Effects of nitric oxide and Fe supply on recovery of Fe deficiency induced chlorosis in peanut plants

The effects of nitric oxide (NO) and/or iron (Fe) supplied to Fe deficient plants have been investigated in peanut (Arachis hypogaea L.) grown in Hoagland nutrient solution with or without Fe. Two weeks after Fe deprivation, recovery was induced by addition of 250 μM sodium nitroprusside (SNP, a NO donor) and/or 50 μM Fe (Fe-EDTA) to the Fe deprived (-Fe) nutrient solution. Activities of antioxidant enzymes, leaf chlorophyll (Chl), and active Fe content decreased, whereas activities of H⁺-ATPase, ferric-chelate reductase (FCR), nitrate reductase, and nitric oxide synthase and NO production increased in Fe deficient plants, consequently an Fe chlorosis symptom appeared obviously. In contrast, these symptoms disappeared gradually after two weeks with NO and/or Fe supply, which caused an increases in leaf Chl and active Fe content, especially following by co-treatment with NO and Fe to values found in Fe sufficient plants. Increased activities of antioxidant enzymes (superoxide dismutase, peroxidase, and catalase) and decreased accumulation of reactive oxygen species (H₂O₂, O ₂ ^?? ) and malondialdehyde enhanced the ability of resistance to oxidative stress. Supplied NO alone had the obvious effect on increased NO production and on activity of H⁺-ATPase and FCR, whereas root length and root/shoot ratio were most effectively increased by Fe supplied alone. Co-treatment with NO and Fe did the best effects on recovery peanut chlorosis symptoms by significantly increased Chl and available Fe content and adjusted distribution of Fe and other mineral elements (Ca, Mg, and Zn) in both leaves and roots.     

Hepatic and adipocyte cells respond differentially to iron overload, hypoxic and inflammatory challenge

Adipose tissue secretes numerous pro-inflammatory cytokines, such as interleukin (IL)-6 and tumor necrosis factor (TNF)-α that can lead to insulin resistance (IR). In the liver, both IL-6 and TNF-α induce IR by inhibiting phosphorylation or ubiquitination of IRS1. In IR development, Fe is a risk factor in type-2 diabetes development. We studied the expression of genes related to inflammation, hypoxia, and mitochondrial function in hepatic (HepG2) and adipose (3T3-L1) cells. HepG2 and 3T3-L1 cells were incubated with 20?μM Fe, 40?μM Fe, or 40?μM Fe/20?mM glucose for 7?days and then challenged with 20?ng/ml IL-6 and/or 100?μM CoCl(2) for 20?h. We measured intracellular Fe levels and the relative expression of hepcidin, NF-κB, IL-6, TNF-α, hypoxia inducible factor 1α (HIF-1α), and mitofusin 2 (Mfn-2) mRNA using qRT-PCR. The intracellular Fe concentration in HepG2 cells did not change with 20 or 40?μM Fe. However, levels were decreased with Fe/glucose and IL-6 and/or CoCl(2). 3T3-L1 cells showed an increase in intracellular Fe with high Fe plus either IL-6 or CoCl(2). HepG2 cells incubated with 40?μM Fe alone or Fe/glucose and challenged with IL-6 and/or CoCl(2) showed increased IL-6, NF-κB, and TNF-α mRNA expression and decreased mRNA expression of Mfn-2 in all experimental conditions.?3T3-L1 cells incubated with 40?μM Fe alone or Fe/glucose and challenged with IL-6 showed increased NF-κB mRNA expression and decreased Mfn-2 expression in all experimental conditions. Thus, high Fe, inflammation, and hypoxia trigger the expression of genes related to inflammation and Fe metabolism in HepG2 cells, in 3T3-L1 cells the same stimuli increased NF-kB and hepcidin expression.     

