Iron Uptake In Plants Research Articles

The transcription factor Dof3.6/OBP3 regulates iron homeostasis in Arabidopsis.

Iron is an essential element for plants. Iron uptake by plants is highly regulated, but the underlying mechanism is poorly understood. Using a truncated fragment of the iron deficiency-responsive bHLH100 gene promoter, we screened the Arabidopsis transcription factor yeast one-hybrid (Y1H) library and identified the DOF family protein, OBP3, as a crucial component of the iron deficiency-signaling pathway. OBP3 is a transcriptional repressor with a C-terminal activation domain. Its expression is induced by iron deficiency. The transgenic lines that overexpress OBP3 exhibited iron overload and premature leaf necrosis, while the obp3 mutant was less tolerant of iron deficiency. It was discovered that OBP3 directly targets the Ib subgroup of bHLH gene promoters. OBP3 interacts with the bHLH transcription factor ILR3 (IAA-LEUCINE RESISTANT3), and their interaction enhances the DNA-binding ability and transcriptional promoting activity of OBP3, resulting in the positive regulation of iron deficiency-response genes. In addition, the E3 Ligase BRUTUS facilitates 26S proteasome-mediated degradation of OBP3 protein to prevent excessive iron uptake in plants. In conclusion, our research emphasizes the vital role of OBP3 in regulating plant iron homeostasis.

Initial agronomic benefits of enhanced weathering using basalt: A study of spring oat in a temperate climate.

Addressing soil nutrient degradation and global warming requires novel solutions. Enhanced weathering using crushed basalt rock is a promising dual-action strategy that can enhance soil health and sequester carbon dioxide. This study examines the short-term effects of basalt amendment on spring oat (Avena sativa L.) during the 2022 growing season in NE England. The experimental design consisted of four blocks with control and basalt-amended plots, and two cultivation types within each treatment, laid out in a split plot design. Basalt (18.86 tonnes ha-1) was incorporated into the soil during seeding. Tissue, grain and soil samples were collected for yield, nutrient, and pH analysis. Basalt amendment led to significantly higher yields, averaging 20.5% and 9.3% increases in direct drill and ploughed plots, respectively. Soil pH was significantly higher 256 days after rock application across cultivation types (direct drill: on average 6.47 vs. 6.76 and ploughed: on average 6.69 vs. 6.89, for control and basalt-amended plots, respectively), likely due to rapidly dissolving minerals in the applied basalt, such as calcite. Indications of growing season differences in soil pH are observed through direct measurement of lower manganese and iron uptake in plants grown on basalt-amended soil. Higher grain and tissue potassium, and tissue calcium uptake were observed in basalt-treated crops. Notably, no accumulation of potentially toxic elements (arsenic, cadmium, chromium, nickel) was detected in the grain, indicating that crops grown using this basaltic feedstock are safe for consumption. This study indicates that basalt amendments can improve agronomic performance in sandy clay-loam agricultural soil under temperate climate conditions. These findings offer valuable insights for producers in temperate regions who are considering using such amendments, demonstrating the potential for improved crop yields and environmental benefits while ensuring crop safety.

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

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

Genetic basis of the historical iron-accumulating dgl and brz mutants in pea.

The Pisum sativum (pea) mutants degenerate leaves (dgl) and bronze (brz) accumulate large amounts of iron in leaves. First described several decades ago, the two mutants have provided important insights into iron homeostasis in plants but the underlying mutations have remained unknown. Using exome sequencing we identified an in-frame deletion associated with dgl in a BRUTUS homolog. The deletion is absent from wild type and the original parent line. BRUTUS belongs to a small family of E3 ubiquitin ligases acting as negative regulators of iron uptake in plants. The brz mutation was previously mapped to chromosome 4, and superimposing this region to the pea genome sequence uncovered a mutation in OPT3, encoding an oligopeptide transporter with a plant-specific role in metal transport. The causal nature of the mutations was confirmed by additional genetic analyses. Identification of the mutated genes rationalizes many of the previously described phenotypes and provides new insights into shoot-to-root signaling of iron deficiency. Furthermore, the non-lethal mutations in these essential genes suggest new strategies for biofortification of crops with iron.

A molecular link between organ size control and iron uptake in plants.

A molecular link between organ size control and iron uptake in plants.

Simultaneous Enhancement of iron Deficiency Tolerance and Iron Accumulation in Rice by Combining the Knockdown of OsHRZ Ubiquitin Ligases with the Introduction of Engineered Ferric-chelate Reductase

