The transcription factor bZIP44 cooperates with MYB10 and MYB72 to regulate the response of Arabidopsis thaliana to iron deficiency stress.

Nicotianamine (NA) plays a crucial role in transporting metal ions, including iron (Fe), in plants; therefore, NICOTIANAMINE SYNTHASE (NAS) genes, which control NA synthesis, are tightly regulated at the transcriptional level. However, the transcriptional regulatory mechanisms of NAS genes require further investigations. In this study, we determined the role of bZIP44 in mediating plant response to Fe deficiency stress by conducting transformation experiments and assays. bZIP44 positively regulated the response of Arabidopsis to Fe deficiency stress by interacting with MYB10 and MYB72 to enhance their abilities to bind at NAS2 and NAS4 promoters, thereby increasing NAS2 and NAS4 transcriptional levels and promote NA synthesis. In summary, the transcription activities of bZIP44, MYB10, and MYB72 were induced in response to Fe deficiency stress, which enhanced the interaction between bZIP44 and MYB10 or MYB72 proteins, synergistically activated the transcriptional activity of NAS2 and NAS4, promoted NA synthesis, and improved Fe transport, thereby enhancing plant tolerance to Fe deficiency stress.

Epoxide Ring-Opening Reactions for Abundant Production of Mugineic Acids and Nicotianamine Probes.

A succinct synthetic approach to mugineic acids and 2'-hydroxynicotianamine was established. Unlike all other synthetic methods, this approach utilized epoxide ring-opening reactions to form two C-N bonds and is characterized by the absence of redox reactions. Mugineic acid was synthesized from three readily available fragments on a gram scale in 6 steps. The protected 2'-hydroxynicotianamine was also synthesized in 4 steps, and the dansyl group, serving as a fluorophore, was introduced through a click reaction after propargylation of the 2'-hydroxy group. The dansyl-labeled nicotianamine (NA) iron complexes were internalized by oocytes overexpressing ZmYS1 (from maize) or PAT1 (from human) transporters, indicating successful transport of the synthesized NA-probe through these transporters.

Total synthesis of [13 C2 ]-labeled phytosiderophores of the mugineic and avenic acid families.

We, herein, report the synthesis of 13 C2 -labeled natural products from the mugineic acid and avenic acid family. These phytosiderophores ("plant iron carriers") are built up from non-proteinogenic amino acids and play a key role in micronutrient uptake in gramineous plants. In this work, two central building blocks are prepared from labeled starting materials (13 C2 -bromoacetic acid, 13 C2 -glycine) and further employed in our recently reported divergent, branched synthetic strategy delivering eight isotopically labeled phytosiderophores. The required labeled building blocks (13 C2 -l-allylglycine and a related hydroxylated derivative) were prepared via enantioselective phase-transfer catalysis and enantio- and diastereoselective aldol condensation with a chiral auxiliary, respectively, both potentially valuable themselves for other synthetic routes toward labeled (natural) products.

Theoretical studies on the coordination chemistry of phytosiderophores with special reference to Fe-nicotianamine complexes in graminaceous plants.

Nicotianamine (NA) is one of the metal-chelating molecules found in higher plants in abundance. Synthesized by the enzyme nicotianamine synthase, NA has a major role in the transport of iron in plant tissues. This research paper deals with the coordination chemistry of the possible complexes of NA, [FeII (NA)]-, and [FeIII (NA)] in detail, from a theoretical standpoint. The chemical computations on the [FeII (NA)]- and [FeIII (NA)] complexes show that NA can bind with both Fe (+ 2) and Fe (+ 3) ions. The calculations confirm that the [FeIII (NA)] is thermodynamically more stable in comparison with [FeII (NA)]-, while [FeII (NA)]- is kinetically more stable than [FeIII (NA)]. Under the physiological conditions prevailing in plant tissues, [FeIII (NA)] can undergo reduction, but the auto-oxidation of [FeII (NA)]- to [FeIII (NA)] is prevented. In summary, NA can translocate Fe ions within plant tissues, wherever required, both as Fe (+ 2) and Fe (+ 3) complexes.

Maize Interveinal Chlorosis 1 links the Yang Cycle and Fe homeostasis through Nicotianamine biosynthesis.

