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We, herein, report the synthesis of 13C2‐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 (13C2‐bromoacetic acid, 13C2‐glycine) and further employed in our recently reported divergent, branched synthetic strategy delivering eight isotopically labeled phytosiderophores. The required labeled building blocks (13C2‐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. [ABSTRACT FROM AUTHOR]

Rice (Oryza sativa L.) is a very important cereal worldwide, since it is the staple food for more than half of the world's population. Iron (Fe) deficiency is among the most important agronomical concerns in calcareous soils where rice plants may suffer from this deficiency. Current production systems are based on the use of high-yielding varieties and the application of large quantities of agrochemicals, which can cause major environmental problems. The use of beneficial rhizosphere microorganisms is considered a relevant sustainable alternative to synthetic fertilizers. The main goal of this study was to determine the ability of the nonpathogenic strain Fusarium oxysporum FO12 to induce Fe-deficiency responses in rice plants and its effects on plant growth and Fe chlorosis. Experiments were carried out under hydroponic system conditions. Our results show that the root inoculation of rice plants with FO12 promotes the production of phytosiderophores and plant growth while reducing Fe chlorosis symptoms after several days of cultivation. Moreover, Fe-related genes are upregulated by FO12 at certain times in inoculated plants regardless of Fe conditions. This microorganism also colonizes root cortical tissues. In conclusion, FO12 enhances Fe-deficiency responses in rice plants, achieves growth promotion, and reduces Fe chlorosis symptoms. [ABSTRACT FROM AUTHOR]

Les atteintes des articulations carpo-métacarpiennes ne se limitent pas aux rhizarthroses. Certains traumatismes sévères peuvent induire des luxations des articulations carpo-métacarpiennes II à V, et des impacts répétés peuvent aussi induire leur arthrose précoce avec (carpe bossu), mais aussi sans ostéophytose dorsale. Ces arthroses sont facilitées par des ossicules surnuméraires entre les carpo-métacarpiennes II et III. Les arthrites chroniques juvéniles et de l'adulte peuvent aussi induire des érosions précoces des carpo-métacarpiennes. Les travaux récents sur la pathogénie des rhizarthroses attribuent un rôle central à une instabilité acquise de la 1re carpo-métacarpienne dans la genèse des douleurs (d'origine surtout capsulaire, lors des mouvements de cisaillement). Les lésions osseuses semblent plus source de raideurs et malpositions. Ceci explique la nette prédominance féminine, et l'absence de corrélation fréquente entre douleurs et chondrolyse/ostéophytose. Cette instabilité peut résulter de dysplasies du trapèze, mais surtout de distensions de certains des 16 ligaments ceinturant l'articulation, dont le 'beak-ligament' intra-articulaire. Leur atteinte affecte aussi la qualité de verrouillage de la 1re carpo-métacarpienne par les muscles qui s'insèrent à la base du 1er métacarpien. Ceci explique que le traitement de référence non-chirurgical reste le port durable d'une attelle rigide. Les études randomisées versus placebo de corticoïdes ou d'acide hyaluronique n'ont pour l'instant pas démontré de nette efficacité. Du fait d'une évolution naturelle fréquente vers l'amélioration spontanée des rhizarthroses, il faut n'adresser au chirurgien que les patients au contexte psychologique favorable, et après un délai suffisant de traitement médical, mais plus tôt si une subluxation dorsale de la base du 1er métacarpien est durablement documentée. Carpometacarpal (CMCs) joints II to V can also be sources of pain, either following serious injuries with luxations of CMCs II to V, or chronic stresses leading to osteoarthritis, with (carpal boss) or without dorsal osteophytosis. These osteoarthritis can be fostered by surnumerous ossicles between CMC II and III. Early erosions of CMC II to V are frequently observed in juvenile chronic polyarthritis, whereas only chondrolysis occurs in most adult polyarthritis. Recent works on CMC-1 osteoarthritis point to a central role of instability, chondrolysis and osteophytosis being responsible for stiffness but poorly associated with pain, which seems to arise mostly from capsular stretching during shearing stresses. The CMC-1 instability can result from trapezal dysplasia and/or various lesions of the 16 ligaments stabilizing this joint, including the beak ligament (which also leads to less efficient thenar muscle contractions). Secretion of relaxin may account for such increased instability and the greater and earlier occurrence of CMC-1 osteoarthritis in females. A rigid cast of the thumb seems the most effective non-surgical treatment. Double-blind randomised studies versus placebo could not demonstrate the usefulness of either corticosteroids or hyaluronan. Since spontaneous improvement of pain and disability are often noticed, surgery should not be considered before several months, but may be even more appropriate in patients with chronic dorsal sub-luxation of the first metacarpal bone. [ABSTRACT FROM AUTHOR]

Intrinsic improvement of iron (Fe) concentration in rice grains, called rice Fe biofortification, is a promising countermeasure against widespread human Fe deficiency. In this study, two novel rice Fe biofortification approaches are reported. The first approach (Y approach) involved the expression of maize YELLOW STRIPE 1 controlled by the HEAVY METAL ATPASE 2 promoter. The Y approach increased the polished grain Fe concentrations up to 4.8-fold compared with the non-transgenic (NT) line. The second approach (T approach) involved the expression of rice TRANSPORTER OF MUGINEIC ACID 1 controlled by the FERRIC REDUCTASE DEFECTIVE LIKE 1 promoter. The T approach increased the polished grain Fe concentrations by up to 3.2-fold. No synergistic increases in the polished grain Fe concentrations were observed when Y and T approaches were combined (YT approach). However, the polished grain Fe concentrations further increased by 5.1- to 9.3-fold compared with the NT line, when YT approach was combined with the endosperm-specific expression of FERRITIN (YTF approach), or when YTF approach was combined with the constitutive expression of NICOTIANAMINE SYNTHASE (YTFN approach). Total grain weight per plant in most Y, T, YT, and YTFN lines was comparable to that in the NT line, while it was significantly decreased in most YTF lines. The novel approaches reported in this study expand the portfolio of genetic engineering strategies that can be used for Fe biofortification in rice. [ABSTRACT FROM AUTHOR]

Rice (Oryza sativa L.) is a very important cereal worldwide, since it is the staple food for more than half of the world’s population. Iron (Fe) deficiency is among the most important agronomical concerns in calcareous soils where rice plants may suffer from this deficiency. Current production systems are based on the use of high-yielding varieties and the application of large quantities of agrochemicals, which can cause major environmental problems. The use of beneficial rhizosphere microorganisms is considered a relevant sustainable alternative to synthetic fertilizers. The main goal of this study was to determine the ability of the nonpathogenic strain Fusarium oxysporum FO12 to induce Fe-deficiency responses in rice plants and its effects on plant growth and Fe chlorosis. Experiments were carried out under hydroponic system conditions. Our results show that the root inoculation of rice plants with FO12 promotes the production of phytosiderophores and plant growth while reducing Fe chlorosis symptoms after several days of cultivation. Moreover, Fe-related genes are upregulated by FO12 at certain times in inoculated plants regardless of Fe conditions. This microorganism also colonizes root cortical tissues. In conclusion, FO12 enhances Fe-deficiency responses in rice plants, achieves growth promotion, and reduces Fe chlorosis symptoms.

