Internal Zinc Research Articles

Large Expression Differences in Genes for Iron and Zinc Homeostasis, Stress Response, and Lignin Biosynthesis Distinguish Roots of Arabidopsis thaliana and the Related Metal Hyperaccumulator Thlaspi caerulescens

The micronutrient zinc has an essential role in physiological and metabolic processes in plants as a cofactor or structural element in 300 catalytic and noncatalytic proteins, but it is very toxic when available in elevated amounts. Plants tightly regulate their internal zinc concentrations in a process called zinc homeostasis. The exceptional zinc hyperaccumulator species Thlaspi caerulescens can accumulate up to 3% of zinc, but also high amounts of nickel and cadmium, without any sign of toxicity. This should have drastic effects on the zinc homeostasis mechanism. We examined in detail the transcription profiles of roots of Arabidopsis thaliana and T. caerulescens plants grown under deficient, sufficient, and excess supply of zinc. A total of 608 zinc-responsive genes with at least a 3-fold difference in expression level were detected in A. thaliana and 352 in T. caerulescens in response to changes in zinc supply. Only 14% of these genes were also zinc responsive in A. thaliana. When comparing A. thaliana with T. caerulescens at each zinc exposure, more than 2,200 genes were significantly differentially expressed (>or=5-fold and false discovery rate < 0.05). While a large fraction of these genes are of yet unknown function, many genes with a different expression between A. thaliana and T. caerulescens appear to function in metal homeostasis, in abiotic stress response, and in lignin biosynthesis. The high expression of lignin biosynthesis genes corresponds to the deposition of lignin in the endodermis, of which there are two layers in T. caerulescens roots and only one in A. thaliana.

Reproductive toxicity of dietary zinc to Daphnia magna

Regulatory assessments of metals in freshwaters are mostly based on dissolved metal concentrations, assuming that toxicity is caused by waterborne metal only. Little attention has been directed to the toxicity of dietary metals to freshwater invertebrates. In this study the chronic toxicity of dietary zinc to Daphnia magna was investigated. The green alga Pseudokirchneriella subcapitata was exposed for 64 h to a control and three dissolved zinc concentrations, i.e. 23, 28 and 61 μg L −1, resulting in internal zinc burdens in the algae of 130, 200, 320 and 490 μg g −1 dry weight, respectively. These algae were used as a food source in chronic, 21-day bioassays with D. magna in a test medium to which no dissolved zinc was added. None of the treatments resulted in effects on feeding rates or somatic growth of D. magna. In contrast, a significant 40% decrease of total reproduction (number of juveniles per adult) was observed in the 28 and 61 μg L −1 treatments. Time to first brood was not affected, whereas the mean brood size and the fraction of reproducing parent daphnids were reduced from the second brood onwards and the magnitude of these reductions increased with each subsequent brood. The reduced reproduction was accompanied with an elevated zinc accumulation in the 61 μg L −1 treatment only, suggesting that total body burden is no good indicator of dietary zinc toxicity. Overall our data suggest that dietary zinc specifically targets reproduction in D. magna through accumulation in particular target sites, possibly cells or tissues where vitellogenin synthesis or processing occur. Further, our data illustrate that the potential importance of the dietary exposure route should be carefully considered and interpreted in regulatory assessments of zinc.

Influence of ageing on zinc bioavailability in soils

Currently, soil quality criteria or soil risk assessments of metals are based on laboratory toxicity tests which are carried out in soils freshly spiked with metal salts. With these data, species sensitivity distributions are fitted, from which hazardous concentrations and predicted no effect concentrations are derived. However, due to long-term processes, called ageing, soil metal availability decreases with time. Here we show that pH is the most important parameter determining the effect of ageing on zinc partitioning in soils, with the effect of ageing becoming more important with increasing pH. Furthermore, zinc bioavailability, expressed as the internal zinc concentrations in red clover ( Trifolium pratense) is closely related to pore water zinc concentration. In addition, there is a clear dose–response relationship between the survival of the earthworm Eisenia fetida and the calcium chloride-extracted zinc fraction. These results indicate that zinc partitioning can be used to predict zinc bioavailability to terrestrial organisms. However, the use of spiked soils in toxicity assays can result in an over-estimation of the effects of zinc, especially at a high pH.

