmental challenges. Improved crop yield and plant mineral nutrition through a fungal symbiont has been widely described. In return, the host plant supplies carbon substrates to its fungal partner. We review here recent progress on molecular players of membrane transport involved in nutritional exchanges between mycorrhizal plants and fungi. We cover the transportome, from the transport proteins involved in sugar fluxes from plants towards fungi, to the uptake from the soil and exchange of nitrogen, phosphate, potassium, sulfate, and water. Together, these advances in the comprehension of the mycorrhizal transportome will help in developing the future engineering of new agro-ecological systems.

What is the P value of Siberian soils? Soil phosphorus status in south-western Siberia and comparison with a global data set

Abstract. Climate change is particularly strong in northern Eurasia and substantial ecological changes are expected in this extensive region. The reshaping and migration northwards of bioclimatic zones may offer opportunities for agricultural development in western and central Siberia. However, the bioclimatic vegetation models currently employed for projections still do not consider soil fertility, in spite of this being highly critical for plant growth. In the present study, we surveyed the phosphorus (P) status in the south-west of Siberia where soils have developed on loess parent material. We selected six sites differing in pedoclimatic conditions and the soil was sampled at different depths down to 1 m in aspen (Populus tremula L.) forest as well as in grassland areas. The P status was assessed by conventional methods and by isotope dilution kinetics. We found that P concentrations and stocks, as well as their distribution through the soil profile, were fairly homogeneous on the regional scale studied, although there were some differences between sites (particularly in organic P). The young age of the soils, together with slow kinetics of soil formation processes have probably not yet resulted in a sufficiently wide range of soil physico-chemical conditions to observe a more diverging P status. The comparison of our data set with similar vegetation contexts on the global scale revealed that the soils of south-western Siberia, and more generally of northern Eurasia, often have (very) high levels of total, organic and inorganic P. The amount of plant-available P in topsoils, estimated by the isotopically exchangeable phosphate ions, was not particularly high but was intermediate on the global scale. However, large stocks of plant-available P are stored in subsurface layers which currently have low fine-root exploration intensities. These results suggest that the P resource is unlikely to constrain vegetation growth and agricultural development under the present conditions or in the near future.

The Expression of Ubiquitous Mitochondrial Creatine Kinase Is Downregulated as Prostate Cancer Progression.

Background: Mitochondria play crucial roles in cell signaling events, interorganellar communication, aging, cell proliferation and apoptosis, and mitochondrial impairment has been shown to accelerate or modulate cancer progression. Ubiquitous mitochondrial creatine kinase (uMtCK) is predominantly localized in the intermembrane space of mitochondria and catalyzes the reversible exchange of high-energy phosphate between adenosine tri-phosphate (ATP) and phosphocreatine. However, little is known about its expression and function in human prostate cancer progression.Method: We investigated the expression of uMtCK in 148 prostate carcinoma tissues and matched normal tissue by immunohistochemistry. The expression and localization of uMtCK and hexokinase II, a marker of glycolysis, were examined in prostate carcinoma cell lines using western blot and immunofluorescence.Results: MtCK expression was significantly lower in high Gleason grade carcinoma compared with normal prostate or low grade carcinoma. Western blot further revealed that uMtCK was highly expressed in LNCaP and 22Rv1 cell lines, as well as in the normal prostate cell line RWPE-1. However, uMtCK expression was almost absent in PC3 and DU145 cell lines, in correlation with absent or mutant p53 expression, respectively. In contrast, hexokinase II was overexpressed in PC3 cells. Moreover, in the low uMtCK expressing cell lines, glycolytic ATP production was increased, whereas mitochondrial ATP production was decreased.Conclusions: These data suggest that uMtCK is downregulated as prostate cancer progresses in correlation with a metabolic switch in ATP usage.

Common Creatine Kinase gene mutation results in falsely reassuring CK levels in muscle disorders.

Learning point for clinicians The mean allele frequency of this SNP is 0.02 (∼2.5 million people in the UK are carriers). Therefore, greater awareness of this CKM SNP is needed as there may be instances where the diagnosis of rhabdomyolysis, statin-induced myopathy, poly-/dermatomyositis and other muscle conditions that result in raised CK’s, is missed in these patients. Creatine Kinase (CK) is the enzyme responsible for catalysing the exchange of phosphates in the creatine/phosphocreatine shuttle.1 Skeletal muscle CK is made …

In vitro analyses of mitochondrial ATP/phosphate carriers from Arabidopsis thaliana revealed unexpected Ca2+-effects