Iron is an essential micronutrient for living organisms, but its solubility is extremely low under alkaline conditions. Plants often suffer from iron deficiency chlorosis in calcareous soils, which consist of approximately 30% of the world’s cultivated area, severely limiting plant productivity. Iron deficiency anemia is also a widespread problem in humans, especially in Asian and African people who take up iron mainly from staple foods containing low iron concentrations. Transgenic manipulation of genes involved in plant iron uptake, translocation, and storage has made improvements in enhancing iron deficiency tolerance or iron accumulation in edible parts, but these two properties have been characterized separately. We previously produced transgenic rice lines, with concomitant improvement of iron deficiency tolerance and grain iron accumulation by knocking-down OsHRZ ubiquitin ligases, which negatively regulate iron deficiency response and iron accumulation in rice. In the present report, we aimed to further improve the iron deficiency tolerance and grain iron accumulation of OsHRZ knockdown rice by the simultaneous introduction of the engineered ferric-chelate reductase gene Refre1/372 under the control of the OsIRT1 promoter for further enhancement of iron uptake. We obtained several transgenic rice lines with repressed OsHRZ expression and induced Refre1/372 expression. These lines showed a variable degree of iron deficiency tolerance in calcareous soils, with increased iron accumulation in brown seeds under both iron-deficient and iron-sufficient soil cultures. Selected OsHRZ knockdown plus Refre1/372 lines showed similar or better growth compared with that of singly introduced OsHRZ knockdown or Refre1/372 lines in calcareous soils under both non-submerged and submerged conditions. After submerged calcareous soil cultivation, these OsHRZ knockdown plus Refre1/372 lines accumulated 2.5–4.3 times and 17–23 times more iron concentrations than that of non-transformants in brown rice and straw, respectively, which was comparable or superior to a single OsHRZ knockdown line. Our results indicate that the combined introduction of OsHRZ knockdown and OsIRT1 promoter-Refre1/372 is highly effective in further improving the iron deficiency tolerance without compromising the iron accumulation of the OsHRZ knockdown effects.

Importance of the Rhizosphere Microbiota in Iron Biofortification of Plants.

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

Iron chelating bacteria: a carrier for biofortification and plant growth promotion

Biofortification is the process by which the nutritional quality of food crops is improved through agronomic practices, conventional plant breeding, or modern biotechnology to focus on malnourishment in developing countries. Under iron restricted environment certain bacteria (iron chelating bacteria) produced iron chelating molecules called as siderophore. This review gives an overview of Need for biofortification, Plant growth promoting rhizobacteria, Plant growth promoting consortia, importance of iron for human health, uptake of iron in plants, iron chelating (siderophore producing) bacteria as plant growth promotor, siderophore, generalized mechanism for siderophore-mediated iron transport in bacteria and the possible approaches to enhancing iron content in plants by implementing iron chelating bacteria as biotechnological carrier for increasing plant nutrition, yield and quality.
 
 
 

The Potential of Plant-Based Compounds As Iron Chelators

Introduction: The use of iron-chelators is an important clinical treatment for iron overload diseases such as β-Thalassemia (Thal) and neurodegeneration with brain iron accumulation. Iron overload can impair immune cell, cardiac and neurological function. Iron chelation can alleviate some of this morbidity, but at increasing doses certain chelating agents can have serious side effects. Plant-based treatments may offer an alternative. In plants, Fe is required for photosynthesis and enzyme production but is often limited for uptake from the soil. When Fe is limited, plant roots may produce a range of compounds, including chelators, to assist in solubilizing Fe precipitates. Plant-produced phenolic acids such as p-coumaric acid (Cou), caffeic acid (Caf), or chlorogenic acid (CGA) have shown an affinity for Fe and may play a role in plant iron uptake. Plants adapted to environments where Fe is more difficult to access, such as alkaline soils, could show a higher prevalence of these compounds, along with plants generally abundant in phenolics. In this project, the alkaline tolerant plants Thuja plicata (cedar) and Lavandula x intermedia (lavender), along with the phenolic rich Populus trichocarpa x deltoides(Poplar), were investigated for their potential to produce Fe-chelators in response to low Fe.Methods: Cedar, lavender, and poplar cuttings were clonally propagated and cultivated aeroponically to improve efficiency of root collection. Extracts or exudates from roots grown with or without Fe were isolated for characterization as Fe-chelators. Phenolics from root washings were captured with chromatography and separated by collection into fractions in different solvents. These were evaluated for total phenolic concentration against gallic acid as a standard. An in vitro competition assay was used to characterize Fe-binding ability of root isolates. Isolates were compared to standard chelators DFO and EDTA, and model compounds Cou, Caf, and CGA to determine inhibition of the competition reaction. A bioassay quantified intracellular Fe in monocytic THP-1 cells (to model RE system) grown for 8 weeks with chronic relevant non-transferrin bound iron levels (4-20 μM Fe-citrate, CrFe) and without (Con). Cultures were also investigated for other effects of acute Fe treatment and potential chelators over time.Results: Aeroponic plant cultivation improved root health and growth compared to previous hydroponic methods. Fe-deficient plants produced isolates that were different from Fe-normal plants following an analysis of phenolic fractions. Isolates in isopropanol were found to be 104% more plentiful in Fe-deficient poplars, which may indicate Fe-chelating potential. Between species, lavender had the highest phenolic concentration in root isolates, followed by cedar and poplar. Cedar roots showed an increased composition of phenolics compared to Fe-deficient poplar, supporting the potential for species-specific Fe responses. Analysis of Fe responses between species is ongoing. Competition assays showed that lavender root isolates exhibited 36% greater inhibition than 80 μM EDTA and 46% greater than 100 μM DFO. In direct comparison to DFO at 50 μM, Caf was equivalent, CGA had 30% greater inhibition, and inhibition by Cou was 41% lower. CrFe cells had 104% greater intracellular Fe compared to Con cells. Addition of acute Fe over 24 h significantly increased Fe content of cells grown in both CrFe and Con conditions and altered cell viability. A dose-dependent reduction in Fe levels was seen with increasing CGA in both CrFe and Con cells. Overall, Fe in samples treated with CGA were comparable to those with DFO. The effect of plant root isolates on intracellular Fe and cell viability is ongoing.Conclusion: Plant species from different soil types have altered responses to Fe-deficiency. Lavender and cedar, more tolerant of unfavorable soils, may produce more Fe-chelating phenolics as part of their response to low Fe. This was observed in vitro, as lavender isolates contain chelators that stimulate inhibition of the competition reaction similarly to DFO and EDTA at moderate concentrations. As a model, Caf, CGA and Cou also prove to have Fe-chelating activity comparable to DFO at lower concentrations. After using these plant compounds in bioassays, their successful reduction of intracellular Fe in CrFe THP-1 cells show the promise of plant root isolates to be clinically useful Fe-chelators. DisclosuresNo relevant conflicts of interest to declare.

