Iron-deficiency response and expression of genes related to iron homeostasis in poplars

Iron (Fe) deficiency is a serious agricultural problem, especially in calcareous soils, which are distributed worldwide. Poplar trees are an important biomass plant, and overcoming Fe deficiency in poplars will increase biomass productivity worldwide. The poplar Fe-deficiency response and the genes involved in poplar Fe homeostasis remain largely unknown. To identify these genes and processes, we cultivated poplar plants under Fe-deficient conditions, both in calcareous soil and hydroponically, and analyzed their growth rates, leaf Soil and Plant Analyzer Development (SPAD) values, and metal concentrations. The data clearly showed that poplars have notable growth defects in both calcareous soil and a Fe-deficient hydroponic culture. They exhibited serious chlorosis of young leaves after 3 weeks of Fe-deficient hydroponic culture. The Fe concentrations in old leaves with high SPAD values were markedly lower in Fe-deficient poplars, suggesting that poplars may have good translocation capability from old to new leaves. The Zn concentration in new leaves increased in Fe-deficient poplars. The pH of the hydroponic solution decreased in the Fe-deficient culture compared to the Fe-sufficient culture. This finding shows that poplars may be able to adjust the pH of a culture solution to better take up Fe. We also analyzed the expression of Fe homeostasis-related genes in the roots and leaves of Fe-sufficient and Fe-deficient poplars. Our results demonstrate that PtIRT1, PtNAS2, PtFRO2, PtFRO5, and PtFIT were induced in Fe-deficient roots. PtYSL2 and PtNAS4 were induced in Fe-deficient leaves. PtYSL3 was induced in both Fe-deficient leaves and roots. These genes may be involved in the Fe uptake and/or translocation mechanisms in poplars under Fe-deficient conditions. Our results will increase a better understanding of the Fe-deficiency response of poplars and hence improve the breeding of Fe-deficiency-tolerant poplars for improved biomass production, the greening of high pH soils, and combatting global warming.     

EFFECT OF CADMIUM ON PHYSIOLOGICAL RESPONSES OF WHEAT AND CORN TO IRON DEFICIENCY

This work evaluated the effect of cadmium (Cd) on the physiological responses of corn (Zea Mays L.) and wheat (Triticum aestivum L.) to iron (Fe) deficiency. For this purpose, seedlings of corn and wheat were cultivated under controlled conditions, plants were grown in different strength Hoagland's solutions for one month. In the fifth week, some seedlings were still in full strength Hoagland's solution (+Fe) and others were in full strength Hoagland's solutions without iron (?Fe). The plants were exposed to different cadmium (Cd) concentrations for four days. The plant chlorophyll content of young leaves, Fe and Cd content in shoots and roots, biomass production, and phytosiderophores (PS) release by roots were assessed. Results showed that Cd decreased the chlorophyll content of young leaves, accompanied by a significant shoot and root biomass reduction for Fe-deficient and Fe-sufficient wheat and corn across all Cd treatments. However, chlorophyll content and shoot and root biomass of Fe-deficient wheat and corn were lower than Fe-sufficient plants at different Cd concentrations. Iron-deficiency induced Cd accumulation compared to Fe-sufficient in wheat and corn; however, a depressive effect of Cd on iron acquisition in shoots and roots of Fe-deficient and Fe-sufficient wheat and corn across all Cd treatments was observed. Cadmium also inhibited PS release in Fe-deficient and Fe-sufficient wheat and corn. Iron-deficient PS release was higher than Fe-sufficient corn and wheat across all Cd treatments. These results suggested that Cd might reduce capacity of plants to acquire iron from solution by inhibiting PS release.     

IRON IS REQUIRED FOR THE INDUCTION OF ROOT FERRIC CHELATE REDUCTASE ACTIVITY IN IRON-DEFICIENT TOMATO

Two mutants of tomato and their corresponding wild-type genotypes, Tfer/TFER and chloronerva/Bonner Beste, were grown in nutrient solution under conditions leading to iron (Fe) deficiency. Iron deficiency caused decreases in growth, leaf chlorosis, and changes in the morphology of roots. Ferric chelate reductase activities of whole roots were generally lower in Fe-deficient plants than in control, Fe-sufficient plants. Plants grown for 7 days without Fe, however, had transient increases in whole root ferric chelate reductase activity after the addition of small amounts of Fe (2 μM) to the nutrient solution. Also, adding sequential 0.5 μM Fe pulses to the nutrient solution led to high whole root ferric chelate reductase activities. Similar results were obtained with a protocol using excised root tips instead of whole root systems to measure ferric chelate reductase activities. The protocol using root tips generally gave higher ferric chelate reductase rates than the method using whole roots, due to the localized expression of the enzyme in the distal root zones.     

