Fe Excess Research Articles

Anomalous dependence ofc-axis polarized FeB1gphonon mode with Fe and Se concentrations in Fe1+yTe1−xSex

We report on an investigation of the lattice dynamical properties in a range of Fe${}_{1+y}$Te${}_{1\ensuremath{-}x}$Se${}_{x}$ compounds, with special emphasis on the $c$-axis polarized vibration of Fe with ${\mathrm{B}}_{1g}$ symmetry, a Raman active mode common to all families of Fe-based superconductors. We have carried out a systematic study of the temperature dependence of this phonon mode as a function of Se $x$ and excess Fe $y$ concentrations. In parent compound Fe${}_{1+y}$Te, we observe an unconventional broadening of the phonon between room temperature and magnetic ordering temperature ${T}_{N}$. The situation smoothly evolves toward a regular anharmonic behavior as Te is substituted for Se and long-range magnetic order is replaced by superconductivity. Irrespective to Se contents, excess Fe is shown to provide an additional damping channel for the ${\mathrm{B}}_{1g}$ phonon at low temperatures. We performed density functional theory ab initio calculations within the local density approximation to calculate the phonon frequencies, including magnetic polarization and Fe nonstoichiometry in the virtual crystal approximation. We obtained a good agreement with the measured phonon frequencies in the Fe-deficient samples, while the effects of Fe excess are poorly reproduced. This may be due to excess Fe-induced local magnetism and low-energy magnetic fluctuations that cannot be treated accurately within these approaches. As recently revealed by neutron scattering and muon spin rotation studies, these phenomena occur in the temperature range where anomalous decay of the ${\mathrm{B}}_{1g}$ phonon is observed and suggests a peculiar coupling of this mode with local moments and spin fluctuations in Fe${}_{1+y}$Te${}_{1\ensuremath{-}x}$Se${}_{x}$.

Chemically Mediated Quantum Criticality inNbFe2

Laves-phase Nb(1+c)Fe(2-c) is a rare itinerant intermetallic compound exhibiting magnetic quantum criticality at c(cr)∼1.5%Nb excess; its origin, and how alloying mediates it, remains an enigma. For NbFe(2), we show that an unconventional band critical point above the Fermi level E(F) explains most observations and that chemical alloying mediates access to this unconventional band critical point by an increase in E(F) with decreasing electrons (increasing %Nb), counter to rigid-band concepts. We calculate that E(F) enters the unconventional band critical point region for c(cr) > 1.5%Nb and by 1.74%Nb there is no Nb site-occupation preference between symmetry-distinct Fe sites, i.e., no electron-hopping disorder, making resistivity near constant as observed. At larger Nb (Fe) excess, the ferromagnetic Stoner criterion is satisfied.

Phytoremediation potential of Amaranthus hybrids: Antagonism between nickel and iron and chelating role of polyamines

Three amaranth hybrids (Amaranthus paniculatus f. cruentus (Vishnevyi dzhem), A. paniculatus (Bronzovyi vek), and A. caudatus f. iridis (Izumrud) were grown in the climate-controlled chamber on Jonson nutrient medium supplemented with 2 μM Fe3+-EDTA. When plants developed 5–6 true leaves (six-week-old plants), NiCl2 was added to medium to final concentrations of 0 (control), 50, 100, 150, 200, and 250 μM. In 6 days, the increment in biomass of young and mature leaves, stems, and roots, and also the contents of Ni and Fe in them were measured. The red leaf amaranth hybrid Vishnevyi dzhem manifested the highest phytoremediation potential. i.e., the highest capacity for Ni accumulation in the shoots and the most pronounced symptoms of Fe deficit. In the presence of 150 and 250 μM NiCl2 in medium, the shoots of these plants contained about 2 and 4 mg Ni/g dry wt, respectively. In experiments with Fe deficit in plants grown for a week in the presence of NiCl2 (0, 25, 50, 75, and 100 μM), it was established that all tested nickel concentrations suppressed iron reduction in intact roots, which is catalyzed by ferric-chelate reductase, and this may underlie the antagonism between the two metals. In the presence of 50 μM NiCl2 in medium and 2 μM Fe3+ (Fe deficit) and especially 100 μM Fe3+ (Fe excess), the content of MDA and proline in leaves increased and superoxide dismutase was activated; this indicates a development of oxidative stress. Leaf treatment with polyamines (putrescine or spermidine) with aminoguanidine (the inhibitor of H2O2 generation at polyamine oxidation) and with 1,3-diaminopropane led to the increase in nickel accumulation in leaves but did not result in the appearance of any signs of injury. This confirms our previous suggestion that polyamines manifest their protectory action as Ni chelators and detoxicants.

