Mn Transport Research Articles

Differential manganese and iron recycling and transport in continental margin sediments of the Northern Gulf of Mexico

Pore water and solid phase geochemical profiles of sediment cores collected along two transects on the western and eastern sides of the Mississippi River mouth in the northern Gulf of Mexico were incorporated into a reactive transport model to determine the role of manganese and iron in the remineralization of carbon. Reactive transport model calculations indicate that sedimentation rates control the intensity of anaerobic carbon remineralization and select for the dominant anaerobic carbon remineralization pathways. Although sulfate reduction dominates the shelf station (65 m water depth), denitrification and microbial manganese reduction appear equally significant anaerobic respiration processes along the continental slope the closest to the Mississippi River, whereas microbial iron reduction does not represent an important process in these sediments. These findings suggest that the differential kinetics of manganese and iron redox transformations influence carbon remineralization processes on the continental slope. The fast kinetics of Fe2+ oxidation near the sediment-water interface and high sedimentation rates maintain Fe under the form of Fe(III) oxides and thermodynamically prevent sulfate reduction from dominating carbon remineralization processes on the slope, whereas the much slower Mn2+ oxygenation kinetics allows diffusion of Mn2+ across the sediment-water interface of the shelf station closest to the river mouth. Exposure to oxygenated bottom waters and entrainment within mobile muds typical of deltaic sediments during high riverine discharge likely promote the formation and downslope transport of Mn(III/IV) oxides within the nepheloid layer. This phenomenon appears to form a manganese ‘conveyor belt’ that selectively enriches Mn(III/IV) oxides relative to Fe(III) oxides in the deep sediment. In contrast, the intensity of anaerobic carbon remineralization processes along the eastern continental slope the farthest from the Mississippi River plume is much lower due to the low organic and lithogenic inputs, and denitrification dominates anaerobic respiration. Overall, these findings suggest that manganese cycling and its role in carbon remineralization processes in continental slope sediments exposed to large riverine inputs may be more important than previously considered.

Manganese Accumulation in the Brain via Various Transporters and Its Neurotoxicity Mechanisms.

Manganese (Mn) is an essential trace element, serving as a cofactor for several key enzymes, such as glutamine synthetase, arginase, pyruvate decarboxylase, and mitochondrial superoxide dismutase. However, its chronic overexposure can result in a neurological disorder referred to as manganism, presenting symptoms similar to those inherent to Parkinson’s disease. The pathological symptoms of Mn-induced toxicity are well-known, but the underlying mechanisms of Mn transport to the brain and cellular toxicity leading to Mn’s neurotoxicity are not completely understood. Mn’s levels in the brain are regulated by multiple transporters responsible for its uptake and efflux, and thus, dysregulation of these transporters may result in Mn accumulation in the brain, causing neurotoxicity. Its distribution and subcellular localization in the brain and associated subcellular toxicity mechanisms have also been extensively studied. This review highlights the presently known Mn transporters and their roles in Mn-induced neurotoxicity, as well as subsequent molecular and cellular dysregulation upon its intracellular uptakes, such as oxidative stress, neuroinflammation, disruption of neurotransmission, α-synuclein aggregation, and amyloidogenesis.

Effects of Fe and Mn cations on Cd uptake by rice plant in hydroponic culture experiment.

Iron (Fe) and manganese (Mn) are nutritional components of rice, plays an important role in its physiological processes and can minimize absorption of cadmium (Cd) in rice. Fe, Mn, and Cd transporters such as CAL1, OsNRAMP5, OsNRAMP1, OsIRT1, OsHMA3, and OsNAAT1 regulate uptake of Cd in rice. However, the effect of exogenous application of Fe, and Mn on the accumulation of Cd and relative expression (RE) of these transporters in rice has not been investigated. Therefore, a hydroponic culture experiment was conducted to investigate the impact of Fe and Mn on Cd uptake and RE of these transporters in rice. The results showed that the Fe and Mn application significantly decreased Cd in the roots and shoots of rice. Whereas, Cd concentration in the rice significantly increased with increasing Cd concentration in the solution. The addition of manganese in the culture medium can reduce the cadmium content of rice roots by 11.9–82.3% and shoots by 11.6–85.0%, while the addition of iron in the culture medium can reduce the cadmium content of rice roots and shoots by 26–65% and 9–683% respectively. Meanwhile, application of sufficient doses of Fe and Cd in solution culture increased RE of CAL1, OsNRAMP5, OsNRAMP1, OsIRT1, and OsNAAT1 in roots, whereas expression level of OsHMA3 was decreased. Similarly, expression level of CAL1, OsNRAMP5, and OsNRAMP1 significantly increased in roots in high Cd and Mn deficient treatments. This may be concluded that the Cd increases expression of CAL1, OsNRAMP5, OsNRAMP1, OsIRT1, and OsNAAT1 but decreases OsHMA3 expression in rice roots, which resulted in increased Cd uptake in hydroponically grown rice.

