Morphological and physiological responses of root tip cells to Fe<Superscript>2+</Superscript> toxicity in rice

Two genotypes of rice (Oryza sativa L.), Azucena (iron tolerant) and IR64 (iron sensitive), were used to investigate the numbers and survival rates of root border cells (namely, in situ border cells) in plants that were exposed to excess iron (Fe²⁺). Additionally, we examined the changes in the root tip cell morphology and activities of protective enzymes in response to Fe²⁺ toxicity. The results showed that Fe²⁺ toxicity hindered the development of root border cells (RBCs) and that higher Fe²⁺ concentrations caused root cap cell walls to thicken. In the iron-sensitive rice variety, these changes lowered RBC survival rate and lead to programmed cell death. Low concentrations of Fe²⁺ were shown to facilitate the development of RBCs in the iron-tolerant rice variety and that the activities of the protective enzymes superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were elevated in the iron-tolerant variety, thus suggesting that rice root tips could defend against Fe²⁺ toxicity by producing RBCs, root cap cells, and protective enzymes.     

Effect of toxic Fe2+ levels on the biological characteristics of rice root border cells

Root border cells are a population of rhizosphere cells surrounding the root tips but separated from them. The root tip is a major target of Fe²⁺ toxicity; thus, it was hypothesized that the border cells might protect or exacerbate Fe²⁺ toxicity. To explore the effects of excess Fe²⁺ on the border cells in rice (Oryza sativa L.), experiments were carried out using the border cells in vitro (Shanyou No. 10). The border cells were precultured under ??hanging in the air?? and detached from the root tips. The shape, numbers, and viability of border cells were examined during exposure to toxic levels of Fe²⁺. When the root was 1 mm long, there were 205 border cells on average. With the growth of the root, more border cells were observed. When the root grew to 25 mm long, the total number of border cells reached a maximum, while the maximum activity of border cells appeared when the root was 20 mm long. The pectin methyl esterase (PME) activity of the root cap peaked at a root length of 2 mm. Border cell development was related to PME activity in rice. Excessive Fe²⁺ was toxic to detached border cells. After treatment with 200 ??M Fe²⁺ solution for 48 h, cell viability decreased by 72.70%. However, when treated with 400 ??M Fe²⁺ solution, the number of viable cells was actually higher, suggesting the induction of a cellular self-protection response. The activity of PME first increased under high concentrations of Fe²⁺ and then decreased. These results indicate that toxic levels of Fe²⁺ modulate PME activity and border cell survival.     

Ferrous Iron Induces Nrf2 Expression in Mouse Brain Astrocytes to Prevent Neurotoxicity

Free radical damage caused by ferrous iron is involved in the pathogenesis of secondary brain injury after intracerebral hemorrhage (ICH). NF‐E2‐related factor 2 (Nrf2), a major phase II gene regulator that binds to antioxidant response element, represents an important cellular cytoprotective mechanism against oxidative damage. We hypothesized that Nrf2 might protect astrocytes from damage by Fe²⁺. Therefore, we examined cytotoxicity in primary astrocytes induced by iron overload and evaluated the effects of Fe²⁺ on Nrf2 expression. The results demonstrated that 24‐h Fe²⁺ exposure exerted time‐ and concentration‐dependent cytotoxicity in astrocytes. Furthermore, Fe²⁺ exposure in astrocytes resulted in time‐ and concentration‐dependent increases in Nrf2 expression, which preceded Fe²⁺ toxicity. Nrf2‐specific siRNA further knocked down Nrf2 levels, resulting in greater Fe²⁺‐induced astrocyte cytotoxicity. These data indicate that induction of Nrf2 expression could serve as an adaptive self‐defense mechanism, although it is insufficient to completely protect primary astrocytes from Fe²⁺‐induced neurotoxicity.     