Arabidopsis CYP82C4 expression is dependent on Fe availability and circadian rhythm, and correlates with genes involved in the early Fe deficiency response

Under conditions of reduced iron availability, most frequent in calcareous soils, plants induce the “Fe Deficiency Response” to improve root Fe uptake. The transcription factor FIT is essential for such a response in strategy I plants, such as Arabidopsis thaliana. From microarray analysis of Arabidopsis roots, it is known that three different cytochrome P450 genes, CYP82C4, CYP82C3 and CYP71B5 are up-regulated under Fe deficiency through a FIT-dependent pathway. We show that, out of these three P450 genes, only CYP82C4 strongly correlates with genes involved in metal uptake/transport. The CYP82C4 promoter, unlike those of CYP82C3 and CYP71B5, contains several IDE1-like sequences ( iron deficiency-responsive element) as well as an RY element. While confirming that the CYP82C4 transcript accumulates in Fe-deficient Arabidopsis seedlings, with circadian fluctuations in a light-dependent way, we also demonstrate that such accumulation is suppressed under Fe excess. Full suppression of CYP82C4 expression, as observed in the atc82c4-1 KO mutant, is associated with longer roots at the seedling stage. We propose that CYP82C4 is involved in the early Fe deficiency response, possibly through an IDE1-like mediated pathway.

Identification of an Arabidopsis mitoferrinlike carrier protein involved in Fe metabolism

Iron has a major role in mitochondrial as well as in chloroplast metabolism, however the processes involved in organelle iron transport in plants are only partially understood. To identify mitochondrial iron transporters in Arabidopsis, we searched for proteins homologous to the Danio rerio (zebrafish) Mitoferrin2 MFRN2, a mitochondrial iron importer in non-erythroid cells. Among the identified putative Arabidopsis mitoferrinlike proteins, we focused on that one encoded by At5g42130, which we named AtMfl1 (MitoFerrinLike1). AtMfl1 expression strongly correlates with genes coding for proteins involved in chloroplast metabolism. Such an unexpected result is supported by the identification by different research groups, of the protein encoded by At5g42130 and of its homologs from various plant species in the inner chloroplastic envelope membrane proteome. Notably, neither the protein encoded by At5g42130 nor its homologs from other plant species have been identified in the mitochondrial proteome. AtMfl1 gene expression is dependent on Fe supply: AtMfl1 transcript strongly accumulates under Fe excess, moderately under Fe sufficiency and weakly under Fe deficiency. In order to understand the physiological role of AtMfl1, we isolated and characterized two independent AtMfl1 KO mutants, atmfl1-1 and atmfl1-2: both show reduced vegetative growth. When grown under conditions of Fe excess, atmfl1-1 and atmfl1-2 mutants (seedlings, rosette leaves) contain less total Fe than wt and also reduced expression of the iron storage ferritin AtFer1. Taken together, these results suggest that Arabidopsis mitoferrinlike gene AtMfl1 is involved in Fe transport into chloroplasts, under different conditions of Fe supply and that suppression of its expression alters plant Fe accumulation in various developmental stages.