Zinc and cadmium body burdens in terrestrial oligochaetes: Use and significance in environmental risk assessment

Uptake and elimination kinetics of zinc and cadmium were studied in the oligochaetes Enchytraeus albidus and Eisenia fetida. Even at the highest exposure concentrations where E. fetida survived, the internal zinc concentration was still regulated to a constant level. Enchytraeus albidus could not regulate the internal zinc concentration as well, and the body burden increased after exposure to high zinc concentrations. After transfer to clean soil, the internal zinc concentration dropped back to the control level within a few weeks. For both species, internal cadmium concentrations did not reach equilibrium during the uptake experiments. The internal concentrations causing 50% reduction in cocoon production for E. fetida exposed to cadmium varied between different soil types, indicating that no fixed critical body burdens exist. For both zinc and cadmium, bioaccumulation factors decreased with increasing soil metal concentrations. Bioaccumulation factors may therefore be poor indicators of environmental risk. Their dependence on the total soil concentration makes bioaccumulation factors also unsuitable for assessing the influence of soil characteristics on the bioavailability of metals in contaminated field soils. For the same reason, uptake rate constants are probably not suited for this purpose.

Interaction between the Transcription Factor SPBP and the Positive Cofactor RNF4: AN INTERPLAY BETWEEN PROTEIN BINDING ZINC FINGERS

The activator of stromelysin 1 gene transcription, SPBP, interacts with the RING finger protein RNF4. Both proteins are ubiquitously expressed and localized in the nucleus. RNF4 facilitates accumulation of specific SPBP-DNA complexes in vitro and acts as a positive cofactor in SPBP-mediated transactivation. SPBP harbors an internal zinc finger of the PHD/LAP type. This domain can form intra-chain protein-protein contacts in SPBP resulting in negative modulation of SPBP-RNF4 interaction.

Effects of zinc on l-

Epithelial brush-border membrane vesicles (BBMVs) from the hepatopancreas of the lobster Homarus americanus were prepared using a magnesium precipitation technique and employed in transport experiments designed to demonstrate the effects of external and internal divalent cationic heavy metals on the uptake of l-[(3)H]proline. When BBMVs were exposed to a high external concentration (2.5 mmol l(-)(1)) of Cd(2+), Cu(2+), Fe(2+), Mn(2+) or Zn(2+), l-[(3)H]proline (0.5 mmol l(-)(1)) uptake was significantly (P<0.05) decreased by each metal. However, if a 30 min pre-incubation period with each metal was used before incubation of the vesicles with amino acid and metal, a significant (P<0.05) enhancement of l-[(3)H]proline transport occurred. Zinc was the most stimulatory metal of those tested. Proline influxes (1.0 and 2.5 mmol l(-)(1)) were hyperbolic functions of bilateral [Zn(2+)], with a lower apparent zinc half-saturation constant (K(m)) at the higher amino acid concentration. l-[(3)H]proline influx was a hyperbolic function of external [l-proline] (K(m)=2.10+/-0.26 mmol l(-)(1); J(max)=2290+/-600 pmol mg(-)(1 )protein 10 s(-)(1)) (means +/- s.e.m., N=3), and bilateral exposure to zinc significantly (P<0.05) increased the maximal rate of influx, J(max), of proline (J(max)=4890+/-250 pmol mg(-)(1 )protein 10 s(-)(1)), but had no effect (P>0.05) on apparent l-[(3)H]proline binding to the membranes (K(m)=1.66+/-0.23 mmol l(-)(1)) (means +/- s.e.m., N=3). In the presence of 0.5 mmol l(-)(1 )l-pipecolate, bilateral zinc-stimulated, carrier-mediated, l-[(3)H]proline influx was abolished. At low external concentrations of zinc alone (e.g. below 1.0 mmol l(-)(1)), l-[(3)H]proline influx was enhanced by the metal. Enhanced amino acid uptake in the presence of external zinc alone was abolished by l-pipecolate. A model accounting for external and internal zinc enhancements of l-[(3)H]proline influx by the Na(+)-dependent l-pipecolate-sensitive IMINO transport system in these membranes is proposed.

Tolerance to Zinc in Populations of the Earthworm Lumbricus rubellus from Uncontaminated and Metal-Contaminated Ecosystems.

