Iron Uptake, Translocation, and Regulation in Higher Plants

For all plants to survive and grow, iron is necessary. The reduction strategy-I of nongraminaceous plants and the chelation strategy-II of graminaceous plants are two different ways that higher plants have evolved to obtain iron, which is only marginally soluble, from the rhizosphere. Both techniques’ essential molecular elements, such as transporters, enzymes and chelators, have been elucidated. Many of these elements are now believed to also work inside the plant to promote internal iron transport. Also being clarified are the transporters involved in intracellular iron trafficking. The bulk of the genes that encode these components are transcriptionally regulated in response to iron availability.

Iron is an essential micronutrient element for most living organisms. However,although iron is abundant in many soils,iron availability is very often limiting for plant growth. In addition,iron is potentially highly toxic to cells. Therefore,iron homeostasis needs to be strictly regulated. Higher plants have developed a complex regulatory network in their cells to control the uptake,translocation,transportation,and metabolism of Fe. Nongraminaceous and graminaceous plant species acquire iron from the soil through two distinct strategies based on iron reduction and iron chelation,respectively. The acquisition of iron by plants is regulated at several levels by local and systemic signals. The systemic signaling pathway appears to integrate multiple inputs from hormonal signals,NO signals,and the plant nutritional demand. This paper reviewed the molecular mechanisms by which these strategies depend and the factors that are responsible for inducing these strategies under iron deficiency.

The application of 57Fe Mössbauer spectroscopy in the investigation of iron uptake and translocation in plants

Iron is an essential element for all living organisms, playing a major role in plant biochemistry as a redox catalyst based on iron redox properties. Iron is the fourth most abundant element of the Earth's crust, but its uptake by plants is complex because it is often in insoluble forms that are not easily accessible for plants to use. The physical and chemical speciation of iron, as well as rhizosphere activity, are key factors controlling the bioavailability of Fe. Iron can be under reduced (Fe2+) or oxidized (Fe3+) ionic forms, adsorbed onto mineral surfaces, forming complexes with organic molecules, precipitated to form poorly crystalline hydroxides to highly crystalline iron oxides, or included in crystalline Fe-rich mineral phases. Plants must thus adapt to a complex and changing iron environment, and their response is finely regulated by multiple signaling pathways initiated by a diversity of stimulus perceptions. Higher plants possess two separate strategies to uptake iron from rhizosphere soil: the chelation strategy and the reduction strategy in grass and non-grass plants, respectively. Molecular actors involved in iron uptake and mobilization through the plant have been characterized for both strategies. All these processes that contribute to iron homeostasis in plants are highly regulated in response to iron availability by downstream signaling responses, some of which are characteristic signaling signatures of iron dynamics, while others are shared with other environmental stimuli. Recent research has thus revealed key transcription factors, cis-acting elements, post-translational regulators, and other molecular mechanisms controlling these genes or their encoded proteins in response to iron availability. In addition, the most recent research is increasingly highlighting the crosstalk between iron homeostasis and nutrient response regulation. These regulatory processes help to avoid plant iron concentrations building up to potential cell functioning disruptions that could adversely affect plant fitness. Indeed, when iron is in excess in the plant, it can lead to the production and accumulation of dangerous reactive oxygen species and free radicals (H2O2, HO•, O2•-, HO•2) that can cause considerable damages to most cellular components. To cope with iron oxidative stress, plants have developed defense systems involving the complementary action of antioxidant enzymes and molecular antioxidants, safe iron-storage mechanisms, and appropriate morphological adaptations.

Revisiting the mechanisms of arsenic uptake, transport and detoxification in plants

The uptake of iron by molten magnesium from uncoated new mild steel crucibles at temperatures 680°C, 730°C, and 780°C has been investigated. It was shown that the uptake of iron was sluggish at 680°C and the use of 0.05% zirconium addition could effectively suppress the increase in iron content within the first 2 h of holding at temperature. Rapid and severe uptake of iron was observed at 780°C. As a consequence, it was found that the grain refinement of pure magnesium achieved by 1% zirconium addition nearly vanished after 60 min hold at 780°C due to the depletion of soluble zirconium. The uptake of iron at 730°C was conspicuous but it was still controllable by use of 0.05% zirconium addition within the first 60 min of holding at temperature. The work conducted using an aluminium titanite crucible and a boron nitride coated mild steel crucible at 730°C further confirmed the highly detrimental influence of the uptake of iron on the grain refinement of pure magnesium by zirconium. The characteristic zirconium rich coring structures developed from circular to rosette like when the melt was held at 730°C in an uncoated mild steel crucible, while no such evolution was observed when held in an aluminium titanite crucible at the same temperature. Recommendations to minimise the consumption of zirconium by the uptake of iron were made based on the results obtained from this investigation. The mechanism of grain refinement of magnesium by a low concentration of zirconium is discussed.

