Fe Translocation Research Articles

Potassium ameliorates iron deficiency by facilitating the remobilization of iron from root cell walls and promoting its translocation from roots to shoots

Iron (Fe) is a vital microelement, and is beneficial for living organisms. Several studies have demonstrated that ample supplied of potassium (K) can alleviate Fe-deficiency-induced chlorosis in plants. In this work, the mechanism underlying K-mediated amelioration of Fe deficiency in Arabidopsis was investigated. Five-week-old Arabidopsis thaliana (Col-0) plants with similar sizes were grown either on complete nutrient solution (+Fe + K) or lacking of K (+Fe–K) or lacking of Fe (–Fe + K), or lacking both of Fe and K (–Fe–K) for 4 days:. The plants were then harvested, and their Fe content, soluble Fe content, phenolic compounds content, Fe translocation and uptake-related genes expression levels, polysaccharides concentration were analyzed, moreover, we also determined the pectin methylesterase activity and its methylation. Under Fe deficiency, K-deficient plants accumulated higher amounts of root apoplastic Fe along with a higher Fe content in pectin and hemicellulose 1, and which was rapidly decreased when K was included in the nutrition solution, indicating the operation of a cell wall Fe-remobilization mechanism. Under Fe-deficient condition, K supply significantly increased the secretion of phenolic compounds and the degree of pectin methylation, while decreased pectin and hemicellulose 1 contents as compared with –Fe–K, thereby promoting Fe reutilization from root cell walls. Furthermore, K supply also enhanced the reutilization of Fe from vacuoles through up-regulation of AtNRAMP3 expression. In addition, K supply stimulated several genes associated with long-distance transport of Fe expression, including AtFRD3, AtYSL2, and AtNAS1, suggesting ample K supply can enhance Fe transportation from roots to leaves. Stimulation of Fe reutilization from cell walls and vacuoles, as well as an enhancement of Fe transportation from roots to leaves were the major mechanism underlying K-mediated amelioration of Fe-deficiency in Arabidopsis plants.

Potassium Ion Channel Gene OsAKT1 Affects Iron Translocation in Rice Plants Exposed to Iron Toxicity.

Iron toxicity is one of the most widely spread mineral disorders in anaerobic soils, but the tolerance mechanisms in plants are poorly understood. Here we characterize the involvement of a rice potassium ion channel gene, OsAKT1, in Fe toxic conditions. Two knock-down lines of OsAKT1 together with azygos lines were investigated. Mutant lines did not differ from azygos lines regarding plant growth, gas exchange rate or chlorophyll fluorescence in control conditions. However, loss-of-function of OsAKT1 increased the sensitivity to excess Fe regarding leaf bronzing symptoms, reactive oxygen species generation, leaf spectral reflectance indices, and chlorophyll fluorescence. Fe toxicity leads to largely reduced uptake of other nutrients into shoots, which illustrates the complexity of Fe stress related to multiple mineral disorders. Less potassium uptake in the mutants compared to azygos lines co-occurred with higher amounts of Fe accumulated in the shoot tissues but not in the roots. These results were consistent with a higher level of Fe loaded into the xylem sap of mutants compared to azygos lines in the early phase of Fe toxicity. In conclusion, OsAKT1 is crucial for the tolerance of rice against Fe toxicity as K homeostasis affects Fe translocation from root to shoot.

AhFRDL1-mediated citrate secretion contributes to adaptation to iron deficiency and aluminum stress in peanuts.

