A transporter for delivering zinc to the developing tiller bud and panicle in rice.

Tiller number is one of the most important agronomic traits that determine rice (Oryza sativa) yield. Active growth of tiller bud (TB) requires high amount of mineral nutrients; however, the mechanism underlying the distribution of mineral nutrients to TB with low transpiration is unknown. Here, we found that the distribution of Zn to TB is mediated by OsZIP4, one of the ZIP (ZRT, IRT-like protein) family members. The expression of OsZIP4 was highly detected in TB and nodes, and was induced by Zn deficiency. Immunostaining analysis revealed that OsZIP4 was mainly expressed in phloem of diffuse vascular bundles in the nodes and the axillary meristem. The mutation of OsZIP4 did not affect the total Zn uptake, but altered Zn distribution; less Zn was delivered to TB and new leaf, but more Zn was retained in the basal stems at the vegetative growth stage. Bioimaging analysis showed that the mutant aberrantly accumulated Zn in enlarged and transit vascular bundles of the basal node, whereas in wild-type high accumulation of Zn was observed in the meristem part. At the reproductive stage, mutation of OsZIP4 resulted in delayed panicle development, which is associated with decreased Zn distribution to the panicles. Collectively, OsZIP4 is involved in transporting Zn to the phloem of diffuse vascular bundles in the nodes for subsequent distribution to TBs and other developing tissues. It also plays a role in transporting Zn to meristem cells in the TBs.

Zinc isotope fractionation during grain filling of wheat and a comparison of zinc and cadmium isotope ratios in identical soil-plant systems.

Remobilization of zinc (Zn) from shoot to grain contributes significantly to Zn grain concentrations and thereby to food quality. On the other hand, strong accumulation of cadmium (Cd) in grain is detrimental for food quality. Zinc concentrations and isotope ratios were measured in wheat shoots (Triticum aestivum) at different growth stages to elucidate Zn pathways and processes in the shoot during grain filling. Zinc mass significantly decreased while heavy Zn isotopes accumulated in straw during grain filling (Δ66 Znfull maturity-flowering  = 0.21-0.31‰). Three quarters of the Zn mass in the shoot moved to the grains, which were enriched in light Zn isotopes relative to the straw (Δ66 Zngrain-straw -0.21 to -0.31‰). Light Zn isotopes accumulated in phloem sinks while heavy isotopes were retained in phloem sources likely because of apoplastic retention and compartmentalization. Unlike for Zn, an accumulation of heavy Cd isotopes in grains has previously been shown. The opposing isotope fractionation of Zn and Cd might be caused by distinct affinities of Zn and Cd to oxygen, nitrogen, and sulfur ligands. Thus, combined Zn and Cd isotope analysis provides a novel tool to study biochemical processes that separate these elements in plants.

Earthworm Uptake Routes and Rates of Ionic Zn and ZnO Nanoparticles at Realistic Concentrations, Traced Using Stable Isotope Labeling.

The environmental behavior of ZnO nanoparticles (NPs), their availability to, uptake pathways by, and biokinetics in the earthworm Lumbricus rubellus were investigated using stable isotope labeling. Zinc isotopically enriched to 99.5% in (68)Zn ((68)Zn-E) was used to prepare (68)ZnO NPs and a dissolved phase of (68)Zn for comparison. These materials enabled tracing of environmentally relevant (below background) NP additions to soil of only 5 mg (68)Zn-E kg(-1). Uptake routes were isolated by introducing earthworms with sealed and unsealed mouthparts into test soils for up to 72 h. The Zn isotope compositions of the soils, pore waters and earthworms were then determined using multiple collector inductively coupled plasma mass spectrometry. Detection and quantification of (68)Zn-E in earthworm tissue was possible after only 4 h of dermal exposure, when the uptake of (68)Zn-E had increased the total Zn tissue concentration by 0.03‰. The results demonstrate that at these realistic exposure concentrations there is no distinguishable difference between the uptake of the two forms of Zn by the earthworm L. rubellus, with the dietary pathway accounting for ∼95% of total uptake. This stands in contrast to comparable studies where high dosing levels were used and dermal uptake is dominant.

Nickel and zinc isotope fractionation in hyperaccumulating and nonaccumulating plants.

