Iron Nutrition Of Plants Research Articles

Iron status and root cell morphology of Arabidopsis thaliana as modified by a bacterial ferri-siderophore.

We previously provided evidence for the contribution of pyoverdine to the iron nutrition of Arabidopsis. In the present article, we further analyze the mechanisms and physiology of the adaptations underlying plant iron nutrition through Fe(III)-pyoverdine (Fe(III)-pvd). An integrated approach combining microscopy and nanoscale secondary ion mass spectrometry (NanoSIMS) on plant samples was adopted to localize pyoverdine in planta and assess the impact of this siderophore on the plant iron status and root cellular morphology. The results support a possible plant uptake mechanism of the Fe(III)-pvd complex by epidermal root cells via a non-reductive process associated with the presence of more vesicles. Pyoverdine was transported to the central cylinder via the symplastic and/or trans-cellular pathway(s), suggesting a possible root-to-shoot translocation. All these processes led to enhanced plant iron nutrition, as previously shown. Overall, these findings suggest that bacterial siderophores contribute to plant iron uptake and homeostasis.

Iron Nutrition in Plants: Towards a New Paradigm?

Iron (Fe) is an essential micronutrient for plant growth and development. Fe availability affects crops' productivity and the quality of their derived products and thus human nutrition. Fe is poorly available for plant use since it is mostly present in soils in the form of insoluble oxides/hydroxides, especially at neutral to alkaline pH. How plants cope with low-Fe conditions and acquire Fe from soil has been investigated for decades. Pioneering work highlighted that plants have evolved two different strategies to mine Fe from soils, the so-called Strategy I (Fe reduction strategy) and Strategy II (Fe chelation strategy). Strategy I is employed by non-grass species whereas graminaceous plants utilize Strategy II. Recently, it has emerged that these two strategies are not fully exclusive and that the mechanism used by plants for Fe uptake is directly shaped by the characteristics of the soil on which they grow (e.g., pH, oxygen concentration). In this review, recent findings on plant Fe uptake and the regulation of this process will be summarized and their impact on our understanding of plant Fe nutrition will be discussed.

Minireview: Chromatin-based regulation of iron homeostasis in plants

Plants utilize delicate mechanisms to effectively respond to changes in the availability of nutrients such as iron. The responses to iron status involve controlling gene expression at multiple levels. The regulation of iron deficiency response by a network of transcriptional regulators has been extensively studied and recent research has shed light on post-translational control of iron homeostasis. Although not as considerably investigated, an increasing number of studies suggest that histone modification and DNA methylation play critical roles during iron deficiency and contribute to fine-tuning iron homeostasis in plants. This review will focus on the current understanding of chromatin-based regulation on iron homeostasis in plants highlighting recent studies in Arabidopsis and rice. Understanding iron homeostasis in plants is vital, as it is not only relevant to fundamental biological questions, but also to agriculture, biofortification, and human health. A comprehensive overview of the effect and mechanism of chromatin-based regulation in response to iron status will ultimately provide critical insights in elucidating the complexities of iron homeostasis and contribute to improving iron nutrition in plants.

Rahnella aquatilis JZ-GX1 alleviates iron deficiency chlorosis in Cinnamomum camphora by secreting desferrioxamine and reshaping the soil fungal community.