Iron overload prevents oxidative damage to rat brain after chlorpromazine administration

The hypothesis tested is that Fe administration leads to a response in rat brain modulating the effects of later oxidative challenges such as chlorpromazine (CPZ) administration. Either a single dose (acute Fe overload) or 6 doses every second day (sub-chronic Fe overload) of 500 or 50 mg Fe-dextran/kg, respectively, were injected intraperitoneally (ip) to rats. A single dose of 10 mg CPZ/kg was injected ip 8 h after Fe treatment. DNA integrity was evaluated by quantitative PCR, lipid radical (LR^·) generation rate by electron paramagnetic resonance (EPR), and catalase (CAT) activity by UV spectrophotometry in isolated brains. The maximum increase in total Fe brain was detected after 6 or 2 h in the acute and sub-chronic Fe overload model, respectively. Mitochondrial and nuclear DNA integrity decreased after acute Fe overload at the time of maximal Fe content; the decrease in DNA integrity was lower after sub-chronic than after acute Fe overload. CPZ administration increased LR^· generation rate in control rat brain after 1 and 2 h; however, CPZ administration after acute or sub-chronic Fe overload did not affect LR^· generation rate. CPZ treatment did not affect CAT activity after 1–4 h neither in control rats nor in acute Fe-overloaded rats. However, CPZ administration to rats treated sub-chronically with Fe showed increased brain CAT activity after 2 or 4 h, as compared to control values. Fe supplementation prevented brain damage in both acute and sub-chronic models of Fe overload by selectively activating antioxidant pathways.     

Components involved in assembly and dislocation of iron-sulfur clusters on the scaffold protein Isu1p

The mitochondrial proteins Isu1p and Isu2p play an essential role in the maturation of cellular iron-sulfur (Fe/S) proteins in eukaryotes. By radiolabelling of yeast cells with 55Fe we demonstrate that Isu1p binds an oxygen-resistant non-chelatable Fe/S cluster providing in vivo evidence for a scaffolding function of Isu1p during Fe/S cluster assembly. Depletion of the cysteine desulfurase Nfs1p, the ferredoxin Yah1p or the yeast frataxin homologue Yfh1p by regulated gene expression causes a strong decrease in the de novo synthesis of Fe/S clusters on Isu1p. In contrast, depletion of the Hsp70 chaperone Ssq1p, its co-chaperone Jac1p or the glutaredoxin Grx5p markedly increased the amount of Fe/S clusters bound to Isu1p, even though these mitochondrial proteins are crucial for maturation of Fe/S proteins. Hence Ssq1p/Jac1p and Grx5p are required in a step after Fe/S cluster synthesis on Isu1p, for instance in dissociation of preassembled Fe/S clusters from Isu1p and/or their insertion into apoproteins. We propose a model that dissects Fe/S cluster biogenesis into two major steps and assigns its central components to one of these two steps.     

Effects of time and dietary iron on tissue iron concentration as an estimate of relative bioavailability of supplemental iron sources for ruminants

Two experiments were conducted to investigate the effects of time and dietary Fe on tissue Fe concentrations following short-term, high level supplementation for use as a bioassay procedure for supplemental Fe sources for ruminants. In Experiment 1, 28 wethers were allotted randomly to four experimental diets which were fed for 15 or 30 days. The basal maize–soyabean meal–cottonseed hulls diet (193 mg kg⁻¹ Fe) was supplemented with 0, 400, 800 or1200 mg kg⁻¹ added Fe from reagent grade ferrous sulfate (FeSO₄·7H₂O). Iron concentrations in liver, kidney, and spleen increased (P<0.05) as dietary Fe increased; however, muscle, heart, and bone Fe concentrations were unaffected. A logarithmic transformation of liver or kidney Fe concentrations at 30 days regressed on added dietary Fe produced the best fits to a linear model. In Experiment 2, bioavailability of Fe from three feed grade ferrous carbonates known to differ (carbonates A, B, and C) was compared to that from reagent grade ferrous sulfate. The dietary treatments fed for 30 days included the above basal diet (90 mg kg⁻¹ Fe) supplemented with 0, 300, 600 or 900 mg kg⁻¹ added Fe from ferrous sulfate or 600 mg kg⁻¹ Fe from ferrous carbonates A, B, or C. Liver Fe concentrations from sheep fed ferrous sulfate were numerically greater than those of animals fed the carbonate sources or control diet. Kidney Fe concentrations from lambs fed ferrous sulfate at 600 mg kg⁻¹ Fe or carbonate-A were greater (P<0.05) than those fed carbonates B or C. Iron concentrations in spleen were lower (P<0.05) in lambs fed carbonate-B than for those fed 600 mg kg⁻¹ Fe as ferrous sulfate, but were similar to other carbonates. Overall average bioavailability estimates based on multiple regression slope ratios for the three tissues were ferrous sulfate 1.00, carbonate-A 0.55, carbonate-B 0.00, and carbonate-C 0.20. Estimates for carbonates A and C were similar to those based on hemoglobin concentrations reported previously for young swine supplemented at dietary concentrations near the requirement.     

