Fe-deficient Plants Research Articles

Indole-3-acetaldoxime delays root iron-deficiency responses and modify auxin homeostasis in Medicago truncatula

Iron (Fe) is an essential plant micronutrient, being a major limiting growth factor in calcareous soils. To increase Fe uptake, plants induce lateral roots growth, the expression of a Fe(III)-chelate reductase (FCR), a Fe(II)-transporter and a H+-ATPase and the secretion of flavins. Furthermore, auxin hormone family is involved in the Fe-deficiency responses but the action mechanism remains elusive. In this work, we evaluated the effect of the auxin-precursor indole-3-acetaldoxime (IAOx) on hydroponically grown Medicago truncatula plants under different Fe conditions.Upon 4-days of Fe starvation, the pH of the nutrient solution decreased, while both the FCR activity and the presence of flavins increased. Exogenous IAOx increased lateral roots growth contributing to superroot phenotype, decreased chlorosis, and delayed up to 3-days the pH-decrease, the FCR-activity increase, and the presence of flavins, compared to Fe-deficient plants. Gene expression levels were in concordance with the physiological responses. Resultsshowed that IAOx was immediately transformed to IAN in roots and shoots to maintain auxin homeostasis. IAOx plays an active role in iron homeostasis delaying symptoms and responses in Fe-deficient plants. We may speculate that IAOx or its derivatives remobilize Fe from root cells to alleviate Fe-deficiency. Overall, these results point out that the IAOx-derived phenotype may have advantages to overcome nutritional stresses.

Combined effect of elevated CO2 and Fe deficiency on common bean metabolism and mineral profile

Abstract Aims Elevated atmospheric CO2 (eCO2) and restricted iron (Fe) supply are known to impact plant growth and nutritional quality of food crops. However, studies aimed at understanding how eCO2 will interact with Fe deficiency are scarce. Changes in the nutritional status of the common bean (Phaseolus vulgaris L.) may significantly impact the nutritional status of populations that rely heavily on this crop. Methods To understand the combined effects of eCO2 and Fe deficiency on mechanisms relevant to plant nutrient uptake and accumulation, common bean plants were grown under Fe sufficiency (Fe+, 20 mM Fe-EDDHA) and Fe deficiency (Fe-, 0 mM Fe-EDDHA) combined with eCO2 (800 ppm) or ambient CO2 (aCO2, 400 ppm) in hydroponics until maturity. Results Elevated CO2, besides stimulating photosynthesis and stomatal closure, highly affected plant Fe metabolism: stimulated root ferric chelate reductase (FCR) activity by 6-fold and downregulated the expression of root FRO1 and IRT1 expressions by about 4-fold. In leaves, citrate and oxalate increased, but ferritin expression decreased by 9-fold. Such changes may have determined the differences on mineral accumulation patterns particularly the lower levels of Fe in roots (62%), leaves (38%) and seeds (50%). The combination of Fe deficiency and eCO2 doubled the effect of a single factor on FCR up-regulation, balanced the internal pH of Fe deficient plants, and resulted in the lowest Fe accumulation in all plant parts. Conclusions These results suggest that eCO2 directly affects the Fe uptake mechanism of common bean plants, decreasing plant Fe content.

Effects of salinity and iron deficiency on growth and physiological attributes of Avicennia marina (Forssk.) Vierh

ABSTRACT The grey mangrove, Avicennia marina, grows in coastal zones in which salinity is frequently associated with iron deficiency. Its response to these combined stresses has not yet explored. The current study aims to assess the physiological and biochemical effects of iron deficiency (ID), salt stress (SS) and their combination (ID + SS) on A. marina seedlings. Iron deficiency reduced growth at non-saline treated plants by 27% while its deleterious effect was mitigated by the supply of 600 mM NaCl, mainly through the increase of photosynthetic pigment contents, iron accumulation in leaves, and intrinsic water use efficiency (iWUE), and the maintain of iron use efficiency (FeUE). Iron deficiency restricted iron accumulation in leaves (31%), iron absorption efficiency (FeAE) (38%), photosynthetic activity and pigment contents, and enhanced FeUE (48%) at saline treated plants. Otherwise, salinity enhanced growth (47%), root volume (20%), Fe accumulation in leaves (8%), and pigment contents at Fe-deficient plants. However, it reduced their FeAE (18%), transpiration rate (77%) and stomatal conductance (86%). Equally, it increased Na and Cl accumulation, the net photosynthetic assimilation rate and iWUE at Fe-deficient. Interestingly, the combined stresses had no additive effects and stressed plants (ID +SS) had comparable biomass to that of the control.