Although citrate transporters are involved in iron (Fe) translocation and aluminum (Al) tolerance in plants, to date none of them have been shown to confer both biological functions in plant species that utilize Fe-absorption Strategy I. In this study, we demonstrated that AhFRDL1, a citrate transporter gene from peanut (Arachis hypogaea) that is induced by both Fe-deficiency and Al-stress, participates in both root-to-shoot Fe translocation and Al tolerance. Expression of AhFRDL1 induced by Fe deficiency was located in the root stele, but under Al-stress expression was observed across the entire root-tip cross-section. Overexpression of AhFRDL1 restored efficient Fe translocation in Atfrd3 mutants and Al resistance in AtMATE-knockout mutants. Knocking down AhFRDL1 in the roots resulted in reduced xylem citrate and reduced concentrations of active Fe in young leaves. Furthermore, AhFRDL1-knockdown lines had reduced root citrate exudation and were more sensitive to Al toxicity. Compared to an Al-sensitive variety, enhanced AhFRDL1 expression in an Fe-efficient variety contributed to higher levels of Al tolerance and Fe translocation by promoting citrate secretion. These results indicate that AhFRDL1 plays a significant role in Fe translocation and Al tolerance in Fe-efficient peanut varieties under different soil-stress conditions. Given its dual biological functions, AhFRDL1 may serve as a useful genetic marker for breeding for high Fe efficiency and Al tolerance.

Combined deficiency of nitrogen and iron increases senescence induced remobilization of plant immobile iron in wheat

Iron (Fe), an important micronutrient and a critical determinant of plant growth and human nutrition, is deficient in cultivable soils and limits crop productivity and nutritional quality of food grains. Plants tolerant to Fe deficiency reveal either or all of these i.e., a higher uptake of Fe, better root to shoot partitioning of Fe or a higher remobilization of relatively immobile Fe. The physiological and biochemical regulators of in-plant Fe-remobilization are not clearly understood. The present study was conducted to elucidate the effect of Fe and nitrogen (N) deficiency, either alone or in combination, on plant growth attributes, shoot, root Fe and N uptake and Fe remobilization from a fully developed 2nd older leaf (OL) to a younger developing 3rd leaf (YL) in bread and durum wheat. Dual nutrient deficiency of N and Fe induced senescence, measured in terms of reduced chlorophyll and higher expression of NAM-B1activity. High nitrogen availability reduced Fe translocation as evident from a higher Fe retention in OL under N sufficient treatments (N+Fe+ and N+Fe−) than the N deficient treatments (N−Fe+ and N−Fe−) and could be correlated with transcript level expression of the DMAS gene. The present study provides evidence for the N and Fe deficiency induced senescence as the key determinant of Fe-remobilization in wheat, facilitated by a hyped biosynthesis of phytosiderophore. The results indicate that any favourable manipulation or selection for higher Fe remobilization process could improve nutrient deficiency tolerance of wheat and aid in grain biofortification.

Autophagy is essential for optimal translocation of iron to seeds in Arabidopsis.

Micronutrient deficiencies affect a large part of the world's population. These deficiencies are mostly due to the consumption of grains with insufficient content of iron (Fe) or zinc (Zn). Both de novo uptake by roots and recycling from leaves may provide seeds with nutrients. Autophagy, which is a conserved mechanism for nutrient recycling in eukaryotes, was shown to be involved in nitrogen remobilization to seeds. Here, we have investigated the role of this mechanism in micronutrient translocation to seeds. We found that Arabidopsis thaliana plants impaired in autophagy display defects in nutrient remobilization to seeds. In the atg5-1 mutant, which is completely defective in autophagy, the efficiency of Fe translocation from vegetative organs to seeds was severely decreased even when Fe was provided during seed formation. Combining atg5-1 with the sid2 mutation that counteracts premature senescence associated with autophagy deficiency and using 57Fe pulse labeling, we propose a two-step mechanism in which Fe taken up de novo during seed formation is first accumulated in vegetative organs and subsequently remobilized to seeds. Finally, we show that translocation of Zn and manganese (Mn) to seeds is also dependent on autophagy. Fine-tuning autophagy during seed formation opens up new possibilities to improve micronutrient remobilization to seeds.