Mössbauer and EPR study of iron in vacuoles from fermenting Saccharomyces cerevisiae

Vacuoles were isolated from fermenting yeast cells grown on minimal medium supplemented with 40 μM (57)Fe. Absolute concentrations of Fe, Cu, Zn, Mn, Ca, and P in isolated vacuoles were determined by ICP-MS. M?ssbauer spectra of isolated vacuoles were dominated by two spectral features: a mononuclear magnetically isolated high-spin (HS) Fe(III) species coordinated primarily by hard/ionic (mostly or exclusively oxygen) ligands and superparamagnetic Fe(III) oxyhydroxo nanoparticles. EPR spectra of isolated vacuoles exhibited a g(ave) ~ 4.3 signal typical of HS Fe(III) with E/D ~ 1/3. Chemical reduction of the HS Fe(III) species was possible, affording a M?ssbauer quadrupole doublet with parameters consistent with O/N ligation. Vacuolar spectral features were present in whole fermenting yeast cells; however, quantitative comparisons indicated that Fe leaches out of vacuoles during isolation. The in vivo vacuolar Fe concentration was estimated to be ~1.2 mM while the Fe concentration of isolated vacuoles was ~220 μM. M?ssbauer analysis of Fe(III) polyphosphate exhibited properties similar to those of vacuolar Fe. At the vacuolar pH of 5, Fe(III) polyphosphate was magnetically isolated, while at pH 7, it formed nanoparticles. This pH-dependent conversion was reversible. Fe(III) polyphosphate could also be reduced to the Fe(II) state, affording similar M?ssbauer parameters to that of reduced vacuolar Fe. These results are insufficient to identify the exact coordination environment of the Fe(III) species in vacuoles, but they suggest a complex closely related to Fe(III) polyphosphate. A model for Fe trafficking into/out of yeast vacuoles is proposed.     

A comparison of two procedures used for complexing Fe(III) with human apotransferrin. II. Uptake of Fe(III) by K-562 cells from 55Fe . transferrins and Fe . [3H]transferrins

Samples of human apotransferrin (apo . HTr) were saturated with Fe(III) by two different techniques, a method employing excess trisodium citrate to chelate Fe(III) and a nonchelating approach which involves the ferroxidase activity of ceruloplasmin to convert Fe(II)----Fe(III). The samples were radiolabelled with either 55Fe or 3H. Using an initial molar Fe/apo . HTr ratio of 2.0-2.1, preparations of human transferrin with bound Fe (Fe . HTr) using the citrate method invariably contained 2.2-2.4 atoms Fe/molecule, whereas Fe . HTr (ceruloplasmin method) contained 2.0 atoms/molecule as shown by spectrophotometric and radioactivity measurements. Uptake of Fe from these Fe . HTr preparations by K-562 cells grown in a serum-free medium was marginally, but consistently, more rapid from 55Fe . HTr (citrate) than from 55Fe . HTr (ceruloplasmin). Taking account of the different Fe contents of the Fe . HTr preparations, the rate measured over a 2-h period amounted to approximately 12,700 and 16,100 Fe atoms/(cell . min) for Fe . HTr (ceruloplasmin) and Fe . HTr (citrate), respectively. However, cell binding by the two Fe . [3H]HTr preparations did not differ significantly over the 8-h incubation period. Furthermore, from the 3H distribution, the quantities of Fe . HTr bound reversibly at the cell surface and contained within the cell were similar for the two Fe . HTr preparations. The results indicate that apo . HTr may bind Fe in different ways depending on the method of Fe presentation and that the Fe . HTr product can donate Fe to K-562 cells at a rate which may reflect the method used for Fe-complex formation.     