Iron is an essential element for all living organisms. The ability of plants to absorb inorganic iron from soil is important not only for plants but also for mammals, which ultimately rely on plants as their nutrient source. In contrast to most plant species, Poaceae plants, including rice, have developed a distinct chelation strategy to efficiently acquire insoluble soil iron using iron-chelating substances such as mugineic acid (MAs), called phytosiderophores. Genes involved in the biosynthesis and transport of MAs and their resulting iron(III)-MA complexes across membranes have been identified. On the other hand, an efficient short-step synthesis of the substrates MA and 2′-deoxymugineic acid (DMA) has enabled a sufficient supply of these compounds. Furthermore, owing to the chemical synthesis of proline-2′-deoxymugineic acid (PDMA), a cost-effective analog of DMA, the eff ectiveness of phytosiderophores in promoting rice growth in alkaline soil has been demonstrated at an experimental fi eld scale. Nicotianamine (NA), an MAs precursor essential for metal translocation within plant tissues, was recently shown to be absorbed as an iron(II) complex in the mouse small intestine by an amino acid transporter. The discovery of the biological role of NA in iron absorption by the small intestine not only highlights the biological significance of NA across the plant and animal kingdoms but also opens new possibilities for biofortification approaches. Here, we discuss the recent findings in MA research in terms of plant growth, application in agriculture, and the emerging nutraceutical value of NA in iron absorption in mammals. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Most plant species develop stress symptoms when exposed to high ammonium (NH4+) concentrations. The root is the first organ in contact with high NH4+ and therefore the first barrier to cope with ammonium stress. In this work, we focused on root adaptation to ammonium nutrition in the model plant Brachypodium distachyon. Proteome analysis revealed changes associated with primary metabolism, cell wall remodelling, and redox homeostasis. In addition, it showed a strong induction of proteins related to methionine (Met) metabolism and phytosiderophore (PS) synthesis in ammonium-fed plants. In agreement with this, we show how ammonium nutrition impacts Met/ S -adenosyl-Met and PS metabolic pathways together with increasing root iron content. Nevertheless, ammonium-fed plants displayed higher sensitivity to iron deficiency, suggesting that ammonium nutrition triggers impaired iron utilization and root to shoot transport, which entailed an induction in iron-related responses. Overall, this work demonstrates the importance of iron homeostasis during ammonium nutrition and paves a new way to better understand and improve ammonium use efficiency and tolerance. [ABSTRACT FROM AUTHOR]

Mineral nutrition is one of the key factors determining plant productivity. In plants, metal homeostasis is achieved through the functioning of a complex system governing metal uptake, translocation, distribution, and sequestration, leading to the maintenance of a regulated delivery of micronutrients to metal-requiring processes as well as detoxification of excess or non-essential metals. Low-molecular-weight ligands, such as nicotianamine, histidine, phytochelatins, phytosiderophores, and organic acids, play an important role in metal transport and detoxification in plants. Nicotianamine and histidine are also involved in metal hyperaccumulation, which determines the ability of some plant species to accumulate a large amount of metals in their shoots. In this review we extensively summarize and discuss the current knowledge of the main pathways for the biosynthesis of these ligands, their involvement in metal uptake, radial and long-distance transport, as well as metal influx, isolation and sequestration in plant tissues and cell compartments. It is analyzed how diverse endogenous ligand levels in plants can determine their different tolerance to metal toxic effects. This review focuses on recent advances in understanding the physiological role of these compounds in metal homeostasis, which is an essential task of modern ionomics and plant physiology. It is of key importance in studying the influence of metal deficiency or excess on various physiological processes, which is a prerequisite to the improvement of micronutrient uptake efficiency and crop productivity and to the development of a variety of applications in phytoremediation, phytomining, biofortification, and nutritional crop safety. [ABSTRACT FROM AUTHOR]

Metal uptake, transport and storage in plants depend on specialized ligands with closely related functions. Individual studies differing by species, nutrient availability, tissue type, etc. are not comprehensive enough to understand plant metal homeostasis in its entirety. A thorough review is required that distinguishes the role of ligands directly involved in chelation from the myriad of plant responses to general stress. Distinguishing between the functions of metal chelating compounds is the primary focus of this review; reactive oxygen species mediation and other aspects of metal homeostasis are also discussed. High molecular weight ligands (polysaccharides, phytochelatin, metallothionein), low molecular weight ligands (nicotianamine, histidine, secondary metabolites) and select studies which demonstrate the complex nature of plant metal homeostasis are explored. • The function of chelating ligands in plants requires further clarification. • Metal binding properties alone do not fully describe the function of ligands. • Notable studies and lacking areas of research in plant homeostasis are explored. • Iron-chelating phytotoxins may serve primarily as phytosiderophores. • Metal hyperaccumulators uniquely demonstrate the role of ligands in homeostasis. [ABSTRACT FROM AUTHOR]