影响菜豆体内铁再利用效率的因素及其机理

本文在人工气候室中，用营养液培养方法，并结合同位素示踪技术研究了铁的供应状况，两种形态氮素（ＮＯ＾－３－Ｎ和ＮＨ＾＋４－Ｎ）及叶处遮光对菜豆体内铁再利用效率的影响，并对其有关机理进行了深入的研究。结果表明，铁的缺乏有利于累积在根和初生叶中的铁身新生组织中转移，铁的再利用效率明显提高。无论有缺铁还供铁条件下，ＮＨ＾＋４－Ｎ的供应使得菜豆新叶中活性铁含量、新叶叶绿素含量及体内铁的再利用效率都明显高于Ｎ     

Construction of artificial promoters highly responsive to iron deficiency

Iron deficiency-responsive element 1 (IDE1) and IDE2 are cis-acting elements that are responsible for Fe-deficiency-inducible and root-specific expression of the barley (Hordeum vulgare L.) gene IDS2 (Fe-deficiency-specific clone no. 2). Using these cis-acting elements, we aimed to construct super-promoters that would induce prominent gene expression in the roots of Fe-deficient rice plants (Oryza sativa L.). Modules containing IDE1 and IDE2 of the IDS2 promoter were used as repeats or were linked to the Fe-deficiency-responsive promoter of barley IDS3, and were connected to known enhancer-like sequences. Five artificial promoters, as well as the native promoters of barley IDS2 or IDS3, were connected individually upstream of β-glucuronidase (GUS) and were introduced into rice. Transgenic rice plants were grown under control or Fe-deficient conditions, and GUS expression was analyzed. The artificial promoter that contained one module of IDE1 and IDE2 conferred strong Fe-deficiency-inducible GUS expression to the roots of rice plants. Each of the five artificial promoters induced a similar level of GUS expression in Fe-deficient roots, which did not exceed the GUS expression driven by the native IDS2 or IDS3 promoter. Artificial and native promoters induced GUS expression in response to Fe-deficiency in leaves, although the level of expression was lower than that in roots. Histochemical observations revealed that GUS expression driven by artificial and native promoters was spatially similar, and expression was dominant within vascular bundles and root exodermis. These findings suggest that there is coordinated expression of the genes that are involved in Fe-deficiency-induced Fe uptake in rice.     

缺铁水稻根表铁膜对硒的转运和吸收的影响

Under anaerobic conditions, ferric hydroxide deposits on the surface of rice roots and affects uptake and translocation of certain nutrients. In the present study, rice plants were cultured in Fe-deficient or sufficient solutions and placed in a medium containing selenium （Se） for 2 h. Then, FeSO4 was added at the various concentrations of 0, 10, 40, or 70 mg L-1 to induce varying levels of iron plaque on the root surfaces and subsequent uptake of Se was monitored. The uptake of Se was inhibited by the iron plaque, with the effect proportional to the amount of plaque induced. The activity of cysteine synthase was decreased with increasing amounts of iron plaque on the roots. This may be the important reason for iron plaque inhibition of Se translocation. At each level of iron plaque, Fe-deficient rice had more Se than Fe-sufficient rice. Furthermore, with plaque induced by 20 mg Fe L-1, plants from Fe-deficient media accumulated more Se than those from Fe-sufficient media, as the Se concentration was increased from 10 to 30 or 50 mg L^-1. We found that phytosiderophores, highly effective iron chelating agents, could desorb selenite from ferrihydrite. Root exudates of the Fe-deficient rice, especially phytosiderophores in the exudates, could enhance Se uptake by rice plants with iron plaque.     