The quest for selective Cs+ transport in plants

be 2.8k0.41 x lo-’ ( n = 6 ) and 1.5+0.12x lo-’ ( n = 6 ) mol/mg of protein for adult and neonate, respectively ( P = 0.1 14). Fe3+ and Fez+ uptake by BBM vesicles showed saturation kinetics (Fig. l a and b ) with similar results being obtained using vesicles prepared from neonates and adults. Values for Fe3+ uptake at the highest concentration used (256 PM) were similar to those obtained at 91 p~ (Debnam et al., 1987) confirming saturation of the uptake process. These results imply that the enhanced duodenal iron uptake by the neonatal guinea-pig noted previously (Srai et al., 1988) does not involve changes in iron binding or uptake at the BBM. This is in contrast to adaptation of iron uptake following iron deficiency, where the increased iron absorption is a consequence of enhanced uptake at the BBM (Muir & Hopfer, 1985). This suggests that iron uptake by enterocytes is subject to control at more than one level. Possible alternative explanations for increased iron absorption in the neonate include alteration in the profile of enterocyte binding proteins (Srai et af., 1987) and change in movement across the basolateral membrane. We wish to thank North East Thames Regional Health Authority for financial support.

The aim of this review article is to explore and establish the current status of 2-deoxy-2-fluoro-D-glucose (FDG) applications in plant imaging. In the present article, we review the previous literature on its experimental merits to formulate a consistent and inclusive picture of FDG applications in plant-imaging research. 2-deoxy-2-fluoro-D-glucose is a [18F]fluorine-labeled glucose analog in which C-2 hydroxyl group has been replaced by a positron-emitting [18F] radioisotope. As FDG is a positron-emitting radiotracer, it could be used in in vivo imaging studies. FDG mimics glucose chemically and structurally. Its uptake and distribution are found to be similar to those of glucose in animal models. FDG is commonly used as a radiotracer for glucose in medical diagnostics and in vivo animal imaging studies but rarely in plant imaging. Tsuji et al. (2002) first reported FDG uptake and distribution in tomato plants. Later, Hattori et al. (2008) described FDG translocation in intact sorghum plants and suggested that it could be used as a tracer for photoassimilate translocation in plants. These findings raised interest among other plant scientists, which has resulted in a recent surge of articles involving the use of FDG as a tracer in plants. There have been seven studies describing FDG-imaging applications in plants. These studies describe FDG applications ranging from monitoring radiotracer translocation to analyzing solute transport, root uptake, photoassimilate tracing, carbon allocation, and glycoside biosynthesis. Fatangare et al. (2015) recently characterized FDG metabolism in plants; such knowledge is crucial to understanding and validating the application of FDG in plant imaging research. Recent FDG studies significantly advance our understanding of FDG translocation and metabolism in plants but also raise new questions. Here, we take a look at all the previous results to form a comprehensive picture of FDG translocation, metabolism, and applications in plants. In conclusion, we summarize current knowledge, discuss possible implications and limitations of previous studies, point to open questions in the field, and comment on the outlook for FDG applications in plant imaging.