Growth, ionic homeostasis, and physiological responses of cotton under different salt and alkali stresses

To better understand the mechanism of salt tolerance, we analyzed cotton growth and the ionomes in different tissues under different types of salt–alkali stress. Cotton was exposed to the soil salt and alkali stresses, NaCl, Na2SO4, and Na2CO3 + NaHCO3, in a pot study. Salt and alkali stress significantly inhibited cotton growth, significantly reduced root length, surface area, and volume, and significantly increased relative electrical conductivity (REC) and malondialdehyde (MDA) content but also significantly increased antioxidant enzyme activities, and proline (Pro) content. The REC in leaves was higher under salt stress than under alkali stress, but the effects on Pro were in the order Na2CO3 + NaHCO3 > NaCl > Na2SO4. Principal component analysis showed a significant difference in ion composition under the different types of salt–alkali stress. Under the three types of salt–alkali stress, concentrations of Na and Mo increased significantly in different organs of cotton plants. Under NaCl stress, the absorption of Ca was inhibited, the transport capacity of P, Mg, and Cu was reduced, and the ion balance was maintained by promoting the uptake and transport of Zn, Mn, Al, and Mo. Under Na2SO4 stress, the absorption of P and Ca was inhibited, the transport capacity of Mg, B, and Cu was reduced, and the ion balance was maintained by promoting the uptake and transport of S, Zn, Fe, Mo, Al, and Co. Under Na2CO3 + NaHCO3 stress, the absorption of P and S was inhibited, the transport capacity of Mg and B was reduced, but that of Al and Fe increased, and the ion balance was maintained by promoting the uptake and transport of Mn, Mo, Ni, and Co. The relative expression of GhSOS1 and GhNHX1 in leaves increased significantly under salt stress but decreased under alkali stress. These results suggest that cotton is well-adapted to salt–alkali stress via the antioxidant enzyme system, adjustment of osmotic substances, and reconstruction of ionic equilibrium; neutral salt stress primarily disrupts the ion balance, whereas alkali stress decreases the ability to regulate Na and inhibits the absorption of mineral elements, as well as disrupts the ion balance; and the changes in the expression of salt tolerance-related genes may partially explain the accumulation of Na ions in cotton under salt–alkali stress.

Electrophysiology Measurements of Metal Transport by MntH2 from Enterococcus faecalis.

Transition metals are essential trace elements and their high-affinity uptake is required for many organisms. Metal transporters are often characterised using metal-sensitive fluorescent dyes, limiting the metals and experimental conditions that can be studied. Here, we have tested whether metal transport by Enterococcus faecalis MntH2 can be measured with an electrophysiology method that is based on the solid-supported membrane technology. E. faecalis MntH2 belongs to the Natural Resistance-Associated Macrophage Protein (Nramp) family of proton-coupled transporters, which transport divalent transition metals and do not transport the earth metals. Electrophysiology confirms transport of Mn(II), Co(II), Zn(II) and Cd(II) by MntH2. However, no uptake responses for Cu(II), Fe(II) and Ni(II) were observed, while the presence of these metals abolishes the uptake signals for Mn(II). Fluorescence assays confirm that Ni(II) is transported. The data are discussed with respect to properties and structures of Nramp-type family members and the ability of electrophysiology to measure charge transport and not directly substrate transport.

