Iron dissociates from the NaFeEDTA complex prior to or during intestinal absorption in rats

Sodium iron ethylenediaminetetraacetate (NaFeEDTA) has superior iron bioavailability especially in foods containing iron absorption inhibitors. However, mechanisms involved in the absorption and subsequent partitioning of iron complexed with EDTA are poorly understood. Our objectives were to compare retention and tissue distribution of iron administered to rats either as FeSO4 or NaFeEDTA, either orally (OR) or subcutaneously (SC). Weanling rats were fed semipurified diets supplemented with either FeSO4 or NaFeEDTA for 7 days. They were then given a meal containing 59Fe-labeled FeSO4 or NaFeEDTA, or they were injected SC with these two forms of radiolabeled Fe. 59Fe retention was measured by whole body counting. Urine was collected and counted at 24 h intervals throughout the counting period. Tissue samples were analyzed for nonheme iron and 59Fe activity. Absorption of iron from FeSO4 or NaFeEDTA was similar (57.7 and 53.4%, respectively). Seventy-seven percent of the injected Na59FeEDTA was excreted in the urine within 24 h, whereas only 0.5, 0.8, and 1.4% of the injected 59FeSO4, oral 59FeSO4, and oral Na59FeEDTA, respectively, was excreted in the urine. The nonheme iron content was lower in the liver and spleen, by 56.8 and 28.4%, respectively, among rats consuming the NaFeEDTA diet as compared to rats fed FeSO4. We conclude that iron is dissociated from EDTA prior to or during intestinal absorption and that some fraction of the dissociated EDTA is absorbed separately from the iron.     

Tissue iron distribution and urinary mineral excretion vary depending on the form of iron (FeSO4 or NaFeEDTA) and the route of administration (oral or subcutaneous) in rats given high doses of iron

Sodium iron ethylenediaminetetraacetate (NaFeEDTA) has considerable promise as an iron fortificant in food. However, effects of administering high levels of NaFeEDTA on tissue iron distribution and mineral excretion are not well understood. The objectives of this study were to assess nonheme iron distribution in the body and urinary excretion of Ca, Mg, Cu, Fe, and Zn after daily administration of high levels of iron to rats over 21 days. Iron was either given orally with food or injected subcutaneously, as either FeSO 4 or NaFeEDTA. Selected tissues were collected for nonheme iron analysis. Estimated total body nonheme iron levels were similar in rats fed NaFeEDTA or FeSO 4, but the tissue distribution was different: it was 53% lower in the liver and 86% higher in the kidneys among rats fed NaFeEDTA than among those fed FeSO 4. In contrast, body nonheme iron was 3.2-fold higher in rats injected with FeSO 4 than in rats injected with NaFeEDTA. Administering NaFeEDTA orally elevated urinary Cu, Fe, and Zn excretion compared with FeSO 4 (1.41-, 11.9-, and 13.9-fold higher, respectively). We conclude that iron is dissociated from the EDTA complex prior to or during intestinal absorption. A portion of intact FeEDTA may be absorbed via a paracellular route at high levels of intake but is mostly excreted in the urine. Metal-free EDTA may be absorbed and cause elevated urinary excretion of Fe, Cu, and Zn.     

Tissue iron distribution and adaptation of iron absorption in rats exposed to a high dietary level of NaFeEDTA

Although it has been shown that iron absorption from NaFeEDTA, a promising iron fortificant, is effectively down-regulated in iron-loaded rats, effects of prolonged exposure to high dietary levels of NaFeEDTA are not well understood. The objectives of this study were to determine whether rats can adapt to a high dietary level of NaFeEDTA by down-regulating iron absorption, and to determine effects on tissue iron distribution, with or without an iron absorption inhibitor. Male Sprague-Dawley rats were exposed to diets supplemented with FeSO4 or NaFeEDTA at 1200 mg of Fe/kg of diet, with or without tea, for 27 days. Iron absorption measured by whole-body counting before and after exposure showed that rats adapted to the high dietary level of FeSO4 or NaFeEDTA by down-regulating iron absorption to a similar extent. However, nonheme iron concentrations in liver and spleen were about 35-50% lower, whereas the concentration in kidney was about 300% higher in rats fed NaFeEDTA, compared to rats fed FeSO4. Tea had no major impact on iron absorption or iron status, regardless of iron source. Our results showed that although iron absorption was down-regulated similarly, body iron distribution was markedly different between rats exposed to FeSO4 and those exposed to NaFeEDTA. Further studies are warranted to determine the effects of prolonged exposure to dietary NaFeEDTA on kidney iron accumulation and kidney function.     