Until now, there has been little data on the isotope fractionation of nickel (Ni) in higher plants and how this can be affected by plant Ni and zinc (Zn) homeostasis. A hydroponic cultivation was conducted to investigate the isotope fractionation of Ni and Zn during plant uptake and translocation processes. The nonaccumulator Thlaspi arvense, the Ni hyperaccumulator Alyssum murale and the Ni and Zn hyperaccumulator Noccaea caerulescens were grown in low (2 µM) and high (50 µM) Ni and Zn solutions. Results showed that plants were inclined to absorb light Ni isotopes, presumably due to the functioning of low-affinity transport systems across root cell membrane. The Ni isotope fractionation between plant and solution was greater in the hyperaccumulators grown in low Zn treatments (Δ(60)Ni(plant-solution) = -0.90 to -0.63‰) than that in the nonaccumulator T. arvense (Δ(60)Ni(plant-solution) = -0.21‰), thus indicating a greater permeability of the low-affinity transport system in hyperaccumulators. Light isotope enrichment of Zn was observed in most of the plants (Δ(66)Zn(plant-solution) = -0.23 to -0.10‰), but to a lesser extent than for Ni. The rapid uptake of Zn on the root surfaces caused concentration gradients, which induced ion diffusion in the rhizosphere and could result in light Zn isotope enrichment in the hyperaccumulator N. caerulescens. In high Zn treatment, Zn could compete with Ni during the uptake process, which reduced Ni concentration in plants and decreased the extent of Ni isotope fractionation (Δ(60)Ni(plant-solution) = -0.11 to -0.07‰), indicating that plants might take up Ni through a low-affinity transport system of Zn. We propose that isotope composition analysis for transition elements could become an empirical tool to study plant physiological processes.

Systemic translocation of (70)zinc: kinetics following intratracheal instillation in rats.

Mechanisms of particulate matter (PM)-induced cardiotoxicity are not fully understood. Direct translocation of PM-associated metals, including zinc, may mediate this effect. We hypothesized that following a single intratracheal instillation (IT), zinc directly translocates outside of the lungs, reaching the heart. To test this, we used high resolution magnetic sector field inductively coupled plasma mass spectrometry to measure levels of five stable isotopes of zinc ((64)Zn, (66)Zn, (67)Zn, (68)Zn, (70)Zn), and copper in lungs, plasma, heart, liver, spleen, and kidney of male Wistar Kyoto rats (13 weeks old, 250-300 g), 1, 4, 24, and 48 h following a single IT or oral gavage of saline or 0.7 micromol/rat (70)Zn, using a solution enriched with 76.6% (70)Zn. Natural abundance of (70)Zn is 0.62%, making it an easily detectable tracer following exposure. In IT rats, lung (70)Zn was highest 1 h post IT and declined by 48 h. Liver endogenous zinc was increased 24 and 48 h post IT. (70)Zn was detected in all extrapulmonary organs, with levels higher following IT than following gavage. Heart (70)Zn was highest 48 h post IT. Liver, spleen and kidney (70)Zn peaked 4 h following gavage, and 24 h following IT. (70)Zn IT exposure elicited changes in copper homeostasis in all tissues. IT instilled (70)Zn translocates from lungs into systemic circulation. Route of exposure affects (70)Zn translocation kinetics. Our data suggests that following pulmonary exposure, zinc accumulation and subsequent changes in normal metal homeostasis in the heart and other organs could induce cardiovascular injury.

Measurement of zinc absorption from meals: comparison of extrinsic zinc labeling and independent measurements of dietary zinc absorption.

BACKGROUND: Extrinsic labeling techniques are typically used to measure fractional absorption of zinc (FAZ(extrinsic)) but none have been adequately evaluated. OBJECTIVE: To compare determination of the quantity of zinc absorbed (TAZ(extrinsic)) using measurements of FAZ(extrinsic) with results of simultaneous determinations of dietary zinc absorbed (TAZ(metabolic)) that are not dependent on labeling ingested food with an extrinsic tracer (modified metabolic balance technique). DESIGN: (70)Zn was administered orally with all meals for 6 consecutive days to 21 healthy, free-living adult women consuming a constant diet. (68)Zn and (67)Zn were administered intravenously. FAZ(extrinsic) was measured using a dual isotope tracer ratio technique and multiplied by dietary zinc to give TAZ(extrinsic). TAZ(metabolic) was determined by addition of net absorption of zinc and endogenous fecal zinc, the latter determined by an isotope dilution technique. RESULTS: TAZ(extrinsic) and TAZ(metabolic) were 3.0 +/- 1.1 mg/day and 3.1 +/- 1.1 mg/day respectively, paired t-test p = 0.492. The correlation coefficient for TAZ(extrinsic) and TAZ(metabolic) was 0.91, and for FAZ(extrinsic) and FAZ(metabolic) was 0.95. A Bland Altman analysis indicated a bias of 0.07, and the limits of agreement of -0.86 to 1.01 for TAZ(extrinsic) and TAZ(metabolic). CONCLUSION: These results from two independent methods provide reasonable validation of our extrinsic labeling technique for a wide range of composite diets.