The Yang cycle is involved in many essential metabolic pathways in plant growth and development. As extended products of the Yang cycle, the function and regulation network of ethylene and polyamines are well characterized. Nicotianamine (NA) is also a product of this cycle and works as a key metal chelator for iron (Fe) homeostasis in plants. However, interactions between the Yang cycle and NA biosynthesis remain unclear. Here, we cloned maize interveinal chlorosis 1 (mic1), encoding a 5'-methylthioadenosine nucleosidase (MTN), that is essential for 5'-methylthioadenosine (MTA) salvage and NA biosynthesis in maize (Zea mays). A single base G-A transition in the fourth exon of mic1 causes a Gly to Asp change, resulting in increased MTA, reduced Fe distribution, and growth retardation of seedlings. Knockout of ZmMIC1 but not its paralog ZmMTN2 by CRISPR/Cas9 causes interveinal chlorosis, indicating ZmMIC1 is mainly responsible for MTN activity in maize. Transcriptome analysis showed a typical response of Fe deficiency. However, metabolic analysis revealed dramatically reduced NA content in mic1, suggesting NA biosynthesis was impaired in the mutant. Exogenous application of NA transiently reversed the interveinal chlorosis phenotype of mic1 seedlings. Moreover, the mic1 mutant overexpressing a NA synthase gene not only recovered from interveinal chlorosis and growth retardation but was also fertile. These findings provide a link between the Yang cycle and NA biosynthesis, which highlights an aspect of Fe homeostasis regulation in maize.

Genome-wide analysis of the NAAT, DMAS, TOM, and ENA gene families in maize suggests their roles in mediating iron homeostasis.

BACKGROUND: Nicotianamine (NA), 2'-deoxymugineic acid (DMA), and mugineic acid (MA) are chelators required for iron uptake and transport in plants. Nicotianamine aminotransferase (NAAT), 2'-deoxymugineic acid synthase (DMAS), transporter of MAs (TOM), and efflux transporter of NA (ENA) are involved in iron uptake and transport in rice (Oryza sativa), wheat (Triticum aestivum), and barley (Hordeum vulgare); however, these families have not been fully identified and comprehensively analyzed in maize (Zea mays L.). RESULTS: Here, we identified 5 ZmNAAT, 9 ZmDMAS, 11 ZmTOM, and 2 ZmENA genes by genome mining. RNA-sequencing and quantitative real-time PCR analysis revealed that these genes are expressed in various tissues and respond differently to high and low iron conditions. In particular, iron deficiency stimulated the expression of ZmDMAS1, ZmTOM1, ZmTOM3, and ZmENA1. Furthermore, we determined protein subcellular localization by transient expression of green fluorescent protein fusions in maize mesophyll protoplasts. ZmNAAT1, ZmNAAT-L4, ZmDMAS1, and ZmDMAS-L1 localized in the cytoplasm, whereas ZmTOMs and ZmENAs targeted to plasma and tonoplast membranes, endomembranes, and vesicles. CONCLUSIONS: Our results suggest that the different gene expression profiles and subcellular localizations of ZmNAAT, ZmDMAS, ZmTOM, and ZmENA family members may enable specific regulation of phytosiderophore metabolism in different tissues and under different external conditions, shedding light on iron homeostasis in maize and providing candidate genes for breeding iron-rich maize varieties.

A highly conserved mechanism for the detoxification and assimilation of the toxic phytoproduct L-azetidine-2-carboxylic acid in Aspergillus nidulans.

Plants produce toxic secondary metabolites as defense mechanisms against phytopathogenic microorganisms and predators. L-azetidine-2-carboxylic acid (AZC), a toxic proline analogue produced by members of the Liliaceae and Agavaciae families, is part of such a mechanism. AZC causes a broad range of toxic, inflammatory and degenerative abnormalities in human and animal cells, while it is known that some microorganisms have evolved specialized strategies for AZC resistance. However, the mechanisms underlying these processes are poorly understood. Here, we identify a widespread mechanism for AZC resistance in fungi. We show that the filamentous ascomycete Aspergillus nidulans is able to not only resist AZC toxicity but also utilize it as a nitrogen source via GABA catabolism and the action of the AzhA hydrolase, a member of a large superfamily of detoxifying enzymes, the haloacid dehalogenase-like hydrolase (HAD) superfamily. This detoxification process is further assisted by the NgnA acetyltransferase, orthologue of Mpr1 of Saccharomyces cerevisiae. We additionally show that heterologous expression of AzhA protein can complement the AZC sensitivity of S. cerevisiae. Furthermore, a detailed phylogenetic analysis of AzhA homologues in Fungi, Archaea and Bacteria is provided. Overall, our results unravel a widespread mechanism for AZC resistance among microorganisms, including important human and plant pathogens.