Inhibition of iron uptake from iron salts and chelates by divalent metal cations in intestinal epithelial cells

Iron chelates, namely, ferrous bisglycinate and ferric EDTA, are promising alternatives to iron salts for food fortification. The objectives of this study were to compare iron uptake from radiolabeled ferrous sulfate, ferrous ascorbate, ferrous bisglycinate, ferric chloride, ferric citrate, and ferric EDTA by Caco-2 cells with different iron status and in the presence of divalent metal cations. Iron-loaded Caco-2 cells, with reduced DMT-1 and elevated HFE mRNA levels, down-regulated uptake from ferrous ascorbate and bisglycinate but not from ferric compounds. Nevertheless, iron uptake from all compounds was markedly inhibited in the presence of 100-fold molar excess of Co2+ and Mn2+ cations, with ferrous compounds showing a greater percent reduction. Our results suggest that ferrous iron is the predominant form of iron taken up by intestinal epithelial cells and the DMT-1 pathway is the major pathway for uptake. Iron uptake from chelates appears to follow the same pathway as uptake from salts.     

Studies on water transport through the sweet cherry fruit surface. 7. Fe3+ and Al3+ reduce conductance for water uptake

The effects of the chloride salts LiCl, CaCl(2), MgCl(2), AlCl(3), EuCl(3), and FeCl(3) and the iron salts FeCl(2), FeCl(3), Fe(NO(3))(3), FeSO(4), and Fe(2)(SO(4))(3) on water conductance of exocarp segments (ES) and rates of water uptake into detached sweet cherry fruit (Prunus avium L. cv. Adriana, Early Rivers, Namare, Namosa, and Sam) were studied. ES were excised from the cheek of mature fruit and mounted in stainless steel diffusion cell; water penetration was monitored gravimetrically from donor solutions containing the above mineral salts into a PEG 6000 (osmolality = 1.14 osM, pH 4.8, 25 degrees C) receiver solution. Conductance of ES was calculated from the amount of water taken up per unit of surface area and time by dividing by the gradient in water activity across ES. LiCl, CaCl(2), MgCl(2), FeCl(2), and FeSO(4) had no significant effect on conductance, but AlCl(3), FeCl(3), Fe(NO(3))(3), and Fe(2)(SO(4))(3) significantly reduced conductance compared to water only as a donor. Also, EuCl(3) lowered conductance; however, this effect was not always significant. Effects of salts on water conductance of ES and rates of water uptake into detached fruit were closely related (R 2 = 0.97***). Upon application of an FeCl(3)-containing donor conductance decreased instantaneously. FeCl(3) concentrations of <6.6 x 10(-)(4) M had no effect on conductance, but concentrations at or above this threshold decreased conductance. FeCl(3) lowered water conductance at a receiver pH of 4.8, but not at pH < or =2.6. The effect of FeCl(3) on conductance was largest in cv. Namare and smallest in cv. Adriana. There was no significant effect of FeCl(3) on conductance for transpiration. Formation of aluminum and iron oxides and hydroxides in the exocarp as a result of a pH gradient between donor and receiver solution is discussed as the potential mechanism for Fe(3+) and Al(3+) reducing conductance for water uptake.     

Determination of Fe2+ in Rice Leaves (Oryza sativa L.) by Using the Chelator BPDS Alone or Combined with the Chelator EDTA