Nutrient acquisition and eucalyptus growth affected by humic acid sources and concentrations

Humic acid (HA) can increase eucalyptus growth due to its biostimulant effect and improvement in plant nutrient uptake. Magnitude of these stimuli varies according to the source, chemical composition, presence of bioactive fragments, and concentration of HA. The aim of this study was to evaluate the effect of HA sources and concentrations on dry matter, accumulation and uptake efficiency (UpE) of nutrients for eucalyptus seedlings cultivated in nutrient solution. A randomized block experimental design was adopted, with four replications, in a 3x4+1 factorial scheme, in which three sources of HA (HA-L1 and HA-L2, derived from different commercial HA extracted from leonardite with 0.5 mol L-1 NaOH and 0.5 mol L-1 KOH, respectively, and HA-Com, which was extracted from compost with 0.5 mol L-1 KOH) were combined with four concentrations of C-HA (5, 10, 25, and 100 mg L-1) as well as a control treatment in which eucalyptus was cultivated without HA. Eucalyptus seedlings were grown for 20 days, maintaining three plants per pot. At the end of the experiment, production of shoot dry matter (SDM), root dry matter (RDM), and total dry matter (TDM); the Root: Shoot dry matter ratio; and the accumulations of N, P, K, Ca, B, Cu, Fe, and Zn in the shoot and root were evaluated as well as the UpE of these nutrients by the seedlings. Maximum production of SDM was reached at the concentrations of 14 and 13.5 mg L-1 of C-HA, for HA-L1 and HA-Com, respectively. The RDM increased with the use of HA-Com, with optimal concentration of 55 mg L-1 of C-HA. Accumulation of Fe in the eucalyptus shoot decreased in HA-treated pots, compromising Fe translocation from the root to the shoot. Regardless of HA source used, Cu accumulation by plants diminishes as C-HA concentration increases. A greater growth of eucalyptus at concentrations lower than 15 mg L-1 of C-HA occurs more through the stimulus to shoot and root growth than due to greater acquisition and UpE of nutrients by plants. Use of high concentrations of C-HA requires greater concentration of some micronutrients in the nutrient solution tested.

Differential effects of iron starvation and iron excess on nickel uptake kinetics in two Iranian nickel hyperaccumulators, Odontarrhena bracteata and Odontarrhena inflata

To characterize Ni hyperaccumulation mechanisms in naturally Ni-hyperaccumulating Odontarrhena species, Ni uptake kinetics, and the effect of Fe starvation and Fe or Zn excess thereon, were investigated in the Iranian serpentine endemics O. bracteata (one population) and O. inflata (two populations). Plants were exposed to a series of Ni concentrations for 4 h, and Ni uptake rates were plotted against the Ni concentration in the solution. Kinetic parameters, Km and Vmax, were calculated from Lineweaver-Burke plots. Ni uptake consistently showed Michaelis–Menten kinetics. Under normal Fe supply the Km was not significantly different between species or populations, however, the Vmax was 3-fold higher in O. bracteata and O. inflata from Baneh than in O. inflata from Marivan. The rate of Ni translocation to the shoot was similar in all of the species/populations. Fe starvation (1 wk) significantly increased the Vmax for Ni uptake in O. bracteata, but not in O. inflata, and a very similar increase in Fe uptake capacity in all the species/populations. Fe excess in the nutrient solution significantly increased the Km for Ni uptake in O. bracteata, but not in O. inflata. Zn excess in the nutrient solution (300 μM) marginally inhibited Ni uptake in O. inflata, but not in O. bracteata. Ni uptake seems to proceed via a Fe deficiency-inducible Fe transporter in O. bracteata, but not in O. inflata. Ni root-to-shoot translocation seems to be mediated by a Fe deficiency-inducible Fe translocation mechanism in all of the species/populations.

Iron Retention in Root Hemicelluloses Causes Genotypic Variability in the Tolerance to Iron Deficiency-Induced Chlorosis in Maize.