Increase of TC in UFe 2+ x synthesized by ultrafast cooling

The uranium Laves phase UFe 2 was prepared by ultrafast cooling, which allows to incorporate excessive Fe of about 0.3 Fe/f.u. into the nanocrystalline Laves phase structure. 57Fe Mössbauer spectroscopy reveals that such Fe atoms occupy the U sites. Stronger magnetic hyperfine field points to larger Fe moments of such antistructure Fe. Higher Fe excess leads to its segregation in the form of α-Fe. The Curie temperature of the UFe 2+ x phase increases to the limit value 230–240 K.

Disorder-driven electronic localization and phase separation in superconductingFe1+yTe0.5Se0.5single crystals

We have investigated the influence of Fe-excess on the electrical transport and magnetism of Fe1+yTe0.5Se0.5 (y=0.04 and 0.09) single crystals. Both compositions exhibit resistively determined superconducting transitions (Tc) with an onset temperature of about 15 K. From the width of the superconducting transition and the magnitude of the lower critical field Hc1, it is inferred that excess of Fe suppresses superconductivity. The linear and non-linear responses of the ac-susceptibility show that the superconducting state for these compositions is inhomogeneous. A possible origin of this phase separation is a magnetic coupling between Fe-excess occupying interstitial sites in the chalcogen planes and those in the Fe-square lattice. The temperature derivative of the resistivity drho/dT in the temperature range Tc < T < Ta with Ta being the temperature of a magnetic anomaly, changes from positive to negative with increasing Fe. A log 1/T divergence of the resistivity above Tc in the sample with higher amount of Fe suggests a disorder driven electronic localization.

Feedback under the microscope - I. Thermodynamic structure and AGN-driven shocks in M87

(abridged) Using a deep Chandra exposure (574 ks), we present high-resolution thermodynamic maps created from the spectra of $\sim$16,000 independent regions, each with $\sim$1,000 net counts. The excellent spatial resolution of the thermodynamic maps reveals the dramatic and complex temperature, pressure, entropy and metallicity structure of the system. Excluding the 'X-ray arms', the diffuse cluster gas at a given radius is strikingly isothermal. This suggests either that the ambient cluster gas, beyond the arms, remains relatively undisturbed by AGN uplift, or that conduction in the intracluster medium (ICM) is efficient along azimuthal directions. We confirm the presence of a thick ($\sim$40 arcsec or $\sim$3 kpc) ring of high pressure gas at a radius of $\sim$180 arcsec ($\sim$14 kpc) from the central AGN. We verify that this feature is associated with a classical shock front, with an average Mach number M = 1.25. Another, younger shock-like feature is observed at a radius of $\sim$40 arcsec ($\sim$3 kpc) surrounding the central AGN, with an estimated Mach number M > 1.2. As shown previously, if repeated shocks occur every $\sim$10 Myrs, as suggested by these observations, then AGN driven weak shocks could produce enough energy to offset radiative cooling of the ICM. A high significance enhancement of Fe abundance is observed at radii 350 - 400 arcsec (27 - 31 kpc). This ridge is likely formed in the wake of the rising bubbles filled with radio-emitting plasma that drag cool, metal-rich gas out of the central galaxy. We estimate that at least $\sim1.0\times10^6$ solar masses of Fe has been lifted and deposited at a radius of 350-400 arcsec; approximately the same mass of Fe is measured in the X-ray bright arms, suggesting that a single generation of buoyant radio bubbles may be responsible for the observed Fe excess at 350 - 400 arcsec.