Abstract

Iron toxicity is a problem in many areas of wetland rice. Since Fe²⁺ is considered to be the toxic form of iron, the objective of this research was to determine the Fe²⁺ concentration in rice leaves using the chelator bathophenanthroline disulfonate (BPDS), disodium salt alone or combined with the chelator ethylenediaminetetraacetate (EDTA), disodium salt, where BPDS should solely chelate the Fe²⁺ and EDTA chelate only Fe³⁺. Thus, the combination of these chelators should stabilize the Fe oxidation states. It was also tested whether the chelators BPDS and EDTA could stabilize the oxidation states of Fe during the extraction of rice leaves. Extractions of rice leaves were carried out using an 1 mM BPDS or BPDS‐EDTA extractant solution. To test the stabilization of the Fe oxidation states by the combination of BPDS with EDTA, the extraction solution for one part of the samples contained 0.07 mM Fe³⁺. An extraction without plant material as control was also taken into consideration. The results indicated that the chelators were able to stabilize the oxidation states of Fe in the control (extraction without plant material). However, in the presence of plant material, Fe³⁺ was partly reduced to Fe²⁺, i.e., the chelators could not stabilize the oxidation states of Fe. Accordingly, we concluded that the BPDS‐EDTA method may function for the Fe²⁺ determination in water and soil, but it is apparently not suited for rice leaves.     

The relative efficiency of ionic iron(III) and iron(II) utilization by the rice plant

Uptake of iron by rice plants was equally rapid when supplied as ionic iron(II) or iron(III) at pH 3 and 4. Iron(III) uptake was reduced at pH 5 and uptake of iron when supplied as FeEDTA was relatively low at all three pH levels.

At pH 4 in the presence of plant roots, reduction of iron(III) to iron(II) occurred as indicated by Fe²⁺ BPDS formation. BPDS in a 3:1 ratio to iron(III) suppressed iron uptake by about 70%. The reduction was observed to be located in the endodermis of young roots and exodermis of older roots.

A capacity to oxidize iron(II) at the root surface was also observed under local anaerobic and relatively high pH conditions.

The significance of these two counteracting processes in affecting the oxidation state of iron at the root surface is discussed.     

不同铁形态对水稻根表铁膜及铁吸收的影响

通过溶液培养试验研究了FeCl2?4H2O和FeCl3?6H2O对水稻根表铁膜数量及铁吸收的影响。结果表明,FeCl2处理时水稻根表铁膜浓度是FeCl3处理的197%～233%。利用EDTA-BPDS对铁膜形态分析看出,根表铁膜中Fe3+占85%～92%,Fe2+占8%～15%。水稻天优998根表铁膜数量显著高于培杂泰丰,其铁吸收是培杂泰丰的115%～138%。两种铁形态处理明显提高水稻的根系活力,其中,FeCl2处理时水稻根系活力增加24%～69%,FeCl3为16%～54%。FeCl2处理时水稻根系SOD、POD和CAT活性分别增加11%～32%、15%～30%和30%～31%,但FeCl3处理没有明显影响。上述结果表明一定浓度铁处理明显增加水稻根表铁浓度和铁吸收;与FeCl3处理相比,FeCl2处理能提高根系抗氧化酶活性,增加水稻的铁吸收和根表铁膜数量。     

Comparison of iron uptake from reduced iron powder and FeSO4 using the Caco-2 cell model: effects of ascorbic acid, phytic acid, and pH

The reduced iron powder has considerable potential for use as an iron fortificant because it does not change organoleptically during storage or food preparation for cereal flour, and its bioavailability is scarcely influenced by iron absorption inhibitors in foods. The objective of this article is to study the effects of ascorbic acid, phytic acid, and pH on iron uptake from reduced iron powder (43 microm) and FeSO 4, and to compare iron bioavailability of reduced iron powders among four selected granularity levels. The cell ferritin formation is used as a marker of iron uptake. Obviously, iron uptake of reduced iron powder is increased with decreasing of powder granularity and is much lower than FeSO 4 when the size is above 43 microm, but significantly higher at 40-60 nm. In the presence of ascorbic acid or phytic acid, Caco-2 cell iron absorption from reduced iron powder (43 microm) is significantly higher than that from FeSO 4. And iron uptake of Caco-2 cells is decreased with increasing of pH from 5.5 to 7.5. Moreover, the decrease trend is more obvious for reduced iron powder than for FeSO 4. Our results indicated that iron bioavailability of reduced iron powder by intestinal enterocytes is similar to that of iron salts, and reduced iron powder is more excellent than FeSO 4 as food fortificant, especially at ultramicroscopic granularity.     