Plant growth-promoting rhizobacteria are important for improving plant iron nutrition, but the interactions among inoculants, host plants and soil microorganisms have not been greatly explored. Rahnella aquatilis JZ-GX1 was applied to treat the increasingly serious iron deficiency chlorosis in Cinnamomum camphora, and the resulting improvement in chlorosis was determined by assessing the contents of chlorophyll, active iron, Fe2+ and antioxidant enzymes in leaves, the effects on the soil microbial community and the metabolism in the rhizosphere by high-throughput sequencing techniques and liquid chromatography–mass spectrometry (LC–MS). The results showed that inoculation with JZ-GX1 significantly increased the chlorophyll content of C. camphora, which promoted the redistribution of active iron in roots and leaves, increased the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX), and thus reduced membrane damage in iron-deficient C. camphora caused by reactive oxygen species. According to genome prediction and ultra-performance liquid chromatography–mass spectrometry (UPLC–MS) analysis, the JZ-GX1 strain could secrete desferrioxamine (DFO), and the concentration of DFO in C. camphora rhizosphere was 21-fold higher than that in uninoculated soil. The exogenous application of DFO increased the SPAD and Fe2+ contents in leaves. In addition, the inoculant affected the fungal community structure and composition in the C. camphora rhizosphere soil and increased the abundances of specific taxa, such as Glomus, Mortierella, Trichoderma, and Penicillium. Therefore, R. aquatilis JZ-GX1 application promoted iron absorption in C. camphora trees by secreting DFO and alleviated iron deficiency chlorosis through interactions with the local fungal community.

Physiological and Transcriptome Analyses Revealed the Mechanism by Which Deferoxamine Promotes Iron Absorption in Cinnamomum camphora.

Iron deficiency causes chlorosis and growth inhibition in Cinnamomum camphora, an important landscaping tree species. Siderophores produced by plant growth-promoting rhizobacteria have been widely reported to play an indispensable role in plant iron nutrition. However, little to date has been determined about how microbial siderophores promote plant iron absorption. In this study, multidisciplinary approaches, including physiological, biochemical and transcriptome methods, were used to investigate the role of deferoxamine (DFO) in regulating Fe availability in C. camphora seedlings. Our results showed that DFO supplementation significantly increased the Fe2+ content, SPAD value and ferric-chelate reductase (FCR) activity in plants, suggesting its beneficial effect under Fe deficiency. This DFO-driven amelioration of Fe deficiency was further supported by the improvement of photosynthesis. Intriguingly, DFO treatment activated the metabolic pathway of glutathione (GSH) synthesis, and exogenous spraying reduced glutathione and also alleviated chlorosis in C. camphora. In addition, the expression of some Fe acquisition and transport-related genes, including CcbHLH, CcFRO6, CcIRT2, CcNramp5, CcOPT3 and CcVIT4, was significantly upregulated by DFO treatment. Collectively, our data demonstrated an effective, economical and feasible organic iron-complexing agent for iron-deficient camphor trees and provided new insights into the mechanism by which siderophores promote iron absorption in plants.

Siderophore production in pseudomonas SP. strain SP3 enhances iron acquisition in apple rootstock.

The purpose of this study was to analyse the effects of siderophore-producing bacteria and bacterial siderophore on the iron nutrition of apple rootstocks under iron-deficient conditions. We isolated three Pseudomonas strains, SP1, SP2 and SP3 from the rhizosphere of the Fe-efficient apple rootstocks using the chrome azurol S agar plate assay. We found that all three strains had the ability to secrete indole acetic acid-like compounds and siderophores, especially SP3. When Fe-inefficient rootstocks treated with SP3 were grown in alkaline soil, an increase in the biomass, root development, and Fe concentration was observed in the plants. In addition, SP3 secreted pyoverdine, a siderophore that can chelate Fe3+ to enhance the bioavailability of Fe for plants. We purified the pyoverdine from the SP3 culture supernatant. Hydroponic experiments were conducted with a Fe-deficient solution supplemented with pyoverdine, resulting in a reduction in the chlorosis caused by Fe deficiency and marked improvement in Fe uptake. Under iron-deficient conditions, Pseudomonas sp. strain SP3 can effectively promote apple rootstock growth and improve plant iron nutrition by secreting siderophores that enhance Fe availability. This study showed that plant growth-promoting rhizobacteria from Fe-efficient plants have the potential to improve iron nutrition in Fe-inefficient plants, and Fe-siderophore chelates can be used as an effective source of iron for apple plants. Based on these findings, it may be possible to develop biological agents such as siderophore-producing bacteria for sustainable agricultural and horticultural production.

Plant iron nutrition: the long road from soil to seeds.