Sixty-nine fungal isolates were cultured on PDA and YMA media, with 42 testingpositive for siderophore production via the CAS blue agar assay. The highest producers—VL4, RC5, RY1, Mpe9, and RL3—exceeded 80% siderophore units (SU), with RC5 achieving 92.73 ± 0.56% SU. The ferric perchlorate test showed RL3 had the highest hydroxamate siderophore concentration at 1,060.92 ± 3.00 µg/ml. Siderophore production decreased when FeSO₄ was added to the culture medium, and varying media impacted the levels of siderophore and hydroxamate production. Samples from earthworm guts, vermicompost, and organic agricultural soil demonstrated low siderophore production (<60%) and hydroxamate concentrations (<10 µg/ml). Notably, siderophores significantly improved iron uptake in plants, evidenced by increased iron content and shoot height in rice. Morphological and ITS1 region analyses identified RL3 as Aspergillus sp. (closely related to Aspergillus niger) and RC5 as Mucor sp. (related to Talaromyces angelicus). The study concluded that fungi from economic and agricultural earthworm sources are found to be potent producers of siderophores and hydroxamate siderophores, offering potential applications for enhancing plant iron uptake and soil health.

Effect of solid-state fermentation on mineral binding efficiency of chickpea protein: Characterization and in-vitro mineral uptake

Regulation of Iron Accumulation In Food Crops: Studies Using Single Gene Pea Mutants

Despite the usually high abundance of iron (Fe) in soils, the low solubility of Fe‐bearing minerals restricts the available Fe pools in most aerobic soils to levels that are far below those required for microbial or plant growth. To acquire the necessary amounts of Fe from the environment, organisms have evolved mechanisms that enhance the solubility and dissolution rate of Fe(iii) oxyhydroxides prevailing in aerobic soils. Chemically, these mechanisms are based on weakening of the Fe–O bond by reduction, chelation and protonation. Physiologically, two distinct and in all known cases mutually exclusive strategies can be distinguished: the excretion of siderophores capable of solubilizing external ferric Fe and subsequent uptake of the ferric siderophore complex; and reduction of Fe(iii) prior to uptake of the more soluble Fe2+ ion. With the exception of graminaceous species, in which Fe uptake is based on the former mechanism, the latter strategy is found in all cormophytes and certain algae, yeast and bacteria. In higher plants, the increase in their capacity to convert extracellular ferric to ferrous Fe is part of a series of physiological and morphological events that act in concert to achieve appropriate internal levels of Fe. It is this amalgam of features that determines the Fe efficiency of a species or cultivar that in turn affects the yield of economically important plants and the natural distribution of species. Adaptive changes to limited Fe availability have been studied at the molecular, physiological and whole‐plant level. This review summarises current knowledge of the components of reduction‐based Fe uptake in plants and presents an integrated view of the present understanding of mechanisms that control the rate and extent of Fe absorption by roots.

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Isotope technique including radioisotopes and stable isotopes is useful and potent tool for various scientific areas. Especially, enriched stable isotopes are indispensable tools for researchers in biological systems (Sturup et al. 2008). Stable isotope ratios are usually used in examining the biogeochemical cycling of light elements such as carbon(C), oxygen (O), nitrogen (N) and sulphur (S) in the environment. Thermal ionization mass spectrometry (TIMS) for the isotope analysis has been the most standard technique for many years. However, for TIMS analysis, time for sample preparation is needed because sample need to ensure efficient ionization. On the other hand, ICP-MS analysis has some advantages that sample preparation is simple and high sample throughput for isotope experiments where a large amount of samples need to be analyzed (Sturup et al. 2008). The disadvantage to resolve in isotope analysis using ICP-MS is spectroscopic interferences in the process of analysis. It is therefore needed to be resolved these interferences. When plant physiologists investigate mineral absorption mechanisms in roots of plant, evaluation of symplastic mineral absorption capacity in roots cell in kinetics and time course experiments is very important because mineral translocation in shoots is mainly contributed to capacity of symplastic absorption in roots. In these experiments, radioisotopes methods are mainly used for element uptake in plants. Radioisotopes in solute were the most useful markers used in nutrient uptake and translocation in plants because they are chemically similar to the solute and can be distinguished from non-labeled solutes already contained in the roots (Davenport 2007). However, there are limitations to this method, including radioisotope administrative restriction and the restricted half-life of the radioisotope. Isotope tracer experiments, using a stable isotope, are very similar to those using a radioisotope on element to analyse plant mechanisms (Sturup et al. 2008). Accurate and precise determination of mineral isotope ratios is required for analysis of enriched stable isotopes. Inductive coupled plasma mass spectrometry (ICP-MS) has now become the effective and potent technique for enriched stable isotope tracer experiments due to increased availability. Therefore, the application of enriched stable isotopes in various biological systems increased rapidly.