Transport and superconducting properties of Fe-based superconductors: a comparison betweenSmFeAsO1−xFx andFe1+yTe1−xSex

In this paper we carry out a direct comparison between transport and superconductingproperties—namely resistivity, magnetoresistivity, Hall effect, Seebeck effect,thermal conductivity, upper critical field—of two different families of Fe-basedsuperconductors, which can be viewed in many respects as end members:SmFeAsO1 − xFx with the largestTc and the largestanisotropy and Fe1 + yTe1 − xSex, with the largest Hc2, the lowest Tc and the lowest anisotropy. In the case of theSmFeAsO1 − xFx series, we find that a single-band description allows us to extract an approximate estimation ofband parameters such as carrier density and mobility from experimental data, although thebehaviour of the Seebeck effect as a function of doping demonstrates that a multibanddescription would be more appropriate. On the contrary, experimental data for theFe1 + y(Te1 − x, Sex) series exhibit a strongly compensated behaviour, which can be described only within amultiband model.In the Fe1 + y(Te1 − x, Sex) series, the role of the excess Fe, tuned by Se stoichiometry, is found to be twofold: on one handit dopes electrons in the system and on the other hand it introduces localized magneticmoments, responsible for Kondo like scattering and likely pairbreaking of Cooper pairs. Hence,Fe excess also plays a crucial role in determining superconducting properties such as theTc and the uppercritical field Hc2. The huge Hc2 values of the Fe1 + yTe1 − xSex samples are described by a dirty limit law, opposed to the clean limit behaviour of theSmFeAsO1 − xFx samples. Hence, magnetic scattering by excess Fe seems to drive the system inthe dirty regime, but its detrimental pairbreaking role seems not to be as severeas predicted by theory. This issue has yet to be clarified, addressing the morefundamental issue of the interplay between magnetism and superconductivity.

Effect of excess Fe on the superconducting and magnetic properties of the FeTe0.70Se0.30 compound

We have studied the properties of stoichiometric FeTe0.7Se0.3 and the effect of Fe excess in this system. The excess Fe compound is shown to display spin glasslike order below 26 K. Microscopic studies using F57e Mössbauer spectroscopy show the gradual evolution of the magnetic hyperfine field below the spin glass order. The dc magnetization and hyperfine field distribution show that there is a strong moment on the Fe in this system.

Effect of Fe excess on structural, magnetic and superconducting properties of single-crystalline Fe 1+ xTe 1− ySe y

Single crystals of Fe 1+ x Te 1− y Se y have been grown with a controlled Fe excess and Se doping, and the crystal structure has been refined for various compositions. The systematic investigation of magnetic and superconducting properties as a function of the structural parameters shows how the material can be driven into various ground states, depending on doping and the structural modifications. Our results prove that the occupation of the additional Fe site, Fe2, enhances the spin localization. By reducing the excess Fe, the antiferromagnetic ordering is weakened, and the superconducting ground state is favored. We have found that both Fe excess and Se doping in synergy determine the properties of the material and an improved 3-dimensional phase diagram is proposed.

Crystal chemistry, superconductivity and magnetism in iron chalcogenides

The structural simplicity of FeCh (Ch = S, Se, Te), in which the conducting layers are not separated by any third-atom layers, offers the best tool for investigating the nature of superconductivity and magnetism in Fe-based compounds. Either the pressure or the chemical composition distort the FeCh4 tetrahedron and tune the electronic properties. When partially substituting Se for Te in the antiferromagnetic Fe1+xTe, the excess of Fe is reduced and superconductivity appears over a wide range of compositions. Both the Fe excess and the Se substitution affect the structure and must be kept under control for tuning the structure deformation and the electronic properties. The excess of Fe stretches the FeCh4 tetrahedron, thus inducing spin and charge localization. Below a critical Fe-Ch distance, the antiferromagnetism is weakened and superconductivity occurs, mediated by spin fluctuations as in the similar families of Fe-based oxy-pnictides. Uniaxial rather than hydrostatic pressure has a strong effect on the magnetic and superconducting properties of FeCh.

Uranium compounds prepared by sputter deposition: UFe2+x

UFe2 is one of rare examples of combination of 3d and 5f magnetism in a compound with relatively high TC = 162 K. U-excess is known to reduce the TC value markedly. To prepare the Laves phase with an Fe excess is much more difficult. It can be achieved by sputter deposition, but the structure becomes amorphous. TC can increase at least to 240 K (for UFe4), but the segregation of α-Fe cannot be avoided for very high Fe concentrations.

