Absorption Of 59Fe Research Articles

Fetal factors disrupt placental and maternal iron homeostasis in murine β-thalassemia

AbstractPregnancy rates in β-thalassemia are increasing but the risk of complications is higher; thus, better understanding of maternal and fetal iron homeostasis in this disorder is needed. HbbTh3/+ (Th3/+) mice model human β-thalassemia. Both the murine and human diseases are characterized by low hepcidin, high iron absorption, and tissue iron overload, with concurrent anemia. We hypothesized that disordered iron metabolism in pregnant Th3/+ mice would negatively affect their unborn offspring. The experimental design included these groups: wild-type (WT) dams carrying WT fetuses (WT1); WT dams carrying WT and Th3/+ fetuses (WT2); Th3/+ dams carrying WT and Th3/+ fetuses (Th3/+); and age-matched, nonpregnant adult females. Serum hepcidin was low, and mobilization of splenic and hepatic storage iron was enhanced in all 3 groups of experimental dams. Intestinal 59Fe absorption was lower in Th3/+ dams (as compared with WT1/2 dams) but splenic 59Fe uptake was higher. Th3/+ dams had hyperferremia, which led to fetal and placenta iron loading, fetal growth restriction, and placentomegaly. Notably, Th3/+ dams loaded Th3/+ and WT fetuses, with the latter situation more closely mirroring human circumstances when mothers with thalassemia have relatively unaffected (thalassemia trait) offspring. Iron-related oxidative stress likely contributed to fetal growth impairment; enhanced placental erythropoiesis is a probable cause of placental enlargement. Moreover, high fetal liver iron transactivated Hamp; fetal hepcidin downregulated placental ferroportin expression, limiting placental iron flux and thus mitigating fetal iron loading. Whether gestational iron loading occurs in human thalassemic pregnancy, when blood transfusion can further elevate serum iron, is worth consideration.

Four AAs increase DMT1 abundance in duodenal brush-border membrane vesicles and enhance iron absorption in iron-deprived mice

AbstractIron-deficiency anemia is common worldwide and typically treated by oral iron supplementation. Excess enteral iron, however, may cause pathological outcomes. Developing new repletion approaches is thus warranted. Previous experimentation revealed that select amino acids (AAs) induce trafficking of transporters onto the enterocyte brush-border membrane (BBM) and enhance electrolyte absorption/secretion. Here, we hypothesized that certain AAs would increase the abundance of the main intestinal iron importer, divalent metal-ion transporter 1 (DMT1), on the BBM of duodenal enterocytes, thus stimulating iron absorption. Accordingly, all 20 AAs were screened using an ex vivo duodenal loop/DMT1 western blotting approach. Four AAs (Asp, Gln, Glu, and Gly) were selected for further experimentation and combined into a new formulation. The 4 AAs stimulated 59Fe transport in mouse duodenal epithelial sheets in Ussing chambers (∼4-fold; P < .05). In iron-deprived mice, oral intragastric administration of the 4 AA formulation increased DMT1 protein abundance on the enterocyte BBM by ∼1.5-fold (P < .05). The 4 AAs also enhanced in vivo 59Fe absorption by ∼2-fold (P < .05), even when ∼26 µg of cold iron was included in the transport solution (equal to a human dose of ∼73 mg). Further experimentation using DMT1int/int mice showed that intestinal DMT1 was required for induction of iron transport by the 4 AAs. Select AAs thus enhance iron absorption by inducing DMT1 trafficking onto the apical membrane of duodenal enterocytes. We speculate that further refinement of this new 4 AA formulation will ultimately allow iron repletion at lower effective doses (thus mitigating negative side effects of excess enteral iron).

Oral Administration of Ginger-Derived Lipid Nanoparticles and Dmt1 siRNA Potentiates the Effect of Dietary Iron Restriction and Mitigates Pre-Existing Iron Overload in Hamp KO Mice.