Effect of exogenous potassium on photosynthesis and antioxidant enzymes of rice under iron toxicity

A solution culture experiment was conducted to determine the effects of different potassium concentrations on the chlorophyll fluorescence and oxidation resistance of the Fe²⁺-tolerant rice (Oryza sativa L.) genotype Xieyou 9308 and the Fe²⁺-sensitive genotype IIyou 838 exposed to 250 mg/L of Fe²⁺. The minimal fluorescence, maximum fluorescence efficiency, maximum fluorescence, and non-photochemical quenching coefficient showed no significant changes. However, the photochemical quenching coefficient increased. Under 200 mg/L K⁺ concentration, the effects of Fe²⁺ stress decreased. Compared with the control group, chlorophyll content and peroxidase, superoxide dismutase, and catalase activities decreased, whereas MDA content increased under Fe²⁺ stress. Exogenous K⁺ alleviated Fe²⁺ toxicity in the test subjects compared with the control group. Overall, external K⁺ could alleviate the toxic effects of Fe²⁺ toxicity.     

Iron toxicity and stress-induced ethylene production in rice leaves

The relationship among iron toxicity, bronzing symptom, and stress-induced ethylene production (SEP) was investigated in detached rice (Oryza sativa L.) leaves during the vegetative-ripening stage and in whole plants during the vegetative stage. When Fe²⁺ (200 mg L^-1) was applied to the detached leaf through a transpiration stream, SEP was higher in the first leaf than in the second and third leaves from the top and maximal around the panicle primordia initiation stage. The genotype difference in SEP was more pronounced in the second and third leaves than in the first leaf. Bronzing intensity increased as SEP increased; iron concentration increase during treatment in the tissue did not correlate with bronzing intensity or with SEP among the 16 genotypes tested. When the roots of an intact plant were exposed to 300 mg L^-1 of Fe²⁺ in culture solution little stress-induced ethylene was produced. By partially or totally derooting the plant, however, stress-induced ethylene was evoked, indicating that roots reduced the Fe²⁺ uptake so that little stress ethylene is produced in the intact plant. Leaf tissue tolerance for Fe²⁺ may contribute to genotype differences in iron toxicity tolerance of rice plants when roots are injured during transplanting or exposed to toxic substances in the soil.     

Cadmium toxicity of rice leaves is mediated through lipid peroxidation

Oxidative stress, in relation to toxicity of detached rice leaves,caused by excess cadmium was investigated. Cd content inCdCl₂-treated detached rice leaves increased with increasingdurationof incubation in the light. Cd toxicity was followed by measuring the decreasein chlorophyll and protein. CdCl₂ was effective in inducing toxicityand increasing lipid peroxidation of detached rice leaves under both light anddark conditions. These effects were also observed in rice leaves treated withCdSO₄, indicating that the toxicity was indeed attributed to cadmiumions. Superoxide dismutase (SOD), ascorbate peroxidase (APOD), and glutathionereductase (GR) activities were reduced by excess CdCl₂ in the light.The changes in catalase and peroxidase activities were observed inCdCl₂-treated rice leaves after the occurrence of toxicity in thelight. Free radical scavengers reduced CdCl₂-induced toxicity and atthe same time reduced CdCl₂-induced lipid peroxidation and restoredCdCl₂-decreased activities of SOD, APOD, and GR in the light. Metalchelators (2,2-bipyridine and 1,10-phenanthroline) reducedCdCl₂ toxicity in rice leaves in the light. The reduction ofCdCl₂ toxicity by 2,2-bipyridine (BP) is closely associatedwith a decrease in lipid peroxidation and an increase in activities ofantioxidative enzymes. Furthermore, BP-reduced toxicity of detached riceleaves,induced by CdCl₂, was reversed by adding Fe²⁺ orCu²⁺, but not by Mn²⁺ or Mg²⁺.Reduction of CdCl₂ toxicity by BP is most likely mediated throughchelation of iron. It seems that toxicity induced by CdCl₂ mayrequire the participation of iron.     