Significance of non-esterified fatty acids in iron uptake by intestinal brush-border membrane vesicles

Iron uptake from Fe/ascorbate by mouse brush-border membrane vesicles is not greatly inhibited by prior treatment with a variety of protein-modification reagents or heat. Non-esterified fatty acid levels in mouse proximal small intestine brush-border membrane vesicles show a close positive correlation with initial Fe uptake rates. Loading of rabbit duodenal brush-border membrane vesicles with oleic acid increases Fe uptake. Depletion of mouse brush-border membrane vesicle fatty acids by incubation with bovine serum albumin reduces Fe uptake. Iron uptake by vesicles from Fe/ascorbate is enhanced in an O2-free atmosphere. Iron uptake from Fe/ascorbate and Fe3+-nitrilotriacetate (Fe3+-NTA) were closely correlated. Incorporation of oleic acid into phosphatidylcholine/cholesterol (4:1) liposomes leads to greatly increased permeability to Yb3+, Tb3+, Fe2+/Fe3+ and Co2+. Ca2+ and Mg2+ are also transported by oleic acid-containing liposomes, but at much lower rates than transition and lanthanide metal ions. Fe3+ transport by various non-esterified fatty acids was highest with unsaturated acids. The maximal transport rate by saturated fatty acids was noted with chain length C14-16. It is suggested that Fe transport can be mediated by formation of Fe3+ (fatty acid)3 complexes.     

Preparation of iron-deficient tissue culture medium by deferoxamine-sepharose treatment and application to the differential actions of apotransferrin and diferric transferrin.

We have shown that triiodothyronine-dependent GH1 rat pituitary cell growth in serum-free defined culture required apotransferrin (apoTf) (D. A. Sirbasku, et al., Biochemistry 30, 295-304, 7466-7477, 1991). These studies were done in "low-Fe" medium without Fe(III)/Fe(II) salts. Nonetheless, significant concentrations of iron may have been contributed by other components, making this medium unsuitable for study of the differential effects of apoTf and diferric transferrin (2Fe.Tf). Measuring residual iron in culture medium has been troublesome because the most sensitive method (i.e., atomic absorption) detected levels only in excess of 10 ng/ml and did not distinguish between the forms of iron present. To estimate the Fe(III) available to bind to apoTf, we developed a more sensitive and specific method. Urea-polyacrylamide gel electrophoresis (PAGE) separates apoTf, the two monoferric transferrins, and 2Fe.Tf. [125I]apoTf was incubated with medium, or components, and the formation of [125I]-2Fe.Tf was monitored by urea-PAGE/autoradiography. By this method, the concentration of Fe(III) in low-Fe medium was estimated at 8.4 to 20 ng/ml and the sources were identified. We next sought to remove the Fe(III). Standard chelators were ineffective or cytotoxic. In contrast, an affinity method with deferoxamine-Sepharose depleted greater than or equal to 90% of the Fe(III). In this medium, apoTf and 2Fe.Tf showed differential effects with GH1 cells and with MCF-7, MTW9/PL2, an MDCK cells. With the methods described here, the effects of apoTf and 2Fe.Tf on growth can be studied separately.     