Nitric oxide acts as an inducer of Strategy-I responses to increase Fe availability and mobilization in Fe-starved broccoli (Brassica oleracea var. oleracea)

Iron (Fe) deficiency causes reduced growth and yield in broccoli. This study elucidates how sodium nitroprusside (SNP), known as nitric oxide (NO) donor, mitigates the retardation caused by Fe deficiency in broccoli. The SNP caused substantial nitric oxide accumulation in the roots of Fe-deficient plants, which resulted in a significant improvement in chlorophyll levels, photosynthetic efficiency, and morphological growth parameters, showing that it has a favorable influence on recovering broccoli health. Ferric reductase activity and the expression of BoFRO1 (ferric chelate reductase) gene in roots were consistently increased by SNP under Fe deficiency, which likely resulted in increased Fe mobilization. Furthermore, proton (H+) extrusion and BoHA2 (H+-ATPase 2) expression were significantly increased, suggesting that they may be involved in lowering rhizospheric pH to restore Fe mobilization in roots of bicarbonate-treated broccoli plants. The levels of Fe in root and shoot tissues and the expression of BoIRT1 (Fe-regulated transporter) both increased dramatically after SNP supplementation under Fe deprivation. Furthermore, SNP-induced increase in citrate and malate concentrations suggested a role of NO in improved Fe chelation in Fe-deficient broccoli. A NO scavenger (cPTIO) ceased the elevated FCR activity and IAA (indole-3-acetic acid) concentration in Fe-starved plants treated with SNP. These findings suggest that SNP may play a role in initiating Fe availability by elevated IAA concentration and BoEIR1 (auxin efflux carrier) expression in the roots of broccoli during Fe shortage. Therefore, SNP may improve Fe availability and mobilization by increasing Strategy-I Fe uptake pathways, which may help broccoli tolerate Fe deficiency.

Mechanistic assessment of tolerance to iron deficiency mediated by Trichoderma harzianum in soybean roots.

Iron (Fe) deficiency in soil is a continuing problem for soybean (Glycine max L.) production, partly as a result of continuing climate change. This study elucidates how Trichoderma harzianum strain T22 (TH) mitigates growth retardation associated with Fe-deficiency in a highly sensitive soybean cultivar. Soil TH supplementation led to mycelial colonization and the presence of UAOX1 gene in roots that caused substantial improvement in chlorophyll score, photosynthetic efficiency and morphological parameters, indicating a positive influence on soybean health. Although rhizosphere acidification was found to be a common feature of Fe-deficient soybean, the upregulation of Fe-reductase activity (GmFRO2) and total phenol secretion were two of the mechanisms that substantially increased the Fe availability by TH. Heat-killed TH applied to soil caused no improvement in photosynthetic attributes and Fe-reductase activity, confirming the active role of TH in mitigating Fe-deficiency. Consistent increases in tissue Fe content and increased Fe-transporter (GmIRT1, GmNRAMP2a, GmNRAMP2b and GmNRAMP7) mRNA levels in roots following TH supplementation were observed only under Fe-deprivation. Root cell death, electrolyte leakage, superoxide (O2 •- ) and hydrogen peroxide (H2 O2 ) substantially declined due to TH in Fe-deprived plants. Further, the elevation of citrate and malate concentration along with the expression of citrate synthase (GmCs) and malate synthase (GmMs) caused by TH suggest improved chelation of Fe in Fe-deficient plants. Results also suggest that TH has a role in triggering antioxidant defence by increasing the activity of glutathione reductase (GR) along with elevated S-metabolites (glutathione and methionine) to stabilize redox status under Fe-deficiency. TH increases the availability and mobilization of Fe by inducing Fe-uptake pathways, which appears to help provide resistance to oxidative stress associated with Fe-shortage in soybean. These findings indicate that while Fe deficiency does not affect the rate or degree of TH hyphal association in soybean roots, the beneficial effects of TH alone may be Fe deficiency-dependent.