Water- and pyrophosphate-extractable humic substances fractions as a source of iron for Fe-deficient cucumber plants

The capacity of Fe-deficient cucumber plants to utilise water-extractable and pyrophosphate-extractable humic substances as a source of Fe was investigated. Plants were grown for 13 days in nutrient solution in the presence or absence of Fe and during the last 7 days water-extractable and pyrophosphate-extractable humic substances were added to the solution at a final concentration of 5 μg organic C ml^–1. The water-extractable humic fraction did not significantly modify leaf area and dry matter accumulation, leaf total Fe or chlorophyll content of cucumber plants adequately supplied with Fe. In contrast, pyrophosphate-extractable humic substances caused a slight but significant decrease of all the leaf parameters considered, with the exception of the chlorophyll content. Root Fe content of Fe-sufficient plants was decreased by more than 50% in the presence of each humified fraction. Addition of each humic fraction to Fe-deficient plants led to a partial disappearance of leaf chlorosis symptoms with a significant increase in chlorophyll and leaf Fe content. Fe content of roots was also significantly increased in Fe-deficient plants by the addition of humic substances to the nutrient solution. These results show that Fe-deficient cucumber plants can utilise Fe contained in the two fractions of humified organic matter. However, by calculating the amount of total Fe accumulated per plant in the presence of water-extractable or pyrophosphate-extractable humic substances, it could be seen that Fe contained in the water-extractable humic fraction was almost totally used by Fe-deficient cucumber plants, while that present in the pyrophosphate-extractable fraction could only be partially absorbed. The results strongly support a role of humified organic matter in Fe nutrition of plants and are discussed in terms of a possible interaction between soil humic substances and the biochemical mechanisms involved in the plant response to Fe deficiency. Received: 6 November 1996     

Iron deficiency stress responses amongst citrus rootstocks

Seedlings of citrus rootstocks differing in lime tolerance were grown in nutrient solution with and without Fe. Proton efflux, release of phenolic compounds and Fe reducing substances and root-mediated reduction of Fe^III in FeEDTA and freshly precipitated Fe(OH)₃ in response to Fe deficiency were determined. Sweet orange, Carrizo citrange and trifoliate orange, the three least tolerant rootstocks used in the study, did not decrease nutrient solution pH in response to Fe deficiency. The more lime tolerant rootstocks, rough lemon, Cleopatra mandarin and sour orange, did decrease nutrient solution pH. But in CaSO₄ solution only sour orange increased H⁺ efflux significantly under Fe deficiency. In response to Fe deficiency, the release of phenolic compounds was increased significantly in rough lemon and Cleopatra mandarin seedlings, while the release of reducing substances was increased significantly in rough lemon, sour orange and trifoliate orange. Rough lemon was the only rootstock to respond to Fe deficiency with an increase in root-mediated reduction of chelated Fe^III at pH 6.5. At pH 8.0, both Fe-deficient rough lemon and Cleopatra mandarin roots reduced higher amounts of Fe^III from freshly precipitated Fe(OH)₃ than Fe-sufficient seedlings. Iron reduction by detached roots of Fe-deficient and Fe-sufficient rough lemon did not follow Michaelis-Menten kinetics at high substrate concentrations. Rates of Fe reduction at low substrate concentrations were inconsistent with the existence of an inducible ferric reductase in response to Fe deficiency.     

Diurnal variations in absorption and translocation of a ferrated phytosiderophore in barley as affected by iron deficiency

The release of phytosiderophore (PS) from roots of Fe-deficient graminaceous plants follows a distinct diurnal rhythm with maximum release rates occurring usually 3 to 4 hours after the onset of light. However, it remains to be determined whether absorption of the PS-Fe³⁺ complex shows a diurnal rhythmicity similar to that of PS release, Barley plants grown with or without 10 µM FeEDTA for 7 days were fed with ferreted PS (10 µM labelled with ⁵⁹Fe) at 4-h intervals to study the diurnal variations in the absorption and transloca tion of ⁵⁹Fe, The absorption of ⁵⁹Fe, irrespective of the Fe nutritional status of the plants, was higher during the day and lower during the night but did not show any peak throughout the day-night cycle. On the other hand, the translocation of ⁵⁹Fe into shoots of Fe-deficient plants was lower than that of Fe-sufficient plants, while the Fe nutritional status of the plants did not affect the absorption of ⁵⁹Fe by roots, The formation of root apoplastic ⁵⁹Fe was lower during the day and higher during the night, regardless of the Fe nutritional status of plants. Our results showed that the absorption of the PS-Fe³⁺ complex by roots did not follow the PS release pattern.     