Iron chelates hitch a ride on PAT1.

The nicotianamine-iron chelate [NA-Fe2+], which is found in many plant-based foods, has been recently described as a new form of bioavailable iron in mice and chickens. How NA-Fe2+ is assimilated from the diet, however, remains unclear. The current investigation by Murata et al. has identified the proton-coupled amino acid transporter 1 (PAT1) as the main mechanism by which NA-Fe2+ is absorbed in the mammalian intestine. Discovery of this new form of dietary iron and elucidation of its pathway of intestinal absorption may lead to the development of improved iron supplementation approaches.

The ancient roots of nicotianamine: diversity, role, regulation and evolution of nicotianamine-like metallophores.

Nicotianamine (NA) is a metabolite synthesized by all plants, in which it is involved in the homeostasis of different micronutrients such as iron, nickel or zinc. In some plants it also serves as a precursor of phytosiderophores, which are used for extracellular iron scavenging. Previous studies have also established the presence of NA in filamentous fungi and some mosses, whereas an analogue of NA was inferred in an archaeon. More recently, opine-type metallophores with homology to NA were uncovered in bacteria, especially in human pathogens such as Staphylococcus aureus, Pseudomonas aeruginosa or Yersinia pestis, synthesizing respectively staphylopine, pseudopaline and yersinopine. Here, we review the current state of knowledge regarding the discovery, biosynthesis, function and regulation of these metallophores. We also discuss the genomic environment of the cntL gene, which is homologous to the plant NA synthase (NAS) gene, and plays a central role in the synthesis of NA-like metallophores. This reveals a large diversity of biosynthetic, export and import pathways. Using sequence similarity networks, we uncovered that these metallophores are widespread in numerous bacteria thriving in very different environments, such as those living at the host-pathogen interface, but also in the soil. We additionally established a phylogeny of the NAS/cntL gene and, as a result, we propose that this gene is an ancient gene and NA, or its derivatives, is an ancient metallophore that played a prominent role in metal acquisition or metal resistance. Indeed, our phylogenetic analysis suggests an evolutionary model where the possibility to synthesize this metallophore was present early in the appearance of life, although it was later lost by most living microorganisms, unless facing metal starvation such as at the host-pathogen interface or in some soils. According to our model, NA then re-emerged as a central metabolite for metal homeostasis in fungi, mosses and all known higher plants.

Potential Implications of Interactions between Fe and S on Cereal Fe Biofortification.

Iron (Fe) and sulfur (S) are two essential elements for plants, whose interrelation is indispensable for numerous physiological processes. In particular, Fe homeostasis in cereal species is profoundly connected to S nutrition because phytosiderophores, which are the metal chelators required for Fe uptake and translocation in cereals, are derived from a S-containing amino acid, methionine. To date, various biotechnological cereal Fe biofortification strategies involving modulation of genes underlying Fe homeostasis have been reported. Meanwhile, the resultant Fe-biofortified crops have been minimally characterized from the perspective of interaction between Fe and S, in spite of the significance of the crosstalk between the two elements in cereals. Here, we intend to highlight the relevance of Fe and S interrelation in cereal Fe homeostasis and illustrate the potential implications it has to offer for future cereal Fe biofortification studies.

Nicotianamine-chelated iron positively affects iron status, intestinal morphology and microbial populations in vivo (Gallus gallus).

Wheat flour iron (Fe) fortification is mandatory in 75 countries worldwide yet many Fe fortificants, such as Fe-ethylenediaminetetraacetate (EDTA), result in unwanted sensory properties and/or gastrointestinal dysfunction and dysbiosis. Nicotianamine (NA) is a natural chelator of Fe, zinc (Zn) and other metals in higher plants and NA-chelated Fe is highly bioavailable in vitro. In graminaceous plants NA serves as the biosynthetic precursor to 2' -deoxymugineic acid (DMA), a related Fe chelator and enhancer of Fe bioavailability, and increased NA/DMA biosynthesis has proved an effective Fe biofortification strategy in several cereal crops. Here we utilized the chicken (Gallus gallus) model to investigate impacts of NA-chelated Fe on Fe status and gastrointestinal health when delivered to chickens through intraamniotic administration (short-term exposure) or over a period of six weeks as part of a biofortified wheat diet containing increased NA, Fe, Zn and DMA (long-term exposure). Striking similarities in host Fe status, intestinal functionality and gut microbiome were observed between the short-term and long-term treatments, suggesting that the effects were largely if not entirely due to consumption of NA-chelated Fe. These results provide strong support for wheat with increased NA-chelated Fe as an effective biofortification strategy and uncover novel impacts of NA-chelated Fe on gastrointestinal health and functionality.