This study investigates the influence of arsenic (As) and iron (Fe) on the molecular aspects of rice plants. The mRNA-abundance of As (OsLsi , OsPHT , OsNRAMP1 , OsABCC1) and Fe (OsIRT , OsNRAMP1 , OsYSL, OsFRDL1 , OsVIT2 , OsSAMS1 , OsNAS, OsNAAT1 , OsDMAS1 , OsTOM1 , OsFER) related genes has been observed in 12-d old As and Fe impacted rice varieties. Analyses of phytosiderophores synthesis and Fe-uptake genes affirm the existence of specialized Fe-uptake strategies in rice with varieties PB-1 and Varsha favouring strategy I and II, respectively. Expression of OsNAS3, OsVIT2, OsFER and OsABCC1 indicated PB-1′s tolerance towards Fe and As. Analysis of mitogen-activated protein kinase cascade members (OsMKK3 , OsMKK4 , OsMKK6 , OsMPK3 , OsMPK4 , OsMPK7 , and OsMPK14) revealed their importance in the fine adjustment of As/Fe in the rice system. A conditional network map was generated based on the gene expression pattern that unfolded the differential dynamics of both rice varieties. The mating based split ubiquitin system determined the interaction of OsIRT1 with OsMPK3, and OsLsi1 with both OsMPK3 and OsMPK4. In-silico tools also confirmed the binding affinities of OsARM1 with OsLsi1, OsMPK3 and OsMPK4, and of OsIDEF1/OsIRO2 with OsIRT1 and OsMPK3, supporting our hypothesis that OsARM1, OsIDEF1, OsIRO2 were active in the connections discovered by mbSUS. [Display omitted] • Iron (Fe) affects arsenic (As)-transporter gene's regulation in rice plants. • Studied rice varieties depicts variable Fe-uptake strategies. • MAPKs are responsive to the plant's As and Fe levels. • OsMPK3 interacts with both OsLsi1 and OsIRT1. [ABSTRACT FROM AUTHOR]

This work reports on the concise total synthesis of eight natural products of the mugineic acid and avenic acid families (phytosiderophores). An innovative „east‐to‐west" assembly of the trimeric products resulted in a high degree of divergence enabling the formation of the final products in just 10 or 11 steps each with a minimum of overall synthetic effort. Chiral pool starting materials (l‐malic acid, threonines) were employed for the outer building blocks while the middle building blocks were accessed by diastereo‐ and enantioselective methods. A highlight of this work consists in the straightforward preparation of epimeric hydroxyazetidine amino acids, useful building blocks on their own, enabling the first synthesis of 3"‐hydroxymugineic acid and 3"‐hydroxy‐2'‐deoxymugineic acid. [ABSTRACT FROM AUTHOR]

Despite their economic and ecological interests, Poaceae are affected by the low availability of iron in calcareous soils. Several studies focused on the capacity of this family to secrete phytosiderophores and organic acids as a mechanism of tolerance to iron deficiency. This work aimed at studying the physiological responses of two Poaceae species; Hordeum vulgare (cultivated barley) and Polypogon monspenliensis (spontaneous species) to iron deficiency, and evaluate especially the release of phytosiderophores and organic acids. For this purpose, seedlings of these two species were cultivated in complete nutrient solution with or without iron. The biomass production, iron status, phytosiderophores and organic acids release by roots were studied. The results demonstrated that Polypogon monspenliensis was relatively more tolerant to iron deficiency than Hordeum vulgare. Polypogon monspenliensis had the ability to secrete a higher amount of phytosiderophores and organic acids, especially citric, acetic, oxalic and malic acids, compared to Hordeum vulgare. We propose this spontaneous species as a forage plant in calcareous soils and in intercropping systems with fruit trees to prevent iron chlorosis. [ABSTRACT FROM AUTHOR]

Abstract Background The release of phytosiderephores (PS) to the rhizosphere is the main root response to iron (Fe) deficiency in graminaceous plants. We have investigated the role of the Fe status in the shoot as well as of the signaling pathways controlled by three relevant phytoregulators – indolacetic acid (IAA), ethylene and nitric oxide (NO) – in the regulation of this root response in Fe-starved wheat plants. To this end, the PS accumulation in the nutrient solution and the root expression of the genes encoding the nicotianamine aminotransferase (TaNAAT) and ferritin (TaFER) have been evaluated in plants subjected to different treatments. Results The application of Fe to leaves of Fe-deficient plants prevented the increase in both PS root release and TaNAAT gene expression thus showing the relevant role of the shoot to root communication in the regulation of PS root release and some steps of PS biosynthesis. Experiments with specific hormone inhibitors showed that while ethylene and NO did not positively regulate Fe-deficiency induced PS root release, auxin plays an essential role in the regulation of this process. Moreover, the application of IAA to Fe-sufficient plants promoted both PS root release and TaNAAT gene expression thus indicating that auxin might be involved in the shoot to root signaling network regulating Fe-deficiency root responses in wheat. Conclusions These results therefore indicate that PS root release in Fe-deficient wheat plants is directly modulated by the shoot Fe status through signaling pathways involving, among other possible effectors, auxin.

The major facilitator superfamily (MFS) is a large and diverse group of secondary transporters found across all kingdoms of life. Zinc-induced facilitator-like (ZIFL) transporters are the MFS family members that function as exporters driven by the antiporter-dependent processes. The presence of multiple ZIFL transporters was shown in various plant species, as well as in bryophytes. However, only a few ZIFLs have been functionally characterized in plants, and their localization has been suggested to be either on tonoplast or at the plasma membrane. A subset of the plant ZIFLs were eventually characterized as transporters due to their specialized role in phytosiderophores efflux and auxin homeostasis, and they were also proven to impart tolerance to micronutrient deficiency. The emerging functions of ZIFL proteins highlight their role in addressing important traits in crop species. This review aims to provide insight into and discuss the importance of plant ZIFL in various tissue-specific functions. Furthermore, a spotlight is placed on their role in mobilizing essential micronutrients, including iron and zinc, from the rhizosphere to support plant survival. In conclusion, in this paper, we discuss the functional redundancy of ZIFL transporters to understand their roles in developing specific traits in crop.