Zinc tolerance in Lumbricus rubellus populations from two metal-polluted (smelter and mine) sites was studied by comparing the effects of zinc with responses in a reference site strain. For the study, adult worms were collected directly from the field. Thus, no attempt was made to differentiate between tolerance resulting from population-level genetic adaptation or phenotypic plasticity in metal physiology. To compare relative sensitivity for zinc, worms from the three populations were exposed in laboratory tests. Effects on survival, weight change, cocoon production, and internal zinc levels were measured. Prior to exposure, it was anticipated that worms from the metal-contaminated sites would show substantially increased tolerance to zinc. This was not the case for all measured parameters. Thus, although differences in the shape of the dose-response relationships for survival and cocoon production were found, substantial variations in measured responses, effect concentrations, or zinc accumulation rates were not apparent. Overall, therefore, zinc tolerance is unlikely to be a major factor influencing the distribution of L. rubellus in contaminated regions.http://link.springer-ny.com/link/service/journals/00244/bibs/37n3p332.html

Internal Zinc Accumulation Is Correlated with Increased Growth in Rice Suspension Culture

A high zinc concentration of 520 μm, approximately 100 times that used most often in standard plant tissue culture media, was found to be superior in liquid callus cultures of japonica rice, increasing growth to 146% compared with standard N6 medium. At the same time, the internal zinc concentration increased 40 times in fast growing cells; soluble protein doubled, and free amino acids decreased. Under zinc-free conditions the cultures slowed in growth, and several free amino acids such as aspartic acid, glutamic acid, asparagine, and glutamine accumulated. We suggest that zinc acts as a direct regulatory factor in inducing auxin activity, but not auxin levels, making high internal zinc accumulation mandatory if high auxin concentrations are required as in rice callus cultures.

Influence of Temperature on the Regulation and Toxicity of Zinc in Folsomia candida(Collembola)

To generate reproducible and reliable results, most protocols for standardized toxicity tests prescribe strict limits for test conditions such as temperature and relative humidity. In the field, however, variability of climate can influence the functioning of organisms and induce changes in sensitivity. To evaluate the influence of temperature on the ecotoxicity of zinc, the springtail Folsomia candidawas exposed to zinc-contaminated soil at different temperatures. In one experiment, the toxicity of ZnCl 2was determined at a constant temperature and under alternating temperature conditions. Although control performance of F. candidawas influenced by the temperature treatment, effect concentrations for reproduction were not significantly different between treatments. Levels of internal zinc regulation were higher in animals exposed to alternating temperatures. Based on the observed influence of temperature on the accumulation of zinc, a second experiment was performed to determine the sensitivity of F. candidato zinc at four different exposure temperatures. A decrease in temperature led to an increase in sensitivity when sublethal parameters such as growth and reproduction were considered. However, animals were less sensitive at lower temperatures where mortality was concerned. Internal zinc concentrations in the animals increased with decreasing temperatures, and when the effect on reproduction was based on internal zinc levels, differences between temperature treatments were not significant. From the results of this study it is concluded that for F. candida,constant temperature conditions form a good basis for the extrapolation of toxicity levels to fluctuating temperature conditions. Since the average exposure temperature can alter the sensitivity of F. candidafor zinc, and changes in sensitivity are parameter dependent, exposure temperature should be chosen carefully.

The Role of Zinc Regulation in the Zinc Tolerance Mechanism of the Terrestrial Isopod Porcellio scaber

1. To elucidate mechanisms underlying adaptation to metals in the terrestrial isopod Porcellio scaber (Isopoda) responses to zinc were compared in field animals and laboratory-reared generations of three populations, one from a contaminated smelter site and the others from reference sites. 2. Isopods were exposed to a range of zinc concentrations in the food and their consumption, food and zinc assimilation, zinc concentration and internal zinc distribution were determined. 3. Isopods refused to eat food contaminated with 54 μmol Zn g - 1 4. The zinc concentration of field isopods from the smelter site was three times higher than from the reference isopods. The mean fraction of zinc assimilated, determined as the difference between consumption and defecation (AE Zn ), was 25.3% for the reference isopods and 20.1% in the smelter isopods. When zinc assimilation was determined as the increase of the zinc body burden, the reference field isopods accumulated 3% of the zinc consumed: the increase in the smelter isopods was not significant. Isopods from both populations translocated zinc into the hepatopancreas. 5. In the laboratory-reared generations, food assimilation was reduced by zinc, this effect was more pronounced in the smelter isopods. In the smelter isopods, reduced food assimilation did not, however, result in less growth in comparison to the reference isopods. The AE Zn did not differ significantly between the populations, but the increase in zinc body burden was again lower in the smelter isopods. 6. The higher growth efficiency of smelter isopods and their lower increase in zinc body burden may be regarded as an adaptation to zinc and may be one of the mechanisms contributing to survival of this population at a site severely polluted with zinc.