Effect of fertilization on exudation,dehydrogenase activity,iron-reducing populations and Fe++ formation in the rhizosphere of rice (Oryza sativa L.) in relation to iron toxicity

Summary To explain the mechanism of iron toxicity, greenhouse and growth chamber (¹⁴CO₂ atmosphere) experiments were carried out. In pot experiments (with a typical iron-toxic soil and a fertile clay) we studied the effect of N, P, K and Ca+Mg fertilization (alone or in combination) on dehydrogenase activity, Fe⁺⁺ formation, and the populations of iron-reducing bacteria in the rhizosphere of rice IR22 and IR42. Fe uptake by the plants was measured at regular intervals. Dehydrogenase activity, the number of N₂-fixing iron-reducing bacteria, and the formation and uptake of Fe⁺⁺ decreased with increased supply of K, Ca, and Mg. This effect was clearer with IR22 (susceptible to iron toxicity) than with IR42 (releatively tolerant). Increased exudation and Fe uptake by IR36 at low nutrient and high Fe supply were recorded in a growth chamber experiment. Nutritional conditions, exudation rate (a measure of metabolic root leakage), the iron-reducing activity of the rhizosphere, and Fe⁺⁺ uptake by wetland rice appear to be clearly related. Iron toxicity is considered a physiological disorder caused by multiple nutritional soil stress rather than by a low pH and high Fe supply per sé.     

Expression patterns of iron regulatory proteins after intense light exposure in a cone-dominated retina

Iron is implicated in ocular diseases such as in age-related macular degeneration. Light is also considered as a pathological factor in this disease. Earlier, two studies reported the influence of constant light environment on the pattern of expressions of iron-handling proteins. Here, we aimed to see the influence of light in 12-h light–12-h dark (12L:12D) cycles on the expression of iron-handling proteins in chick retina. Chicks were exposed to 400 lx (control) and 5000 lx (experimental) light at 12L:12D cycles and sacrificed at variable timepoints. Retinal ferrous ion (Fe²⁺) level, ultrastructural changes, lipid peroxidation level, immunolocalization and expression patterns of iron-handling proteins were analysed after light exposure. Both total Fe²⁺ level (p?=?0.0004) and lipid peroxidation (p?=?0.002) significantly increased at 12-, 48- and 168-h timepoint (for Fe²⁺) and 48- and 168-h timepoint (for lipid peroxidation), and there were degenerative retinal changes after 168 h of light exposure. Intense light exposure led to an increase in the levels of transferrin and transferrin receptor-1 (at 168-h) and ferroportin-1, whereas the levels of ferritins, hephaestin, (at 24-, 48- and 168-h timepoint) and ceruloplasmin (at 168-h timepoint) were decreased. These changes in iron-handling proteins after light exposure are likely due to a disturbance in the iron storage pool evident from decreased ferritin levels, which would result in increased intracellular Fe²⁺ levels. To counteract this, Fe²⁺ is released into the extracellular space, an observation supported by increased expression of ferroportin-1. Ceruloplasmin was able to convert Fe²⁺ into Fe³⁺ until 48 h of light exposure, but its decreased expression with time (at 168-h timepoint) resulted in increased extracellular Fe²⁺ that might have caused oxidative stress and retinal cell damage.

     

Reactive oxygen metabolite-induced toxicity to cultured bovine endothelial cells: Status of cellular iron in mediating injury

We aimed to determine the status of iron in mediating oxidant-induced damage to cultured bovine aortic endothelial cells. Chromium-51-labeled cells were exposed to reaction mixtures of xanthine oxidase/hypoxanthine and glucose oxidase/glucose; these produce superoxide and hydrogen peroxide, or hydrogen peroxide, respectively. Xanthine oxidase caused a dose dependent increase of ⁵¹Cr release. Damage was prevented by allopurinol, oxypurinol, and extracellular catalase, but not by superoxide dismutase. Prevention of xanthine oxidase-in-duced damage by catalase was blocked by an inhibitor of catalase, aminotriazole. Glucose oxidase also caused a dose-dependent increase of ⁵¹Ci release. Glucose oxidase-induced injury, which was catalase-inhibitable, was not prevented by extracellular superoxide dismutase. Both addition of and pretreatment with deferoxamine (a chelator of Fe³⁺) prevented glucose oxidase-induced injury. The presence of phenanthroline (a chelator of divalent Fe²⁺) prevented glucose oxidase-induced ⁵¹Cr release, whereas pretreatment with the agent did not. Apotransferrin (a membrane impermeable iron binding protein) failed to influence damage. Neither deferoxamine nor phenanthroline influenced cellular antioxidant defenses, or inhibited lysis by non-oxidant toxic agents. Treatment with allopurinol and oxypurinol, which inhibited cellular xanthine oxidase, failed to prevent glucose oxidase injury. We conclude that (1) among the oxygen species extracellularly generated by xanthine oxidase/hypoxanthine, hydrogen peroxide induces damage via a reaction on cellular iron; (2) deferoxamine and phenanthroline protect cells by chelating Fe³⁺ and Fe²⁺, respectively; and (3) reduction of cellular stored iron (Fe³⁺) to Fe²⁺ may be a prerequisite for mediation of oxidantinduced injury, but this occurs independently of extracellular superoxide or cellular xanthine oxidase-derived superoxide. © 1994 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Assessment of iron toxicity using a luminescent bacterial test with an Escherichia coli recombinant strain