Intestinal iron transport requires an iron importer (Dmt1) and an iron exporter (Fpn1). The hormone hepcidin regulates iron absorption by modulating Fpn1 protein levels on the basolateral surface of duodenal enterocytes. In the genetic, iron-loading disorder hereditary hemochromatosis (HH), hepcidin production is low and Fpn1 protein expression is elevated. High Fpn1-mediated iron export depletes intracellular iron, causing a paradoxical increase in Dmt1-mediated iron import. Increased activity of both transporters causes excessive iron absorption, thus initiating body iron loading. Logically then, silencing of intestinal Dmt1 or Fpn1 could be an effective therapeutic intervention in HH. It was previously established that Dmt1 knock down prevented iron-loading in weanling Hamp (encoding hepcidin) KO mice (modeling type 2B HH). Here, we tested the hypothesis that Dmt1 silencing combined with dietary iron restriction (which may be recommended for HH patients) will mitigate iron loading once already established. Accordingly, adult Hamp KO mice were switched to a low-iron (LFe) diet and (non-toxic) folic acid-coupled, ginger nanoparticle-derived lipid vectors (FA-GDLVs) were used to deliver negative-control (NC) or Dmt1 siRNA by oral, intragastric gavage daily for 21 days. The LFe diet reduced body iron burden, and experimental interventions potentiated iron losses. For example, Dmt1 siRNA treatment suppressed duodenal Dmt1 mRNA expression (by ~50%) and reduced serum and liver non-heme iron levels (by ~60% and >85%, respectively). Interestingly, some iron-related parameters were repressed similarly by FA-GDLVs carrying either siRNA, including 59Fe (as FeCl3) absorption (~20% lower), pancreatic non-heme iron (reduced by ~65%), and serum ferritin (decreased 40–50%). Ginger may thus contain bioactive lipids that also influence iron homeostasis. In conclusion, the combinatorial approach of FA-GDLV and Dmt1 siRNA treatment, with dietary iron restriction, mitigated pre-existing iron overload in a murine model of HH.

Effect of phytosiderophores on 59Fe absorption and translocation in arsenic-induced chlorosis in rice and barley seedlings

In the greenhouse, rice (Oryza sativa L. cv. Akitakomachi) were grown at pH 5.5, treated with 26.8 μM As (arsenite; NaAsO2) for 14 days. We found that As-induced whitish chlorosis in the fully developed young leaves. Control and As-treated seedlings were fed with 10 μM 59Fe in the absence or in the presence of 10 μM PS (phytosiderophores, mugineic acid) for 4 h in the phytotron to observe the efficiency of PS on 59Fe absorption and translocation in plants. Absorption and translocation of 59Fe increased in control plants fed with PS as compared with those without being fed with PS, indicating that PS effectively elevated 59Fe absorption and translocation. In As-treated plants, PS enhanced 59Fe absorption by roots but did not enhance 59Fe translocation from roots to shoots. In addition, 59Fe absorption was lower in As-treated plants as compared to control plants in the absence or presence of PS. In the phytotron, a similar experiment with barley (Hordeum vulgare L. cv. Minorimugi) was conducted. Barley were grown at pH 6.5 treated with 33.5 μM As for 14 days, showing chlorosis, were fed with 59Fe in the absence or presence of PS. In control plants, PS enhanced 59Fe absorption and translocation similarly to rice. In As-treated barley, PS enhanced 59Fe absorption in roots and PS activity enhanced 59Fe translocation from roots to shoots. Our results suggested that As repressed or inhibited the system for PS-Fe3+ absorption in gramineae under severe As-stress condition, resulting in appearance of Fe chlorosis.