Sequence‐Specific Recognition of a Repetitive DNA Element by a C2H2 Zinc‐Finger Protein in Xenopus

XFG 20-1 is one of several hundred C2H2-type zinc finger proteins of unknown biological function in Xenopus. Affinity selection of genomic DNA fragments identifies a 54-bp consensus sequence with high affinity for the XFG 20-1 protein. This sequence is part of a conserved inverted repeat in REM-1, a 0.5-kb repetitive, dispersed genomic DNA element. This finding indicates a possible link between the non-conserved nature of a large subgroup of DNA-binding C2H2 zinc finger proteins and the non-conserved nature of putative genomic target sequences. The 19 zinc finger modules of XFG 20-1 are organized in three structurally distinct groups. Of these, only the first and third ones are required and are sufficient for high-affinity DNA binding. The finding that removal of five internal zinc finger units does not alter the DNase I protection pattern of the complex formed is indicative of a high degree of structural flexibility for linear arrays of zinc fingers, which we imagine to adopt a more rigid structure only upon interaction with their nucleic acid partner molecules.

Evaluating Internal Zinc Requirements of Grain Crops by Seed Analysis

AbstractOur study tested the general opinion that foliar tissues are superior to seeds for determining the nutrient status of crops. Zinc requirements of leaves and seeds were estimated from yield response curves based on greenhouse pot culture experiments using two Zn‐deficient subsoils (Paaloa silty clay; clayey, oxidic, isothermic Humoxic Tropohumult; and Keahua silty clay loam; fine, kaolinitic, isohyperthermic Torroxic Hapulstoll) of Hawaii. These were fertilized with 0, 1, 3, 9, or 27 mg Zn kg−1 of soil. The order of grain yield response to Zn fertilization was: wheat (Triticum aestivum L.) &lt; sorghum [Sorghum bicolor (L.) Moench] &lt; rice (Oryza sativa L.) &lt; millet [Pennisetum americanum (L.) Schumann] &lt; soybean [Glycine max. (L.) Merr.] &lt; cowpea [Vigna unguiculata (L.) Walp.] &lt; corn (Zea mays L.). Fertilizer Zn requirements for near‐maximum grain yield was highest for cowpea (7.5 mg kg−1 soil) and lowest for wheat (0.5 mg kg−1 soil). Zinc concentrations (mg kg−1) in recently matured leaves associated with 95% maximum yields were similar for seven species: corn and millet, 24; soybean, 22; cowpea, 21; sorghum, 20; rice, 19; and wheat, 17. Equivalent concentrations for seeds were soybean, 43; cowpea, 26; corn, 18; millet, rice and wheat, 15; and sorghum, 10. Across all species, fertilizer levels and soils, the range of Zn concentration in leaves was 5 to 115 mg kg−1 (both values for corn); and in grains 6 (sorghum) to 59 mg kg−1 (wheat). Our results indicate that there was little reason to prefer leaves over grain as a diagnostic tissue for Zn; therefore, Zn should be added to the list of elements for which seed analysis may be advantageous.

ZINC TOLERANCE IN BETULA SPP. I. EFFECT OF EXTERNAL CONCENTRATION OF ZINC ON GROWTH AND UPTAKE

Clones of Betula pendula Roth. and B. pubescens Ehrh., collected as seed from zinc-contaminated mine tailings, were grown aseptically in a liquid/perlite medium. Three zinc-tolerant and four non-tolerant genotypes were compared with respect to extension growth and zinc uptake over a range of external concentrations of zinc. The effect of increasing zinc concentration on total root length and root cell length was also examined. Extension growth declined rectilinearly as the external zinc concentration increased, but the relationship between uptake and external concentration was not rectilinear. After an initial proportional increase, concentrations of zinc in tissues remained constant over much of the range of external concentrations at which some growth was possible. Fresh weight concentrations of zinc in tolerant and non-tolerant genotypes were similar at similar external concentrations. However, at a characteristic threshold external concentration, control of uptake broke down and plants were inundated with zinc. The decrease in extension growth was found to be due mainly to a progressive inhibition of cell elongation. Zinc tolerance in Betula lies in an ability to maintain proportionally more extension growth at similar internal and external zinc concentrations. Neither a tolerance mechanism involving internal detoxification, nor binding of zinc ions to electronegative sites in the cell walls, are consistent with the results. However, these findings are compatible with a tolerance mechanism involving control of uptake operating at the endodermis.