Antagonistic interactions of phosphorus (P) hamper iron (Fe) acquisition by plants and can cause Fe deficiency-induced chlorosis. To determine the physiological processes underlying adverse Fe–P interactions, the maize lines B73 and Mo17, which differ in chlorosis susceptibility, were grown hydroponically at different Fe:P ratios. In the presence of P, Mo17 became more chlorotic than B73. The higher sensitivity of Mo17 to Fe deficiency was not related to Fe–P interactions in leaves but to lower Fe translocation to shoots, which coincided with a larger pool of Fe being fixed in the root apoplast of P-supplied Mo17 plants. Fractionating cell wall components from roots showed that most of the cell wall-contained P accumulated in pectin, whereas most of the Fe was bound to root hemicelluloses, revealing that co-precipitation of Fe and P in the apoplast was not responsible for Fe inactivation in roots. A negative correlation between chlorophyll index and hemicellulose-bound Fe in 85 inbred lines of the intermated maize B73 × Mo17 (IBM) population indicated that apoplastic Fe retention contributes to genotypic differences in chlorosis susceptibility of maize grown under low Fe supplies. Our study indicates that Fe retention in the hemicellulose fraction of roots is an important determinant in the tolerance to Fe deficiency-induced chlorosis of graminaceous plant species with low phytosiderophore release, like maize.

Silicon induced Fe deficiency affects Fe, Mn, Cu and Zn distribution in rice (Oryza sativa L.) growth in calcareous conditions

A protective effect by silicon in the amelioration of iron chlorosis has recently been proved for Strategy 1 species, at acidic pH. However in calcareous conditions, the Si effect on Fe acquisition and distribution is still unknown. In this work, the effect of Si on Fe, Mn, Cu and Zn distribution was studied in rice (Strategy 2 species) under Fe sufficiency and deficiency. Plants (+Si or-Si) were grown initially with Fe, and then Fe was removed from the nutrient solution. The plants were then analysed using a combined approach including LA-ICP-MS images for each element of interest, the analysis of the Fe and Si concentration at different cell layers of root and leaf cross sections by SEM-EDX, and determining the apoplastic Fe, total micronutrient concentration and oxidative stress indexes. A different Si effect was observed depending on plant Fe status. Under Fe sufficiency, Si supply increased Fe root plaque formation, decreasing Fe concentration inside the root and increasing the oxidative stress in the plants. Therefore, Fe acquisition strategies were activated, and Fe translocation rate to the aerial parts was increased, even under an optimal Fe supply. Under Fe deficiency, +Si plants absorbed Fe from the plaque more rapidly than –Si plants, due to the previous activation of Fe deficiency strategies during the growing period (+Fe + Si). Higher Fe plaque formation due to Si supply during the growing period reduced Fe uptake and could activate Fe deficiency strategies in rice, making it more efficient against Fe chlorosis alterations. Silicon influenced Mn and Cu distribution in root.

Mechanisms of Exogenous Nitric Oxide and 24-Epibrassinolide Alleviating Chlorosis of Peanut Plants Under Iron Deficiency

Iron (Fe) is a crucial transition metal for all living organisms including plants; however, Fe deficiency frequently occurs in plant because only a small portion of Fe is bioavailable in soil in recent years. To cope with Fe deficiency, plants have evolved a wide range of adaptive responses from changes in morphology to altered physiology. To understand the role of nitric oxide (NO) and 24-epibrassinolide (EBR) in alleviating chlorosis induced by Fe deficiency in peanut (Arachis hypogaea L.) plants, we determined the concentration of chlorophylls, the activation, uptake, and translocation of Fe, the activities of key enzymes, such as ferric-chelate reductase (FCR), proton-translocating adenosine triphosphatase (H+-ATPase), and antioxidant enzymes, and the accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA) of peanut plants under Fe sufficiency (100 pmol L−1 ethylenediaminetetraacetic acid (EDTA)-Fe) and Fe deficiency (0 µmol L−1 EDTA-Fe). We also investigated the production of NO in peanut plants subjected to Fe deficiency with foliar application of sodium nitroprusside (SNP), a donor of NO, and/or EBR. The results showed that Fe deficiency resulted in severe chlorosis and oxidative stress, significantly decreased the concentration of chlorophylls and active Fe, and significantly increased NO production. Foliar application of NO and/or EBR increased the activity of antioxidant enzymes, superoxide dismutase, peroxidase, and catalase, and decreased the ROS and MDA concentrations, thus enhancing the resistance of plants to oxidative stress. Application of NO also significantly increased Fe translocation from the roots to the shoots and enhanced the transfer of Fe from the cell wall fraction to the cell organelle and soluble fractions. Consequently, the concentrations of available Fe and chlorophylls in the leaves were elevated. Furthermore, the activities of H+-ATPase and FCR were enhanced in the Fe-deficient plants. Simultaneously, there was a significant increase in NO production, especially in the plants that received NO, regardless of Fe supply. These suggest that NO or EBR, and, especially, their combination are effective in alleviating plant chlorosis induced by Fe deficiency.