Physiological and molecular characterization of strategy-I responses and expression of Fe-transporters in Fe-deficient soybean

Iron (Fe) deficiency is one of the major nutritional disorders that affect soybean production. This study aimed to better understand the adaptive responses and gene characterization in Fe-deficient soybean. The experiment was conducted on 14-day-old soybean plants in a soil pot under Fe sufficiency and bicarbonate-induced Fe deficiency. In soybean, Fe deficiency caused severe root and shoot morphological retardation, which was accompanied by the reductions in chlorophyll score, Fv/Fm (quantum yield efficiency of PSII), Pi_ABS (photosynthetic performance index) as well as an increase in electrolyte leakage and cell death. This is in accordance with the lower Fe status in the root and shoot of Fe-deficient plants. Further, the expression of GmIRT1 (Fe-regulated transporter) was significantly induced, while the members of NRAMP (natural resistance-associated macrophage proteins) transporters were either downregulated (GmNRAMP2a, GmNRAMP2b, GmNRAMP5a, GmNRAMP7) or constitutively expressed (GmNRAMP5b, GmNRAMP6a, GmNRAMP6b) in roots of Fe-deficient soybean relative to controls. Furthermore, the activity of Fe-chelate reductase and the expression of GmFRO2 (ferric reductase oxidase) in roots of Fe-deficient soybean were both significantly reduced, indicating the impairment of the ability of soybean plants to maintain Fe availability in the rhizosphere. However, plants showed a decrease in rhizospheric pH and upregulation of GmATPase4 in roots, indicating that rhizosphere acidification is one of the adaptive approaches that soybean plants possess in response to Fe-deficiency. In bioinformatics analysis, soybean Fe-uptake genes showed partnership with Arabidopsis FRO2, FRU, NRAMP1, bHLH38, and bHLH39 genes. In addition, Fe-starved plants demonstrated elevated H2O2 and O2•– in roots which were consistent with the inefficient oxidative defense of antioxidant enzymes. These findings could aid in the development of Fe-efficient soybean by breeding or genome editing techniques.

Humic Acid Alleviates Fe Chlorosis in Graminaceous Plants Through Coordinated Fe-Dependent and Fe-Independent Mechanisms.

Many studies have shown the close relationship between the beneficial action of soil and sedimentary humic acids on the growth of plants cultivated in calcareous soils and their ability to improve Fe plant nutrition. These results have been ascribed to the humic acid (HA) capability to improve Fe solubility and bioavailability. However, other effects more related to a humic acid action on the specific mechanisms activated in roots of plants under Fe deficiency cannot be ruled out. Although this question has been studied in dicotyledonous plants, in graminaceous plants there are no specific studies. Here we investigate the ability of a humic acid extracted from peat (HA) to improve Fe nutrition in wheat plants cultivated under Fe deficient and sufficient conditions. The results show that HA can improve the physiological status of Fe deficient wheat plants by alleviating some of the deleterious consequences of Fe deficiency on plant development and increasing the plant ability to secrete phytosiderophores to the nutrient solution. This action of HA is associated with increases in the Fe-active pool in leaves that might be related to the mobilization of the Fe complexed by HA resulting from the interaction of HA with the phytosiderophores in the nutrient solution. The Fe translocation from the root to the shoot may be favored by the action of trans-Zeatin Riboside (tZR) since the leaf concentration of this phytohormone was enhanced by HA in Fe deficient plants.

Short-term exposure to elevated CO2 stimulates growth and metabolic responses that alleviate early-stage iron deficiency symptoms in soybean

ABSTRACT Elevated CO2 (eCO2) increase plant biomass and might lead to nutritional losses. The results showed that eCO2 under Fe-deficiency stimulates root dry weight from 0.37–0.80 g plant−1 and shoot dry weight from 0.82–2.10 g plant−1, without compromising root/shoot ratio. Besides, eCO2 improved the chlorophyl content of Fe-deficient plants. However, downregulation of photosynthesis, reduction in stomatal conductance and transpiration rate, and an increase in water-use efficiency was observed due to eCO2. Moreover, under Fe-deficiency, eCO2 decreased K and Mg in roots, and Mg in leaves, whereas increased P and Zn in roots and leaves. In Fe-sufficient plants, eCO2 increased K, P, Mn, Zn and Fe in leaves and did not change the concentration in roots. The Fe-deficiency-induced responses in roots, including the increase in FCR activity, and the expression of Fe-uptake genes were stimulated by eCO2, but were not sufficient to increase Fe concentration in Fe-deficient plants.