Rates of cuticular penetration of chelated Fe(III): role of humidity, concentration, adjuvants, temperature, and type of chelate

Time courses of cuticular penetration of FeCl3 and Fe(III) complexes of citric acid, EDTA, EDDHA (Sequestrene 138Fe), imidodisuccinic acid (IDHA), and ligninsulfonic acid (Natrel) were studied using astomatous cuticular membranes (CMs) isolated from Populus x canescens leaves. At 100% relative humidity, the Fe(III) chelates disappeared exponentially with time from the surface of the CMs; that is, penetration was a first-order process that can be described using rate constants or half-times of penetration (t(1/2)). Half-times ranged from 20 to 30 h. At 90% humidity, penetration rates were insignificant with the exception of Natrel, for which t(1/2) amounted to 58 h. Rate constants were independent of temperature (15, 25, and 35 degrees C). Permeability decreased with increasing Fe chelate concentration (IDHA and EDTA). At 100% humidity, half-times measured with FeIDHA were 11 h (2 mmol L(-1)), 17 h (10 mmol L(-1)) and 36 h (20 mmol L(-1)), respectively. In the presence of FeEDTA, penetration of CaCl2 was slowed greatly. Half-times for penetration of CaCl2, which were 1.9 h in the absence of FeEDTA, rose to 3.12 h in the presence of an equimolar concentration of EDTA and 13.3 h when the FeEDTA concentration was doubled. Hence, Fe chelates reduced permeability of CMs to CaCl2 and to the Fe chelates themselves. It is suggested that Fe chelates reduced the size of aqueous pores. This view is supported by the fact that rate constants for calcium salts were about 5 times higher than for Fe chelates with the same molecular weights. Adding Tween 20 (5 g L(-1)) as a humectant did not increase permeability to FeIDHA at 90% humidity and below, while addition of glycine betaine did. Penetration of FeCl3 applied at 5 g L(-1) (pH 1.5) was not a first order process as rate constants decreased rapidly with time. Only 2% of the dose penetrated during the first 2 h and less than that in the subsequent 8 h. Recovery was only 70%. This was attributed to the formation of insoluble Fe hydroxide precipitates on CMs. These results explain why in the past foliar application of Fe compounds had limited success. Inorganic Fe salts are instable and phytotoxic because of low pH, while Fe chelates penetrate slowly and 100% humidity is required for significant penetration rates. Concentrations as low as reasonably possible should be used. These physical facts are expected to apply to stomatous leaf surfaces as well, but absolute rates probably depend on leaf age and plant species. High humidity in stagnant air layers may favor penetration rates across stomatous leaf surfaces when humidity in bulk air is below 100%.     

In vitro iron availability from iron-fortified whole-grain wheat flour

Iron deficiency is the most common nutritional disorder worldwide. Iron fortification of foods is considered to be the most cost-effective long-term approach to reduce iron deficiency. However, for fortified foods to be effective in reducing iron deficiency, the added iron must be sufficiently bioavailable. In this study, fortification of whole-grain wheat flour with different sources of iron was evaluated in vitro by measuring the amount of dialyzable iron after simulated gastrointestinal digestion of flour baked into chapatis and subsequent intestinal absorption of the released iron using Caco-2 cell layers. The dialyzability of iron from iron-fortified wheat flour was extremely low. Additions of 50 mg/kg iron to the flour in the form of ferrous sulfate, Ferrochel amino acid chelate, ferric amino acid chelate taste free (TF), Lipofer, ferrous lactate, ferrous fumarate, ferric pyrophosphate, carbonyl iron, or electrolytic iron did not significantly increase the amount of in vitro dialyzable iron after simulated gastrointestinal digestion. In contrast, fortification of flour with SunActive Fe or NaFeEDTA resulted in a significant increase in the amount of in vitro dialyzable iron. Relative to iron from ferrous sulfate, iron from SunActive Fe and NaFeEDTA appeared to be 2 and 7 times more available in the in vitro assay, respectively. Caco-2 cell iron absorption from digested chapatis fortified with NaFeEDTA, but not from those fortified with SunActive Fe, was significantly higher than from digested chapatis fortified with ferrous sulfate. On the basis of these results it appears that fortification with NaFeEDTA may result in whole-grain wheat flour that effectively improves the iron status.     

Inhibition of iron uptake by phytic acid, tannic acid, and ZnCl2: studies using an in vitro digestion/Caco-2 cell model.