Acute Copper Supplementation Does Not Inhibit Non-Heme Iron Bioavailability in Humans

To measure the effect of acute copper (Cu) administration, given as an aqueous solution, on the absorption of iron (Fe), 29 healthy adult women participated in two iron absorption studies. Subjects received 0.5 mg of Fe, as ferrous sulfate, alone or with Cu, as copper sulfate, at 0.5:1, 1:1, or 2:1 Cu/Fe molar ratios (study I) or at 4:1, 6:1, or 8:1 Cu/Fe molar ratios (study II) as an aqueous solution on days 1, 2, 14, and 15 of the study. Fe absorption was assessed by erythrocyte incorporation of iron radioisotopes ⁵⁵Fe and ⁵⁹Fe. Geometric mean (range ± SD) absorption of Fe alone or at 0.5:1, 1:1, 2:1 Cu/Fe molar ratios were 34.4% (17.3–68.5%), 40.9% (24.9–67.2%), 48.3% (24.8–94.1%), and 50.2% (25.3–99.5%), respectively (ANOVA, p = 0.12). Geometric mean (range ± SD) absorption of Fe alone or at 4:1, 6:1, 8:1 Cu/Fe molar ratios were 28.7% (12.1–67.9%), 21.5% (6.5–71.5%), 29.6% (10.3–85.4%), and 36.5% (18.3–73.1%), respectively (ANOVA, p = 0.16). In conclusion, combined Cu and Fe administration in an aqueous solution does not inhibit Fe bioavailability. This information could help in the design of rational guidelines for copper and iron supplementation programs. Our results support the hypothesis that divalent metal transporter 1 is not physiologically relevant for copper absorption in humans.     

Isoelectric Focusing of Plant Plasma Membrane Proteins : Further Evidence that a 55 Kilodalton Polypeptide Is Associated with beta-1,3-Glucan Synthase Activity from Pea

The role of the root apoplasm for iron acquisition was studied in wheat (Triticum aestivum L. cv Ares) grown in nutrient solution under controlled environmental conditions. To obtain different levels of Fe in the root apoplasm, plants were supplied in the dark for 5 hours (preloading period) with various ⁵⁹Fe-labeled Fe compounds [Fe(III) hydroxide; microbial siderophores: Fe rhodotorulic acid (FeRDA) and ferrioxamin (FeDesferal³), and synthetic Fe chelate (FeEDDHA)], each at a concentration of 5 micromolar. Large pools of apoplasmic Fe were formed after supplying Fe(III) hydroxide or FeRDA, but no such pools were observed after supplying FeDesferal or FeEDDHA. Depending on plant Fe nutritional status (preculture ± 0.1 millimolar FeEDTA), apoplasmic Fe was used to different extent for translocation to the shoot. Under Fe deficiency, a much greater fraction of the apoplasmic Fe was utilized than in Fe-sufficient plants, as a result of the different rates of phytosiderophore release. Because of the diurnal rhythm in release of phytosiderophores in Fe-deficient plants, the utilization of the apoplasmic Fe for translocation into the shoot started 2 hours after onset of the light period and was dependent on the concentration of Fe in the apoplasm, which followed the order: Fe(III) hydroxide FeRDA FeDesferal = FeEDDHA. From these results, it can be concluded that in soil-grown plants the apoplasmic Fe pool loaded by various indigenous Fe compounds such as siderophores in the soil solution can be an important Fe source in graminaceous species, particularly during periods of limited Fe supply from the soil.     

Iron Chlorosis in Grafted Sweet Orange (Citrus sinensis L.) Plants: Physiological and Biochemical Responses

Fe deficiency was imposed in Citrus sinensis L. cultivars Valencia and New Hall grafted on C. aurantium and Swingle citrumelo rootstocks by the absence of Fe (-Fe) or by the presence of bicarbonate in the Hoagland nutrient solution. In Fe-deprived leaves total and active Fe concentration, and peroxidase and catalase activities were decreased while the ratios carotenoids/chlorophylls, P/Fe, and K/Ca were increased. Fe(III) chelate reductase activity was induced in (-Fe)-treated roots whereas it was depressed in bicarbonate-treated roots.     