The Molecular Mechanisms Underlying Iron Deficiency Responses in Rice.

Iron (Fe) is an essential element required for plant growth and development. Under Fe-deficientconditions, plants have developed two distinct strategies (designated as strategy I and II) to acquire Fe from soil. As a graminaceous species, rice is not a typical strategy II plant, as it not only synthesizes DMA (2'-deoxymugineic acid) in roots to chelate Fe3+ but also acquires Fe2+ through transporters OsIRT1 and OsIRT2. During the synthesis of DMA in rice, there are three sequential enzymatic reactions catalyzed by enzymes NAS (nicotianamine synthase), NAAT (nicotianamine aminotransferase), and DMAS (deoxymugineic acid synthase). Many transporters required for Fe uptake from the rhizosphere and internal translocation have also been identified in rice. In addition, the signaling networks composed of various transcription factors (such as IDEF1, IDEF2, and members of the bHLH (basic helix-loop-helix) family), phytohormones, and signaling molecules are demonstrated to regulate Fe uptake and translocation. This knowledge greatly contributes to our understanding of the molecular mechanisms underlying iron deficiency responses in rice.

Efficient phloem remobilization of Zn protects apple trees during the early stages of Zn deficiency.

Apple trees are extensively cultivated worldwide but are often affected by zinc (Zn) deficiency. Limited knowledge regarding Zn remobilization within fruit crops has hampered the development of efficient strategies for providing adequate amounts of Zn. In the present study, Zn distribution and remobilization were compared among apple trees cultivated under different Zn conditions. Without Zn application, plants showed visible symptoms of Zn deficiency at the shoot tips after 1 year but appeared to grow normally during the first 6 months (early stage of Zn deficiency). Compared with apple plants under sufficient Zn treatment, plants suffering from early-stage Zn deficiency showed preferential Zn distribution to young leaves and higher Zn levels in phloem, demonstrating that hidden Zn deficiency triggers a highly efficient remobilization of Zn in this species. The in vivo Zn-nicotianamine complex in phloem tissues, combined with the significant enhanced expression of MdNAS3 and MdYSL6, suggested a positive role for nicotianamine in the phloem remobilization of Zn. These results strongly suggest that a proportion of Zn in the old leaves of apple trees can be efficiently remobilized by phloem transport to the shoot tips, partially in the form of Zn-nicotianamine, thus protecting apple trees against the early stages of Zn deficiency.

The ratio of phytosiderophores nicotianamine to deoxymugenic acid controls metal homeostasis in rice.

MAIN CONCLUSION: The ratio of nicotianamine to deoxymugenic acid controls tissue-specific metal homeostasis in rice and regulates metal delivery to the endosperm. The metal-chelating phytosiderophores nicotianamine (NA) and 2'deoxymugenic acid (DMA) are significant factors for the control of metal homeostasis in graminaceous plants. These compounds are thought to influence metal homeostasis, but their individual roles and the effect of altering the NA:DMA ratio are unknown. We purposely generated rice lines with high and low NA:DMA ratios (HND and LND lines, respectively). The HND lines accumulated more iron (Fe), zinc (Zn), manganese (Mn) and copper (Cu) in the endosperm through the mobilization of Fe, Zn and Mn from the seed husk to the endosperm. In contrast, Fe, Zn and Mn were mobilized to the husk in the LND lines, whereas Cu accumulated in the endosperm. Different groups of metals are, therefore, taken up, transported and sequestered in vegetative tissues in the HND and LND lines to achieve this metal distribution pattern in the seeds. We found that different sets of endogenous metal homeostasis genes were modulated in the HND and LND lines to achieve differences in metal homeostasis. Our findings demonstrate that the NA:DMA ratio is a key factor regulating metal homeostasis in graminaceous plants. These findings can help formulate refined strategies to improve nutrient composition and nutrient use efficiency in crop plants.