The objective of this study was to document the effects of phytic acid, tannic acid, and zinc on iron uptake in an in vitro digestion/Caco-2 cell culture model. The effects of phytic acid and tannic acid on iron uptake were measured at increasing molar ratios of FeCl3 to phytic acid or tannic acid. Maximal inhibition of iron uptake by phytic acid occurred at a 1:10 ratio of Fe to phytic acid. Dialyzable Fe decreased with a low Fe to phytic acid ratio but increased with Fe:phytic acid ratios greater than 1:3 indicating that more iron was soluble at higher phytic acid levels but less available. As in human studies, heme iron was less inhibited by phytic acid than nonheme iron. Tannic acid was a more potent inhibitor of nonheme iron uptake, as maximal inhibition (97.5%) of iron uptake occurred at a ratio of 1:1 or less. The addition of ZnCl2 to the digest at ratios of 1:0.5 and 1:1 decreased iron uptake by 57 and 80%, respectively. Overall, the results agree qualitatively with studies in humans and demonstrate the relative effects of these compounds on iron uptake in this model system. This study provides key information for determining iron availability under more complex meal conditions.     

Physiological responses of grapevine callus cultures to iron deficiency

Grapevine is considered a ‘Strategy I’ plant because it performs some peculiar biochemical and physiological responses when grown under iron (Fe) deficiency stress conditions. Callus cultures were started from leaf and internode cuts of micropropagated plantlets of two grapevine genotypes well known for their Fe‐chlorosis characteristic: Vitis riparia a very susceptible genotype and Vitis berlandieri a resistant one. Modification of NADH: ferric (Fe³⁺) reductase activity was spectrophotometrically evaluated by following the formation of the complex ferrous (Fe²⁺)‐(BPDS)₃, while the malic and citric acid production were determined in callus cultures grown both in the presence (+Fe) and absence (‐Fe) of Fe. Moreover, a microsomal fraction was isolated from the calli to evaluate the H⁺‐ATPase and the Fe³⁺‐EDTA reductase activities. As expected, calli of the Fe‐efficient genotype (V. berlandieri) was able to enhance Fe³⁺‐EDTA reductase activity when growing under Fe deficiency while the Fe‐chlorosis susceptible V. riparia could not or did it with lower efficiency. Therefore, the H⁺‐ATPase assay showed a higher enzymatic activity in the microsomal fraction isolated from Vitis berlandieri grown without Fe with respect to its control (+Fe). Organic acid determination gave quite contradictory results, specially regarding malic acid which, under our study conditions, seemed not to be linked with the strategies of response to Fe deficiency.     

Gallium(III) does not actively substitute for iron(III) in iron/gallium competition studies

Strategy II plants respond to Fe stress by releasing a phytosiderophore and are believed to absorb Fe as Fe(III). Gallium(III) has chemical characteristics which have made it useful as a substitute for Fe(III) in biological systems. The objectives of our study were to: 1) determine if Ga(III) acts competitively to reduce Fe(III) uptake or otherwise substitutes for Fe(III) in barley (Hordeum vulgare L.), and 2) determine if the competition for Fe(III) between EDDHA or BPDS and barley further elucidates the form of Fe absorbed by barley. Chlorosis ratings, phytosiderophore production, and tissue Fe contents were indexes of Fe stress.

Gallium was absorbed and translocated by the plant both in the presence and absence of Fe, and slightly alleviated Fe stress in the absence of Fe. However, Fe uptake was not affected by the presence of Ga. Thus, Ga(III) did not seem to compete with Fe(III) for uptake. Increasing EDDHA in solution intensified chlorosis and phytosiderophore production and reduced root Fe, but did not reduce leaf Fe concentration. Increased BPDS had no influence on either chlorosis or leaf Fe, but did cause phytosiderophore production to increase and root Fe to decline. The presence of Fe(II) in solutions containing BPDS suggests a potential for reducing Fe(III) in the roots of barley.     