Diverse functions of multidrug and toxin extrusion (MATE) transporters in citric acid efflux and metal homeostasis in Medicago truncatula.

The multidrug and toxin extrusion (MATE) transporter family comprises 70 members in the Medicago truncatula genome, and they play seemingly important, yet mostly uncharacterized, physiological functions. Here, we employed bioinformatics and molecular genetics to identify and characterize MATE transporters involved in citric acid export, Al3+ tolerance and Fe translocation. MtMATE69 is a citric acid transporter induced by Fe-deficiency. Overexpression of MtMATE69 in hairy roots altered Fe homeostasis and hormone levels under Fe-deficient or Fe-oversupplied conditions. MtMATE66 is a plasma membrane citric acid transporter primarily expressed in root epidermal cells. The mtmate66 mutant had less root growth than the wild type under Al3+ stress, and seedlings were chlorotic under Fe-deficient conditions. Overexpression of MtMATE66 rendered hairy roots more tolerant to Al3+ toxicity. MtMATE55 is involved in seedling development and iron homeostasis, as well as hormone signaling. The mtmate55 mutant had delayed development and chlorotic leaves in mature plants. Both knock-out and overexpression mutants of MtMATE55 showed altered Fe accumulation and abnormal hormone levels compared with the wild type. We demonstrate that the zinc-finger transcription factor MtSTOP is essentially required for MtMATE66 expression and plant resistance to H+ and Al3+ toxicity. The proper expression of two previously characterized MATE flavonoid transporters MtMATE1 and MtMATE2 also depends on several transcription factors. This study reveals not only functional diversity of MATE transporters and regulatory mechanisms in legumes against H+ and Al3+ stresses, but also casts light on their role in metal nutrition and hormone signaling under various stresses.

Transcriptional and physiological analyses of Fe deficiency response in maize reveal the presence of Strategy I components and Fe/P interactions

BackgroundUnder limited iron (Fe) availability maize, a Strategy II plant, improves Fe acquisition through the release of phytosiderophores (PS) into the rhizosphere and the subsequent uptake of Fe-PS complexes into root cells. Occurrence of Strategy-I-like components and interactions with phosphorous (P) nutrition has been hypothesized based on molecular and physiological studies in grasses.ResultsIn this report transcriptomic analysis (NimbleGen microarray) of Fe deficiency response revealed that maize roots modulated the expression levels of 724 genes (508 up- and 216 down-regulated, respectively). As expected, roots of Fe-deficient maize plants overexpressed genes involved in the synthesis and release of 2’-deoxymugineic acid (the main PS released by maize roots). A strong modulation of genes involved in regulatory aspects, Fe translocation, root morphological modification, primary metabolic pathways and hormonal metabolism was induced by the nutritional stress. Genes encoding transporters for Fe2+ (ZmNRAMP1) and P (ZmPHT1;7 and ZmPHO1) were also up-regulated under Fe deficiency.Fe-deficient maize plants accumulated higher amounts of P than the Fe-sufficient ones, both in roots and shoots. The supply of 1 μM 59Fe, as soluble (Fe-Citrate and Fe-PS) or sparingly soluble (Ferrihydrite) sources to deficient plants, caused a rapid down-regulation of genes coding for PS and Fe(III)-PS transport, as well as of ZmNRAMP1 and ZmPHT1;7.Levels of 32P absorption essentially followed the rates of 59Fe uptake in Fe-deficient plants during Fe resupply, suggesting that P accumulation might be regulated by Fe uptake in maize plants.ConclusionsThe transcriptional response to Fe-deficiency in maize roots confirmed the modulation of known genes involved in the Strategy II and revealed the presence of Strategy I components usually described in dicots. Moreover, data here presented provide evidence of a close relationship between two essential nutrients for plants, Fe and P, and highlight a key role played by Fe and P transporters to preserve the homeostasis of these two nutrients in maize plants.