Iron (Fe) is an essential plant micronutrient since many cellular processes including photosynthesis, respiration, and the scavenging of reactive oxygen species depend on adequate Fe levels; however, non-complexed Fe ions can be dangerous for cells, as they can act as pro-oxidants. Hence, plants possess a complex homeostatic control system for safely taking up Fe from the soil and transporting it to its various cellular destinations, and for its subcellular compartmentalization. At the end of the plant's life cycle, maturing seeds are loaded with the required amount of Fe needed for germination and early seedling establishment. In this review, we discuss recent findings on how the microbiota in the rhizosphere influence and interact with the strategies adopted by plants to take up iron from the soil. We also focus on the process of seed-loading with Fe, and for crop species we also consider its associated metabolism in wild relatives. These two aspects of plant Fe nutrition may provide promising avenues for a better comprehension of the long pathway of Fe from soil to seeds.

Importance of the Rhizosphere Microbiota in Iron Biofortification of Plants.

Increasing the iron content of plant products and iron assimilability represents a major issue for human nutrition and health. This is also a major challenge because iron is not readily available for plants in most cultivated soils despite its abundance in the Earth’s crust. Iron biofortification is defined as the enhancement of the iron content in edible parts of plants. This biofortification aims to reach the objectives defined by world organizations for human nutrition and health while being environment friendly. A series of options has been proposed to enhance plant iron uptake and fight against hidden hunger, but they all show limitations. The present review addresses the potential of soil microorganisms to promote plant iron nutrition. Increasing knowledge on the plant microbiota and plant-microbe interactions related to the iron dynamics has highlighted a considerable contribution of microorganisms to plant iron uptake and homeostasis. The present overview of the state of the art sheds light on plant iron uptake and homeostasis, and on the contribution of plant-microorganism (plant-microbe and plant-plant-microbe) interactions to plant nutritition. It highlights the effects of microorganisms on the plant iron status and on the co-occurring mechanisms, and shows how this knowledge may be valued through genetic and agronomic approaches. We propose a change of paradigm based on a more holistic approach gathering plant and microbial traits mediating iron uptake. Then, we present the possible applications in plant breeding, based on plant traits mediating plant-microbe interactions involved in plant iron uptake and physiology.

How Plants Recalibrate Cellular Iron Homeostasis.

Insufficient iron supply poses severe constraints on plants, restricting species with inefficient iron uptake mechanisms from habitats with low iron availability and causing yield losses in agricultural ecosystems. Iron deficiency also poses a severe threat on human health. Anemia resulting from insufficient iron intake is affecting one of four people in the world. It is, therefore, imperative to understand the mechanisms by which plants acquire iron against a huge soil-cell gradient and how iron is distributed within the plant to develop strategies that increase its concentration in edible plant parts. Research into the processes that are employed by plants to adjust cellular iron homeostasis revealed an astonishingly complex puzzle of signaling nodes and circuits, which are intertwined with the perception and communication of other environmental cues such as pathogens, light, nutrient availability and edaphic factors such as pH. In a recent Spotlight issue in this journal, a collection of review articles summarized the state-of-the-art in plant iron research, covering the most active and, debatably, most important topics in this field. Here, we highlight breakthroughs that were reported after the publication date of this review collection, focusing on exciting and potentially influential studies that have changed our understanding of plant iron nutrition.

Impact of Bacterial Siderophores on Iron Status and Ionome in Pea.