Iron uptake mediated by the plant-derived chelator nicotianamine in the small intestine

Iron is an essential metal for all living organisms that is absorbed in the intestinal cells as a heme-chelated or free form. It is unclear how important plant-derived chelators, such as nicotianamine (NA), an organic small molecule that is ubiquitous in crops, vegetables, and various other foods, contribute to iron bioavailability in mammals. We performed electrophysiological assays with Xenopus laevis oocytes and radioactive tracer experiments with Caco-2 cells. The findings revealed that the proton-coupled amino acid transporter SLC36A1 (PAT1) transports iron in the form of NA-Fe (II) complex in vitro. Decreased expression of hPAT1 by RNA interference in Caco-2 cells reduced the uptake of NA-59Fe (II) complex. The uptake of inorganic 59Fe (II) was relatively unaffected. These results imply that PAT1 transports iron as a NA-Fe (II) complex. The rate of 59Fe absorption in the spleen, liver, and kidney was higher when mice were orally administered NA-59Fe (II) compared with free 59Fe (II). The profile of site-specific PAT1 expression in the mouse intestine coincided with those of NA and iron contents, which were the highest in the proximal jejunum. Orally administered NA-59Fe (II) complex in mice was detected in the proximal jejunum by thin layer chromatography. In contrast, much less 59Fe (or NA) was detected in the duodenum, where the divalent metal transporter SLC11A2 (DMT1) absorbs free Fe (II). The collective results revealed the role of PAT1 in NA-Fe (II) absorption in the intestine and potential implication of NA in iron uptake in mammals.

Site-specific intestinal DMT1 silencing to mitigate iron absorption using pH-sensitive multi-compartmental nanoparticulate oral delivery system

Iron is a nutrient metal, but excess iron promotes tissue damage. Since iron chelation therapies exhibit multiple off-target toxicities, there is a substantial demand for more specific approaches to decrease iron burden in iron overload. While the divalent metal transporter 1 (DMT1) plays a well-established role in the absorption of dietary iron, up-regulation of intestinal DMT1 is associated with iron overload in both humans and rodents. Hence, we developed a novel pH-sensitive multi-compartmental particulate (MCP) oral delivery system that encapsulates DMT1 siRNA and validated its efficacy in mice. Using the gelatin NPs coated with Eudragit® L100-55, we demonstrated that DMT1 siRNA-loaded MCPs down-regulated DMT1 mRNA levels in the duodenum, which was consistent with decreased intestinal absorption of orally-administered 59Fe. Together, the Eudragit® L100-55-based oral siRNA delivery system could provide an effective strategy to specifically down-regulate duodenal DMT1 and mitigate iron absorption.

Intestinal brush-border Na+/H+ exchanger-3 drives H+-coupled iron absorption in the mouse.

Divalent metal-ion transporter-1 (DMT1), the principal mechanism by which nonheme iron is taken up at the intestinal brush border, is energized by the H(+)-electrochemical potential gradient. The provenance of the H(+) gradient in vivo is unknown, so we have explored a role for brush-border Na(+)/H(+) exchanger (NHE) isoforms by examining iron homeostasis and intestinal iron handling in mice lacking NHE2 or NHE3. We observed modestly depleted liver iron stores in NHE2-null (NHE2(-/-)) mice stressed on a low-iron diet but no change in hematological or blood iron variables or the expression of genes associated with iron metabolism compared with wild-type mice. Ablation of NHE3 strongly depleted liver iron stores, regardless of diet. We observed decreases in blood iron variables but no overt anemia in NHE3-null (NHE3(-/-)) mice on a low-iron diet. Intestinal expression of DMT1, the apical surface ferrireductase cytochrome b reductase-1, and the basolateral iron exporter ferroportin was upregulated in NHE3(-/-) mice, and expression of liver Hamp1 (hepcidin) was suppressed compared with wild-type mice. Absorption of (59)Fe from an oral dose was substantially impaired in NHE3(-/-) compared with wild-type mice. Our data point to an important role for NHE3 in generating the H(+) gradient that drives DMT1-mediated iron uptake at the intestinal brush border.

Intestinal DMT1 is critical for iron absorption in the mouse but is not required for the absorption of copper or manganese.