Bradyrhizobia and arbuscular mycorrhizal fungi modulate manganese, iron, phosphorus, and polyphenols in soybean (Glycine max (L.) Merr.) under excess zinc

The effect of Bradyrhizobia (R) and Arbuscular mycorrhiza (AM) on manganese, iron, phosphorus, and polyphenols was investigated in soybean cultivated in Zn treated soils. In a completely randomized 3×4 factorial, the experimental treatments – Zn addition (0, 200, and 400mg Zn kg−1 of soil), and Inoculation (uninoculated control, R, AM, and R+AM dual inoculation) were set up in the greenhouse. Zinc treatment increased Zn in roots and shoots, Fe in roots, frequency of root mycorrhization, P in root, and Mn translocation; but decreased Fe translocation, Mn in root, and total polyphenols. Symbionts effected micronutrient balancing in the plants. Mycorrhizal inoculants increased Zn in shoots, and modulated Mn and Fe in shoots and roots; within the whole-plant crosstalk in Zn, Mn, and Fe status. In dual inoculation, synergy for much enhanced Mn translocation was indicated in 400mg Zn kg−1 treatment. Modulations of Zn-Mn-Fe nutrition in dual inoculation was supported with a reduction in cumulative number of fallen leaves, and increases in leaf greenness, shoot P, and root polyphenols, to give higher shoot biomass. Our results suggest the possibility of optimizing the crop production and bio-inoculation outcomes by targeting Mn and Fe status (in roots, shoots, translocation, and ratios with Zn) during cultivation under excess Zn.

Gibberellins regulate iron deficiency-response by influencing iron transport and translocation in rice seedlings (Oryza sativa).

Gibberellins (GAs) are a class of plant hormones with diverse functions. However, there has been little information on the role of GAs in response to plant nutrient deficiency. To evaluate the roles of GAs in regulation of Fe homeostasis, the effects of GA on Fe accumulation and Fe translocation in rice seedlings were investigated using wild-type, a rice mutant ( eui1 ) displaying enhnaced endogenous GA concentrations due to a defect in GA deactivation, and transgenic rice plants overexpressing OsEUI . Exposure to Fe-deficient medium significantly reduced biomass of rice plants. Both exogenous application of GA and an endogenous increase of bioactive GA enhanced Fe-deficiency response by exaggerating foliar chlorosis and reducing growth. Iron deficiency significantly suppressed production of GA 1 and GA 4 , the biologically active GAs in rice. Exogenous application of GA significantly decreased leaf Fe concentration regardless of Fe supply. Iron concentration in shoot of eui1 mutants was lower than that of WT plants under both Fe-sufficient and Fe-deficient conditions. Paclobutrazol, an inhibitor of GA biosynthesis, alleviated Fe-deficiency responses, and overexpression of EUI significantly increased Fe concentration in shoots and roots. Furthermore, both exogenous application of GA and endogenous increase in GA resulting from EUI mutation inhibited Fe translocation within shoots by suppressing OsYSL2 expression, which is involved in Fe transport and translocation. The novel findings provide compelling evidence to support the involvement of GA in mediation of Fe homeostasis in strategy II rice plants by negatively regulating Fe transport and translocation.