Including more grain legumes in cropping systems is important for the development of agroecological practices and the diversification of protein sources for human and animal consumption. Grain legume yield and quality is impacted by abiotic stresses resulting from fluctuating availabilities in essential nutrients such as iron deficiency chlorosis (IDC). Promoting plant iron nutrition could mitigate IDC that currently impedes legume cultivation in calcareous soils, and increase the iron content of legume seeds and its bioavailability. There is growing evidence that plant microbiota contribute to plant iron nutrition and might account for variations in the sensitivity of pea cultivars to iron deficiency and in fine to seed nutritional quality. Pyoverdine (pvd) siderophores synthesized by pseudomonads have been shown to promote iron nutrition in various plant species (Arabidopsis, clover and grasses). This study aimed to investigate the impact of three distinct ferripyoverdines (Fe-pvds) on iron status and the ionome of two pea cultivars (cv.) differing in their tolerance to IDC, (cv. S) being susceptible and (cv. T) tolerant. One pvd came from a pseudomonad strain isolated from the rhizosphere of cv. T (pvd1T), one from cv. S (pvd2S), and the third from a reference strain C7R12 (pvdC7R12). The results indicated that Fe-pvds differently impacted pea iron status and ionome, and that this impact varied both according to the pvd and the cultivar. Plant iron concentration was more increased by Fe-pvds in cv. T than in cv. S. Iron allocation within the plant was impacted by Fe-pvds in cv. T. Furthermore, Fe-pvds had the greatest favorable impact on iron nutrition in the cultivar from which the producing strain originated. This study evidences the impact of bacterial siderophores on pea iron status and pea ionome composition, and shows that this impact varies with the siderophore and host-plant cultivar, thereby emphasizing the specificity of these plant-microorganisms interactions. Our results support the possible contribution of pyoverdine-producing pseudomonads to differences in tolerance to IDC between pea cultivars. Indeed, the tolerant cv. T, as compared to the susceptible cv. S, benefited from bacterial siderophores for its iron nutrition to a greater extent.

Effects of Rahnella aquatilis JZ-GX1 on Treat Chlorosis Induced by Iron Deficiency in Cinnamomum camphora

With the increasing popularity of urban landscaping, there is a greater need to address iron deficiency and chlorosis in Cinnamomum camphora. Beneficial microorganisms can play an important role in improving plant iron nutrition. In this study, we evaluated the greening effect that results from inoculating C. camphora with Rahnella aquatilis JZ-GX1. We conducted in vitro experiments to determine the effectiveness of JZ-GX1 in reducing extracellular iron(III) ions in siderophores and producing organic acids under low-iron conditions. Potted, chlorotic C. camphora seedlings were inoculated, and parameters related to growth and iron nutritional status were measured. Inoculation by JZ-GX1 had a more pronounced greening effect on C. camphora than the traditional iron sulfate treatment for plant iron deficiency. Inoculated plants exhibited higher levels of active iron in the leaves, enhanced rhizosphere acidification capacity and ferric chelate reductase activity. Furthermore, the complete root system and chloroplast developmental structures were observed. Our results demonstrate the potential roles of R. aquatilis JZ-GX1 in promoting iron absorption in C. camphora.

Catechol-Loading Nanofibrous Membranes for Eco-Friendly Iron Nutrition of Plants.

Modern agriculture requires more efficient and low-impact products and formulations than traditional agrochemicals to improve crop yields. Iron is a micronutrient essential for plant growth and photosynthesis, but it is mostly present in insoluble forms in ecosystems so that it is often limiting for plants. This study was aimed at combining natural strategies and biodegradable nanostructured materials to create environmentally friendly and low-toxic bioactive products capable of both supplying iron to Fe-deficient plants and reducing the impact of agricultural products on the environment. Consequently, free-standing electrospun nanofibrous polycaprolactone/polyhydroxybutyrate thin membranes loaded with catechol (CL-NMs) as an iron-chelating natural agent (at two concentrations) were fabricated on purpose to mobilize Fe from insoluble forms and transfer it to duckweed (Lemna minor L.) plants. The effectiveness of CL-NMs in providing iron to Fe-deficient plants, upon catechol release, tested in duckweeds grown for 4 days under controlled hydroponic conditions, displayed temporal variations in both photosynthetic efficiency and biometric parameters measured by chlorophyll fluorescence and growth imaging. Duckweeds supplied with CL-NMs hosting higher catechol concentrations recovered most of the physiological and growth performances previously impaired by Fe limitation. The absence of short-term toxicity of these materials on duckweeds also proved the low impact on ecosystems of these products.

Humic Substances Contribute to Plant Iron Nutrition Acting as Chelators and Biostimulants.