Effect of iron deficiency on the growth,development and grain yield of some selected upland rice genotypes in the rainforest

Abstract

Iron deficiency is a major production constraint of upland rice in the tropics despite is abundance in the soil. This investigation aimed to explicate the effect of iron deficiency on the growth, development, grain yield and its attributes of some selected upland rice in the rainforest. Field experiments were established at Africa Rice sub-Station, Ibadan, Nigeria. The treatments consisted of 35 upland rice genotypes and availability of iron in the soil (Fe-sufficient and Fe-deficient). The treatments were arranged in alpha lattice design with three replications. It was observed that upland rice sown in iron (Fe) deficient soils had significantly lower growth (plant height, number of tillers and seedling vigor), flowered later, with significantly lower yield attributes (1000 grain weight, filled grain) and grain yield than those sown in Fe-sufficient soils. Conversely, the number of unfilled grains were significantly higher in upland rice sown in Fe-deficient than those in sufficient soils. Percentage yield loss was in the range 98.00% to 22.95% for China best and Faro 65 respectively. Genotypes were identified to be tolerant (Faro 65, NERICA 3 and IRAT 109) and susceptible (Ofada 2, NERICA 5 and China Best) to Fe-deficiency based on their percentage grain yield loss. These evidences suggested that despite the increased phenology of upland rice sown in Fe-deficient soils their reproductive growth was suppressed through increased number of unfilled grains as witnessed in China Best and Faro 64.     

Comparison of Iron Availability in Leaves of Barley and Rice

Iron (Fe) is an essential trace element in all eukaryotes. In higher plants, Fe deficiency causes interveinal chlorosis in young leaves. However, in barley and rice, both of which are “Strategy II” plants, the degree and the pattern of Fe-deficiency symptoms differ. In the present study, barley and rice plants were grown in the same container, i.e., by “coculturing,” to compensate for the amount of mugineic acids in rice in the nutrient solution. We examined the differential availability of Fe for distribution and retranslocation in shoots between barley and rice without considering the difference in the iron acquisition ability, which is affected by the differential mugineic acid secretion between barley and rice. Although the Fe concentration of young barley leaves had decreased under the coculture conditions, the SPAD value was similar to that in monocultured barley. In contrast, although there was an increase in the Fe concentration of the young leaves of cocultured rice, the SPAD value decreased, as in the case of monocultured rice. Rice accumulated Fe in old leaves, whereas in barley Fe was efficiently distributed to young leaves. Therefore, the SPAD value of the second leaf in rice remained constantly high. The Fe concentration of the second leaf in barley decreased under Fe-deficient coculture conditions, the SPAD value decreased and the senescence of the second leaf become accelerated. ⁵⁹Fe pulse-labeling experiments suggested that in barley Fe was more efficiently retranslocated from old leaves to young leaves than that in rice. As a result, the level of Fe present in the fraction with a molecular weight lower than the 10,000/water-soluble Fe ratio was higher in the old leaves of barley than in the old leaves of rice under Fe-deficient conditions. Based on the results obtained, we suggest that the distribution and retranslocation characteristics of internal Fe in barley may be well adapted to Fe deficiency.     

Physiological basis of iron chlorosis tolerance in rice (Oryza sativa) in relation to the root exudation capacity

Micronutrient deficiency in cultivable soil, particularly that of iron (Fe) and zinc (Zn), is a major productivity constraint in the world. Low Fe availability due to the low solubility of the oxidized ferric forms is a challenge. An experiment was, thus, executed to assess the performance of eight genetically diverse rice genotypes on Fe-sufficient (100 µM) and Fe-deficient (1 µM) nutrient solution, and their ability to recover from Fe deficiency was measured. Fe efficiency under Fe deficiency in terms of biomass production showed a significant positive correlation with the root release of phytosiderophore (PS) (R² = 0.62*). This study shows that the Fe deficiency tolerance of Pusa 33 was related to both a high release of PS by the root and an efficient translocation of Fe from the root to the shoot as the Fe–PS complex, which could be useful for improving the Fe nutrition of rice particularly under aerobic conditions.     

Iron Mobilization and Mineralogical Alterations Induced by Iron-Deficient Cucumber Plants (Cucumis sativus L.) in a Calcareous Soil