P availability determined the root uptake and root–shoot translocation of micronutrients. Total root 14C exudation was significantly higher under P−Fe− across wheat cultivars. Although malate than citrate was the predominant constituent of the root exudates in wheat, their release was higher under P− than P+ condition, irrespective of the Fe availability.A higher release of phytosiderophores was measured under P−Fe− than P+Fe+ for bread than durum wheat. The study highlights the role of root exudates in influencing the mobilization, uptake and translocation of not only P and Fe but also Mn and to some extent Cu, particularly under the nutrient-starved (P−Fe−) condition of growth. [ABSTRACT FROM AUTHOR]

Iron is essential for most living organisms and is required for normal plant growth. Plants induce iron utilization systems under conditions of low iron availability, but the molecular mechanisms of this gene regulation system remain largely unknown. We identified the rice transcription factor IDEF1, which specifically binds the iron-deficiency-responsive cis-acting element IDE1. IDEF1 belongs to an uncharacterized branch of the plant-specific transcription factor family ABI3/VP1 and efficiently binds to the CATGC sequence within IDE1. IDEF1 transcripts are constitutively present in rice roots and leaves. Transgenic tobacco plants expressing IDEF1 under the control of the constitutive cauliflower mosaic virus 35S promoter transactivate IDE1-mediated expression only in iron-deficient roots. Transgenic rice plants expressing IDEF1 under the control of the iron-deficiency-inducible IDS2 promoter tolerate iron deficiency in hydroponic culture and calcareous soil. Conversely, transgenic rice plants with repressed IDEF1 expression are susceptible to early stage iron deficiency in hydroponic culture. Expression analysis of these transgenic plants revealed that IDEF1 positively regulates iron-deficiency-induced genes, including the ferrous iron transporter gene OsIRT1 and the iron-deficiency-induced transcription factor gene OsIRO2. These data suggest the presence of a sequential gene regulatory network that functions via novel cis element/trans factor interactions to promote the iron-deficiency response.

Iron deficiency is a worldwide agricultural problem on calcareous soils with low iron (Fe) availability and also poses a major human nutritional problem. Plants induce Fe-acquisition systems under conditions of low Fe availability. Previously, we reported that an Fe deficiency-inducible bHLH transcription factor, OsIRO2, is responsible for regulating the genes involved in Fe homeostasis in rice. Here, we show that OsIRO2 overexpression results in improved tolerance to low Fe availability in calcareous soil. In addition to increased Fe content in shoots, rice overexpressing OsIRO2 accumulates more Fe in seeds than non-transformant rice when grown on calcareous soil. OsIRO2 promoter–GUS analysis revealed that OsIRO2 expression could be detected in developing seeds. These results suggest that OsIRO2 plays a crucial role in regulating both Fe uptake from soil and Fe translocation to grain. Improved uptake and translocation of Fe in the OsIRO2-overexpressing rice under low Fe availability provides an approach for producing graminaceous crops that are tolerant to Fe deficiency and have Fe-rich seeds to enhance production and the nutritional quality of food.

Graminaceous plants including rice (Oryza sativa L.) produce and secrete mugineic acid family phytosiderophores (MAs) to solubilize iron [Fe(III)] in the soil. Vesicles derived from the rough endoplasmic reticulum (rER) observed in Fe-deficient barley roots were suggested to be involved in MA biosynthesis. However, the relationship between these vesicles and MA biosynthesis has not been well characterized. Rice produces and secretes deoxymugineic acid (DMA), a representative member of the MAs. DMA is synthesized from S-adenosylmethionine through three sequential enzymatic reactions catalyzed by nicotianamine synthase (NAS), nicotianamine aminotransferase (NAAT), and deoxymugineic synthase (DMAS). The genes that participate in this pathway have been identified. To investigate the site of DMA biosynthesis in rice, we generated transgenic rice plants expressing OsNAS2 and OsNAAT1 fused to the synthetic green fluorescent protein (sGFP) under the control of their own promoters. We observed sGFP fluorescence in both roots and shoots of OsNAS2-sGFP-transformed rice, but not in those of OsNAAT1-sGFP-transformed rice. In roots, OsNAS2:sGFP was observed in the cortex, epidermis, and root hairs. sGFP fluorescence was also observed in the phloem parenchyma cells of the leaf blade and large vascular bundle. Interestingly, in these cells, OsNAS2:sGFP fluorescence was observed in a dot-like pattern. Confocal laser scanning microscopy of root pericycle cells indicated that the structure with OsNAS2:sGFP dot-like labeling moved dynamically within the cell. Our results indicated that OsNAS2 is localized in these rER-derived vesicles, which have been suggested to be involved in DMA production in rice roots.

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. [ABSTRACT FROM AUTHOR]

Bread wheat is an important and the most consumed cereal worldwide. However, people with predominantly cereal-based diets are increasingly affected by micronutrient deficiencies, suggesting the need for biofortified wheat varieties. The limited genetic diversity in hexaploid wheat warrants exploring the wider variation present in wheat wild relatives, among these Aegilops tauschii , the wild progenitor of the bread wheat D genome. In this study, a panel of 167 Ae. tauschii accessions was phenotyped for grain Fe, Zn, Cu, and Mn concentrations for 3 years and was found to have wide variation for these micronutrients. Comparisons between the two genetic subpopulations of Ae. tauschii revealed that lineage 2 had higher mean values for Fe and Cu concentration than lineage 1. To identify potentially new genetic sources for improving grain micronutrient concentration, we performed a genome-wide association study (GWAS) on 114 non-redundant Ae. tauschii accessions using 5,249 genotyping-by-sequencing (GBS) markers. Best linear unbiased predictor (BLUP) values were calculated for all traits across the three growing seasons. A total of 19 SNP marker trait associations (MTAs) were detected for all traits after applying Bonferroni corrected threshold of -log10(P -value) ≥ 4.68. These MTAs were found on all seven chromosomes. For grain Fe, Zn, Cu, and Mn concentrations, five, four, three, and seven significant associations were detected, respectively. The associations were linked to the genes encoding transcription factor regulators, transporters, and phytosiderophore synthesis. The results demonstrate the utility of GWAS for understanding the genetic architecture of micronutrient accumulation in Ae. tauschii , and further efforts to validate these loci will aid in using them to diversify the D-genome of hexaploid wheat. [ABSTRACT FROM AUTHOR]