Zinc absorption in Guatemalan schoolchildren fed normal or low-phytate maize.

BACKGROUND: Poor bioavailability of zinc from high-phytate diets is an important contributory factor to zinc deficiency in low-income populations. OBJECTIVE: The objective of this study was to determine the effect of low-phytate maize consumption on zinc absorption. DESIGN: The participants were apparently healthy children from the Central Highlands of Guatemala. Sixty children (20 per group) were randomly assigned to be fed only the low-phytate maize or 1 of 2 control maizes, the isohybrid wild-type maize or a local maize, for a 10-wk period. During the final week, the fractional absorption of zinc for all meals was measured during 1 d with the use of zinc stable isotopes and a dual isotope ratio technique based on urine enrichment data. RESULTS: Mean (+/-SD) phytate intakes for the low-phytate, wild-type, and local maize groups were 1536 +/- 563, 2056 +/- 517, and 2253 +/- 687 mg/d, respectively. Corresponding zinc intakes were 8.6 +/- 2.5, 8.1 +/- 2.0, and 9.7 +/- 2.6 mg/d, and the dietary phytate:zinc molar ratios were 18 +/- 5, 26 +/- 6, and 23 +/- 5. Corresponding fractional absorptions of zinc were 0.32 +/- 0.07, 0.28 +/- 0.07, and 0.29 +/- 0.06. The respective values for total absorbed zinc were 2.72 +/- 0.88, 2.30 +/- 0.96, and 2.78 +/- 1.04 mg/d. No significant differences in either the fractional absorption of zinc or total absorbed zinc were seen between the maize groups. CONCLUSION: Under the conditions of the present study, zinc absorption was not increased by the long-term use of low-phytate maize in children whose major dietary staple is maize.

Zinc absorption during late pregnancy in rural southern Ethiopia.

BACKGROUND: Little is yet known about zinc absorption in late pregnancy, and no information on absorption from the total diet is available. OBJECTIVE: The objective was to measure the fractional absorption of zinc (FAZ) and to estimate the total quantity of absorbed zinc (TAZ) each day during the third trimester of pregnancy in poor rural southern Ethiopian women. DESIGN: The participants (n = 17) were a convenience sample from a larger study population. The third stage of pregnancy was estimated from fundal height by the Bushulo Health Center prenatal outreach program. FAZ was determined with a dual-isotope tracer ratio technique that uses measurements of urine enrichment with zinc stable isotopes administered intravenously and orally, as an extrinsic label, with all meals in 1 d. Total dietary zinc (TDZ) was calculated from weighed diet records and Ethiopian food-composition tables supported by zinc and phytate analyses of major food items for individual meals. Plasma zinc and exchangeable zinc pool size were also estimated. RESULTS: Mean (+/-SD) FAZ was 0.35 +/- 0.11, TDZ was 6.0 +/- 3.2 mg/d, TAZ was 2.1 +/- 1.0 mg/d, phytate intake was 1033 +/- 843 mg/d, plasma zinc was 44.1 +/- 6.0 microg/dL, and the exchangeable zinc pool size was 142 +/- 39 mg. The molar ratio of phytate to zinc was 17:1. CONCLUSIONS: Women from a poor rural population who were dependent on a moderately high-phytate diet had low TDZ and low plasma zinc concentrations in the third trimester of pregnancy. TAZ was modestly higher than that predicted but did not meet physiologic requirements.

Zinc absorption from low-phytate hybrids of maize and their wild-type isohybrids.