Dicotyledons cope with ion (Fe) shortage by releasing low-molecular-weight organic compounds into the rhizosphere to mobilize Fe through reduction and complexation mechanisms. The effects induced by these root exudates on soil mineralogy and the connections between Fe mobilization and mineral weathering processes have not been completely clarified. In a batch experiment, we tested two different kinds of organic compounds commonly exuded by Fe-deficient plants, i.e., three organic acids (citrate, malate, and oxalate) and three flavonoids (rutin, quercetin, and genistein), alone or in combination, for their ability to mobilize Fe from a calcareous soil and modify its mineralogy. The effect of root exudates on soil mineralogy was assessed in vivo by cultivating Fe-deficient and Fe-sufficient cucumber plants (Cucumis sativus L.) in a RHIZOtest device. Mineralogical analyses were performed by X-ray powder diffraction. The batch experiment showed that citrate and, particularly, rutin (alone or combined with organic acids or genistein) promoted Fe mobilization from the soil. The combinations of rutin and organic acids modified the soil mineralogy by dissolving the amorphous fractions and promoting the formation of illite. These mineralogical alterations were significantly correlated with the amount of Fe mobilized from the soil. The RHIZOtest experiment revealed a drastic dissolution of amorphous components in the rhizosphere soil of Fe-deficient plants, possibly caused by the intense release of phenolics, amino acids, and organic acids, but without any formation of illite. Both batch and RHIZOtest experiments proved that exudates released by cucumber under Fe deficiency concurred to the rapid modification (on a day-scale) of the mineralogy of a calcareous soil.     

The effects of Fe deficiency on low molecular weight organic acid exudation and cadmium uptake by Solanum nigrum L.

Abstract

The influence of Fe-deficiency on the root exudation of low molecular weight organic acids (LMWOAs), pH alteration and cadmium (Cd) accumulation and translocation were investigated in morel (Solanum nigrum L.) in hydroponic culture experiments. Tartaric, citric, malic and acetic acids were monitored because these acids were abundant and often detected as root exudates. Results showed that Fe-deficient plants excreted large amounts of LMWOAs in comparison with Fe-sufficient plants across all Cd treatments (p <0.05). In both cases the concentrations of the four organic acids were tartaric > citric > malic > acetic. The results showed that the Fe-deficient plants with higher concentrations of LMWOAs accumulated more Cd (p <0.05) and induced a decrease in solution pH compared with the Fe-sufficient plants. Cadmium accumulation in the Fe-deficient and Fe-sufficient plants had significant positive correlations with the exudation of malic and acetic acids (p <0.05 and p<0.01). Cadmium accumulation in the Fe-sufficient plants had a significant (p<0.01) positive correlation with the exudation of tartaric acid, whereas there was a negative correlation (p<0.01) between Cd accumulation and the exudation of tartaric acid in the Fe-deficient plants. No significant correlation between the exudation of citric acid and Cd accumulation was obtained. Our results indicate that Fe-deficiency could induce Cd accumulation and translocation through an increase of LMWOAs exudation and pH alteration, both of which enhance Cd bioavailability.     

Comparison of Iron Availability in Leaves of Barley and Rice

Iron (Fe) is an essential trace element in all eukaryotes. In higher plants, Fe deficiency causes interveinal chlorosis in young leaves. However, in barley and rice, both of which are "Strategy II" plants, the degree and the pattern of Fe-deficiency symptoms differ. In the present study, barley and rice plants were grown in the same container, i.e., by "coculturing," to compensate for the amount of mugineic acids in rice in the nutrient solution. We examined the differential availability of Fe for distribution and retranslocation in shoots between barley and rice without considering the difference in the iron acquisition ability, which is affected by the differential mugineic acid secretion between barley and rice. Although the Fe concentration of young barley leaves had decreased under the coculture conditions, the SPAD value was similar to that in monocultured barley. In contrast, although there was an increase in the Fe concentration of the young leaves of cocultured rice, the SPAD value decreased, as in the case of monocultured rice. Rice accumulated Fe in old leaves, whereas in barley Fe was efficiently distributed to young leaves. Therefore, the SPAD value of the second leaf in rice remained constantly high. The Fe concentration of the second leaf in barley decreased under Fe-deficient coculture conditions, the SPAD value decreased and the senescence of the second leaf become accelerated. ⁵⁹Fe pulse-labeling experiments suggested that in barley Fe was more efficiently retranslocated from old leaves to young leaves than that in rice. As a result, the level of Fe present in the fraction with a molecular weight lower than the 10,000/water-soluble Fe ratio was higher in the old leaves of barley than in the old leaves of rice under Fe-deficient conditions. Based on the results obtained, we suggest that the distribution and retranslocation characteristics of internal Fe in barley may be well adapted to Fe deficiency.     