Modification of the in vitro Cytotoxicity of Hydrogen Peroxide by Iron Complexes

The effect of a range of iron chelates on the cytotoxicity of H₂O₂ was studied on a mammalian epithelial cell line. Iron complexes which were internalised enhanced the cytotoxicity of H₂O₂ measured by delayed thymidine incorporation. Iron complexed to 8-hydroxyquinoline (Fe/8-HQ) potentiated the cytotoxicity of 50 µM by 38% and Fe/dextran by 23%. Pre-exposure of cells to Fe/dextran at 4°C did not result in any potentiation of H₂O₂-induced cytotoxicity which we ascribe to failure of the Fe/dextran to be endocytosed at low temperature. Iron complexes which are slowly taken up or remain extracellular protected the cells from H₂O₂-induced cytotoxicity. Thus, Fe/EDTA inhibited the cytotoxicity of 50 µM H₂O₂ by 33%; Fe/ADP by 80% and Fe/ATP by 88%, suggesting mutual extracellular detoxification.     

Cys-His proteases are among the wired proteins of the cell

Integrated cell protein degradation can be paced by the transfer of reductive energy, as revealed by experimental agents of informative actions. The peptidolytic pair of Cys-His proteases can undergo oxidative reactions to inactive derivatives and inhibitory metal binding. Proton-dependent ionizations can modify ongoing activity. If the reaction rate of a Cys-His protease were found responsive to the ranges of metal/redox/proton factors regulated within the cell, then these factors might serve to link the peptidolytic reaction rate to cell controls. Here, cathepsin B (cat B) was found to be inhibited by Zn2+, Fe3+, and Cu2+ (1-50 microM) under excess GSH or DTT protease activators (6 mM). Under DTT or GSH (6 mM) the initial inhibitory action of Zn2+ is stable indefinitely; however, the inhibitory actions of Fe3+ and Cu2+ are reversed over approximately 1h. The 12-14 min half time of reversal of initial protease inhibition is correlated with the measured reduction of Fe3+ to Fe2+ by DTT or GSH (pH 5.5 or 6.5). Endogenous Fe2+ concentrations (100 microM) inhibit cat B only marginally. However, the inhibitory threshold of several microM Fe3+ is only a few percent oxidation of the endogenous pool. Without metals cat B reaction is reportedly proportional to GSH concentration, and is inhibited by increasing GSSG/GSH redox ratio. Following activation with GSH, cat B can be influenced by Fe3+/Fe2+, Cu2+/Cu+, and GSSG/GSH ratios and concentrations. Results are interpreted in relation to properties of the thiolate-imidazolium pair as illustrated by Dock modeling of their shared Fe3+ binding. It is proposed that the interaction of Cys-His with 1 electron transition between Fe2+ and Fe3+ serves as a sensor, signal integrator and switch wiring cat B reaction rate to the transfer of reductive energy in the presence of excess GSH. Speciated metals might also serve among electron acceptors transferring from reduced protease to oxygen. Results provide a model for pharmacologic redox switching of protease functions with metal-interactive drugs, and other nano-technology engineering.     

Signs of iron deficiency in copper-deficient rats are not affected by iron supplements administered by diet or by injection

The goal of this study was to determine the effects of Fe supplementation on the anemia of Cu deficiency in rats. In addition, we observed changes in serum and organ Cu and Fe during the development of Cu deficiency. In Experiment 1, weanling male Sprague-Dawley rats were fed AIN-93G diets containing either <0.3 mg Cu [Cu deficient (CuD)] or 6.0 mg Cu [Cu adequate (CuA)] per kilogram diet, and 35 mg Fe/kg. Five rats from each group were killed at intervals for the analysis of hematologic parameters and mineral content of various organs. In Experiment 2, two groups of 24 rats each were fed either the CuA diet or the CuD diet for 14 days. Then, three sets of eight rats in each group received three separate Fe treatments: (1) daily intraperitoneal injections of 400 mug Fe (Cu-free ferric citrate) per rat for another 14 days, (2) fed similar diets that contained three times the normal amount of Fe (105 mg/kg) for 14 days, or (3) received no further Fe treatment. At day 21, all rats were fed a 1-g meal labeled with (59)Fe to determine Fe absorption. After 28 days, rats were killed for the analyses of Fe and Cu status. Results of Experiment 1 showed that within 14 days, CuD rats had lower blood hemoglobin (Hgb), red blood cell count, and mean corpuscular volume than CuA rats. Copper concentrations in all tissues measured were lower in the CuD rats than in controls. Serum ceruloplasmin (Cp) activity in CuD rats was only 0.8% of CuA rats at day 7. During this period, enterocyte and liver Fe concentrations were elevated and serum Fe was reduced, but there was no change in spleen Fe. Results of Experiment 2 showed that CuD rats absorbed less Fe than CuA rats. Supplemental Fe by diet or by intraperitoneal injections did not prevent anemia in the CuD rats or affect other parameters of Cu status. Serum total iron binding capacity [transferrin (Tf)] was not changed by Cu deficiency or by Fe supplementation; however, percent Tf saturation was reduced in CuD rats but was not enhanced by Fe supplementation. These data suggest that anemia of Cu deficiency occurs because of reduced Fe absorption, and it inhibits release of Fe from the liver and inefficient loading of Fe into Tf because of very low plasma Cp activity. The latter then leads to inefficient delivery of Fe to the erythroid cells for heme and Hgb synthesis.     