Cyclic oxidation behaviour of TP446, TP310, and IN617 in air at 871°C and 982°C

ABSTRACT The influence of frequency of thermal cycling on the oxidation behaviour of alloys TP446, TP310, and Inconel 617 in dry air at very high temperatures (871°C and 982°C) is reported. The effects on the iron-basedalloys were complex, whereas that of the Ni-based alloy was not greatly affected by cycling frequency. Unexpected trends were increased oxidation rates of TP310 and Inconel 617 with increased cycle frequency at 871°C, whereas those of TP446 decreased. At 982°C, the oxidation rates of TP310 and TP446 decreased with increasing cycle frequency, though less so for TP310. While the scales formed on the iron-based alloys consisted of a basal layer corresponding to chromia containing Mn, and an outer layer corresponding to manganese chromate, differences in the rates of transport of Cr, Mn and Si in the alloys at the different temperatures appeared to account in large measure for the differences in response to thermal cycling.

Localization of ZIP14 and ZIP8 in HIBCPP Cells.

The blood–cerebrospinal fluid barrier (BCB) is important in maintaining brain manganese (Mn) homeostasis. This barrier consists of a single layer of epithelial cells, connected by tight junctions, that restrict the passage of nutrients to only allow molecules to be carried through the membrane by a transporter. These epithelial cells are polarized with asymmetrical blood-facing and cerebrospinal fluid-facing sides. Here, we have established a polarized model of a human choroid plexus papilloma cell line, HIBCPP. For the first time, Mn importers ZIP14 and ZIP8 were identified in HIBCPP cells and were found to be enriched at the basolateral and apical sides of the cell monolayer, respectively. The localization of each ZIP protein adds to the understanding of Mn transport across the HIBCPP BCB model to help understand the mechanism of Mn homeostasis within the brain.

Genetic Redundancy in Iron and Manganese Transport in the Metabolically Versatile Bacterium Rhodopseudomonas palustris TIE-1.

The purple nonsulfur bacterium Rhodopseudomonas palustris TIE-1 can produce useful biochemicals such as bioplastics and biobutanol. Production of such biochemicals requires intracellular electron availability, which is governed by the availability and the transport of essential metals such as iron (Fe). Because of the distinct chemical properties of ferrous [Fe(II)] and ferric iron [Fe(III)], different systems are required for their transport and storage in bacteria. Although Fe(III) transport systems are well characterized, we know much less about Fe(II) transport systems except for the FeoAB system. Iron transporters can also import manganese (Mn). We studied Fe and Mn transport by five putative Fe transporters in TIE-1 under metal-replete, metal-depleted, oxic, and anoxic conditions. We observed that by overexpressing feoAB, efeU, and nramp1AB, the intracellular concentrations of Fe and Mn can be enhanced in TIE-1 under oxic and anoxic conditions, respectively. The deletion of a single gene/operon does not attenuate Fe or Mn uptake in TIE-1 regardless of the growth conditions used. This indicates that genetically dissimilar yet functionally redundant Fe transporters in TIE-1 can complement each other. Relative gene expression analysis shows that feoAB and efeU are expressed during Fe and Mn depletion under both oxic and anoxic conditions. The promoters of these transporter genes contain a combination of Fur and Fnr boxes, suggesting that their expression is regulated by both Fe and oxygen availability. The findings from this study will help us modulate intracellular Fe and Mn concentrations, ultimately improving TIE-1's ability to produce desirable biomolecules.IMPORTANCERhodopseudomonas palustris TIE-1 is a metabolically versatile bacterium that can use various electron donors, including Fe(II) and poised electrodes, for photoautotrophic growth. TIE-1 can produce useful biomolecules, such as biofuels and bioplastics, under various growth conditions. Production of such reduced biomolecules is controlled by intracellular electron availability, which, in turn, is mediated by various iron-containing proteins in the cell. Several putative Fe transporters exist in TIE-1's genome. Some of these transporters can also transport Mn, part of several important cellular enzymes. Therefore, understanding the ability to transport and respond to various levels of Fe and Mn under different conditions is important to improve TIE-1's ability to produce useful biomolecules. Our data suggest that by overexpressing Fe transporter genes via plasmid-based expression, we can increase the import of Fe and Mn in TIE-1. Future work will leverage these data to improve TIE-1 as an attractive microbial chassis and future biotechnological workhorse.

Ultra-high strength attributed to retardation of recrystallization during intercritical annealing in cold-rolled (V,Nb) microalloyed 5Mn steel

The effects of V and Nb addition on the microstructure and mechanical properties of a cold-rolled and intercriticallly annealed 5Mn steel were investigated. Compared to a steel without V or Nb the recrystallization in microalloyed steel was retarded significantly from the beginning of annealing, which resulted in a 100–200 MPa increase in both yield and tensile strength while the degradation of ductility was not observed. Negligibly small change in elongation was attributed to a larger degree of carbon enrichment due to the smaller volume fraction of retained austenite and accelerated Mn transport through high density dislocations, which may well have operated to increase the austenite stability.