Effects of Exogenous Salicylic Acid and Nitric Oxide on Peanut Seedlings Growth under Iron Deficiency

ABSTRACTSalicylic acid (SA) and nitric oxide (NO), which are known as important signaling molecules in plants, could be promising compounds for the reduction in stress sensitivity. The aim of the present work was to study the physiological changes in peanut (Arachis hypogaea L.) seedlings grown in growth medium that contained 0.1 mM SA, 0.25 mM sodium nitroprusside (SNP, a NO donor), or in full (SA+SNP) or half [1/2 (SA+SNP)] combined strengths under iron (Fe) deficiency. After 21 days of treatment, Fe deficiency significantly inhibited peanut plant growth, destroyed photosynthetic system, and caused oxidative damages. Addition of SA, SNP, and 1/2 (SA+SNP), especially SA+SNP, alleviated the stress, increased the contents of chlorophylls, and promoted plant growth. They improved Fe uptake, transport, and availability in peanut plants by increasing the activities of H+-ATPase and ferric chelate reductase (FCR), and promoting Fe translocation from cell wall to cell organelle and soluble fraction in leaves. Furthermore, they also effectively mitigated oxidative damages by increasing the activities of antioxidant enzymes in peanut leaves and roots. The results from the present study indicate that application of SA, SNP, or 1/2 (SA+SNP) can overcome the adverse effect of Fe deficiency, but the combined application of SA+SNP is more effective in alleviating Fe deficiency stress.

Incorporation of iron into chloroplasts triggers the restoration of cadmium induced inhibition of photosynthesis

Photosynthetic symptoms of acute Cd stress can be remedied by elevated Fe supply. To shed more light on the most important aspects of this recovery, the detailed Fe trafficking and accumulation processes as well as the changes in the status of the photosynthetic apparatus were investigated in recovering poplar plants. The Cd-free, Fe-enriched nutrient solution induced an immediate intensive Fe uptake. The increased Fe/Cd ratio in the roots initiated the translocation of Fe to the leaf with a short delay that ultimately led to the accumulation of Fe in the chloroplasts. The chloroplast Fe uptake was directly proportional to the Fe translocation to leaves. The accumulation of PSI reaction centers and the recovery of PSII function studied by Blue-Native PAGE and chlorophyll a fluorescence induction measurements, respectively, began in parallel to the increase in the Fe content of chloroplasts. The initial reorganization of PSII was accompanied by a peak in the antennae-based non-photochemical quenching. In conclusion, Fe accumulation of the chloroplasts is a process of prime importance in the recovery of photosynthesis from acute Cd stress.

Involvement of endogenous salicylic acid in iron-deficiency responses in Arabidopsis.

Several phytohormones have been demonstrated to be involved in iron (Fe) homeostasis. We took advantage of a salicylic acid (SA) biosynthesis defective mutant phytoalexin deficient 4 (pad4: T-DNA Salk_089936) to explore the possible effects of endogenous SA on the morphological and physiological responses to Fe deprivation. The morphological and physiological analysis was carried out between Col-0 and the pad4 mutant. Under an Fe-deficiency treatment, Col-0 showed more severe leaf chlorosis and root growth inhibition compared with the pad4 mutant. The soluble Fe concentrations were significantly higher in pad4 than in Col-0 under the Fe-deficiency treatment. Fe deficiency significantly induced SA accumulation in Col-0 and the loss-of-function of PAD4 blocked this process. The requirement of endogenous SA accumulation for Fe-deficiency responses was confirmed using a series of SA biosynthetic mutants and transgenic lines. Furthermore, a comparative RNA sequencing analysis of the whole seedling transcriptomes between Col-0 and the pad4 mutant was also performed. Based on the transcriptome data, the expression levels of many auxin- and ethylene-response genes were altered in pad4 compared with Col-0. Fe deficiency increases SA contents which elevates auxin and ethylene signalling, thereby activating Fe translocation via the bHLH38/39-mediated transcriptional regulation of downstream Fe genes.