Improvement of plant iron nutrition as a consequence of metal complexation by humic substances (HS) extracted from different sources has been widely reported. The presence of humified fractions of the organic matter in soil sediments and solutions would contribute, depending on the solubility and the molecular size of HS, to build up a reservoir of Fe available for plants which exude metal ligands and to provide Fe-HS complexes directly usable by plant Fe uptake mechanisms. It has also been shown that HS can promote the physiological mechanisms involved in Fe acquisition acting at the transcriptional and post-transcriptional level. Furthermore, the distribution and allocation of Fe within the plant could be modified when plants were supplied with water soluble Fe-HS complexes as compared with other natural or synthetic chelates. These effects are in line with previous observations showing that treatments with HS were able to induce changes in root morphology and modulate plant membrane activities related to nutrient acquisition, pathways of primary and secondary metabolism, hormonal and reactive oxygen balance. The multifaceted action of HS indicates that soluble Fe-HS complexes, either naturally present in the soil or exogenously supplied to the plants, can promote Fe acquisition in a complex way by providing a readily available iron form in the rhizosphere and by directly affecting plant physiology. Furthermore, the possibility to use Fe-HS of different sources, size and solubility may be considered as an environmental-friendly tool for Fe fertilization of crops.

Potential alteration of iron\u2013humate complexes by plant root exudates and microbial siderophores

BackgroundTwo humic acids extracted from a volcanic soil (HA1) and a leonardite (HA2) were used to form insoluble complexes with iron metals. To simulate the rhizospheric processes that displace iron from complexes of humic molecules and solubilize the soil humeome, the insoluble iron–humates were treated with a solution of siderophore deferoxamine mesylate (DFOM) and a mixture of citric, oxalic, tartaric and ketoglutaric acids, at different concentrations and contact times.ResultsResults showed that the removal of iron from humic complexes varied depending on the concentration of the extractants and extraction times. At large concentration, the mixture of organic acids was generally a better extractant than the siderophore, probably because of their lower solution pH. However, at smaller concentrations, the extracting capacity of the DFOM solution and the mixture of organic acids was generally similar. Differences in iron extractability between the two iron–humates were attributed to both the humic molecular composition and the steric hindrance of the extractants. Iron was more easily released from complexes formed with HA1 rich in aliphatic C than from those of HA2 rich in aromatic C, possibly because the more flexible conformational structure of HA1 was more accessible to the bulky DFOM than the rigid conformation of iron complexes made by the largely aromatic HA2.ConclusionsThis work provided evidence that iron–humate complexes may be potentially used to enhance iron nutrition of plants, whose exudates rich in organic acids, together with the siderophores produced by rhizospheric microbes, can displace iron from complexes and enhance its solubility. Concomitantly, the same process may solubilize humic molecules from the same iron–humates, thereby enhancing the concentration of bioactive humic matter in the soil solution.

Understanding the regulation of iron nutrition: can it contribute to improving iron toxicity tolerance in rice?

Iron nutrition in plants is highly regulated in order to supply amounts sufficient for optimal growth while preventing deleterious effects. In response to iron deficiency, plants induce either reduction-based or chelation-based mechanisms to enhance iron uptake from the soil. Major physiological traits and genes involved in these mechanisms have been fairly well described in model plants like Arabidopsis thaliana (L. Heynh.) and rice (Oryza sativa L.). However, for rice, iron toxicity presents a major challenge worldwide and causes yield reductions because rice is widely cultivated in flooded soils. Nonetheless, rice employs different mechanisms of adaptation to iron-toxicity, which range from avoidance to tissue tolerance. The physiological and molecular bases of such mechanisms have not been fully investigated and their use in breeding for iron-toxicity tolerance remains limited. Efforts to precisely characterise iron-toxicity control mechanisms may help speed-up the development of tolerant rice varieties. Considering how far the understanding of iron dynamics in the soil and plants has progressed, we consider it valuable to exploit such knowledge to improve rice tolerance to iron toxicity. Here we present the mechanisms that regulate iron uptake from the rhizosphere to the plant tissues together with the possible regulators involved. In addition, a genetic model for iron-toxicity tolerance in rice, which hypothesises possible modulation of key genes involved in iron nutrition and regulation is presented. The possibility of incorporating such relevant regulators in breeding is also discussed.