Maintaining Translational Relevance in Animal Models of Manganese Neurotoxicity

Manganese is an essential metal, but elevated brain Mn concentrations produce a parkinsonian-like movement disorder in adults and fine motor, attentional, cognitive, and intellectual deficits in children. Human Mn neurotoxicity occurs owing to elevated exposure from occupational or environmental sources, defective excretion (e.g., due to cirrhosis), or loss-of-function mutations in the Mn transporters solute carrier family 30 member 10 or solute carrier family 39 member 14. Animal models are essential to study Mn neurotoxicity, but in order to be translationally relevant, such models should utilize environmentally relevant Mn exposure regimens that reproduce changes in brain Mn concentrations and neurological function evident in human patients. Here, we provide guidelines for Mn exposure in mice, rats, nematodes, and zebrafish so that brain Mn concentrations and neurobehavioral sequelae remain directly relatable to the human phenotype.

Evaluation of Metals Leaching in Permeable Asphalt Pavement and Conventional Asphalt Pavement

A permeable asphalt pavement (PP) and a conventional asphalt pavement (PD) have been tested regarding the potential leaching of the metals Cd, Cr, Fe, Pb, Mn, Ni and Zn during 11 rain events immediately after their construction. Water samples were picked up for the rain water and in four sampling points of both pavements during every rain, two located at the surface of the pavements (PPE and PDE), and other two after infiltration in the pavements (PPI and PDI). The results show that there was introduction and transport of Cr, Fe, Pb, Mn, Ni and Zn during surface runoff on pavements. After water infiltration in the pavements, there was significant removal of Cr in the PD pavement, Pb and Zn concentrations did not decrease in depth and concentrations of Fe and Ni increased after infiltration. However, the concentrations of all metals in the leaching water are very low comparing with the minimum standard legal values set up for irrigation and discharge on water courses.

Chromium, manganese, nickel, and cobalt mobility and bioavailability from mafic-to-ultramafic mine spoil weathering in western Massachusetts, USA.

Fragmented ultramafic bodies in New England were important mineral resources until the early twentieth century, yet few studies have addressed their potential to release trace metals to terrestrial and aquatic environments. Here, we evaluate the release of four trace metals (Cr, Co, Mn, and Ni) from a historic serpentine-talc "soapstone" quarry in Blandford, MA, USA. Soil pits, sediment and rock samples, and stream water samples were collected from upslope undisturbed areas, within the mine spoils and mine face, and downslope of the mine. In order to provide a bottom-up approach for understanding metal release, careful petrographic analysis, electron-dispersive spectroscopy, and wavelength-dispersive spectroscopy were employed to provide first-order insight into the mineralogy of the deposit and a determination of potential metal-bearing phases. Trace metals were primarily observed in ultramafic sheet silicates, primary Fe-oxides, and interstitial weathering-related sulfates. Bulk rock concentrations were Cr (1550mgkg-1), Co (230mgkg-1), Mn (1100mgkg-1), and Ni (1960mg kg1); Cr, Co, and Ni were elevated relative to the surrounding country rock. However, soils and sediments total concentrations were comparable to background soil concentrations: Cr (119mgkg-1), Co (73mgkg-1), Mn (894mgkg-1), and Ni (65mgkg-1). Moreover, < 0.5% of the total concentrations were bioavailable (0.1M ammonium acetate extraction), implying that metals are present as insoluble forms. However, ~ 20% of the total Cr, Mn, Ni, and Co concentrations were strong acid extractable, suggesting mobilization over the coming decades. Stream water concentrations of Mn and Cr were < 50µg L-1, below concentrations outlined by USEPA drinking water standards, and WHO water guidelines for Ni. These results suggest that transport of Cr, Mn, Ni, and Co from the serpentine-talc as dissolved compounds or sediments is limited by retention within silicate and oxides.