The toxic effect of the Fe²⁺ and Fe³⁺ ions on the luminescent recombinant Escherichia coli strain with the luxCDABE operon was studied in short- and long-term experiments. At 30-min exposure of bacteria to the iron ions, the effective concentrations of Fe²⁺ and Fe³⁺ resulting in acute toxicity (EC₅₀) were 8.5 and 1.3 mg/L, respectively. In the long-term (24 h) experiment, during active bacterial growth, the toxicity index for Fe²⁺ and Fe³⁺ was 65.5 and 62.8, respectively. Addition of the iron ions into the medium did not suppress growth, although it inhibited luminescence. Comparative analysis of the short- and long-term experiments made it possible to assess iron toxicity at the concentrations from 0.5 to 20 mg/L (as calculated for the Fe²⁺ and Fe³⁺ ions). Iron ions were found to affect only the reactions that were not vitally important for the cell. At the same time, they had no negative effect on the genetic mechanisms and protein synthesis, thus indicating non-specific toxicity of Fe²⁺ and Fe³⁺.     

Spectral response of rice (Oryza sativa L.) leaves to Fe2+ stress

In the management of lake eutrophication, the regulation effect of Fe is considered, in addition to the controlling nitrogen- and phosphorus input. Based on the “Fe hypothesis”, this paper tentatively ap-plied plant spectral response to the remote sensing early-warning mechanism of lake eutrophication. A laboratory water culture experiment with rice (Oryza sativa L.) was conducted to study Fe uptake by plants and the chlorophyll concentration and visible-near infrared spectrum of vegetable leaves as well as their interrelations under Fe²⁺ stress. Three spectral indices, i.e., A₁ (integral value of the changes of spectral reflectivity in the range 460―670 nm under Fe²⁺ stress), A₂ (integral value of the changes of spectral reflectivity in the range of 760―1000 nm under Fe²⁺ stress) and S (blue-shift range of red edge curve under Fe²⁺ stress), were used to establish quantitative models about the relationships between the rice leaf spectrum and Fe²⁺ stress. With the increase of Fe²⁺ in a culture solution, the Fe content in rice plants increased, while the chlorophyll concentration in vegetative leaves decreased. The spectral reflectivity of vegetable leaves increased in the visible light band but decreased in the near infrared band, and the blue-shift range of the red edge curve increased. The indices _A1, A₂ and S all had sig-nificant correlations with the Fe content in rice leaves, the correlation coefficient being respectively 0.951 (P < 0.01), −0.988 (P < 0.01) and 0.851 (P < 0.01), and simulated (multiple correlation coefficients R² > 0.96) and predict the Fe level in rice leaves.     

Maintaining elevated Fe2+ concentration in solution culture for the development of a rapid and repeatable screening technique for iron toxicity tolerance in rice (Oryza sativa L.)

Background and aims

Iron toxicity decreases rice (Oryza sativa) grain yield especially in acid soils after flooding. Our aim was to establish a high-throughput screening technique using nutrient solution culture for identifying Fe-toxicity-tolerant genotypes.

Methods

Varying levels of Fe, pH, and chelators in Yoshida nutrient solution culture were tested to maintain sufficient Fe²⁺ concentration over time to optimize the severity of Fe toxicity stress for distinguishing between a tolerant (Azucena) and sensitive (IR64) genotype. The optimized solution was tested on 20 diverse genotypes in the greenhouse, with measurement of leaf bronzing scores and plant growth characteristics at the seedling stage. The same 20 genotypes were grown to maturity in a field with natural Fe toxicity stress, with measurement of seedling-stage leaf bronzing scores and grain yield to determine their inter-relationship.