Divalent metal-ion transporter-1 (DMT1) is a widely expressed iron-preferring membrane-transport protein that serves a critical role in erythroid iron utilization. We have investigated its role in intestinal metal absorption by studying a mouse model lacking intestinal DMT1 (i.e., DMT1(int/int)). DMT1(int/int) mice exhibited a profound hypochromic-microcytic anemia, splenomegaly, and cardiomegaly. That the anemia was due to iron deficiency was demonstrated by the following observations in DMT1(int/int) mice: 1) blood iron and tissue nonheme-iron stores were depleted; 2) mRNA expression of liver hepcidin (Hamp1) was depressed; and 3) intraperitoneal iron injection corrected the anemia, and reversed the changes in blood iron, nonheme-iron stores, and hepcidin expression levels. We observed decreased total iron content in multiple tissues from DMT1(int/int) mice compared with DMT1(+/+) mice but no meaningful change in copper, manganese, or zinc. DMT1(int/int) mice absorbed (64)Cu and (54)Mn from an intragastric dose to the same extent as did DMT1(+/+) mice but the absorption of (59)Fe was virtually abolished in DMT1(int/int) mice. This study reveals a critical function for DMT1 in intestinal nonheme-iron absorption for normal growth and development. Further, this work demonstrates that intestinal DMT1 is not required for the intestinal transport of copper, manganese, or zinc.

Intestinal divalent metal‐ion transporter‐1 is critical for intestinal iron absorption but not that of copper (996.3)

Divalent metal‐ion transporter‐1 (DMT1) is a widely expressed iron transporter serving iron absorption and erythroid iron uptake. DMT1 can also transport certain other transition metal ions; however, questions have arisen as to the role that DMT1 plays in the absorption of copper. We tested the hypothesis that intestinal DMT1 is essential for the absorption of Fe and Cu by examining (1) hematological variables and Fe status, (2) expression of Fe‐related genes (by using RT‐qPCR), and (3) radiotracer metal absorption in a mouse model lacking intestinal DMT1 (i.e. DMT1int/int, generated by crossing floxed DMT1 and villin‐Cre transgenic lines). The DMT1int/int mouse (at age ≍ 120 d) exhibited a profound hypochromic–microcytic anemia (hemoglobin concentration was 1.8 ± SD 0.5 g/dL in DMT1int/int mice cf. 14.6 ± 0.7 g/dL in wildtype, n = 7–9), and severely depleted serum Fe and liver nonheme Fe stores. mRNA expression of Cybrd1 (ferrireductase) was increased to (30 ± 3)‐fold (mean ± propagated SE, n = 3) in enterocytes of DMT1int/int mice cf. wildtype mice and that of the basolateral Fe exporter ferroportin, (2.7 ± 1.0)‐fold. Liver Hamp1 (hepcidin) expression was depressed by 97% ± 48%. Expression of the apical Cu transporter Ctr1 was increased to (2 ± 1)‐fold in enterocytes of DMT1int/int cf. wildtype mice, consistent with other models of iron deficiency. Parenteral Fe injection corrected the hematological and serum‐Fe variables, Fe stores, and gene expression levels in the DMT1int/int mouse. We measured the absorption of 59Fe and 64Cu in mice fed by intragastric gavage. Loss of intestinal DMT1 decreased the 0–4‐hour appearance of 59Fe in blood by 88% ± 24% cf. wildtype. Enterocyte 59Fe content at 4 h was 93% ± 42% lower in DMT1int/int cf. wildtype mice, indicating that the defect was at the level of apical uptake. Intestinal handling of 64Cu in the DMT1int/int mouse was no different from wildtype (P = 0.26). We conclude that DMT1 is critical for intestinal absorption of Fe but not Cu.Grant Funding Source: Supported by PHS Grant DK080047

Effects of the pyrones, maltol and ethyl maltol, on iron absorption from the rat small intestine