Seasonal manganese transport in the hyporheic zone of a snowmelt-dominated river (East River, Colorado, USA)

Manganese (Mn) plays a critical role in river-water quality because Mn-oxides serve as sorption sites for contaminant metals. The aim of this study is to understand the seasonal cycling of Mn in an alpine streambed that experiences large spring snowmelt events and the potential responses to changes in snowmelt timing and magnitude. To address this goal, annual variations in river-water/groundwater interaction and Mn(aq) transport were measured and modeled in the bed of East River, Colorado, USA. In observations and numerical models, oxygenated river water containing dissolved organic carbon (DOC) mixes with groundwater rich in Mn(aq) in the streambed. The mixing depth increases during spring snowmelt when river discharge increases, leading to a greater DOC supply to the hyporheic zone and net respiration of Mn-oxides, despite an enhanced supply of oxygen. As groundwater upwelling resumes during the subsequent baseflow period, Mn(aq)-rich groundwater mixes with oxygenated river water, resulting in net accumulation of Mn-oxides until the bed freezes in winter. To explore potential responses of Mn transport to different climate-induced hydrological regimes, three hydrograph scenarios were numerically modeled (historic, low-snow, and storm) for the Rocky Mountain region. In a warming climate, Mn(aq) export to the river decreases, and Mn(aq) oxidation is favored in the upper streambed sediments over more of the year. One important implication is that the streambed may have an increased sorption capacity for metals over more of the year, leading to potential changes in river-water quality.

Genome-Wide Identification of Metal Tolerance Protein Genes in Populus trichocarpa and Their Roles in Response to Various Heavy Metal Stresses.

Metal tolerance proteins (MTPs) are plant divalent cation transporters that play important roles in plant metal tolerance and homeostasis. Poplar is an ideal candidate for the phytoremediation of heavy metals because of its numerous beneficial attributes. However, the definitive phylogeny and heavy metal transport mechanisms of the MTP family in poplar remain unknown. Here, 22 MTP genes in P. trichocarpa were identified and classified into three major clusters and seven groups according to phylogenetic relationships. An evolutionary analysis suggested that PtrMTP genes had undergone gene expansion through tandem or segmental duplication events. Moreover, all PtrMTPs were predicted to localize in the vacuole and/or cell membrane, and contained typical structural features of the MTP family, cation efflux domain. The temporal and spatial expression pattern analysis results indicated the involvement of PtrMTP genes in poplar developmental control. Under heavy metal stress, most of PtrMTP genes were induced by at least two metal ions in roots, stems or leaves. In addition, PtrMTP8.1, PtrMTP9 and PtrMTP10.4 displayed the ability of Mn transport in yeast cells, and PtrMTP6 could transport Co, Fe and Mn. These findings will provide an important foundation to elucidate the biological functions of PtrMTP genes, and especially their role in regulating heavy metal tolerance in poplar.

Controls on the shuttling of manganese over the northwestern Black Sea shelf and its fate in the euxinic deep basin

Manganese (Mn) is an essential micronutrient for phytoplankton and its cycling interacts with that of iron (Fe). Continental shelf sediments are a key but poorly quantified source of Mn to marine waters. In this study, we investigate Mn release from shelf sediments, its lateral transport (“shuttling”) in the oxic water column over the northwestern Black Sea shelf and its fate in the adjacent euxinic deep basin. We find a high release of Mn from organic-rich, bioirrigated coastal sediments, but negligible mobilization and release of Mn from sediments in offshore shelf regions, because of a low input of organic matter. Most Mn in the water column is present in dissolved form. We suggest that this dissolved Mn is released from coastal sediments and subsequently transported offshore through physical processes. Surface sediments at open shelf and shelf edge stations are highly enriched in Mn when compared to coastal and deep basin stations. Only part of the surface enrichment can be explained by oxidation of porewater Mn. The remainder of this enrichment is likely the result of oxidative removal of dissolved Mn from the water column and deposition as Mn oxides. Using X-ray spectroscopy we show that Mn in surface sediments in this area predominately consists of Mn(IV) oxides (phyllo- and/or tectomanganates). A key difference between Mn versus Fe shuttling is the form in which the metal is transported: while dissolved Mn dominates in the water column over the shelf, most Fe is present in particulate form. Sediment trap data indicate that the vertical transport of both Mn and Fe through the euxinic water column is correlated and is associated with the sinking flux of biogenic particulate matter following the spring and fall phytoplankton blooms. In the sediments of the euxinic basin, Mn is enriched when compared to a detrital Mn background and its burial correlates with that of Fe. This suggests that Mn could be incorporated in pyrite in the euxinic water column. Our results highlight the critical role of organic matter input as a driver of Mn and Fe shuttling over the Black Sea continental shelf and particulate matter as the carrier of Mn and Fe into the euxinic basin.