Results

Optimized nutrient solution conditions were 300 mg L^?1 Fe supplied as Fe²⁺ at pH 4.0 with a 1:2 molar ratio of Fe:EDTA, which maintained sufficient Fe²⁺ stress over 5 days. The highest correlation of nutrient solution phenotypic data with field grain yield was found with leaf bronzing scores at 4 weeks, with a Pearson r of 0.628 for simple association and a Spearman corrected r of 0.610 for rank association (P?<?0.01) using 20 diverse rice genotypes with proven Fe toxicity tolerance reaction. The Leaf bronzing scores at 4 weeks in nutrient culture solution were also found highly correlated with LBS under natural field stress after 8 weeks that had highest correlation with grain yield under stress.

Conclusion

This culture solution-based standardized screening technique can be used in plant breeding programs as a high-throughput technique to identify genotypes tolerant to Fe toxicity.     

A paradox: Fe2+-containing agents decreased ROS and apoptosis induced by CoNPs in vascular endothelial cells by inhibiting HIF-1α

Cobalt nanoparticles (CoNPs) released from hip joint implants are known to have a toxic effect on several organs probably through increasing reactive oxygen species (ROS). Ferrous ion (Fe²⁺) is well-known to enhance oxidative stress by catalysing the production of ROS. However, in our pilot study, we found that Fe²⁺ conversely inhibited the ROS production induced by CoNPs. To elucidate the underlying mechanism, the present study treated vascular endothelial HUVEC and HMEC-1 cells with CoNPs alone or in combination with ferrous lactate [Fe(CH₃CHOHCOO)₂], ferrous succinate [Fe(CH₂COO)₂], and ferrous chloride (FeCl₂). CoNP toxicity was evaluated by measuring cell viability, rate of apoptosis and lactose dehydrogenase (LDH) release, and intracellular ROS levels. Treatment with CoNPs decreased cell viability, LDH release, and ROS production and increased apoptosis. CoNPs increased hypoxia-inducible factor-1α (HIF-1α) protein level and mRNA levels of vascular endothelial growth factor (VEGF) and glucose transporter 1 (GLUT1) downstream of HIF-1α signalling. Silencing HIF-1α attenuated CoNP toxicity, as seen by recovery of cell viability, LDH release, and ROS levels and reduced apoptosis. CoNPs caused a pronounced reduction of Fe²⁺ in cells, but supplementation with Fe(CH₃CHOHCOO)₂, Fe(CH₂COO)₂, and FeCl₂ restored Fe²⁺ levels and inhibited HIF-1α activation. Moreover, all three Fe²⁺-containing agents conferred protection from CoNPs; Fe(CH₃CHOHCOO)₂ and Fe(CH₂COO)₂ more effectively than FeCl₂. In summary, the present study revealed that CoNPs exert their toxicity on human vascular endothelial cells by depleting intracellular Fe²⁺ level, which causes activation of HIF-1α signalling. Supplements of Fe²⁺, especially in the form of Fe(CH3CHOHCOO)₂ and Fe(CH₂COO)₂, mitigated CoNP toxicity.     

Al<Superscript>3+</Superscript> and Fe<Superscript>2+</Superscript> toxicity reduction potential by acid-resistant strains of <Emphasis Type="Italic">Rhodopseudomonas palustris</Emphasis> isolated from acid sulfate soils under acidic conditions