Core-in-cup/liquisol dual tackling effect on azelnidipine buccoadhesive tablet micromeritics, in vitro release, and mucoadhesive strength.

Reduced bioavailability of azelnidipine is related to its poor aqueous solubility and extensive first-pass metabolism, which hinder its efficacy. These problems were addressed by implementing (1) a liquisol technique for promoting the dissolution rate in a controlled-release manner and (2) a core-in-cup bucco-adhesive drug delivery system as an alternative to the oral route. A 33 factorial design was used to study the effects of polymer type (sodium carboxymethyl cellulose (CMC Na), chitosan, or Carbomer P940) concentration (5, 10 or 15 %) and preparation technique (simple mix, liquisol or wet granulation) on the dissolution and mucoadhesion of core-in-cup azelnidipine buccoadhesive tablets. Tablet micromeritics, swelling index, mucoadhesive strength and in vitro release were characterized. Statistical analyses of these factors show ed significant effects on the studied responses, where F#16 prepared by the liquisol technique and containing 15 % CMC Na was chosen with an overall desirability of 0.953.

A Vacuolar Phytosiderophore Transporter Alters Iron and Zinc Accumulation in Polished Rice Grains.

Essential metals, such as iron (Fe) and zinc (Zn), in grains are important sources for seed germination and nutritional requirements, but the molecular mechanisms underlying their loading into grains are poorly understood. Recently, nodes in rice (Oryza sativa) were reported to play an important role in the preferential distribution of mineral elements to the grains. In this study, we functionally characterized a rice gene highly expressed in nodes, OsVMT (VACUOLAR MUGINEIC ACID TRANSPORTER), belonging to a major facilitator superfamily. OsVMT is highly expressed in the parenchyma cell bridges of node I, where Fe and Zn are highly deposited. The expression of OsVMT was induced by Fe deficiency in the roots but not in the shoot basal region and uppermost node. OsVMT localized to the tonoplast and showed efflux transport activity for 2'-deoxymugineic acid (DMA). At the vegetative stage, knockout of OsVMT resulted in decreased DMA but increased ferric Fe in the root cell sap. As a result, the concentration of DMA in the xylem sap increased but that of ferric Fe decreased in the xylem sap in the mutants. In the polished rice grain, the mutants accumulated 1.8- to 2.1-fold, 1.5- to 1.6-fold, and 1.4- to 1.5-fold higher Fe, Zn, and DMA, respectively, than the wild type. Taken together, our results indicate that OsVMT is involved in sequestering DMA into the vacuoles and that knockout of this gene enhances the accumulation of Fe and Zn in polished rice grains through DMA-increased solubilization of Fe and Zn deposited in the node.

Cytokinin-dependent regulatory module underlies the maintenance of zinc nutrition in rice.

Zinc (Zn) deficiency is a critical problem in human nutrition. Rice is the main source of calories for nearly half the world's population but has the shortcoming, from a nutritional perspective, of being low in Zn and other essential nutrients. Here we performed analyses with cytokinin-related mutants and transgenic lines to provide unequivocal evidence that cytokinins have a key role in controlling Zn status in plants. Transporters responsible for Zn uptake and chelators for the internal transport of Zn were strictly controlled by cytokinins. Moreover, cytokinin metabolism was regulated in a highly dynamic way in response to Zn status, which allows rice to adapt to heterogeneous Zn availability. Subsequently, fine-tuning of cytokinin metabolism by root-specific expression of a cytokinin degradation enzyme was able to improve both Zn nutrient and yield traits. Importantly, X-ray fluorescence imaging revealed that the increased Zn was broadly distributed from the aleurone layer to the inner endosperm. These findings show that metabolic control of cytokinin could provide the key to breeding Zn-enriched rice.

Elevated root nicotianamine concentrations are critical for Zn hyperaccumulation across diverse edaphic environments.