The pyrones, 3-hydroxy-2-methyl-4-pyrone (maltol) and 3-hydroxy-2-ethyl-4-pyrone (ethyl maltol) chelate iron with a high affinity and selectivity. The resulting 1:3 (metal-ligand) complexes, being neutral, are able to partition readily across cell membranes and thus may facilitate iron transport across the intestinal wall. Absorption of radioactive iron (59Fe) in the presence of these pyrones was investigated in male rats 1, 2, 4 and 6 h after intraduodenal administration of a 7 micrograms dose and compared with that of 59Fe given as the sulphate, gluconate, fumarate or complexed to EDTA. Total body absorption and distribution were calculated from the 59Fe content of various tissue samples. With all the iron preparations used, blood levels of 59Fe were highest 1 h after injection whilst the 59Fe content at the major site of deposition, i.e. the bone marrow, increased up to 6 h. No 59Fe was found in the urine. Total body absorption of 59Fe was significantly higher from the pyrones than from the other four preparations. Over the dose range 0.7-700 micrograms, the proportion of 59Fe absorbed from both iron maltol and iron sulphate decreased with increasing dose. Enhanced 59Fe uptake from maltol was evident at 0.7-70 micrograms but not at 700 micrograms suggesting that use of these pyrones will not result in iron overload. Absorption of 59Fe given into the stomach was slower in onset but was sustained longer presumably via a steady delivery of iron to the duodenum from the gastric reservoir.(ABSTRACT TRUNCATED AT 250 WORDS)

Ingestion of Mn and Pb by rats during and after pregnancy alters iron metabolism and behavior in offspring

Manganese (Mn) and lead (Pb) exposures during developmental period can impair development by direct neurotoxicity or through interaction with iron metabolism. Therefore, we examined the effects of maternal ingestion of Mn or Pb in drinking water during gestation and lactation on iron metabolism as well as behavior in their offspring. Pregnant dams were given distilled water, 4.79mg/ml Mn, or 2.84mg/ml Pb in drinking water during gestation and lactation. Pups were studied at time of weaning for 59Fe absorption from the gut, duodenal divalent metal transporter 1 (DMT1) expression, hematological parameters, and anxiety-related behavior using an Elevated Plus Maze (EPM) test. Metal-exposed pups had lower body weights and elevated blood and brain concentrations of the respective metal. Pb-exposed pups had lower hematocrits and higher blood Zn protoporphyrin levels. In contrast, Mn exposed pups had normal hematological parameters but significantly reduced Zn protoporphyrin. Pharmacokinetic studies using 59Fe showed that intestinal absorption in metal-exposed pups was not different from controls, nor was it correlated with duodenal DMT1 expression. However, intravenously injected 59Fe was cleared more slowly in Pb-exposed pups resulting in higher plasma levels. The overall tissue uptake of 59Fe was lower in Mn-exposed and lower in the brain in Pb-exposed pups. The EPM test demonstrated that Mn-exposed, but not Pb-exposed, pups had lower anxiety-related behavior compared to controls. We conclude that gestational and lactational exposures to Mn or Pb differentially alter Fe metabolism and anxiety-related behavior. The data suggest that perturbation in Fe metabolism may contribute to the pathophysiologic consequences of Mn and Pb exposure during early development.

Does lead use the intestinal absorptive pathways of iron? Impact of iron status on murine 210Pb and 59Fe absorption in duodenum and ileum in vivo

Background Human isotope studies and epidemiological trials are controversial as to whether lead absorption shares the absorptive pathways of iron and whether body lead content can be reduced by iron supplementation. Aim To compare the impact of iron-deficiency on 59Fe- and 210Pb-absorption rates in duodenal and ileal segments. Methods 59Fe- and 210Pb-absorption was determined in ligated duodenal and ileal segments from juvenile and adult iron-deficient and iron-adequate C57Bl6 wild-type mice ( n = 6) in vivo at luminal concentrations corresponding to human exposure (Fe: 1 and 100 μmol/L; Pb: 1 μmol/L). Results and discussion 59Fe-absorption increased 10–15-fold in iron-deficient duodena from adult and adolescent mice. Ileal 59Fe-absorption was 4–6 times lower than in iron-adequate duodena showing no adaptation to iron-deficiency. This in accordance to expectation as the divalent metal transport 1 (DMT1) shows low ileal expression levels. Juvenile 59Fe-absorption was about twice as high as in adult mice. In contrast, duodenal 210Pb-absorption was increased only 1.5–1.8-fold in iron-deficiency in juvenile and adult mice and, again in contrast to 59Fe, ileal 210Pb-absorption was as high as in iron-adequate duodena. Conclusions The findings suggest a DMT1-independent pathway to mediate lead absorption along the entire small intestine in addition to DMT1-mediated duodenal uptake. Ileal lead absorption appears substantial, due the much longer residence of ingesta in the distal small intestine. Differences in lead-solubility and -binding to luminal ligands can, thus, explain the conflicting findings regarding the impact of iron-status on lead absorption. They need to be considered in future studies.