Effects of external Mn2+ activities on OsNRAMP5 expression level and Cd accumulation in indica rice

Manganese (Mn) transporter OsNRAMP5 was widely reported to regulate cadmium (Cd) uptake in rice. However, the relationship between OsNRAMP5 expression level and Cd accumulation, impacts of external ion activities on OsNRAMP5 expression level and Cd accumulation are still unclear. Investigations of the relationship between OsNRAMP5 expression level and Cd accumulation in three indica rice genotypes were conducted under various external Mn2+ activities ranging from Mn deficiency to toxicity in EGTA-buffered nutrient solution. Results in this work indicated that OsNRAMP5 expression level in roots significantly up-regulated at Mn phytotoxicity compared to that at Mn deficiency, which may stimulate by the increasing uptake of Mn. Our work also demonstrated that root Cd concentration of all the tested rice decreased notably when external Mn2+ activity reached the level of toxicity. This may explain by the increasing competition between the excess Mn2+ and Cd2+ as well as the disorder of element absorption caused by root damage at Mn toxicity. Our work also revealed that the relationship between OsNRAMP5 expression level in roots and Cd accumulation in roots was insignificant for all the tested genotypes. Besides, OsNRAMP5 expression level in roots seemed more related to root Mn accumulation. The fact that function of OsNRAMP5 mainly focuses on Mn uptake, together with the fact that many transporter genes involved in Cd uptake might result in the insignificant correlation between OsNRAMP5 expression level and Cd accumulation in roots. At last, multi-level regulating and processing of the process from gene expression to protein translation might account for the inconsistent relationship between root OsNRAMP5 expression level and Cd accumulation in roots.

Manganese Uptake, Mediated by SloABC and MntH, Is Essential for the Fitness of Streptococcus mutans.

Early epidemiological studies implicated manganese (Mn) as a possible caries-promoting agent, while laboratory studies have indicated that manganese stimulates the expression of virulence-related factors in the dental pathogen Streptococcus mutans To better understand the importance of manganese homeostasis to S. mutans pathophysiology, we first used RNA sequencing to obtain the global transcriptional profile of S. mutans UA159 grown under Mn-restricted conditions. Among the most highly expressed genes were those of the entire sloABC operon, encoding a dual iron/manganese transporter, and an uncharacterized gene, here mntH, that codes for a protein bearing strong similarity to Nramp-type transporters. While inactivation of sloC, which encodes the lipoprotein receptor of the SloABC system, or of mntH alone had no major consequence for the overall fitness of S. mutans, simultaneous inactivation of sloC and mntH (ΔsloC ΔmntH) impaired growth and survival under Mn-restricted conditions, including in human saliva or in the presence of calprotectin. Further, disruption of Mn transport resulted in diminished stress tolerance and reduced biofilm formation in the presence of sucrose. These phenotypes were markedly improved when cells were provided with excess Mn. Metal quantifications revealed that the single mutant strains contained intracellular levels of Mn similar to those seen with the parent strain, whereas Mn was nearly undetectable in the ΔsloC ΔmntH strain. Collectively, these results reveal that SloABC and MntH work independently and cooperatively to promote cell growth under Mn-restricted conditions and that maintenance of Mn homeostasis is essential for the expression of major virulence attributes in S. mutansIMPORTANCE As transition biometals such as manganese (Mn) are essential for all forms of life, the ability to scavenge biometals in the metal-restricted host environment is an important trait of successful cariogenic pathobionts. Here, we showed that the caries pathogen Streptococcus mutans utilizes two Mn transport systems, namely, SloABC and MntH, to acquire Mn from the environment and that the ability to maintain the cellular levels of Mn is important for the manifestation of characteristics that associate S. mutans with dental caries. Our results indicate that the development of strategies to deprive S. mutans of Mn hold promise in the combat against this important bacterial pathogen.