BACKGROUND: Identification of allelic variants in a single gene that determine the phytate content of maize kernels and the subsequent breeding of low-phytate maize have facilitated studies designed to determine quantitatively the effects of maize phytate on the bioavailability of minerals in maize. OBJECTIVE: The objective was to determine the relation between the fractional absorption of zinc (FAZ) and the phytate content and phytate:zinc molar ratios of maize tortillas prepared from hybrids with different phytate contents. DESIGN: Six healthy adults were fed, as the only food for 2 d, maize tortillas prepared from 1 of 2 low-phytate mutants: lpa1-1 (lpa1-1-LP) or Nutridense Low Phytate (ND-LP), which have phytate reductions of approximately 60% and approximately 80%, respectively, compared with their respective wild-type isohybrids. Four additional subjects were fed tortillas prepared from the corresponding wild-type isohybrids (lpa1-1-WT and ND-WT) according to the same study design. Meals were extrinsically labeled with zinc stable isotopes, and FAZ was determined with a dual-isotope-tracer ratio technique. Overall FAZ values were examined in relation to dietary phytate and phytate:zinc molar ratios by using a mixed nonlinear regression model. RESULTS: The mean (+/-SD) FAZ values from tortillas prepared from ND-LP, lpa1-1-LP, lpa1-1-WT, and ND-WT were 0.38 +/- 0.07, 0.28 +/- 0.04, 0.15 +/- 0.07, and 0.13 +/- 0.05, respectively. A negative relation (P < 0.001) was found between FAZ and both dietary phytate and the phytate:zinc molar ratio. The effect of dietary zinc (8-14 mg Zn/d) under these experimental conditions was not significant. CONCLUSIONS: FAZ from maize tortillas is positively related to the extent of phytate reduction achieved with low-phytate hybrids.

Iron and zinc absorption from two bean (Phaseolus vulgaris L.) genotypes in young women.

Extrinsic and intrinsic iron and zinc labels were used to test iron and zinc absorption from two bean (Phaseolus vulgaris) genotypes, containing normal (common beans, CB) or higher (HFeZnB) iron and zinc concentrations, fed in single meals to young women with low iron reserves. The women were divided into two groups, with one receiving a CB test meal (n = 12) and the other, an HFeZnB test meal (n = 11). The beans were intrinsically labeled hydroponically with (55)Fe (CB and HFeZnB) and with (70)Zn (HFeZnB). Concentrations of zinc and iron were 98 and 65% higher, respectively, in HFeZnB as compared to CB, but phytic acid contents were similar. Extrinsic labels were (59)Fe (CB and HFeZnB), (67)Zn (CB), and (68)Zn (HFeZnB). Iron and zinc percent absorption levels were calculated from radio-iron activity in red blood cells and from urinary excretion of zinc isotopes. Intrinsic and extrinsic iron absorption measures were highly correlated (R (2) = 0.986) (average extrinsic/intrinsic ratio was 1.00). Iron absorption was low (geometric mean < 2%) in both bean types, and total iron absorbed was not different between types. Intrinsic zinc absorption from the HFeZn beans was higher than extrinsic absorption (15.2% vs 13.4%, p < 0.05) (average extrinsic/intrinsic was 0.90). The correlation between intrinsic and extrinsic zinc measures was not as high as that for iron (R (2) = 0.719). Percent zinc absorption levels were similar in both bean types, but total extrinsic zinc absorbed was 90% higher (p < 0.05) from the HFeZnB meal. Thus, the less expensive and time-consuming extrinsic labeling may be used to screen various varieties of beans for iron bioavailability in humans, but it underestimates zinc absorption by approximately 10%. Selective breeding for high-zinc bean genotypes may improve zinc status. However, high-iron genotypes appear to have little effect on iron status when fed alone in single meals to women with low iron reserves.

Effects of the relationship between 65Zn and blood cells. A dynamic and morphological study.

We have studied the dynamic pathway of 65Zn and its autoradiographic location in blood cells, even at the ultra-structural level. We have found evidence that tends to confirm the old biochemical postulates about the capacity of this isotope to displace iron in the haemoglobin molecule. Recently, the bibliography has demonstrated that 57Co is also able to perform this displacement, but unlike 65Zn it does not invalidate the Redox function of the molecule. In the case of 65Zn, the mentioned displacement invalidates this function because the radionuclide can only use valence 2. We have also contributed evidence of erythrocytes destruction by the spleen after the incorporation of 65Zn, as well as the clearly marked degradation of haematic pigments inside the spleen.

Zinc isotope ratio imaging of rat brain thin sections from stable isotope tracer studies by LA-MC-ICP-MS.