Effect of SrTiO3 buffer layer on the phase formation and properties of direct-patternable BiFeO3 thin films fabricated using photochemical metal-organic deposition

The formation of BiFeO3 without impurity phases, such as excess bismuth and iron, has been possible in only a narrow pressure-temperature-stoichiometric window. A direct-patterned BiFeO3 film using photochemical metal-organic deposition (PMOD) was fabricated without a conventional etching. BiFeO3 film was formed on a SrTiO3 buffer layer with a perovskite structure and a lattice constant of 3.905 A in order to study the substrate effect during phase formation. This study showed the phase formation and electrical properties of the direct-patternable PMOD BiFeO3 thin films. The SrTiO3 buffer layer was found to somewhat prevent the formation of a Fe excess phase in BiFeO3 after anneal at 550°C for 20 min under O2 and N2 atmospheres. The measured remnant polarization (Pr) and coercive field (Ec) values of the Pt/BiFeO3(200 nm)/SrTiO3(40 nm)/Pt/Si structure were 10 µC/cm2 and 300 kV/cm, respectively. Leakage current of perovskite BiFeO3 film was found to be dominated by Poole–Frenkel emission as other perovskite ferroelectrics. To obtain an image, a spin-coated BiFeO3 film was exposed to UV for 15 min and then rinsed in hexane. From this work, it was revealed that the direct-patterning of BiFeO3 films could be applicable for the fabrication of micro-patterned systems using a SrTiO3 buffer layer with controlled reactant stoichiometry.

Knocking out of the mitochondrial AtFer4 ferritin does not alter response of Arabidopsis plants to abiotic stresses

Ferritins are iron-storage proteins which, in Arabidopsis, have a clear role in protection against oxidative stress. Plant ferritins are localized mainly in chloroplasts, but they can also be targeted to mitochondria; the ATFER4 ferritin isoform, according to bioinformatic subcellular predictors, has the highest scores for such localization in Arabidopsis. We isolated atfer4-2 mutant KO in the AtFer4 gene and we characterized it together with a second, independent mutant atfer4-1. We show that ATFER4 is indeed localized in mitochondria of Fe-treated Arabidopsis plants; when grown under Fe excess, atfer4 plants manifest, however, the same toxicity symptoms and O 2 consumption rates as wt plants. No enhanced sensitivity to oxidative conditions was observed in atfer4 seedlings exposed to salinity, osmotic stress, cold stress or oxidative stress elicited by paraquat. The growth response of roots and aerial parts in atfer4 plants under different light conditions was the same as wt. Also, the process of natural senescence, in which AtFer1 takes active part, was not perturbed in atfer4 plants. We conclude that the ATFER4 ferritin role in counteracting the environmental or developmental oxidative conditions in Arabidopsis plants is ancillary to that of the other isoforms, regardless of its mitochondrial localization.

Temperature and abundance profiles of hot gas in galaxy groups - II. Implications for feedback and ICM enrichment

We investigate the history of galactic feedback and chemical enrichment within a sample of 15 X-ray bright groups of galaxies, on the basis of the inferred Fe and Si distributions in the hot gas and the associated metal masses produced by core-collapse and Type Ia supernovae (SNe). Most of these cool-core groups show a central Fe and Si excess, which can be explained by prolonged enrichment by SN Ia and stellar winds in the central early-type galaxy alone, but with tentative evidence for additional processes contributing to core enrichment in hotter groups. Inferred metal mass-to-light ratios inside r500 show a positive correlation with total group mass but are generally significantly lower than in clusters, due to a combination of lower global intracluster medium (ICM) abundances and gas-to-light ratios in groups. This metal deficiency is present for products from both SN Ia and SN II, and suggests that metals were either synthesized, released from galaxies or retained within the ICM less efficiently in lower mass systems. We explore possible causes, including variations in galaxy formation and metal release efficiency, cooling out of metals, and gas and metal loss via active galactic nuclei (AGN) – or starburst-driven galactic winds from groups or their precursor filaments. Loss of enriched material from filaments coupled with post-collapse AGN feedback emerges as viable explanations, but we also find evidence for metals to have been released less efficiently from galaxies in cooler groups and for the ICM in these to appear chemically less evolved, possibly reflecting more extended star formation histories in less massive systems. Some implications for the hierarchical growth of clusters from groups are briefly discussed.