Hepcidin-Independent Regulation of Dietary Iron Absorption

Iron homeostasis in mammals is maintained at the level of iron absorption by the gut. Hepcidin plays a central role in homeostasis by binding to ferroportin and regulating cellular iron export. We found that mice weaned onto diets ranging from 35–350 mg Fe/kg for a period of 4 wk did not change body iron levels as measured by organ iron content and hematological parameters. Direct measure of absorption of 59Fe administered by gavage revealed an inverse correlation between dietary iron content and absorption. Gavage experiments were done following a 4h fast when the stomach and proximal small bowel were free of dietary content. Although iron absorption changed, liver expression of hepcidin mRNA did not. We measured the absorptive response in mice weaned onto diets containing 35 mg Fe/kg for 4 wk and abruptly changed to 350 mg Fe/kg. There was no change in iron absorption at day 1 but by day 3 absorption was reduced nearly 3-fold compared to controls and remained at this level for at least 7d. During this time neither liver nor spleen iron content changed but transferrin saturation increased approximately 1.5-fold. Most importantly, serum hepcidin levels, measured by a competitive binding assay (De Domenico et al. Cell Metab. 2008, 8:146–156), were unchanged. Mice were then changed from diets containing 350 mg Fe/kg to diets containing 35 mg Fe/kg. Within 24h mice increased absorption of 59Fe 3-fold. Elevated absorption continued for at least 3d, declined by 7d and at 14d was at a level found in mice maintained on a diet containing 35 mg Fe/kg. During this period there was no change in organ iron content or in transferrin saturation. Serum hepcidin did not change on day 1, but was reduced by approximately 40% on days 3 through 7. Increased iron absorption could be attributed in part to increased expression of Dmt1 but no change in ferroportin message was detected. Enterocyte ferritin levels doubled on day 1 but returned to control levels on days 3 through 7. Finally, mice with a targeted disruption of the hepcidin gene were challenged with an abrupt reduction in dietary iron content and absorption increased approximately 3-fold. These data suggest that iron absorption can respond to changes in dietary iron content independent of hepcidin and that response to changes in luminal iron content are at the level of uptake and storage in a manner intrinsic to the enterocyte.

Effect of supplied phytosiderophore on 59Fe absorption and translocation in Fe-deficient barley grown hydroponically in low phosphorus media

Hydroponically grown barley plants (Hordeum vulgare L. cv. Minorimugi) under iron-deficient (–Fe) and high phosphorus (P) conditions (500 µmol L−1) showed Fe chlorosis and lower growth compared with plants grown in –Fe and low P conditions (50, 5 and 0.5 µmol L−1). To understand the physiological role of P in regulating the growth of plants in –Fe medium, we carried out an Fe feeding experiment using four P levels (500, 50, 5 and 0.5 µmol L−1) and phytosiderophores (PS), mugineic acid. Our results suggest that plants grown in a high P medium had higher absorption activity of 59Fe compared with plants grown in low P media, irrespective of the presence or absence of added PS. Translocation of 59Fe from roots to shoots was not affected by the P level. The relative translocation rate of 59Fe increased with decreasing levels of P in the medium. In general, the addition of PS enhanced the absorption of 59Fe and its translocation. Taken together these results suggest that the lower relative translocation rate of Fe in high P plants may be induced by the physiological inactivation of Fe in the roots, and the higher absorption activity of Fe in high P conditions possibly results from the response of barley plants to Fe deficiency.