Red grape juice inhibits iron availability: application of an in vitro digestion/caco-2 cell model

Adequate bioavailable Fe intake is essential for optimal growth and intellectual development of infants and children. Fruit juices are nutritious and popular drinks for infants and children and are known to contain Fe uptake inhibitors (e.g., polyphenolic compounds) and a dominant promoter, ascorbic acid. Ascorbic acid is naturally present in fruit juices and is added during processing to almost all juices found in supermarkets. With these facts taken into account, an in vitro digestion/Caco-2 cell culture model was developed to compare the effects of apple, pear, white grape, red grape, prune, grapefruir, and orange juices on iron bioavailability. In two series of experiments, juices from a local supermarket were combined with FeCl(3) or commercial infant cereal fortified with elemental iron and subject to simulated gastric and intestinal digestion. Caco-2 cell ferritin formation in response to exposure to the digests served as the measure of Fe uptake. The pear, apple, grapefruit, orange, and white grape juice significantly increased Fe bioavailability from FeCl(3). For the infant cereal studies, the apple, orange, pear, and white grape juices increased the Fe bioavailability of the infant cereal. In contrast, the red grape juice and prune juice had profound inhibitory effects on iron bioavailability. These inhibitory effects were likely due to high levels of polyphenolic compounds that bind and thereby prevent absorption of soluble Fe. These inhibitory compounds appeared to counteract the promotional effects of ascorbic acid as they were in considerable molar excess relative to ascorbic acid and Fe in the digest. From a nutritional standpoint, the results suggest that individuals in need of optimal Fe absorption should avoid red grape and prune juice or at least vary the types of juices consumed. Alternatively, individuals seeking to limit Fe uptake (e.g., hemochromatitics and astronauts) may be able to utilize red grape or prune juice as effective inhibitors of Fe uptake. Consumers should be aware that the compounds that inhibit Fe availability are also linked to anticancer benefits; thus, a dietary balance of the above juices may be optimal.     

Meat and ascorbic acid can promote Fe availability from Fe-phytate but not from Fe-tannic acid complexes

This study utilized an in vitro digestion/Caco-2 cell model to determine the levels of ascorbic acid (AA) and "meat factor" needed to promote Fe absorption from Fe complexed with phytic acid (PA) or tannic acid (TA). AA reversed the inhibition of Fe absorption by PA beginning at a molar ratio of 1:20:1 (Fe:PA:AA) but essentially had no effect on the Fe complexed with TA. Fish also reversed the inhibition of Fe uptake by PA but not by TA. TA and fish decreased total Fe solubility. Iron in the presence of PA was highly soluble. AA, but not fish, increased the percentage of soluble Fe as Fe2+ in the presence of both inhibitors. The results indicate that monoferric phytate is a form of Fe that can be available for absorption in the presence of uptake promoters. In contrast, a TA-Fe complex is much less soluble and unavailable in the presence of promoters.     

Determination of suitable chemical extraction methods for the available iron content of brown forest soils in Turkey

The aim of this research was to determine the available iron (Fe) content of brown forest soils of Edirne Province and the most suitable chemical extraction method. Eight chemical extraction methods (the 0.005 M DTPA + 0.01 M CaCl2 + 0.1 MTEA, 0.05 M HCl + 0.012 M H2SO4, 1 M NH4OAc (pH: 4.8), 0.01 M EDTA + 1 M NH4OAc, 1 M MgCl2, 0.01 M EDTA + 1 M (NH4)2CO3, 0.005 M DTPA + 1 M NH4HCO3, and 0.001 M EDDHA methods) and six biological indices (the dry matter yield, Fe concentration, Fe uptake, relative dry matter yield, relative Fe concentration, and relative Fe uptake) were compared. The biological indices were determined with barley (Hordeum vulgare L.) grown under greenhouse conditions. At the end of the experiment, the highest correlation coefficients (r) were determined to be between the 0.005 M DTPA + 0.01 M CaCl2 + 0.1 M TEA method and the biological indices and between the 0.005 M DTPA + 1 M NH4HCO3 method and the biological indices. The corresponding correlation coefficients (r) for the 0.005 M DTPA + 0.01 M CaCl2 + 0.1 M TEA method and the six biological indices were 0.621**, 0.823**, 0.810** 0.433**, 0.558**, and 0.640**, respectively. For the 0.005 M DTPA + 1 M NH4HCO3 method, these coefficients were equal to 0.618**, 0.520**, 0.679**, 0.521**, 0.492**, and 0.641**, respectively (** indicate the validity of the relationships at p < 0.01) These extraction methods, out of all the methods tested, were suggested for the determination of the available Fe content of the brown forest soils. Published in Russian in Pochvovedenie, 2006, No. 9, pp. 1068–1074. The text was submitted by the author in English.     