Image changes in chlorophyll fluorescence of cucumber leaves in response to iron deficiency and resupply

Iron (Fe) is an essential element for plants and its deficiency causes decrease not only in the photosynthetic rate but also in the actual photosystem II efficiency at steady‐state photosynthesis. The aim of this work was to determine the effect of Fe deficiency in plants of Cucumis sativus (L.) in two different experimental conditions. In the first experiment, plants were grown with or without Fe for 7 d. After 7 d, Fe‐deficient plants were resupplied with Fe and sampled after 12 h and 48 h. In the second experiment, plants were grown with Fe in the nutrient solution for 3 d and after this period, Fe was withdrawn and plants sampled after 3 and 6 d. Iron and chlorophyll (Chl) concentration and Chl‐fluorescence imaging were measured. In cucumber leaves subjected to Fe deficiency, fluorescence imaging of Chl a evidenced spatial changes on leaf lamina. Following Fe deficiency both after 7 d (Exp. 1) or 6 d (Exp. 2) leaves showed a slight, nonsignificant decrease in F_v/F_m ratio. However Chl‐fluorescence parameters determined in light conditions showed significant changes which indicate an alteration in the photosynthetic process. Surprisingly, the effect of Fe deficiency was more pronounced in leaves of plant of Exp. 2 as compared to those that had grown in complete absence of Fe (Exp. 1). In the latter case down‐regulated mechanisms preserved leaves from irreversible photoinhibition leading to complete recovery when plants were resupplied with the microelement.     

Detection of the regions of phytosiderophore release from barley roots

Abstract

We devised a method to detect regions of phytosiderophore release from barley (Hordeum vulgare cv. Minorimugi) roots. Plants were grown in Fe-sufficient (+Fe) or Fe-deficient (?-Fe) water cultures for 14 d in a phytotron. Intact or excised roots were sampled and put between two sheets of filter papers just after the onset of the light period. The filter papers with roots were wrapped with vinyl film to avoid drying out and covered with aluminum foil to shade. The roots between the filter paper were kept in the phytotron for 4 h and phytosiderophores (PS) released from roots were absorbed by the filter paper. Then, the shape of the roots was preserved by photocopy and PS released on the filter paper were visualized by the method employed for detecting PS on thin layer chromatography (TLC). Gelatinous Fe solubilizing activity was employed for detecting PS on the filter paper. Released PS were detected as white spots on the orange-colored background and the regions of PS release from the roots were visible on the filter paper. It was evident that the apical zones of roots were the main regions of PS release. It was apparent that a distinct primary root newly formed on the basal parts had higher activity to release PS than the other roots of ?Fe plants. It was also shown that apical root zones of +Fe plants released PS.     

Efficacy of an artificial microbial siderophore-Fe(III) with high redox potential on correcting Fe chlorosis in rice

ABSTRACT

Microbial siderophore-chelated Fe(III) is suggested to be an important source of Fe for plants, although it is hardly reduced by plant roots. Here, we investigated the efficacy of the easily reducible artificial microbial siderophore tris[2-{(N-acetyl-N-hydroxy)glycylamino}ethyl]amine (TAGE)-Fe(III) as an alternative Fe source to correct Fe deficiency in rice plants, and compared it to that of the natural siderophore deferoxamine B (DFOB)-Fe(III). We also evaluated the absorption of Fe from TAGE-Fe(III) by the Strategy I-like system of gramineous plants using nicotianamine aminotransferase 1 (naat1) mutant rice, which does not synthesize phytosiderophores. Fe(III)-siderophores were synthesized in vitro. Nipponbare rice and its naat1 mutant were reared in soil and gel cultures to determine Fe availability. Hydroponically grown naat1 mutant seedlings were used for reducibility assays to determine the ability of rice roots to reduce Fe(III) chelated by TAGE or DFOB. The expression of a Fe-deficiency inducible gene was also determined, as well as chlorophyll and Fe concentrations. Reduci bility assays on naat1 mutant seedlings revealed that the reduction level of TAGE-Fe(III) was approximately three times higher than that of DFOB-Fe(III). Application of TAGE-Fe(III) to both culture medium and alkaline soil improved Fe chlorosis, growth, and Fe concentration in both naat1 and wild type plants, whereas application of DFOB-Fe(III) only did so in wild type plants. Easily reducible Fe(III)-chelates such as TAGE-Fe(III) can be a better source of Fe for rice plants than most natural microbial siderophores-Fe(III). Our study also demonstrated that rice plants have the ability to utilize microbial siderophores-Fe(III) as the Fe source through the Strategy I-like Fe acquisition system.