BackgroundAdenine nucleotide/phosphate carriers (APCs) from mammals and yeast are commonly known to adapt the mitochondrial adenine nucleotide pool in accordance to cellular demands. They catalyze adenine nucleotide - particularly ATP-Mg - and phosphate exchange and their activity is regulated by calcium. Our current knowledge about corresponding proteins from plants is comparably limited. Recently, the three putative APCs from Arabidopsis thaliana were shown to restore the specific growth phenotype of APC yeast loss-of-function mutants and to interact with calcium via their N-terminal EF-hand motifs in vitro. In this study, we performed biochemical characterization of all three APC isoforms from A. thaliana to gain further insights into their functional properties.ResultsRecombinant plant APCs were functionally reconstituted into liposomes and their biochemical characteristics were determined by transport measurements using radiolabeled substrates. All three plant APCs were capable of ATP, ADP and phosphate exchange, however, high preference for ATP-Mg, as shown for orthologous carriers, was not detectable. By contrast, the obtained data suggest that in the liposomal system the plant APCs rather favor ATP-Ca as substrate. Moreover, investigation of a representative mutant APC protein revealed that the observed calcium effects on ATP transport did not primarily/essentially involve Ca2+-binding to the EF-hand motifs in the N-terminal domain of the carrier.ConclusionBiochemical characteristics suggest that plant APCs can mediate net transport of adenine nucleotides and hence, like their pendants from animals and yeast, might be involved in the alteration of the mitochondrial adenine nucleotide pool. Although, ATP-Ca was identified as an apparent import substrate of plant APCs in vitro it is arguable whether ATP-Ca formation and thus the corresponding transport can take place in vivo.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0616-0) contains supplementary material, which is available to authorized users.

Determination of water-soluble phosphate content of soil using heterogeneous exchange reaction with 32P radioactive tracer

The nutrient uptake by plants is significantly influenced by the quantity of phosphate in the soil solution. Optimal fertilization rate demands the determination of water soluble phosphate quantity, the rate of desorption and phosphate exchange between the soil and soil solution at steady state. The aim of this paper was to determine the ratio of water-soluble/exchangeable to mineralized/organic phosphate after incubation of the soil with different phosphate quantities. The sorption process of phosphate on soil was studied by heterogeneous isotope exchange using a radioactive isotope of phosphorous. Using the correct mathematical analysis of the kinetics of heterogeneous isotope exchange, the rate of phosphate exchange was established under steady state condition. The distribution of radioactivity in equilibrium provided information on the reversibility or irreversibility of phosphate sorption. The results revealed that during a relatively short incubation period, the water-soluble/exchangeable phosphorous quantity, namely the portion of phosphate which can easily be taken up by plants, was proportional to the added phosphorous quantity. The tightly sorbed phosphorous quantity, however, reached a limit, suggesting that the reactants leading to tight sorption are consumed. The exchange rate of phosphorous between the soil and the solution was found to be proportional to the phosphorous quantity in the soil solution, showing that the rate-determining step of the heterogeneous isotope exchange process was the diffusion of phosphate ions.

Potential health risks of arsenic, antimony and mercury in the Takab geothermal field, NW Iran

This study investigates the bioavailability, water–soil to plant transfer and health risks of arsenic (As), antimony (Sb) and mercury (Hg) in the Takab geothermal field north-west of Iran. Water used for irrigation, surface soils from agricultural lands and cultivated plants were collected from three polluted sites and analysed for As, Sb and Hg to assess associated health risks. As content in irrigation water ranges from 23.4 to 986.4 μg/L, whereas total As content in the surface soil is in the range of 16.3–492 mg/kg−1. The results agree with other reports that metal (loid) concentrations in leaves are usually much higher than in grain. Most investigated plant species showed a significant correlation between As, Sb and Hg contents in their aerial parts and that available in the soil (r = 0.82, p = 0.012; r = 0.84, p = 0.004; r = 0.79, p = 0.011). Factors influencing the bioavailability of metal (loids) and their occurrences in plants are soil pH, cation exchange capacity, phosphate, calcite and organic matter content, soil texture and interaction between target elements. Available As in analysed soils is relatively low, implying that phosphate, as well as Fe-oxy-hydroxides and calcite are effective in absorbing As. But, sequential extraction analysis indicates that iron oxy-hydroxide surface can bind both As and Sb, with As being more strongly bound. The calculated bioaccumulation factor based on total metal (loids) and available metal (loids) in soil indicates that alfalfa (Medicago sativa L.) and sage (Saliva syriaca L.) are effective accumulators of As, Sb and Hg. The health risk index of the studied plants ranged from 0.0003 to 5.71, with the maximum being in wheat (Triticun aestivum L.), an alarming sign for human health. It is suggested that health risks from long-term consumption of wheat and other As-rich foodstuffs must be managed by monitoring contamination in the water–soil–plant pathway.