Modulation of aminopyridine block of potassium currents in squid axon

Aminopyridines are known to block potassium (K) currents in excitable membranes in a manner dependent upon membrane potential, such that the block is relieved by depolarization and restored upon repolarization. In the present study, the effects of aminopyridines on voltage-dependent potassium (K) channels were examined in internally perfused, voltage-clamped squid giant axons. The time course of block restoration after conditioning depolarization was found to be modulated by membrane electric field, K-channel gating, and external cations. Depolarized holding potentials accelerated block restoration without altering steady-state block levels, suggesting that the voltage dependence of block restoration may be related to K channel gating rather than drug binding per se. In support of this notion, low external calcium concentration, which shifts the voltage dependence of K-channel gating to more negative potentials, also accelerated block restoration. Conversely, the relationship between the rate of block restoration and membrane holding potential was shifted in the depolarizing direction by phloretin, an agent that shifts the dependence of K-channel opening on membrane potential in a similar manner. Modification of K-channel gating also was found to alter the rate of block restoration. Addition of internal zinc or internal treatment with glutaraldehyde slowed the time course of both K-channel activation and aminopyridine block restoration. Aminopyridines also were found to interact in the K channel with external Cs+, NH4+, and Rb+, each of which slowed aminopyridine block restoration. Our results suggest that aminopyridines enter and occlude K channels, and that the availability of the binding site may be modulated by channel gating such that access is limited by the probability of the channel reaching an intermediate closed state at the resting potential.

Investigation of chemical reactions in the shaft process of zinc and lead production using65Zn

The scheme of the shaft process of simultaneous zinc and lead production is shown. The residence time distribution of zinc vapour leaving the furnace is measured using65Zn. The distribution curve is determined by deconvolution procedure of convolution integral which connects the input function, impuls response and output function. The analysis of this curve showed that in the furnace an internal zinc recirculation connected with secondary oxidation of zinc vapour takes place in the upper zone of the shaft. The localization of the secondary oxidation zone and the degree of zinc reoxidation was determined.

Effects of internal divalent cations on voltage-clamped squid axons.

We have studied the effects of internally applied divalent cations on the ionic currents of voltage-clamped squid giant axons. Internal concentrations of calcium up to 10 mM have little, if any, effect on the time-course, voltage dependence, or magnitude of the ionic currents. This is inconsistent with the notion that an increase in the internal calcium concentration produced by an inward calcium movement with the action potential triggers sodium inactivation or potassium activation. Low internal zinc concentrations ( approximately 1 mM) selectively and reversibly slow the kinetics of the potassium current and reduce peak sodium current by about 40% with little effect on the voltage dependence of the ionic currents. Higher concentrations ( approximately 10 mM) produce a considerable (ca. 90%) nonspecific reversible reduction of the ionic currents. Large hyperpolarizing conditioning pulses reduce the zinc effect. Internal zinc also reversibly depolarizes the axon by 20-30 mV. The effects of internal cobalt, cadmium, and nickel are qualitatively similar to those of zinc: only calcium among the cations tested is without effect.

Distribution of protein-bound zinc in normal and cirrhotic serum

The distribution of ⁶⁵Zn among the serum proteins of 18 cirrhotic patients and 10 normal individuals was studied. Total zinc was measured in each serum. Zinc was bound to albumin, transferrin and <i>α</i>₂-macroglobulin in all subjects. It was bound to IgG in all cirrhotics and five of ten normals. Utilizing the percentage distribution of ⁶⁵Zn and total serum zinc, the amount bound in each fraction was calculated. Albumin-bound zinc correlated well with total serum zinc (r = 0.97). Total serum zinc was lower in cirrhotics than in normals (p < 0.01). The low serum zinc found in cirrhotics appears to be a function of serum albumin concentration. Zinc was consistently bound to transferrin and <i>α₂</i>-macroglobulin. The total amount bound to these proteins (Tf-<i>α₂</i>M) was of remarkably constant and equivalent size in normals and cirrhotics. Transferrin concentration was significantly lower (p < 0.01) in cirrhotics. The mean concentration of <i>α</i>₂-macroglobulin was higher in cirrhotics although the difference was not significant (p < 0.10). There appears to be a reciprocal relationship between the amount of zinc bound to transferrin and that bound to <i>α</i>₂-macroglobulin. However, the total amount bound to Tf-<i>α₂</i>M remains remarkably constant even when total serum zinc falls as low as 12 μg./ml. The constancy of the amount of zinc bound to Tf-<i>α₂</i>M implies metabolic control of this fraction. When serum zinc falls to very low levels, it may account for nearly one-half of the total serum zinc. It is suggested that transferrin and <i>α₂</i>-macroglobulin may have an important role in internal zinc exchange.