Fast Determination of a Novel Iron Chelate Prototype Used as a Fertilizer by Liquid Chromatography Coupled to a Diode Array Detector.

The environmental risk of the application of synthetic chelates has favored the implementation of new biodegradable ligands to correct Fe-deficient plants. This study developed and validated an analytical method for determination of a new prototype iron chelate—Fe(III)-benzeneacetate, 2-hydroxy-α-[(2-hydroxyethyl)amino]—(BHH/Fe3+) based on liquid chromatography with diode array detection, as a potential sustainable alternative. Chromatographic analysis was performed on a LiChrospher RP-18 in reverse-phase mode, with a mobile phase consisting of a mixture of acetonitrile (solvent A) and sodium borate buffer 0.20 mM at pH = 8 (solvent B) at a flow rate of 1.0 mL/min in isocratic elution mode. This method was fully validated and found to be linear from the limit of quantification (LOQ) to 50 mg/L and precise (standard deviation below 5%). The proposed method was demonstrated to be selective, precise, and robust. The developed methodology indicated that it is suitable for the quantification of iron chelate BHH/Fe3+.

Short Term Elevated CO2 Interacts with Iron Deficiency, Further Repressing Growth, Photosynthesis and Mineral Accumulation in Soybean (Glycine max L.) and Common Bean (Phaseolus vulgaris L.)

Elevated CO2 (eCO2) has been reported to cause mineral losses in several important food crops such as soybean (Glycine max L.) and common bean (Phaseolus vulgaris L.). In addition, more than 30% of the world’s arable land is calcareous, leading to iron (Fe) deficiency chlorosis and lower Fe levels in plant tissues. We hypothesize that there will be combinatorial effects of eCO2 and Fe deficiency on the mineral dynamics of these crops at a morphological, biochemical and physiological level. To test this hypothesis, plants were grown hydroponically under Fe sufficiency (20 μM Fe-EDDHA) or deficiency (0 μM Fe-EDDHA) at ambient CO2 (aCO2, 400 ppm) or eCO2 (800 ppm). Plants of both species exposed to eCO2 and Fe deficiency showed the lowest biomass accumulation and the lowest root: shoot ratio. Soybean at eCO2 had significantly higher chlorophyll levels (81%, p < 0.0001) and common bean had significantly higher photosynthetic rates (60%, p < 0.05) but only under Fe sufficiency. In addition, eCO2 increased ferric chelate reductase acivity (FCR) in Fe-sufficient soybean by 4-fold (p < 0.1) and in Fe-deficient common bean plants by 10-fold (p < 0.0001). In common bean, an interactive effect of both environmental factors was observed, resulting in the lowest root Fe levels. The lowering of Fe accumulation in both crops under eCO2 may be linked to the low root citrate accumulation in these plants when grown with unrestricted Fe supply. No changes were observed for malate in soybean, but in common bean, shoot levels were significantly lower under Fe deficiency (77%, p < 0.05) and Fe sufficiency (98%, p < 0.001). These results suggest that the mechanisms involved in reduced Fe accumulation caused by eCO2 and Fe deficiency may not be independent, and an interaction of these factors may lead to further reduced Fe levels.

Efficiency of antioxidant system in barrel medic (

Iron (Fe) deficiency leads to an overproduction of reactive oxygen species (ROS) in plants that activate their antioxidant systems to control oxidative burst. In this study, contrasting Medicago truncatula genotypes, A17 and TN8.20 (tolerant) and TN1.11 (sensitive), were grown under Fe deficiency. The superoxide dismutase (SOD: EC1.15.1.1) activity, their isoforms’ coding genes, the copper chaperone expression patterns, and leaf phenolic contents were analysed. Our results showed that Fe deficiency decreases the photosynthetic capacity and plant biomass production with a prominent effect on TN1.11 genotype. The tolerance of A17 and TN8.20 was correlated with a maintenance of Fe content and the photosynthetic apparatus and an increase of Cu concentration compared with the sensitive genotype. We revealed a significant increase of H2O2 in Fe-deficient plants, mainly in TN1.11 sensitive genotype. TN8.20 and A17 tolerance were concomitant with a significant increase of SOD activities (SOD, Cu/Zn-SOD, and Mn-SOD) under Fe deficiency. This increment was correlated to an induction of the copper chaperone gene expression level, as well as an accumulation of isoquercitin phenolic compound. Our study provides new insights into the orchestration of SOD’s isoforms activities, the expression of the copper chaperone, FeSOD, Cu/ZnSOD genes, and the leaf phenolic compounds accumulation that allows Medicago truncatula to overcome Fe deficiency.