Z-Type 바리움 페라이트 분말의 연자성 특성에 미치는 Ba 및 Fe 농도의 영향

Z-Type 바리움 페라이트(<TEX>$Ba_{3}Co_{0.8}Zn_{1.2}Fe_{24}O_{41}$</TEX>)를 공침법으로 제조하고 결정구조와 자기적 성질을 조사하였다. <TEX>$Ba_{3+{\delta}}Co_{0.8}Zn_{1.2}Fe_{24}O_{41}$</TEX>(<TEX>${\delta}$</TEX> = 3, 5, 7, 13 wt%)와 <TEX>$Ba_{3}Co_{0.8}Zn_{1.2}Fe_{{24}+{\delta}}O_{41}$</TEX>(<TEX>${\delta}$</TEX> = 5, 7, 10 wt%)의 조성을 가진 분말의 <TEX>${\delta}$</TEX> 값에 따른 자기적 성질의 변화를 조사하였다. 제조된 모든 바리움 페라이트에는 Z-type으로 상전이 하지 않은 M-type이 상당량 잔류하고 있었다. 포화자화는 Ba와 Fe의 과잉 첨가량 <TEX>${\delta}$</TEX>가 각각 7 wt%와 5 wt% 일 때 최대로 나타났고 보자력은 조사된 모든 분말에서 다소 높게 나타났다. 높은 보자력은 M-type이 잔류하기 때문이다. 과잉의 Ba와 Fe 첨가에 따른 결정구조의 변화는 없었다. Z-type 바리움 페라이트의 연자성 특성을 향상시키기 위해서는 M-type이 Z-type 형성온도에서 상전이가 일어나도록 해야 함을 알았다. Z-type barium ferrite [(<TEX>$Ba_{3}Co_{0.8}Zn_{1.2}Fe_{24}O_{41}$</TEX>, <TEX>$Ba_{3+{\delta}}Co_{0.8}Zn_{1.2}Fe_{24}O_{41}$</TEX> <TEX>${\delta}$</TEX> = 3, 5, 7, 13 wt%. <TEX>$Ba_{3}Co_{0.8}Zn_{1.2}Fe_{24+{\delta}}O_{41}$</TEX> <TEX>${\delta}$</TEX> = 5, 7, 10 wt% )] were synthesized using co-precipitation method. The microstructure and magnetic properties of synthesized particles were investigated. In all prepared particles M-type Ba ferrite is identified with Z-type Ba ferrite together. It is found that particles having 7 wt% for Ba and 5 wt% for Fe excess addition revealed high saturation magnetization, respectively. All synthesized particles showed relatively high coercivity for device application. This result may be attributed to the contribution of M-type Ba ferrite. Ba and Fe excess addition was not affected to the structural change of CoZnZ Ba ferrite. The certain amount of excess additions of Ba and Fe and the 2 step heat-treatment may be beneficial to the improvement of soft magnetic properties of Z-type barium hexa-ferrite

Crystal and magnetic structures of the brownmillerite compound Ca 2Fe 1.039(8)Mn 0.962(8)O 5