The metallophyte Arabidopsis halleri thrives across an extremely broad edaphic range. Zn hyperaccumulation is found on soils differing in available Zn by up to six orders of magnitude, raising the question as to whether a common set of mechanisms confers this species-wide ability. Elevated root concentrations of the metal chelator nicotianamine due to strong constitutive expression of AhNAS2 are important for hyperaccumulation. In order to analyse the relevance of AhNAS2 under more natural conditions representing a range of metalliferous and nonmetalliferous habitats, we collected soil at eight different A. halleri sites and cultivated wild-type and AhNAS2-RNAi lines in these soils. AhNAS2 transcript abundance and root nicotianamine concentrations in wild-type plants were barely influenced by soil metal concentrations. The RNAi effect was fully expressed in different soils. Zn hyperaccumulation in AhNAS2-silenced lines was significantly reduced in seven soils. Root-to-shoot translocation of Cd, Mn, Cu, Ni, and Co was also affected by AhNAS2 silencing, albeit to a lower extent and less consistently. Leaf Fe levels were unaffected by AhNAS2 knockdown. Results demonstrate that elevated nicotianamine production in roots of A. halleri is a Zn hyperaccumulation factor regardless of the edaphic environment, that is, contributes to Zn hyperaccumulation in soils with contrasting Zn availability.

Transcriptome profiles of soybean leaves and roots in response to zinc deficiency.

Zinc (Zn) deficiency is a widespread agricultural problem in arable soils of the whole world. However, the molecular mechanisms underlying Zn-deficiency response are largely unknown. Here, we analyzed the transcriptomic profilings of soybean leaves and roots in response to Zn deficiency through Illumina's high-throughput RNA sequencing in order to understand the molecular basis of Zn-deficiency response in the plants. A total of 614 and 1011 gene loci were found to be differentially expressed in leaves and roots, respectively, and 88 loci were commonly found in both leaves and roots. Twelve differentially expressed genes (DEGs) were randomly selected for validation by quantitative reverse transcription polymerase chain reaction, and their fold changes were similar to those of RNA-seq. Gene ontology enrichment analysis showed that ion transport, nicotianamine (NA) biosynthetic process and queuosine biosynthetic process were enriched in the upregulated genes, while oxidation-reduction process and defense response were enriched in the downregulated genes. Among the DEGs, 20 DEGs are potentially involved in Zn homeostasis, including seven ZRT, IRT-related protein (ZIP) transporter genes, three NA synthase genes, and seven metallothionein genes; 40 DEGs are possibly involved in diverse hormonal signals such as auxin, cytokinin, ethylene and gibberellin; nine DEGs are putatively involved in calcium signaling; 85 DEGs are putative transcription factor genes. Nine DEGs were found to contain zinc-deficiency-response element in their promoter regions. These results could provide comprehensive insights into the soybean response to Zn deficiency and will be helpful for further elucidation of the molecular mechanisms of Zn-deficiency response and Zn-deficiency tolerance in plants.

Chloroplasts preferentially take up ferric-citrate over iron-nicotianamine complexes in Brassica napus.

MAIN CONCLUSION: Fe uptake machinery of chloroplasts prefers to utilise Fe(III)-citrate over Fe-nicotianamine complexes. Iron uptake in chloroplasts is a process of prime importance. Although a few members of their iron transport machinery were identified, the substrate preference of the system is still unknown. Intact chloroplasts of oilseed rape (Brassica napus) were purified and subjected to iron uptake studies using natural and artificial iron complexes. Fe-nicotianamine (NA) complexes were characterised by 5 K, 5 T Mössbauer spectrometry. Expression of components of the chloroplast Fe uptake machinery was also studied. Fe(III)-NA contained a minor paramagnetic Fe(II) component (ca. 9%), a paramagnetic Fe(III) component exhibiting dimeric or oligomeric structure (ca. 20%), and a Fe(III) complex, likely being a monomeric structure, which undergoes slow electronic relaxation at 5 K (ca. 61%). Fe(II)-NA contained more than one similar chemical Fe(II) environment with no sign of Fe(III) components. Chloroplasts preferred Fe(III)-citrate compared to Fe(III)-NA and Fe(II)-NA, but also to Fe(III)-EDTA and Fe(III)-o,o'EDDHA, and the Km value was lower for Fe(III)-citrate than for the Fe-NA complexes. Only the uptake of Fe(III)-citrate was light-dependent. Regarding the components of the chloroplast Fe uptake system, only genes of the reduction-based Fe uptake system showed high expression. Chloroplasts more effectively utilize Fe(III)-citrate, but hardly Fe-NA complexes in Fe uptake.