Zinc stable isotope tracers (67Zn and 7°Zn) were injected into rats at two different time points to investigate the feasibility of using tracers to study zinc kinetics at the microscale within distinct tissue features. Laser ablation coupled to multi-collector ICP-MS was used to analyse average isotope ratios in liver thin sections and to generate bio-images showing zinc isotope ratio distribution in brain thin sections. Average isotope ratios of all samples from treated animals were found to be statistically different (P < 0.05) from samples from untreated control animals. Furthermore, differing isotope ratios in physiological features of the brain, namely hippocampus, amygdala, cortex and hypothalamus, were identified. This indicates that these regions differ in their zinc metabolism kinetics. While cortex and hypothalamus contain more tracer two days after injection than 14 days after injection, the opposite is true for hippocampus and amygdala. This study showed that stable isotope tracer experiments can be combined with laser ablation MC-ICP-MS to measure trace element kinetics in tissues at a microscale level.

Characterization of (68)Zn uptake, translocation, and accumulation into developing grains and young leaves of high Zn-density rice genotype.

Zinc (Zn) is an essential micronutrient for humans, but Zn deficiency has become serious as equally as iron (Fe) and vitamin A deficiencies nowadays. Selection and breeding of high Zn-density crops is a suitable, cost-effective, and sustainable way to improve human health. However, the mechanism of high Zn density in rice grain is not fully understood, especially how Zn transports from soil to grains. Hydroponics experiments were carried out to compare Zn uptake and distribution in two different Zn-density rice genotypes using stable isotope technique. At seedling stage, IR68144 showed higher (68)Zn uptake and transport rate to the shoot for the short-term, but no significant difference was observed in both genotypes for the long-term. Zn in xylem sap of IR68144 was consistently higher, and IR68144 exhibited higher Zn absorption ratio than IR64 at sufficient (2.0 µmol/L) or surplus (8.0 µmol/L) Zn supply level. IR64 and IR68144 showed similar patterns of (68)Zn accumulation in new leaves at seedling stage and in developing grains at ripening stage, whereas (68)Zn in new leaves and grains of IR68144 was consistently higher. These results suggested that a rapid root-to-shoot translocation and enhanced xylem loading capacity may be the crucial processes for high Zn density in rice grains.

Measurement of total Zn and Zn isotope ratios by quadrupole ICP-MS for evaluation of Zn uptake in gills of brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss).

This study evaluates the potential use of stable zinc isotopes in toxicity studies measuring zinc uptake by the gills of brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss). The use of stable isotopes in such studies has several advantages over the use of radioisotopes, including cost, ease of handling, elimination of permit requirements, and waste disposal. A pilot study using brown trout was performed to evaluate sample preparation methods and the ability of a quadrupole inductively coupled plasma mass spectrometer (ICP-MS) system to successfully measure changes in the (67)Zn/(66)Zn ratios for planned exposure levels and duration. After completion of the pilot study, a full-scale zinc exposure study using rainbow trout was performed. The results of these studies indicate that there are several factors that affect the precision of the measured (67)Zn/(66)Zn ratios in the sample digests, including variations in sample size, endogenous zinc levels, and zinc uptake rates by individual fish. However, since these factors were incorporated in the calculation of the total zinc accumulated by the gills during the exposures, the data obtained were adequate for their intended use in calculating zinc binding and evaluating the influences of differences in water quality parameters.

Bioavailability of iron and zinc from a multiple micronutrient-fortified beverage.

OBJECTIVE: To test the hypothesis that micronutrient beverages can provide the daily iron and zinc needs of small children. STUDY DESIGN: Forty children aged 6 to 9 years were recruited (Lima, Peru). For 4 weeks, they received a daily serving of a beverage containing multiple micronutrients. Over 2 consecutive days, subjects received stable isotope-labeled servings of the beverage with and without a meal as well as an intravenous dose of zinc. Iron and zinc bioavailability were assessed using mass spectrometry. RESULTS: Iron absorption was significantly lower with a meal than without (9.8 +/- 6.7% versus 11.6 +/- 6.9%, P=.04), but zinc absorption was not (24.5 +/- 10.7% versus 22.8 +/- 7.6%, P=.2). In either case, however, a single daily serving provided most of the iron and zinc requirements for the children. CONCLUSIONS: Single daily servings of multinutrient-fortified beverages can meet much of the mineral needs for small children. Food has a small inhibitory effect on iron, but not zinc, absorption; therefore, these beverages can be efficacious even when given with a meal.