The crystal and magnetic structures of the brownmillerite material, Ca 2Fe 1.039(8)Mn 0.962(8)O 5 were investigated using powder X-ray and neutron diffraction methods, the latter from 3.8 to 700 K. The compound crystallizes in Pnma space group with unit cell parameters of a=5.3055(5) Å, b=15.322(2) Å, c=5.4587(6) Å at 300 K. The neutron diffraction study revealed the occupancies of Fe 3+ and Mn 3+ ions in both octahedral and tetrahedral sites and showed some intersite mixing and a small, ∼4%, Fe excess. While bulk magnetization data were inconclusive, variable temperature neutron diffraction measurements showed the magnetic transition temperature to be 407(2) K below which a long range antiferromagnetic ordering of spins occurs with ordering wave vector k=(000). The spins of each ion are coupled antiferromagnetically with the nearest neighbors within the same layer and coupled antiparallel to the closest ions from the neighboring layer. This combination of intra- and inter-layer antiparallel arrangement of spins forms a G-type magnetic structure. The ordered moments on the octahedral and tetrahedral sites at 3.8 K are 3.64(16) and 4.23(16) μ B, respectively.

Preparation, thermal stability and permeability behavior of substituted Z-type hexagonal ferrites for multilayer inductors

Co2Z-type hexagonal ferrites with iron excess Ba3Co2 − xFe24 + xO41 (0 ≤ x ≤ 0.8) and deficiency Ba3Co2 + yFe24 − yO41 (0 ≤ y ≤ 0.6) were prepared by an oxalate coprecipitation technique. This synthesis route leads to almost single phase Z-type ferrites for x = 0 after calcination and sintering at 1330 °C. The Z-type formation is enhanced for x > 0 and single phase ferrites are obtained for 0.4 ≤ x ≤ 0.8. The permeability of Z-type ferrites varies with composition x: Maximum permeability of μ′ = 28 is observed for 0.4 ≤ x ≤ 0.6 for samples sintered at 1330 °C. The frequency dispersion shows broad peaks of μ″ stretching from 200 MHz to >1 GHz. For iron deficient samples 0 ≤ y ≤ 0.6 multi-phase mixtures were obtained. For Ag-based multilayer inductor applications sintering at 950 °C is required. Co2Z ferrites with Fe excess are not stable at this temperature as demonstrated by XRD. The permeability of samples sintered at 950 °C is drastically reduced to μ′ = 3. This demonstrates that these materials are not able to provide sufficient permeability for multilayer inductors for high-frequency operations since they are not compatible with the low temperature ceramic cofiring technology.

Influence of iron on mineral status of two rice (Oryza sativa L.) cultivars

Iron is an essential nutrient for plants. In aerobic conditions, Fe is highly unavailable for plant uptake, and Fe deficiency can be severe in plants grown in calcareous soils. In waterlogged soils, however, Fe availability increases and can reach toxic concentrations. Rice is an important staple crop worldwide and faces iron deficiency or excess, depending on the growth conditions. To contribute to the study of mechanisms involved in response to Fe deficiency and resistance to Fe excess, experiments were carried out with rice cultivars BR-IRGA 409 (I409, susceptible to Fe toxicity) and EPAGRI 108 (E108, resistant to Fe toxicity) grown in culture solutions and submitted to Fe excess, control concentration or deficiency (500, 6.5 or zero mg L-1 Fe, respectively). Analysis of shoot dry weight confirmed the resistance of E108 plants to Fe excess. Mössbauer spectroscopy analysis indicated the presence of four different Fe3+compounds. The parameters obtained match those expected for ferrihydrite, lepidocrocite (and/or citrate) and Fe-nicotianamine. Mineral concentrations were determined using the PIXE (Particle Induced X-Ray Emission) technique. E108 plants had lower Fe concentrations than I409 plants when exposed to excess Fe. Except for lower Mn levels in roots and shoots, the excess of Fe did not result in lower nutrient concentrations in the susceptible cultivar compared to the resistant one. I409 plants seem to be affected directly by Fe toxicity rather than by secondary effects on mineral nutrition, whereas E108 plants seem to make use of the avoidance mechanism in the resistance to Fe overload. Both cultivars responded to Fe deficiency with allocation of P from roots to shoots. In addition to being more resistant to iron overload, E108 plants seem to be more efficient in inducing Fe deficiency responses.