Distribution of protein-bound zinc in normal and cirrhotic serum

The distribution of 65Zn among the serum proteins of 18 cirrhotic patients and 10 normal individuals was studied. Total zinc was measured in each serum. Zinc was bound to albumin, transferrin and α2-macroglobulin in all subjects. It was bound to IgG in all cirrhotics and five of ten normals. Utilizing the percentage distribution of 65Zn and total serum zinc, the amount bound in each fraction was calculated. Albumin-bound zinc correlated well with total serum zinc (r = 0.97). Total serum zinc was lower in cirrhotics than in normals (p < 0.01). The low serum zinc found in cirrhotics appears to be a function of serum albumin concentration. Zinc was consistently bound to transferrin and α2-macroglobulin. The total amount bound to these proteins (Tf-α2M) was of remarkably constant and equivalent size in normals and cirrhotics. Transferrin concentration was significantly lower (p < 0.01) in cirrhotics. The mean concentration of α2-macroglobulin was higher in cirrhotics although the difference was not significant (p < 0.10). There appears to be a reciprocal relationship between the amount of zinc bound to transferrin and that bound to α2-macroglobulin. However, the total amount bound to Tf-α2M remains remarkably constant even when total serum zinc falls as low as 12 μg./ml. The constancy of the amount of zinc bound to Tf-α2M implies metabolic control of this fraction. When serum zinc falls to very low levels, it may account for nearly one-half of the total serum zinc. It is suggested that transferrin and α2-macroglobulin may have an important role in internal zinc exchange. The distribution of 65Zn among the serum proteins of 18 cirrhotic patients and 10 normal individuals was studied. Total zinc was measured in each serum. Zinc was bound to albumin, transferrin and α2-macroglobulin in all subjects. It was bound to IgG in all cirrhotics and five of ten normals. Utilizing the percentage distribution of 65Zn and total serum zinc, the amount bound in each fraction was calculated. Albumin-bound zinc correlated well with total serum zinc (r = 0.97). Total serum zinc was lower in cirrhotics than in normals (p < 0.01). The low serum zinc found in cirrhotics appears to be a function of serum albumin concentration. Zinc was consistently bound to transferrin and α2-macroglobulin. The total amount bound to these proteins (Tf-α2M) was of remarkably constant and equivalent size in normals and cirrhotics. Transferrin concentration was significantly lower (p < 0.01) in cirrhotics. The mean concentration of α2-macroglobulin was higher in cirrhotics although the difference was not significant (p < 0.10). There appears to be a reciprocal relationship between the amount of zinc bound to transferrin and that bound to α2-macroglobulin. However, the total amount bound to Tf-α2M remains remarkably constant even when total serum zinc falls as low as 12 μg./ml. The constancy of the amount of zinc bound to Tf-α2M implies metabolic control of this fraction. When serum zinc falls to very low levels, it may account for nearly one-half of the total serum zinc. It is suggested that transferrin and α2-macroglobulin may have an important role in internal zinc exchange.

合金化処理した溶融亜鉛メッキ鋼板の腐食挙動

Corrosion behavior of galvannealed steel was studied under various corrosive circumstances and was compared with that of galvanized or electrogalvanized steel.The results obtained were as follows:1) The corrosion rate of galvannealed steel was lower than those of other zinc plated steels.2) The coating layer of the galvannealed steel was composed of Fe-Zn alloy (mainly of δ1-phase) and its natural electrode potential was nobler than those of other zinc plated steels.3) Zinc of the coating layer was preferentially dissolved by corrosion so that iron was enriched on the coating surface to be converted into red rust, which prevented the internal zinc from dissolution. However, it took a longer time for the substrate metal of galvannealed steel than other zinc plated steels to be corroded into the red rust. Therefore, it was concluded that the coating layer of galvannealed steel has very high corrosion resistance.