Phytosiderophores (PS) are root exudates released by grass species (Poaceae) that play a pivotal role in iron (Fe) plant nutrition. A direct determination of PS in biological samples is of paramount importance in understanding micronutrient acquisition mediated by PS. To date, eight plant-born PS have been identified; however, no analytical procedure is currently available to quantify all eight PS simultaneously with high analytical confidence. With access to the full set of PS standards for the first time, we report comprehensive methods to both fully characterize (IM-QTOFMS) and quantify (LC-ESI-MS/MS) all eight naturally occurring PS belonging to the mugineic acid family. The quantitative method was fully validated, yielding linear results for all eight analytes, and no unwanted interferences with soil and plant matrices were observed. LOD and LOQ values determined for each PS were below 11 and 35 nmol L−1, respectively. The method's precision under reproducibility conditions (intra- and inter-day) of measurement was less than 2.5% RSD for all analytes. Additionally, all PS were annotated with high-resolution mass spectrometric fragment spectra and further characterized via drift tube ion mobility-mass spectrometry. The collision cross-sections obtained for primary ion species yielded a valuable database for future research focused on in-depth PS studies. The new quantitative method was applied to analyse root exudates from Fe-controlled and deficient barley, oat, rye, and sorghum plants. All eight PS, including mugineic acid (MA), 3"-hydroxymugineic acid (HMA), 3"- epi -hydroxymugineic acid (epi -HMA), hydroxyavenic acid (HAVA), deoxymugineic acid (DMA), 3"-hydroxydeoxymugineic acid (HDMA), 3"- epi -hydroxydeoxymugineic acid (epi -HDMA) and avenic acid (AVA) were for the first time successfully identified and quantified in root exudates of various graminaceous plants using a single analytical procedure. These newly developed methods can be applied to studies aimed at improving crop yield and micronutrient grain content for food consumption via plant-based biofortification. [Display omitted] • Fully validated LC-ESI-MS/MS for PS quantification with internal standards. • Drift tube IM-QTOFMS characterization of PS. • MS library compilation including RT, fragment spectra, and DT CCS N2 for all analytes. • Quantification of PS in root exudates of graminaceous plants. [ABSTRACT FROM AUTHOR]

Fe chlorosis is considered as one of the major constraints on crop growth and yield worldwide, being particularly worse when associated with S shortage, due to the tight link between Fe and S. Plant adaptation to inadequate nutrient availabilities often relies on the release of root exudates that enhance nutrients, mobilization from soil colloids and favour their uptake by roots. This work aims at characterizing the exudomic profile of hydroponically grown tomato plants subjected to either single or combined Fe and S deficiency, as well as at shedding light on the regulation mechanisms underlying Fe and S acquisition processes by plants. Root exudates have been analysed by untargeted metabolomics, through liquid chromatography–mass spectrometry as well as gas chromatography–mass spectrometry following derivatization. More than 200 metabolites could be putatively annotated. Venn diagrams show that 23%, 10% and 21% of differential metabolites are distinctively modulated by single Fe deficiency, single S deficiency or combined Fe–S deficiency, respectively. Interestingly, for the first time, a mugineic acid derivative is detected in dicot plants root exudates. The results seem to support the hypothesis of the co-existence of the two Fe acquisition strategies in tomato plants.

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.

The micronutrient iron (Fe) is essential for photosynthesis, respiration, and many other processes, but it is only sparingly soluble in aqueous solution, making adequate acquisition by plants a serious challenge. Fe is a limiting factor for plant growth on approximately 30% of the world’s arable lands. Moreover, Fe deficiency in humans is a global health issue, affecting 1.62 billion people, or about 25% of the world’s population. It is imperative that we gain a better understanding of the mechanisms that plants use to regulate iron homeostasis, since these will be important targets for future biofortification and crop improvement strategies. Grasses and non-grasses have evolved independent mechanisms for primary iron uptake from the soil. The grasses, which include most of the world’s staple grains, have evolved a distinct ‘chelation’ mechanism to acquire iron from the soil. Strong iron chelators called phytosiderophores (PSs) are synthesized by grasses and secreted into the rhizosphere where they bind and solubilize Fe(III). The Fe(III)-PS complex is then taken up into root cells via transporters specific for the Fe(III)-PS complex. In this study, 31 novel, uncharacterized striped maize mutants available through the Maize Genetics Cooperation Stock Center (MGCSC) were analyzed to determine whether their mutant phenotypes are caused by decreased iron. Many of these proved to be either pale yellow or white striped mutants. Complementation tests were performed by crossing the MGCSC mutants to ys1 and ys3 reference mutants. This allowed assignment of 10 ys1 alleles and 4 ys3 alleles among the novel mutants. In addition, four ys∗ mutant lines were identified that are not allelic to either ys1 or ys3. Three of these were characterized as being non-allelic to each other and as having low iron in leaves. These represent new genes involved in iron acquisition by maize, and future cloning of these genes may reveal novel aspects of the grass iron acquisition mechanism.

We, herein, report the synthesis of 13 C 2 -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 C 2 -bromoacetic acid, 13 C 2 -glycine) and further employed in our recently reported divergent, branched synthetic strategy delivering eight isotopically labeled phytosiderophores. The required labeled building blocks ( 13 C 2 -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., (© 2023 The Authors. Journal of Labelled Compounds and Radiopharmaceuticals published by John Wiley & Sons Ltd.)

Highlights • Two Sorghum bicolor genotypes with contrasting alkalinity tolerance were identified. • Alkalinity and -Fe elicited similar responses, tolerance followed parallel trends. • Both stresses caused early damage to the oxygen evolving complex in PSII. • Upregulation of genes for phytosiderophore synthesis and transport was observed under both conditions. • Lower expression of these genes may be related to alkalinity sensitivity. Abstract Soil alkalinity is a significant limitation to agricultural productivity and it is associated to several soil features, among them, Fe deficiencies. In this work, we explored the hypothesis that alkalinity tolerance in Sorghum bicolor is related to Fe-deficiency tolerance and its underlying mechanisms. An initial screening involving 8 sorghum genotypes identified two with contrasting growth responses to alkalinity (susceptible Minu II and more tolerant Silero INTA Pemán) that were subsequently studied under Fe-deprivation (-Fe) conditions. Sorghum sudanense (sudangrass) was included as control tolerant species for Fe deficiency. Growth in hydroponics and in soil indicated that responses to both alkaline and -Fe substrates followed parallel trends in the three genotypes: Minu II was the most sensitive, followed by Silero and sudangrass. Decreases in carbon fixation ( A ) and stomatal conductance were observed earlier in -Fe than in alkalinity, and the intensity in the three genotypes followed the same tendency as growth depressions. Calculations derived from the analysis of A as a function of internal CO 2 concentration ( A /C i curves) indicated increased C i concentration along with a decrease in the efficiency of phosphoenol pyruvate caboxylase activity in Minu II. Fast chlorophyll a fluorescence transients (OJIP-test) revealed decreased PSII connectivity in both Minu II and Silero under -Fe, but Minu II disclosed more damage to the oxygen evolving complex under alkalinity, while sudangrass was largely unresponsive. Expression of the genes for phytosiderophore (Phys) synthesis and transport genes was induced under both alkalinity and -Fe conditions in both S. bicolor genotypes, and more strongly in Silero than in Minu II. Lower induction of gene expression in Minu II may be related to its sensitivity to alkalinity conditions associated to reduced Fe availability, leading to alteration in photochemical and biochemical reactions involving Fe. Thus, our results provide support to the concept that susceptibility to Fe-deficiency and alkalinity conditions are associated in Sorghum bicolor and highlight some of the physiological traits that underlie this association. [ABSTRACT FROM AUTHOR]