Translocation, Leaf Distribution, and Nutritional Status of Manganese in Cucumber Plants as Affected by Foliar Application of Exogenous Amino Acids

The present study was carried out to investigate the effect of exogenous amino acids (AAs) on leaf apoplastic retention and symplastic absorption, leaf distribution, translocation, and nutritional status of manganese (Mn) in cucumber plants. Results showed that application of AAs increased the symplastic to apoplastic Mn proportion in leaves of cucumber. Furthermore, a greater part of Mn applied with AAs accumulated in the internal area of newly growing leaves suggesting the transport of Mn mostly in the phloem in the presence of AAs. In contrast, Mn preferentially accumulated in the marginal area of treated leaves indicating the Mn movement in xylem according to the transpiration stream. The AAs used in the present study also increased the relative translocation of Mn from treated leaves to the upper leaves and roots. More time was needed for long-distance translocation of Mn from treated leaves to the upper leaves than that to the roots. Application of AAs mainly increased the transport of Mn in the phloem. The leaf PO (peroxidase) activity was the better marker to index the nutritional status of Mn than PPO (polyphenoloxidase) activity. In conclusion, exogenous AAs especially lysine (Lys) promoted the mobility and bioavailability of applied Mn as foliar spray.

Transport and transformation of uranium and heavy metals from uranium tailings under simulated rain at different pH

Uranium tailings are radioactive and toxic solid wastes that could contaminate waters, soils and sediments. Actually the risk of contamination is poorly known due to the lack of knowledge on the mobility of contaminants, especially the influence of acid rain on leaching, transformation and speciation of contaminants. Here, we studied the effect of simulated rain at different pH on the transport and transformation of Mn, Sr, Pb and U from uranium tailings. Semi-dynamic leaching tests and sequential extraction were conducted for Mn, Sr, Pb and U to determine their leaching patterns and to determine their speciation in uranium tailings. Results show that Mn, Sr, Pb and U become more leachable with decreasing rain pH. The release of these metals is initially rapid and then reaches a near steady state. After leaching with simulated rain, concentrations of metal-exchangeable and metal-carbonate fractions in tailings are highly reduced. The process governing the leaching of Mn and U is mainly wash-off, whereas the leached Sr and Pb are dissolution-controlled.

Chemical Heterogeneity of Mg, Mn, Na, S, and Sr in Benthic Foraminiferal Calcite

The chemical composition of fossil foraminiferal shells (tests) is widely used as tracers for past ocean chemistry. It is, therefore, important to understand how different (trace) elements are transported and incorporated into these tests from adjacent seawater. The elemental distribution within the walls of foraminiferal tests might be used to differentiate between proposed transport mechanisms. Here, the microdistribution of Mg, Mn, Na, S, and Sr in tests of three species of foraminifera, known to have contrasting test chemistry, is investigated by a combination of electron probe microanalysis (EPMA) and nanoscale secondary ion mass spectrometry (nanoSIMS), micro-X-ray fluorescence (μXRF), and micro-X-ray absorption near-edge structure (μXANES) analyses. The three investigated species are the symbiont-barren Ammonia sp. T6 and Bulimina marginata, which precipitate a low-Mg calcite test, and the symbiont-bearing species Amphistegina lessonii, which produces a test with intermediate Mg content. Because all analyzed tests were formed under controlled and identical laboratory conditions, the observed distributions of elements are not due to environmental variability but are a direct consequence of the processes involved in calcification or, in the case of A. lessonii, possibly symbiont activity. Despite some variability in elemental microdistribution between specimens from a given species, our combined dataset shows species-specific distributions of the elements (e.g., peak heights and/or band-widths) and also a systematic colocation of Mg, Na, S, and Sr for all three species, suggesting a coupled or simultaneous uptake, transport, and incorporation of these elements during chamber addition. The observed trace element patterns generally reflect a laminar calcification model, suggesting that heterogeneity of these elements is intrinsically linked to chamber addition. Although the incorporation of redox-sensitive Mn depends on the Mn concentration of the culture medium, the Mn distribution observed in Ammonia sp. suggests that Mn transport is similarly linked to laminar calcification dynamics. However, for B. marginata, Mn banding was sometimes anticorrelated with Mg banding, suggesting that (bio)availability, uptake, and transport of Mn differ from those for Ammonia sp. Our results from symbiont-bearing A. lessonii suggest that the activity of symbionts (i.e., photosynthesis/respiration) may influence the incorporation of Mn owing to alternation of the chemistry in the microenvironment of the foraminifera, an important consideration in the development of this potential proxy for past oxygenation of the oceans.