The effects of bacterial volatile emissions on plant abiotic stress tolerance.

Plant growth-promoting rhizobacteria (PGPR) are beneficial plant symbionts that have been successfully used in agriculture to increase seedling emergence, plant weight, crop yield, and disease resistance. Some PGPR strains release volatile organic compounds (VOCs) that can directly and/or indirectly mediate increases in plant biomass, disease resistance, and abiotic stress tolerance. This mini-review focuses on the enhancement of plant abiotic stress tolerance by bacterial VOCs. The review considers how PGPR VOCs induce tolerance to salinity and drought stress and also how they improve sulfur and iron nutrition in plants. The potential complexities in evaluating the effects of PGPR VOCs are also discussed.

Regulation of Iron Uptake by IRT1: Endocytosis Pulls the Trigger

The past two decades of research on plant iron nutrition have completed the casting of the major transporters involved in iron uptake from the soil, long-distance transport, and intracellular distribution. Among these transporters, most of the attention was given to the root iron transporter IRT1, which plays a critical role in iron uptake from the soil and mediates transport of other non-iron metals (zinc, manganese, cobalt, cadmium) under iron-limiting conditions. As such, IRT1 is the primary determinant of iron and heavy metal homeostasis in plants.

Iron economy in Chlamydomonas reinhardtii

While research on iron nutrition in plants has largely focused on iron-uptake pathways, photosynthetic microbes such as the unicellular green alga Chlamydomonas reinhardtii provide excellent experimental systems for understanding iron metabolism at the subcellular level. Several paradigms in iron homeostasis have been established in this alga, including photosystem remodeling in the chloroplast and preferential retention of some pathways and key iron-dependent proteins in response to suboptimal iron supply. This review presents our current understanding of iron homeostasis in Chlamydomonas, with specific attention on characterized responses to changes in iron supply, like iron-deficiency. An overview of frequently used methods for the investigation of iron-responsive gene expression, physiology and metabolism is also provided, including preparation of media, the effect of cell size, cell density and strain choice on quantitative measurements and methods for the determination of metal content and assessing the effect of iron supply on photosynthetic performance.

Iron homeostasis and iron acquisition in plants: maintenance, functions and consequences

Iron homeostasis and iron acquisition in plants: maintenance, functions and consequences

Nitric oxide and frataxin: two players contributing to maintain cellular iron homeostasis

Nitric oxide (NO) is a signalling and physiologically active molecule in animals, plants and bacteria. The specificity of the molecular mechanism(s) involved in transducing the NO signal within and between cells and tissues is still poorly understood. NO has been shown to be an emerging and potent signal molecule in plant growth, development and stress physiology. The NO donor S-nitrosoglutathion (GSNO) was shown to be a biologically active compound in plants and a candidate for NO storage and/or mobilization between plant tissues and cells. NO has been implicated as a central component in maintaining iron bioavailavility in plants. Iron is an essential nutrient for almost all organisms. This review presents an overview of the functions of NO in iron metabolism in animals and discusses how NO production constitutes a key response in plant iron sensing and availability. In plants, NO drives downstream responses to both iron deficiency and iron overload. NO-mediated improvement of iron nutrition in plants growing under iron-deficient conditions represents a powerful tool to cope with soils displaying low iron availability. An interconversion between different redox forms based on the iron and NO status of the plant cells might be the core of a metabolic process driving plant iron homeostasis. Frataxin, a recently identified protein in plants, plays an important role in mitochondria biogenesis and in maintaining mitochondrial iron homeostasis. Evidence regarding the interaction between frataxin, NO and iron from analysis of frataxin knock-down Arabidopsis thaliana mutants is reviewed and discussed.