In graminaceous plants, nicotianamine (NA) is an important component of metal acquisition. NA is synthesized from S-adenosyl- l -methionine (SAM) catalyzed by nicotianamine synthase (NAS). Here, eight Triticum monococcum NAS ( TmNAS ) genes were cloned and characterized. Amino acid sequence analysis showed that TmNAS genes had high sequence identity with those from Triticum aestivum , Zea mays , Oryza sativa and Hordeum vulgare . Phylogenetic analysis showed that NAS genes were classified into two distinct groups, e.g. group I and group II. Expression analysis demonstrated that two of the TmNAS genes in group II were highly expressed in shoot tissues, and the other six TmNAS genes in group I were expressed in root tissues. Further analysis indicated that root-specific TmNAS genes were up-regulated under conditions of Fe- or Zn-deficiency growth, while shoot-specific TmNAS genes were up-regulated under conditions of Fe- or Zn-sufficiency. These results help us understand the NAS genes in T . monococcum and provide novel genetic resources for improving Fe and Zn concentrations in common wheat. [ABSTRACT FROM AUTHOR]

Intercropping is a vital technology in resource-limited agricultural systems with low inputs. Peanut/maize intercropping enhances iron (Fe) nutrition in calcareous soil. In this study, the transcriptome of peanut and maize roots was analyzed by suppression subtractive hybridization (SSH) and microarray analysis separately. We constructed four SSH libraries using the cDNA of peanut roots based on two cropping patterns: monocropping and intercropping, and two growth stages: vegetative stage and reproductive stage. Lib M1, I1, M2 and I2 comprised 53, 51, 37 and 54 genes, respectively. Six and four transporters were found in the two intercropping-specific SSH libraries, which may facilitate Fe acquisition and protoplasmic homeostasis of metal ions and anions. Specifically, AhNARMP1 and MTP may play a role in boosting Fe nutrition during the vegetative stage. The expression of MYC2 was also upregulated by intercropping, while an ethylene-responsive transcription factor was downregulated during two growth periods. Microarrays indicated that homocysteine S-methyltransferase and serine acetyltransferase 1 upregulated in intercropped maize roots, which directly associated with methionine biosynthesis. It may account for the enhanced phytosiderophore released capacity in intercropping, which benefited the Fe nutrition of intercropped peanut in reproductive stage. Two aminocyclopropane-1-carboxylic acid synthase oxidase genes, which are related to ethylene biosynthesis, were downregulated in maize root by intercropping. Taken together with our previous proteomic work, the results indicated that intercropping enhances jasmonate signaling and weakens ethylene signaling in peanut and maize roots, which may improve ecological adaptation of the peanut plant to intercropping systems. [ABSTRACT FROM AUTHOR]

Many elements are scarcely soluble in aqueous conditions found in high pH environments, such as calcareous grassland soils, unless complexed to strong binding organic ligands. To overcome this limitation, some plants and microbes produce chelators that solubilize micronutrient metals such as Fe, Ni, Cu, and Zn from mineral phases. These complexes are taken up by organisms via specific membrane receptors, thereby differentially impacting the bioavailability of these metals to the plant and microbial community. Although the importance of these chelation strategies for individual organisms has been well established, little is known about which pathways coexist within rhizosphere microbiomes or how they interact and compete for metal binding. Identifying these metallophores within natural ecosystems has remained a formidable analytical challenge due to the vast diversity of compounds and poorly defined metabolic processes in complex soil matrices. Herein, we employed recently developed liquid chromatography (LC) mass spectrometry (MS) methods to characterize the speciation of water-soluble dissolved trace elements (Fe, Ni, Cu, and Zn) of soils from native tallgrass prairies in Kansas and Iowa. Both plant and fungal metallophores were identified, revealing compound-specific patterns of chelation to biologically essential metals. Numerous metabolites typically implicated in plant Fe acquisition and homeostasis, including mugineic acids, deoxymugineic acid, nicotianamine, and hydroxynicotianamines, dominated the speciation of divalent metals such as Ni, Cu, and Zn (2–90 pmol/g soil). In contrast, the fungal siderophore ferricrocin was specific for trivalent Fe (7–32 pmol/g soil). These results define biochemical pathways that underpin the regulation of metals in the grassland rhizosphere. They also raise new questions about the competition of these compounds for metal binding and their bioavailability to different members of the rhizosphere population. Small structural modifications result in significant differences in metal ligand selectivity, and likely impact metal uptake within the rhizosphere of grassland soils. [ABSTRACT FROM AUTHOR]

Phytosiderophore (PS) release, which occurs mainly under iron deficiencies in the representative Poaceae, has been speculated to be a general adaptive response to enhance the acquisition of micronutrient metals. However, it is very common to encounter deficiency of micronutrients other than iron (Fe) in soils and interactions with respect of multi-micronutrient deficiency to effect on PS release are not known. Further, the diurnal rhythm for the release of PS may also be affected under multiple micronutrient deficiency. PS release capacity and PS content of roots and the diurnal rhythm of PS release was measured in selected efficient and inefficient wheat genotypes varied on individual and combined deficiency of Fe, zinc (Zn), copper (Cu) and manganese (Mn) in nutrient solution culture. A nutrient sufficient treatment was also taken as experimental control. Lack of Fe in the nutrient medium caused a significantly higher release of PSs followed by Zn, Mn and Cu in the same order. The diurnal rhythm of PS release was similar in the absence of either of the micronutrients or under their combined deficiency. Micronutrient sufficient control did not release any PS. Fe-use-efficient cultivars produced and released a larger amount of PS and differed from the inefficient cultivars in terms of the PS release but not in the PS biosynthesis in the roots. Thus, indicating that the limitation at the level of release of the PS is responsible for low Fe use efficiency of the Fe deficiency susceptible cultivars. Further, the diurnal variation in the PS release was similar for all the investigated wheat cultivars and did not influence the variation in the Fe use efficiency. [ABSTRACT FROM AUTHOR]