Iron absorption by healthy women is not associated with either serum or urinary prohepcidin

Although hepcidin is proposed as a regulator of iron absorption, this has not been assessed in humans. Our objective was to assess the relation between serum or urinary prohepcidin and iron absorption in healthy premenopausal women. The subjects were 28 healthy women aged 22-51 y with normal hemoglobin concentrations (120-152 g/L). Absorption of 0.5 mg Fe with 0.2 microCi 59Fe tracer, both as FeSO4, was measured by whole-body scintillation counting 13 d after oral administration. Fasting blood and urine samples were collected the day of and 16 wk after the absorption measurement. Serum and urinary prohepcidin concentrations were measured by an enzyme-linked immunosorbent assay by using an antibody against amino acid residues 28-47 of the proregion. Mean (+/-SD) iron absorption was 36 +/- 19% (range: 4-81%), and serum ferritin (geometric x) was 27 microg/L (range: 4-122 microg/L), as commonly observed in healthy premenopausal women. Serum prohepcidin was 196 microg/L (range: 99-376 microg/L) and, in contrast with urinary prohepcidin, was relatively consistent for the women between 0 and 16 wk. Serum prohepcidin correlated directly with serum ferritin (R2 = 0.28, P < 0.01) but was unrelated to 59Fe absorption, in contrast to serum ferritin (R2 = 0.33, P < 0.01). Serum prohepcidin concentrations were relatively stable within subjects and correlated with serum ferritin. However, unlike serum ferritin, neither serum nor urinary prohepcidin concentrations were related to iron absorption in healthy women.

Iron and zinc supplementation during pregnancy affects intestinal iron transporter expression in rat pups

Iron (Fe) and zinc (Zn) deficiencies are common during pregnancy and may result in neonatal Fe and Zn deficiency. Although co-supplementation of these micronutrients may interact in the pregnant woman, effects of maternal Fe and/or Zn supplementation on neonatal Fe status, Fe absorption and Fe transporters are unknown. Rats were fed a low Fe and Zn diet (12 μg/g Fe; 10 μg/g Zn) for 1 mo, then bred. Pregnant rats were supplemented 3 times/wk with vehicle (UnS), Fe (FeS; 9.0 mg), Zn (ZnS; 1.5 mg) or Fe and Zn (FeZnS). At weaning, Fe status, 59Fe absorption, and intestinal Fe transporter expression were determined in the pups. Pups from dams given FeS and FeZnS had higher hemoglobin (91 ± 4 and 80 ± 3 g/L, respectively) compared to UnS (56 ± 11 g/L) and ZnS (63 ± 5 g/L). Liver Fe was higher in FeS pups (31.1 ± 9.8 μg/g) compared to UnS, ZnS and FeZnS (20.2 ± 3.6, 20.1 ± 3.7, 22.2 ± 4.9 μg/g, respectively). Iron absorption was higher in UnS (98.0 ± 0.3%) compared to FeS (94.8 ± 1.6%), ZnS (93.1 ± 2.1%) and FeZnS (87.6 ± 6.0%) pups. Intestinal 59Fe retention was higher in ZnS (7.2 ± 0.8%) compared to UnS (3.8 ± 0.8%), FeS (4.6 ± 0.9%) and FeZnS (4.8 ± 0.3%) pups. FeS decreased DMT1 expression but ZnS and FeZnS had no effect. There was no effect on FPN. When compared to UnS, hephaestin expression was higher in both FeS and FeZnS pups. Pups born from Fe supplemented dams had better Fe status which resulted in decreased DMT1 expression and Fe absorption. Zn supplementation interfered with Fe absorption by trapping Fe in the intestine, potentially through altered FPN localization or reduced hephaestin activity. Maternal Zn supplementation alone or in combination with Fe may compromise neonatal Fe status.