This research aimed to evaluate the capacity of acid-resistant purple nonsulfur bacteria, Rhodopseudomonas palustris strains VNW02, TLS06, VNW64, and VNS89, to resist Al³⁺ and Fe²⁺ and to investigate their potential to remove both metals from aqueous solutions using exopolymeric substances (EPS) and biomasses. Based on median inhibition concentration (IC₅₀), strain VNW64 was the most resistant to both metals under conditions of aerobic dark and microaerobic light; however, strain TLS06 was more resistant to Al³⁺ under aerobic dark conditions. High metal concentrations resulted in an altered cellular morphology, particularly for strain TLS06. Metal accumulation in all tested PNSB under both incubating conditions as individual Al³⁺ or Fe²⁺ was in the order of cell wall?>?cytoplasm?>?cell membrane. This was also found in a mixed metal set only under conditions of aerobic dark as microaerobic light was in the degree of cytoplasm?>?cell wall?>?cell membrane. Of all strains tested, EPS from strain VNW64 had the lowest carbohydrate and the highest protein contents. Metal biosorption under both incubating conditions, EPS produced by strains VNW64 and TLS06, achieved greater removal (80 mg Al³⁺ L^?1 and/or 300 mg Fe²⁺ L^?1) than their biomasses. Additionally, strain VNW64 had a higher removal efficiency compared to strain TLS06. Based on the alteration in cellular morphology, including biosorption and bioaccumulation mechanisms, R. palustris strains VNW64 and TLS06 demonstrated their resistance to metal toxicity. Hence, they may have great potential for ameliorating the toxicity of Al³⁺ and Fe²⁺ in acid sulfate soils for rice cultivation.     

A new technique of plant analysis to resolve iron chlorosis

Summary Iron though indispensable for the biosynthesis of chlorophyll, its total content in the plant was not associated with the occurrence of chlorosis. In order to overcome this inconsistency a new technique of plant iron analysis has been developed. It consists of the determination of Fe²⁺, the fraction of iron involved in the synthesis of chlorophyll.The choice of 1–10 o-phenanthroline (o-Ph) as an extractant for Fe²⁺ was based on its remarkably higher stability constant for Fe²⁺ than Fe³⁺. On this basis, it could preferentially chelate Fe²⁺. The highly specific organce colour of the Fe²⁺-phenanthroline complex made possible the determination of Fe²⁺ by reading the transmittancy at 510 nm.The procedure involves extraction of 2 g of thoroughly washed, chopped, fresh plant by 20 ml of o-phenanthroline extractant (pH 3.0, conc. 1.5%). The plant samples treated with the extractant are allowed to stand for 16 hours and Fe²⁺ is determined in the filtrate by reading the transmittancy at 510 nm.In sharp contrast to total iron the green plants always contained more Fe²⁺ than chlorotic plants. The technique has been developed for rice but is expected to be successful for other crops also.     

Studies on copper toxicity in nickel-resistant strains ofNeurospora crassa

Copper toxicity has been studied in three nickel-resistant strains ofNeurospora crassa (Ni^R1, Ni^R2, and Ni^R3). Ni^R1 and Ni^R2, but not Ni^R3, were two-to threefold more sensitive than the parent wild strain (N. crassa EM 5297a) to Cu²⁺ on a normal N medium. On a nitrate N medium, Cu²⁺ was 16-fold more toxic to Ni^R3 because of reduced synthesis of nitrite reductase; Ni^R1 and Ni^R2 were only fivefold more sensitive to Cu²⁺, and nitrite reductase synthesis was unaffected. Mn²⁺ reversed Cu²⁺ toxicity on normal N medium only, in all strains. Fe³⁺ counteracted Cu²⁺ toxicity on nitrate N medium also. It was shown that Cu²⁺ affected Fe³⁺ utilization for nitrite reductase synthesis in Ni^R3 only and that in these Ni²⁺-resistant strains, Fe³⁺ antagonized effects of Cu²⁺, but not of other toxic metal ions.     

Protective effects of pretreatment with Fe2+, Cu2+, and Rb+ on phoxim poisoning in silkworm,Bombyx mori