The micronutrient iron (Fe) is essential for photosynthesis, respiration, and many other processes, but it is only sparingly soluble in aqueous solution, making adequate acquisition by plants a serious challenge. Fe is a limiting factor for plant growth on approximately 30% of the world's arable lands. Moreover, Fe deficiency in humans is a global health issue, affecting 1.62 billion people, or about 25% of the world's population. It is imperative that we gain a better understanding of the mechanisms that plants use to regulate iron homeostasis, since these will be important targets for future biofortification and crop improvement strategies. Grasses and non-grasses have evolved independent mechanisms for primary iron uptake from the soil. The grasses, which include most of the world's staple grains, have evolved a distinct 'chelation' mechanism to acquire iron from the soil. Strong iron chelators called phytosiderophores (PSs) are synthesized by grasses and secreted into the rhizosphere where they bind and solubilize Fe(III). The Fe(III)-PS complex is then taken up into root cells via transporters specific for the Fe(III)- PS complex. In this study, 31 novel, uncharacterized striped maize mutants available through the Maize Genetics Cooperation Stock Center (MGCSC) were analyzed to determine whether their mutant phenotypes are caused by decreased iron. Many of these proved to be either pale yellow or white striped mutants. Complementation tests were performed by crossing the MGCSC mutants to ys1 and ys3 reference mutants. This allowed assignment of 10 ys1 alleles and 4 ys3 alleles among the novel mutants. In addition, four ys* mutant lines were identified that are not allelic to either ys1 or ys3. Three of these were characterized as being non-allelic to each other and as having low iron in leaves. These represent new genes involved in iron acquisition by maize, and future cloning of these genes may reveal novel aspects of the grass iron acquisition mechanism. [ABSTRACT FROM AUTHOR]

Ravenna grass, Erianthus ravennae (L.) Beauv. (E. ravennae) is a potential high biomass-energy crop with low input requirements. Iron (Fe) deficiency in calcareous soils is a widespread agronomic problem which reduces crop yields. Fe is sparingly soluble under aerobic conditions at high soil pH, such as in calcareous soils; therefore, plants cannot take up enough Fe. Increasing crop productivity of giant grasses, such as Ravenna grass in calcareous soil, has a positive effect by alleviating environmental problems. However, the growth character in calcareous soil and Fe homeostatic trait of Ravenna grass are largely unknown. In this study, we analyzed characteristics of Ravenna grass. The growth of E. ravennae plants were impaired in calcareous soil compared to those in the normal soil. In calcareous soil, the growth of E. ravennae plants differ among the water and fertilizer conditions; E. ravennae plants were grown better in the submerged condition adding micronutrient among conditions. These results suggested that impaired growth of E. ravennae in calcareous soil might be micronutrient shortage. We found that E. ravennae roots possess Fe reductase activities which were upregulated under Fe-deficient conditions. E. ravennae produced and secreted mugineic acid (MA) and deoxymugineic acid (DMA) to acquire Fe from the soil. The amount of MA was higher than that of DMA. Thus, E. ravennae might have both partial Strategy-I and Strategy-II Fe uptake systems. E. ravennae intercropped with transgenic rice plants producing and secreting MA through the introduction of the barley MA synthase gene showed improved growth compared to monocropped E. ravennae plants, suggesting that the increased amounts of MA enhanced their tolerance to Fe deficiency. Our results suggest that there is a considerable potential to improve the growth of E. ravennae plants in calcareous soils by enhancement of their Fe uptake systems through increase of MA production. [ABSTRACT FROM AUTHOR]

Key message: Rice OsYSL9 is a novel transporter for Fe(II)-nicotianamine and Fe(III)-deoxymugineic acid that is responsible for internal iron transport, especially from endosperm to embryo in developing seeds. Abstract: Metal chelators are essential for safe and efficient metal translocation in plants. Graminaceous plants utilize specific ferric iron chelators, mugineic acid family phytosiderophores, to take up sparingly soluble iron from the soil. Yellow Stripe 1-Like (YSL) family transporters are responsible for transport of metal-phytosiderophores and structurally similar metal-nicotianamine complexes. Among the rice YSL family members (OsYSL) whose functions have not yet been clarified, OsYSL9 belongs to an uncharacterized subgroup containing highly conserved homologs in graminaceous species. In the present report, we showed that OsYSL9 localizes mainly to the plasma membrane and transports both iron(II)-nicotianamine and iron(III)-deoxymugineic acid into the cell. Expression of OsYSL9 was induced in the roots but repressed in the nonjuvenile leaves in response to iron deficiency. In iron-deficient roots, OsYSL9 was induced in the vascular cylinder but not in epidermal cells. Although OsYSL9-knockdown plants did not show a growth defect under iron-sufficient conditions, these plants were more sensitive to iron deficiency in the nonjuvenile stage compared with non-transgenic plants. At the grain-filling stage, OsYSL9 expression was strongly and transiently induced in the scutellum of the embryo and in endosperm cells surrounding the embryo. The iron concentration was decreased in embryos of OsYSL9-knockdown plants but was increased in residual parts of brown seeds. These results suggested that OsYSL9 is involved in iron translocation within plant parts and particularly iron translocation from endosperm to embryo in developing seeds. [ABSTRACT FROM AUTHOR]

Plants acquire mineral nutrients mostly through the rhizosphere; they secrete a large number of metabolites into the rhizosphere to regulate nutrient availability and to detoxify undesirable metal pollutants in soils. The secreted metabolites are inorganic ions, gaseous molecules, and mainly carbon-based compounds. This review focuses on the mechanisms and regulation of low-molecular-weight organic-compound exudation in terms of metal acquisition. We summarize findings on riboflavin/phenolic-facilitated and phytosiderophore-facilitated iron acquisition and discuss recent studies of the functions and secretion mechanisms of low-molecular-weight organic acids in heavy-metal detoxification. [ABSTRACT FROM AUTHOR]