Alleviation of Manganese Phytotoxicity in Barley with Calcium

ABSTRACT In order to clarify the mechanism by which calcium (Ca) alleviates manganese (Mn) phytotoxicity, barley plants were grown under the following conditions: (1) nutrient solution alone (control), (2) nutrient solution + 25 μM Mn (Mn-toxic), and (3) nutrient solution + 25 μ M Mn + 20 mM Ca (Ca-alleviated). Feeding experiments using 54Mn and 59Fe (iron) with 2.0 or 20 mM Ca to the plant roots were also conducted. The absorption and translocation of 54Mn in the control plants were lowered by the high-Ca (20 mM) feeding condition. The translocation of 54Mn to shoots of Mn-toxic or Ca-alleviated plants was also lowered by the high-Ca feeding condition, but 54Mn absorption by roots of the plants was unaffected. The absorption and translocation of 59Fe in the plants was unaffected by the high-Ca feeding condition. Calcium alleviation of Mn phytotoxicity in barley may be induced mainly by the inhibition of Mn translocation to shoots.

Effectiveness of Phytosiderophore in Absorption and Translocation of 59Iron in Barley in the Presence of Plant-Borne, Synthetic, and Microbial Chelators

ABSTRACT The mechanisms of iron (Fe) absorption and translocation in plants have received much study because they are the key processes in the supply of Fe to plants. The objective of this research was to study the effectiveness of phytosiderophore (PS) in the absorption and translocation of 59Fe in Fe-deficient barley (Hordeum vulgare L. cv. ‘Minorimugi’) plants in the presence of plant-borne, synthetic, or microbial chelators. Plants grown under Fe-deficient conditions in a phytotron at pH 5.5 for 7–18 d were fed with Fe3+ (10 μ M labeled with 59Fe) in the presence of 10 μ M of different chelators with or without 10 μ M PS for 4 h starting at 2 p.m. (6 h after the onset of light period). The absorption and translocation of 59Fe in plants treated with PS and Fe3 + were increased relative to plants fed solely with Fe3 + (control). There was no effect found on absorption and translocation of 59Fe in plants treated with EDTA or p-coumarate relative to the control, but a differential increase was observed in 59Fe absorption and translocation in plants treated with EDTA or p-coumarate in the presence of PS. In comparison with the control, a decrease in 59Fe absorption and translocation was observed in plants treated with HEDTA or EDDHA or FOB, but this decrease was avoided in plants treated with HEDTA or EDDHA or FOB in the presence of PS. The enhancement of 59Fe absorption and translocation in plants treated with citrate, and the highest 59Fe absorption and translocation in plants treated with citrate and PS, indicated that citrate had an additive effect on Fe absorption and translocation in plants. Our results showed that PS effectively played a role in Fe absorption and translocation in plants in the presence of other chelators. Plants treated with any chelators had lower extracellular 59Fe in the roots compared with the control.

Mechanism of Potassium Alleviation of Manganese Phytotoxicity in Barley

ABSTRACT Manganese (Mn) toxicity and potassium (K) deficiency are the major factors that limit plant growth and development in acid soils. The objective of this study was to assess the role of high K on the alleviation of Mn toxicity in barley (Hordeum vulgare L. cv. ‘Minorimugi’) grown in a phytotron for 14 d. Modified half-strength Hoagland-Arnon solution (pH 5.5) was used as the medium. The treatments were (1) 0.25 μ M Mn + 3 mM K (control); (2) 25 μ M Mn + 3 mM K (Mn-toxic); and (3) 25 μ M Mn + 30 mM K (K-alleviated). The Mn-toxic plants showed the symptoms of Mn toxicity and mild iron (Fe) deficiency, whereas in the K-alleviated plants such symptoms were absent. The K-alleviated plants had dry weight, chlorophyll content, and Fe concentration similar to that in the control plants, indicating that high K (30 mM) in the growth medium could alleviate Mn toxicity and Mn-induced Fe deficiency. Roots of plants fed separately with 54Mn and 59Fe in the presence of 3.0 and 30 mM K for 4 h were also studied. Results showed that high K could help in avoiding the accumulation of 54Mn, indicating that K plays an antagonistic role on Mn absorption by roots of barley and its subsequent translocation to the shoots. However, the absorption of 59Fe was not influenced by the high K concentration in a short-term experiment (4 h), indicating that high K does not affect short-term Fe absorption by the roots of barley plants. These results suggested that the alleviating effect of high K could be attributed to the antagonistic effect of K on Mn absorption by roots and translocation into shoots.

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.