Stomatal Behaviors and Physiological Responses Affected by Iron Deficiency in Peach Plants Grafted onto Garnem and GF 677

Iron (Fe) is a pivotal nutrient taking roles in respiration, photosynthesis and many plant metabolisms. Chlorosis caused by Fe deficiency generally occurs in high pH environments and many fruit trees including peach are known sensitive to iron starvation. Fe starvation declines leaf chlorophyll and carotenoid contents, supresses plant growth and declines photosynthetic capacity. Iron deficiency induces responses in plants and different stomatal behaviors and physiological alterations occur to sustain the increased iron uptake capacity of Fe-deficient plants. In this study, the effects of iron deficiency on stomatal morphology and leaf physiological responses in peach variety Rich May grafted onto Garnem and GF 677 rootstocks were investigated. Plants were exposed to Fe deficient conditions for 3 months. End of the experiment, many leaf and stomatal properties were evaluated. The highest decrease in plant growth (relative growth rates of shoot diameter and length) induced by Fe deficiency was found in Rich May grafted onto Garnem. SPAD and relative anthocyanin decreased by 52 and 70% in Fe deficient Rich May/Garnem grafting combination. Decreases in SPAD and relative anthocyanin values were lower with GF 677. In GF 677, LRWC decreased by 1.8% and membrane permeability increased by 10%. Fe controlled stomatal behaviors in peach plants. Stomatal factors were found more sensitive to Fe deficiency in sensitive rootstock, Garnem. The increment in stomatal and pore areas leaded increase in stomatal conductance. The damage by Fe depletion was found higher in Garnem due to higher loss in SPAD, anthocyanin and increasing membrane permeability. Thus, GF 677 can be used in peach orchards under Fe deficiency conditions.

Evaluation of a Legume-Derived Protein Hydrolysate to Mitigate Iron Deficiency in Plants

Biostimulants play an important role in the development of management practices able to reach adequate productivity to meet the food demand of a growing world population, while following a sustainable agriculture model. This work aims to evaluate the effect of a protein hydrolysate derived from legume seeds by enzymatic hydrolysis on plant growth and also to verify its ability to mitigate Fe deficiency, a widespread problem significantly limiting plant growth and crop productivity. Experiments were performed with tomato (Solanum lycopersicum L.—cv. AKRAI F1) and cucumber (Cucumis sativus L.—cv. EKRON F1). The plants were grown hydroponically under adequate or limited Fe supply. Changes in shoot and root fresh weight, leaf relative chlorophyll content and the accumulation of macro- and microelements in shoots and roots were measured. Plant ability to cope with Fe deficiency was measured by evaluating the activity of root Fe3+-chelate reductase. Our results indicate that the foliar treatments with the protein hydrolysate did not significantly affect growth parameters when plants were grown in full nutrient solution. However, the biostimulant was able to improve the growth performance of Fe-deficient plants. Therefore, the protein hydrolysate can be a powerful tool to stimulate crop growth under Fe-deficient environments, leading to reduced fertilizer inputs with related environmental and economic benefits.

Evidence for a role of nitric oxide in iron homeostasis in plants.

Nitric oxide (NO), once regarded as a poisonous air pollutant, is now understood as a regulatory molecule essential for several biological functions in plants. In this review, we summarize NO generation in different plant organs and cellular compartments, and also discuss the role of NO in iron (Fe) homeostasis, particularly in Fe-deficient plants. Fe is one of the most limiting essential nutrient elements for plants. Plants often exhibit Fe deficiency symptoms despite sufficient tissue Fe concentrations. NO appears to not only up-regulate Fe uptake mechanisms but also makes Fe more bioavailable for metabolic functions. NO forms complexes with Fe, which can then be delivered into target cells/tissues. NO generated in plants can alleviate oxidative stress by regulating antioxidant defense processes, probably by improving functional Fe status and by inducing post-translational modifications in the enzymes/proteins involved in antioxidant defense responses. It is hypothesized that NO acts in cooperation with transcription factors such as bHLHs, FIT, and IRO to regulate the expression of enzymes and proteins essential for Fe homeostasis. However, further investigations are needed to disentangle the interaction of NO with intracellular target molecules that leads to enhanced internal Fe availability in plants.