Many chemicals, including herbicides, are routinely applied to crops for weed management and food production improvement. However, the intensive use of herbicides could lead eventually to a great environmental threat due to their persistence and accumulation in the ecosystems and contamination of soils. Furthermore, the possible effect of these chemicals on nutrient uptake and assimilation in crops has only recently been discussed. The present study aimed at understanding the effect of the herbicide terbuthylazine (TBA), a herbicide commonly applied to control weeds in leguminous species and triazine tolerant crops, on the capability of maize plants to cope with iron (Fe) shortage. The application of 2 and 5 mg L TBA caused a significant reduction of root Fe concentration. This reduction might be attributed to a decreased release of phytosiderophores, which in turn could be ascribed to a reduced sulfur assimilation. Results provide evidence that TBA impairs Fe uptake and accumulation in non-target plants most likely interacting with sulfur-assimilating enzymes [ATP sulfurylase and O-acetylserine(thiol)lyase]. [ABSTRACT FROM AUTHOR]

Background and aims: Graminaceous plants are grown worldwide as staple crops under a variety of climatic and soil conditions. They release phytosiderophores for Fe acquisition (Strategy II). Aim of the present study was to uncover how the rhizosphere pH, background electrolyte and temperature affect the mobilization of Fe and other metals from soil by phytosiderophores. Methods: For this purpose a series of kinetic batch interaction experiments with the phytosiderophore 2′-deoxymugineic acid (DMA), a calcareous clay soil and a mildly acidic sandy soil were performed. The temperature, electrolyte concentration and applied electrolyte cation were varied. The effect of pH was examined by applying two levels of lime and Cu to the acidic soil. Results: Fe mobilization by DMA increased by lime application, and was negatively affected by Cu amendment. Mobilization of Fe and other metals decreased with increasing ionic strength, and was lower for divalent than for monovalent electrolyte cations at equal ionic strength, due to higher adsorption of metal-DMA complexes to the soil. Metal mobilization rates increased with increasing temperature leading to a faster onset of competition; Fe was mobilized faster, but also became depleted faster at higher temperature. Temperature also affected biodegradation rates of metal-DMA complexes. Conclusion: Rhizosphere pH, electrolyte type and concentration and temperature can have a pronounced effect on Strategy II Fe acquisition by affecting the time and concentration 'window of Fe uptake' in which plants can benefit from phytosiderophore-mediated Fe uptake. [ABSTRACT FROM AUTHOR]

We investigated to which extent phytosiderophores (PS), released by grasses for the acquisition of iron, solubilize other metals in contaminated soils, and how this affects metal mobilization and uptake in wheat plants. A plant-based bioassay (‘RHIZOtest’) and batch extraction scheme were carried out for assessing metal mobilisation in soil, PS exudation and metal accumulation in wheat. Increased PS exudation was observed in Fe-deficient wheat, leading to enhanced Zn, Cu, Mn and Ni concentrations in wheat shoots on some soils. In contrast, plant Cd and Pb concentrations were not affected. Likewise, in the batch experiment, strongly increased extractable Cu, Ni and Zn concentrations were observed, in particular when 100 or 1000 μM PS were added. Our results suggest that Fe deficiency can enhance the accumulation of some metals in shoots of grass species. Although our results indicate that the risk of enhanced accumulation of Cd and Pb in Fe deficient wheat shoots is rather small, further experiments conducted on soil for the complete vegetation period would be needed to confirm this observation. [ABSTRACT FROM AUTHOR]

Background: Rice ( Oryza sativa L.) is highly susceptible to iron (Fe) deficiency due to low secretion levels of the mugineic acid (MA) family phytosiderophore (PS) 2′-deoxymugineic acid (DMA) into the rhizosphere. The low levels of DMA secreted by rice have proved challenging to measure and, therefore, the pattern of DMA secretion under Fe deficiency has been less extensively studied relative to other graminaceous monocot species that secrete high levels of PS, such as barley ( Hordeum vulgare L.). Results: Gene expression and metabolite analyses were used to characterise diurnal changes occurring during the Fe deficiency response of rice. Iron deficiency inducible genes involved in root DMA biosynthesis and secretion followed a diurnal pattern with peak induction occurring 3-5 h after the onset of light; a result consistent with that of other Strategy II plant species such as barley and wheat. Furthermore, triple quadrupole mass spectrometry identified 3-5 h after the onset of light as peak time of DMA secretion from Fe-deficient rice roots. Metabolite profiling identified accumulation of amines associated with metal chelation, metal translocation and plant oxidative stress responses occurring with peak induction 10-12 h after the onset of light. Conclusion: The results of this study confirmed that rice shares a similar peak time of Fe deficiency associated induction of DMA secretion compared to other Strategy II plant species but has less prominent daily fluctuations of DMA secretion. It also revealed metabolic changes associated with the remediation of Fe deficiency and mitigation of damage from resulting stress in rice roots. This study complements previous studies on the genetic changes in response to Fe deficiency in rice and constitutes an important advance towards our understanding of the molecular mechanisms underlying the rice Fe deficiency response. [ABSTRACT FROM AUTHOR]

Many metal transporters in plants are promiscuous, accommodating multiple divalent cations including some which are toxic to humans. Previous attempts to increase the iron (Fe) and zinc (Zn) content of rice endosperm by overexpressing different metal transporters have therefore led unintentionally to the accumulation of copper (Cu), manganese (Mn) and cadmium (Cd). Unlike other metal transporters, barley Yellow Stripe 1 (Hv YS1) is specific for Fe. We investigated the mechanistic basis of this preference by constitutively expressing Hv YS1 in rice under the control of the maize ubiquitin1 promoter and comparing the mobilization and loading of different metals. Plants expressing Hv YS1 showed modest increases in Fe uptake, root-to-shoot translocation, seed accumulation and endosperm loading, but without any change in the uptake and root-to-shoot translocation of Zn, Mn or Cu, confirming the selective transport of Fe. The concentrations of Zn and Mn in the endosperm did not differ significantly between the wild-type and Hv YS1 lines, but the transgenic endosperm contained significantly lower concentrations of Cu. Furthermore, the transgenic lines showed a significantly reduced Cd uptake, root-to-shoot translocation and accumulation in the seeds. The underlying mechanism of metal uptake and translocation reflects the down-regulation of promiscuous endogenous metal transporters revealing an internal feedback mechanism that limits seed loading with Fe. This promotes the preferential mobilization and loading of Fe, therefore displacing Cu and Cd in the seed. [ABSTRACT FROM AUTHOR]