秸秆还田配施中微量元素对农田土壤有机碳固持的影响

为研究秸秆还田配施中量元素(S)和微量元素(Fe和Zn)对粮田土壤有机碳固持的影响,进行了为期52 d的室内玉米秸秆腐解培养试验. 结果表明:秸秆腐解过程中分别添加S、Fe和Zn元素,均提高了微生物生物量碳(MBC)及土壤CO₂-C矿化速率,52 d腐解培养结束后,CO₂-C的累积矿化量显著提高,但土壤有机碳含量并未显著降低;3种元素中,添加Fe或Zn的处理提高了土壤惰性碳库、惰性碳库比例及土壤有机碳表观平衡,有利于土壤有机碳固持,而添加S的处理却降低了惰性有机碳比例及土壤有机碳表观平衡,不利于有机碳固持. 因此,在施N、P肥基础上,秸秆还田添加S、Fe或Zn均能促进土壤有机碳的矿化进程,但添加Fe或Zn可使更多有机碳固持于土壤中,添加S不利于土壤有机碳的固持.     

Bactericidal effect of Fe2+, ceruloplasmin, and phosphate.

Fe2+, when combined with ceruloplasmin or phosphate, was bactericidal to Escherichia coli at pH 5.0, and when Fe2+, ceruloplasmin, and phosphate were combined, a bactericidal effect was observed under conditions, i.e., short incubation period, in which Fe2+ plus ceruloplasmin and Fe2+ plus phosphate were ineffective. Bactericidal activity increased with the ceruloplasmin or phosphate concentration to a maximum and then decreased as their concentration was further increased. Fe2+ was oxidized in the presence of ceruloplasmin, phosphate, or, in particular, a combination of the two. A bactericidal effect was observed when there was only a partial loss of Fe2+, with more extensive oxidation resulting in a loss of bactericidal activity. The bactericidal effect of Fe2+ plus ceruloplasmin and/or phosphate was unaffected by catalase or superoxide dismutase and was not associated with iodination. Fe-EDTA was also bactericidal at an Fe2+: EDTA molar ratio of 1:0.5, where Fe2+ was partially oxidized. However, in contrast to Fe2+ plus ceruloplasmin and/or phosphate, bactericidal activity was inhibited by catalase and was associated with iodination. Combinations of Fe2+ and Fe3+ were not bactericidal under the conditions employed. A requirement for Fe2+ plus either a product of Fe2+ oxidation or an iron ceruloplasmin and/or phosphate chelate for bactericidal activity is proposed.     