AtHAP5A regulates iron translocation in iron-deficient Arabidopsis thaliana.

Iron (Fe) deficient plants employ multiple strategies to increase root uptake and root-to-shoot translocation of Fe. The identification of genes that are responsible for these processes, and a comprehensive understanding of the regulatory effects of transcriptional networks on their expression, including transcription factors (TFs), is underway in Arabidopsis thaliana. Here, we show that a Histone- or heme-associated proteins (HAP) transcription factor (TF), HAP5A, is necessary for the response to Fe deficiency in Arabidopsis. Its expression was induced under Fe deficiency, and the lack of HAP5A significantly decreased Fe translocation from the root to the shoot, resulting in substantial chlorosis of the newly expanded leaves, compared with the wild-type (WT, Col-0). Further analysis found that the expression of a gene encoding nicotianamine (NA) synthase (NAS1) was dramatically decreased in the hap5a mutant, regardless of the Fe status. Yeast-one-hybrid and ChIP analyses suggested that HAP5A directly binds to the promoter region of NAS1. Moreover, overexpression of NAS1 could rescue the chlorosis phenotype of hap5a in Fe deficient conditions. In summary, a novel pathway was elucidated, showing that NAS1-dependent translocation of Fe from the root to the shoot is controlled by HAP5A in Fe-deficient Arabidopsis thaliana.

Nitrate reductase rather than nitric oxide synthase activity is involved in 24-epibrassinolide-induced nitric oxide synthesis to improve tolerance to iron deficiency in strawberry (Fragaria × annassa) by up-regulating the ascorbate-glutathione cycle

Involvement of nitrate reductase (NR) and nitric oxide synthase (NOS)-like enzyme in 24-epibrassinolide (EB)-triggered nitric oxide (NO) synthesis to improve iron deficiency (ID) tolerance in strawberry plants was studied. EB was sprayed to strawberry plants every two days for two weeks. Then, the EB-treated plants were pre-treated with inhibitors of NR, tungstate, or NOS, L-NAME for 3 h. During the first three weeks, Fe was supplied as 100 μM EDTA-Fe or FeSO4 to Fe-sufficient or Fe-deficient plants, respectively. Thereafter, plants were subjected for further three weeks to control (100 μM EDTA-Fe) and Fe deficiency (ID; without Fe). ID reduced biomass, chlorophyll, and chlorophyll fluorescence, while increased oxidative stress parameters, ascorbate (AsA), glutathione (GSH), endogenous NO, and the activities of NR, NOS, and antioxidant enzymes. Pre-treatments with EB and EB + SNP improved ID tolerance of strawberry by improving leaf Fe2+, plant growth, and antioxidant enzyme activities, and causing a further elevation in AsA, GSH, NO, NR and NOS. L-NAME application reversed NOS activity, but it did not eliminate NO, however, tungstate application reversed both NR activity and NO synthesis in plants exposed to ID + EB, suggesting that NR is the main contributor of EB-induced NO synthesis to improve ID tolerance in strawberry plants.

Can Bicarbonate Enhance the Performance of Carob Seedlings Grown in Nutrient Solutions with Different Fe Concentrations?