BackgroundPhoxim is a widely used organophosphorus pesticide in agriculture. People are paying more and more attention to its toxicity. At present, there is no appropriate way to solve the phoxim poisoning of silkworm, which severely affected the development of sericulture. Fe²⁺, Cu²⁺, Rb⁺ exerted their biological effects through various forms in vivo.MethodsTo evaluate the effect of Fe²⁺/Cu²⁺/Rb⁺ on phoxim poisoning in silkworm, Bombyx mori were treated with fresh mulberry leaves soaked in 2.5 mg/L phoxim for 2 min with 50 mg/L FeCl₂, 150 mg/L CuCl₂, or 0.5 mg/L RbCl from 5 days of the fifth-instar silkworm.ResultsFe²⁺, Cu²⁺, and Rb⁺ pretreatments significantly inhibited the phoxim-induced reduction of survival rate and alleviated the phoxim-induced poisoning symptoms. The protective effects of Fe²⁺, Cu²⁺, and Rb⁺ on phoxim poisoning might be due to their enhancement of superoxide dismutase (SOD), catalase (CAT), and carboxylesterase (CarE) in the hemolymph and fat body of silkworm. This enhancement might reduce reactive oxygen species (ROS) accumulation and oxidative stress (OS) caused by phoxim poisoning. Thereby it reduced the damage to silkworm tissues and cells.ConclusionsThese results showed that Fe²⁺, Cu²⁺, and Rb⁺ treatments protected the silkworm from phoxim poisoning by directly enhancing the activity of SOD, CAT, and CarE enzymes and reducing oxidative stress, but not dependent on the high expression of CYP genes. The use of Fe²⁺, Cu²⁺, and Rb⁺ to enhance the activity of SOD, CAT, and CarE enzymes may be an underlying effective way to solve phoxim poisoning in the silkworm industry.     

Different target specificities of haptoglobin and hemopexin define a sequential protection system against vascular hemoglobin toxicity

Free hemoglobin (Hb) triggered vascular damage occurs in many hemolytic diseases, such as sickle cell disease, with an unmet need for specific therapeutic interventions. Based on clinical observations the Hb and heme scavenger proteins haptoglobin (Hp) and hemopexin (Hx) have been characterized as a sequential defense system with Hp as the primary protector and Hx as a backup when all Hp is depleted during more severe intravascular hemolysis. In this study we present a mechanistic rationale for this paradigm based on a combined biochemical and cell biological approach directed at understanding the unique roles of Hp and Hx in Hb detoxification. Using a novel in vitro model of Hb triggered endothelial damage, which recapitulates the well-characterized pathophysiologic sequence of oxyHb(Fe²⁺) transformation to ferric Hb(Fe³⁺), free heme transfer from ferric Hb(Fe³⁺) to lipoprotein and subsequent oxidative reactions in the lipophilic phase. The accumulation of toxic lipid peroxidation products liberated during oxidation reactions ultimately lead to endothelial damage characterized by a specific gene expression pattern with reduced cellular ATP and monolayer disintegration. Quantitative analysis of key chemical and biological parameters allowed us to precisely define the mechanisms and concentrations required for Hp and Hx to prevent this toxicity. In the case of Hp we defined an exponential relationship between Hp availability relative to oxyHb(Fe²⁺) and related protective activity. This exponential relationship demonstrates that large Hp quantities are required to prevent Hb toxicity. In contrast, the linear relationship between Hx concentration and protection defines a highly efficient backup scavenger system during conditions of large excess of free oxyHb(Fe²⁺) that occurs when all Hp is consumed. The diverse protective function of Hp and Hx in this model can be explained by the different target specificities of the two proteins.     

Effect of chloride on ferrous iron oxidation by a Leptospirillum ferriphilum‐dominated chemostat culture

Biomining is the use of microorganisms to catalyze metal extraction from sulfide ores. However, the available water in some biomining environments has high chloride concentrations and therefore, chloride toxicity to ferrous oxidizing microorganisms has been investigated. Batch biooxidation of Fe²⁺ by a Leptospirillum ferriphilum‐dominated culture was completely inhibited by 12 g L^?1 chloride. In addition, the effects of chloride on oxidation kinetics in a Fe²⁺ limited chemostat were studied. Results from the chemostat modeling suggest that the chloride toxicity was attributed to affects on the Fe²⁺ oxidation system, pH homeostasis, and lowering of the proton motive force. Modeling showed a decrease in the maximum specific growth rate (µ_max) and an increase in the substrate constant (K_s) with increasing chloride concentrations, indicating an effect on the Fe²⁺ oxidation system. The model proposes a lowered maintenance activity when the media was fed with 2–3 g L^?1 chloride with a concomitant drastic decrease in the true yield (Y_true). This model helps to understand the influence of chloride on Fe²⁺ biooxidation kinetics. Biotechnol. Bioeng. 2010; 106: 422–431. © 2010 Wiley Periodicals, Inc.