The impact of iron and chelators on Lake Kinneret phytoplankton

The response of natural phytoplankton populations from LakeKinneret to the addition of iron (Fe) and chelator (EDTA) wastested by following growth patterns and determining the algalcomposition initially and at the end of the experiments; algalgrowth rates and yield were measured by in vivo chlorophyllfluorescence. Although the pattern of growth response varied,usually some stimulation of phytoplankton growth rate and yieldwas observed with chelator and/or Fe addition in comparisonto unsupplemented samples. However, the major impact of Fe andEDTA on the phytoplankton appeared to be expressed as changesin the algal population composition. There were clear taxonomicdifferences in the response to Fe addition, which in nearlyall experiments stimulated outgrowth of Bacillanophyta and Chlorophyta,compared with the effect of EDTA alone or with Fe which enhancedthe development of Cyanophyta, in addition to Bacillariophyta.The availability of Fe and/or chelators therefore appears tobe important in determining the composition of the phytoplanktonpopulations in Lake Kinneret and presumably in other aquaticenvironments.     

Pathways for production of Fenton's reagent by wood-rotting fungi

Abstract: Many forms of Fe(II) react with H₂0₂ to generate hydroxyl radicals (Fenton reaction). There is evidence that hydroxyl radicals are important in brown-rot, while they can be formed by secondary reactions during lignin breakdown by white-rot fungi. Their involvement in cellulose breakdown creates a range of oxidized sugars. The two reactants of Fenton's reagent can be generated by Fe(II) autoxidation, or by superoxide in reaction with Fe(III). A rapid autoxidation is not possible for complexes with a high Fe(III)/Fe(II) redox potential. Turning to specific pathways for formation of Fenton's reagent, decomposition of Fe(III)-oxalate is probably solely a photochemical process. Lignin peroxidases can act indirectly as a source of superoxide, either by reactions that lead to a peroxyradical, or by 1-electron oxidation of an aliphatic compound creating a strong reductant. Cellobiose dehydrogenase can provide a direct enzymic source for Fenton's reagent (S.M. Kremer and P.M. Wood (1992) Eur. J. Biochem. 208, 807–814). In the experiments as published, hydroxyl radical production was limited by the slow interaction of cellobiose dehydrogenase with O₂. This limitation can be removed by the presence of an iron complex with an autoxidizable Fe(lI) state. The successful use of Fenton's reagent by a living organism requires a spatial separation between initiating enzyme(s) and the site of production of hydroxyl radicals. The mobility of the extra electron on Fe(II) by intermolecular transfer may be important for achieving this separation.     

Redox Properties of Iron in the Binding Site(s) of F1ATPase from Mammalian Mitochondria and Thermophilic Bacterium PS3: A Comparative Study

Iron ions in the two iron centers of beef heart mito-chondrial F, ATPase, which we have been recently characterized (FEBS Letters 1996,379, 231-235), exhibit different redox properties. In fact, the ATP-dependent site is able to maintain iron in the redox state of Fe(II) even in the absence of reducing agents, whereas in the nucleotide-independent site iron is oxidized to Fe(III) upon removal of the reductant. Fe(III) ions in the two sites display different reactivity towards H₂O₂, because only Fe(III) bound in the nucleotide-independent site rapidly reacts with H₂O₂ thus mediating a 30% enzyme inactivation. Thermophilic bacterium PS3 bears one Fe(III) binding site, which takes up Fe(III) either in the absence or presence of nucleotides and is unable to maintain iron in the redox state of Fe(II) in the absence of ascorbate. Fe(III) bound in thermophilic F₁ATPase in a molar ratio 1:1 rapidly reacts with H₂O₂ mediating a 30% enzyme inactivation. These results support the presence in mitochon-drial and thermophilic F₁ATPase of a conserved site involved in iron binding and in oxidative inactivation, in which iron exhibits similar redox properties. On the other hand, at variance with thermophilic F₁ATPase, the mitochondrial enzyme has the possibility of maintaining one equivalent of Fe(II) in its peculiar ATP-dependent site, besides one equivalent of Fe(III) in the conserved nucleotide-independent site. In this case mitochondrial F, ATPase undergoes a higher inactivation (75%) upon exposure to H₂O₂. Under all conditions the inactivation is significantly prevented by PBN and DMSO but not by Cu, Zn superoxide dis-mutase, thus suggesting the formation of OH radicals as mediators of the oxidative damage. No dityrosines, carbonyls or oxidized thiols are formed. In addition, in any cases no protein fragmentation or aggregation is observed upon the treatment with H₂O₂.