EFFECT OF BIODEGRADABLE CHELATING LIGAND ON IRON BIOAVAILABILITY AND RADISH GROWTH

The effect of chelating ligands on iron (Fe) uptake and growth of radish (Raphanus sativus L.) was investigated. The ethylenediaminetetraacetic acid (EDTA) increased ⁵⁵Fe uptake in roots of radish though its subsequent translocation from roots to shoots and leaves did not increase. About 70%—80% of the total ⁵⁵Fe was distributed in the roots while about 5%—15% and 11%—17% were in shoots and leaves, respectively. The EDTA increased iron uptake into the roots of radish, but not in the above ground parts of the plant. The growth of radish (Raphanus sativus L.) decreased drastically in alkaline condition (pH > 9), even though the concentration of iron was sufficient in the growth medium. The growth of radish was enhanced successfully by the addition of hydroxyiminodisuccinic acid (HIDS) and EDTA. This might be because HIDS and EDTA solubilize iron from its precipitation with hydroxides at higher pH, and increase iron bioavailability. The influence of EDTA and HIDS on radish growth was comparable. Increase of radish growth by ethylenediaminedisuccinic acid (EDDS) and methylglicinediacetic acid (MGDA) was less than those by EDTA and HIDS. Considering the reproducibility of the radish growth (biomass production) at pH 10, HIDS is supposed to be more effective compared to EDTA.     

Element uptake in thalli of the lichen Physcia caesia from sandstone and calcareous substratum

Physcia caesia is a foliose, saxicolous lichen commonly found on weakly acidic to alkaline rock and artificial calcareous substrata. Uptake of iron and phosphate, which are known to be significant for governing the calcifuge‐calcicole behavior of lichens (as well as vascular plants), was studied in individuals of P. caesia deriving either from variegated sandstone or concrete. Samples from either substratum originated from walls erected at the same location, i.e., lichens were exposed to the same atmospheric element load and microclimate prior to the experiments. Element uptake was investigated after short‐term incubation in the laboratory involving solutions of FeCl₂, FeCl₃, and KH₂PO₄ at pH 3 and 8. Uptake of Fe²⁺ was significantly higher at either pH in the thalli from concrete than in those from sandstone, whereas Fe³⁺ uptake was not significantly different between the two groups of lichen thalli, though there was an insignificant trend for higher Fe³⁺ uptake at pH 8 in the samples from concrete. Phosphate uptake also was more efficient in thalli deriving from concrete than in those from sandstone, even though the initial P content was higher in the samples from sandstone. The results suggest that the ability of P. caesia to adapt Fe and P uptake to the pH‐dependent availabilities of these nutrients is responsible for the potential of the species to grow both on weakly acidic and alkaline substrata.     

Iron inefficient and efficient oat cultivars. II. Characterization of phytosiderophore released in response to Fe deficiency stress

Abstract

Iron‐inefficient TAM 0–312 and Fe‐efficient Coker 227 oats (Strategy II plants) differ in their release of phytosiderophore in response to iron‐deficiency stress—the Fe‐efficient Coker 227 releases a phytosiderophore whereas the Fe‐inefficient TAM 0–312 does not. The phytosiderophore released by Coker 227 oats in response to Fe‐deficiency stress does not appear to transport Fe into the plant as Fe phytosiderophore. When the Fe‐inefficient TAM 0–312 and Fe‐efficient Coker 227 oats were subjected to Fe supplied as Fe²⁺(BPDS)₃, Fe³⁺HEDTA, as Fe³⁺EDDHA, Coker 227 utilized the Fe more efficiently than TAM 0–312 in every case. Both cultivars reduced Fe³⁺ as FeCl₃ to form Fe²⁺(BPOS)₃ and responded better to this form of Fe than Fe supplied as the ferric chelate. Reduction of Fe³⁺ at the root appears to be a factor that facilitates iron uptake by Coker 227 oats and the release of a phytosiderophore appears to make more Fe available at the root that can be reduced and transported to plant tops.