The aim of this work was to assess the effect of bicarbonate (Bic) ion on the nutritional status and performance of carob-tree seedlings, a species that normally grows in calcareous soil without exhibiting iron chlorosis symptoms. Seedlings were previously grown in nutrient solution with a small concentration of Fe (0.5–1 μM) to induce a moderate chlorosis. Afterwards, two experiments were established: in experiment 1, plants were grown for 21 days in the following treatments: Fe deficiency (Fe0), 0.5 μM Fe, 5 μM Fe, and 5 μM Fe plus calcium carbonate (CaCO3). After assessing these results, a second experiment was conducted for 91 days, with the following treatments: Fe0, 1 μM Fe, 40 μM Fe and 40 μM Fe plus CaCO3 and sodium bicarbonate (NaHCO3). Chlorophyll of young leaves, biomass and mineral composition of leaves, stems and roots were assessed in both experiments. The ferric chelate reductase root activity (FC-R) and the genetic expression of calmodulin-regulated Ca2+-ATPase pump (ACA gene) were evaluated in experiment 2. Fe-deficient plants exhibited reduced growth and enhanced macronutrients in leaves. Root micronutrient homeostasis changed as an adaptive mechanism in carob. The addition of bicarbonate did not aggravate Fe chlorosis, as leaf chlorophyll increased significantly. Root FC-R activity and ACA gene expression was not enhanced under Fe deficiency induced by bicarbonate (Fe40 + BicNa) which suggest a positive effect of bicarbonate in the metabolism of this crop. Nevertheless, small Fe concentrations (Fe1) induced a higher ACA gene expression thus indicating some stress response signalling.

Ethylene and Phloem Signals Are Involved in the Regulation of Responses to Fe and P Deficiencies in Roots of Strategy I Plants.

Iron (Fe) and phosphorus (P) are two essential mineral nutrients whose acquisition by plants presents important environmental and economic implications. Both elements are abundant in most soils but scarcely available to plants. To prevent Fe or P deficiency dicot plants initiate morphological and physiological responses in their roots aimed to specifically acquire these elements. The existence of common signals in Fe and P deficiency pathways suggests the signaling factors must act in conjunction with distinct nutrient-specific signals in order to confer tolerance to each deficiency. Previous works have shown the existence of cross talk between responses to Fe and P deficiency, but details of the associated signaling pathways remain unclear. Herein, the impact of foliar application of either P or Fe on P and Fe responses was studied in P- or Fe-deficient plants of Arabidopsis thaliana, including mutants exhibiting altered Fe or P homeostasis. Ferric reductase and acid phosphatase activities in roots were determined as well as the expression of genes related to P and Fe acquisition. The results obtained showed that Fe deficiency induces the expression of P acquisition genes and phosphatase activity, whereas P deficiency induces the expression of Fe acquisition genes and ferric reductase activity, although only transitorily. Importantly, these responses were reversed upon foliar application of either Fe or P on nutrient-starved plants. Taken together, the results reveal interactions between P- and Fe-related phloem signals originating in the shoots that likely interact with hormones in the roots to initiate adaptive mechanisms to tolerate deficiency of each nutrient.

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.

\u2018Candidatus Phytoplasma solani\u2019 interferes with the distribution and uptake of iron in tomato

Background‘Candidatus Phytoplasma solani’ is endemic in Europe and infects a wide range of weeds and cultivated plants. Phytoplasmas are prokaryotic plant pathogens that colonize the sieve elements of their host plant, causing severe alterations in phloem function and impairment of assimilate translocation. Typical symptoms of infected plants include yellowing of leaves or shoots, leaf curling, and general stunting, but the molecular mechanisms underlying most of the reported changes remain largely enigmatic. To infer a possible involvement of Fe in the host-phytoplasma interaction, we investigated the effects of ‘Candidatus Phytoplasma solani’ infection on tomato plants (Solanum lycopersicum cv. Micro-Tom) grown under different Fe regimes.ResultsBoth phytoplasma infection and Fe starvation led to the development of chlorotic leaves and altered thylakoid organization. In infected plants, Fe accumulated in phloem tissue, altering the local distribution of Fe. In infected plants, Fe starvation had additive effects on chlorophyll content and leaf chlorosis, suggesting that the two conditions affected the phenotypic readout via separate routes. To gain insights into the transcriptional response to phytoplasma infection, or Fe deficiency, transcriptome profiling was performed on midrib-enriched leaves. RNA-seq analysis revealed that both stress conditions altered the expression of a large (> 800) subset of common genes involved in photosynthetic light reactions, porphyrin / chlorophyll metabolism, and in flowering control. In Fe-deficient plants, phytoplasma infection perturbed the Fe deficiency response in roots, possibly by interference with the synthesis or transport of a promotive signal transmitted from the leaves to the roots.Conclusions‘Candidatus Phytoplasma solani’ infection changes the Fe distribution in tomato leaves, affects the photosynthetic machinery and perturbs the orchestration of root-mediated transport processes by compromising shoot-to-root communication.