A WRKY Transcription Factor Regulates Fe Translocation under Fe Deficiency

Iron (Fe) deficiency affects plant growth and development, leading to reduction of crop yields and quality. Although the regulation of Fe uptake under Fe deficiency has been well studied in the past decade, the regulatory mechanism of Fe translocation inside the plants remains unknown. Here, we show that a WRKY transcription factor WRKY46 is involved in response to Fe deficiency. Lack of WRKY46 (wrky46-1 and wrky46-2 loss-of-function mutants) significantly affects Fe translocation from root to shoot and thus causes obvious chlorosis on the new leaves under Fe deficiency. Gene expression analysis reveals that expression of a nodulin-like gene (VACUOLAR IRON TRANSPORTER1-LIKE1 [VITL1]) is dramatically increased in wrky46-1 mutant. VITL1 expression is inhibited by Fe deficiency, while the expression of WRKY46 is induced in the root stele. Moreover, down-regulation of VITL1 expression can restore the chlorosis phenotype on wrky46-1 under Fe deficiency. Further yeast one-hybrid and chromatin immunoprecipitation experiments indicate that WRKY46 is capable of binding to the specific W-boxes present in the VITL1 promoter. In summary, our results demonstrate that WRKY46 plays an important role in the control of root-to-shoot Fe translocation under Fe deficiency condition via direct regulation of VITL1 transcript levels.

Effects of NaHCO3 on photosynthetic characteristics, and iron and sodium transfer in pomegranate

ABSTRACTIn order to study effects of sodium bicarbonate (NaHCO3) stress in irrigation water on photosynthetic characteristics and iron (Fe) and sodium (Na+) translocation content of pomegranate plants, a factorial experiment was conducted based on completely randomized design with three cultivars of pomegranate (“Gorch-e-Dadashi,” “Zagh-e-Yazdi,” and “Ghermez-e-Aliaghai”) and four concentrations of NaHCO3 (0, 5, 10, and 15 mM), with three replications. The results of plant analysis indicated that NaHCO3 affected chlorophyll index, Fv/Fm, and performance index (PI) in upper and lower leaves of shoots and also the translocation of Na+ and Fe. The results also showed that Fe translocation from root to shoot reduced at 15 mM level of NaHCO3. The highest Na translocation and the lowest Fe translocation were observed in Zagh-e-Yazdi and Ghermez-e-Aliaghai cultivars, respectively. The ratio of sodium/potassium (Na+/K+) in stems was higher than that in roots and leaves, and the observed chlorophyll content of upper leaves was also lower than that of lower leaves. Based on the measured parameters Gorch-e-Dadashi cultivar showed less relative sensitivity than other cultivars to NaHCO3 of irrigation water through maintaining the lower Na+ transport to the shoots, and improvement of Fe transport to shoots.

Role of foliar application of 24-epibrassinolide in response of peanut seedlings to iron deficiency

Limited information is available on the role of brassinosteroids (BRs) in response of plants to nutrient deficiency. To understand the functions of BRs in response to iron deficiency, we investigated the effect of 24-epibrassinolide (EBR) on activities of ferric-chelate reductase (FCR), H+-ATPase, Ca2+-ATPase, nitrate reductase (NR), antioxidant enzymes, Fe and other minerals content and distribution, chlorophylls, soluble protein, free proline, reactive oxygen species, and malondialdehyde in peanut (Arachis hypogea L.) plants subjected to Fe deficiency (10−5 M Fe(III)-EDTA) with foliar application of EBR (0, 10−8, 5.0×10−8, 10−7, 5.0×10−7, and10−6 M). Results show that EBR increased Fe translocation from roots to shoots and increased Fe content in cell organelles. Activities of antioxidant enzymes increased and so the ability of resistance to oxidative stress was enhanced. As result of enhancement of H+-ATPase and Ca2+-ATPase activities, the inhibition of Fe, Ca, Mg, and Zn uptake and distribution was ameliorated. Chlorophyll, soluble protein, and free proline content also increased and consequently, chlorosis induced by Fe deficiency was alleviated. The results demonstrate that EBR had a positive role in regulating peanut growth and development under Fe deficiency and an optimal concentration appeared to be 10−7 M.