Comparative RNA-seq analysis of nickel hyperaccumulating and non-accumulating populations of Senecio coronatus (Asteraceae).

Most metal hyperaccumulating plants accumulate nickel, yet the molecular basis of Ni hyperaccumulation is not well understood. We chose Senecio coronatus to investigate this phenomenon as this species displays marked variation in shoot Ni content across ultramafic outcrops in the Barberton Greenstone Belt (South Africa), thus allowing an intraspecific comparative approach to be employed. No correlation between soil and shoot Ni contents was observed, suggesting that this variation has a genetic rather than environmental basis. This was confirmed by our observation that the accumulation phenotype of plants from two hyperaccumulator and two non-accumulator populations was maintained when the plants were grown on a soil mix from these four sites for 12months. We analysed the genetic variation among 12 serpentine populations of S.coronatus, and used RNA-seq for de novo transcriptome assembly and analysis of gene expression in hyperaccumulator versus non-accumulator populations. Genetic analysis revealed the presence of hyperaccumulators in two well supported evolutionary lineages, indicating that Ni hyperaccumulation may have evolved more than once in this species. RNA-Seq analysis indicated that putative homologues of transporters associated with root iron uptake in plants are expressed at elevated levels in roots and shoots of hyperaccumulating populations of S.coronatus from both evolutionary lineages. We hypothesise that Ni hyperaccumulation in S.coronatus may have evolved through recruitment of these transporters, which play a role in the iron-deficiency response in other plant species.

One way. Or another? Iron uptake in plants.

Iron (Fe) and phosphorus (P), the latter taken up by plants as phosphate (Pi), are two essential nutrients that determine species distribution and often limit crop yield as a result of their low availability in most soils. Pi-deficient plants improve the interception of Pi by increasing the density of root hairs, thereby expanding the volume of soil to be explored. The increase in root-hair frequency results mainly from attenuated primary root growth, a process that was shown to be dependent on the availability of external Fe. Recent data support a hypothesis in which cell elongation during Pi starvation is tuned by depositing Fe in the apoplast of cortical cells in the root elongation zone. Uptake of Fe under Pi starvation appears to proceed via an alternative, as yet unidentified, route that bypasses the default Fe transporter. Fe deposits acquired through this noncanonical Fe-uptake pathway compromises cell-to-cell communication that is critical for proper morphogenesis of epidermal cells and leads to shorter cells and higher root-hair density. An auxiliary Fe-uptake system might not only be crucial for recalibrating cell elongation in Pi-deficient plants but may also have general importance for growth on Pi- or Fe-poor soils by balancing the Pi and Fe supply.

Root-level inoculation with iron-reducing microorganisms does not enhance iron uptake by southern highbush blueberry plants

The rate-limiting step in the iron uptake mechanism of strategy-I plants is ferric chelate reductase (FCR)-mediated iron reduction. Southern highbush blueberry (SHB, Vaccinium corymbosum L. interspecific hybrids) is a specialty crop that commonly exhibits iron deficiency in agricultural soils due to its low FCR activity. Extracellular iron reduction has been reported in some fungi and peronosporomycetes (subsequently referred to as oomycetes), and this has the potential to increase iron reduction capacity in the rhizosphere and impact plant iron uptake. Here, we isolated and identified fungi and oomycetes from the roots and nutrient solution of hydroponically grown SHB. Then, we built a consortium of iron-reducing microorganisms and used this to study the iron nutrition of inoculated and non-inoculated SHB plants in vitro and ex vitro. We found isolates of nine fungal species and the oomycete Pythium irregulare complex, all of which exhibited detectable levels of extracellular iron reduction. Isolates of Alternaria alternata, Bjerkandera adusta, and Pythium irregulare exhibited extracellular iron reduction that was equal to or higher than that of SHB roots, and they were used to create a microbial consortium for the inoculation experiments. In vitro, inoculation with a consortium of iron-reducing microorganisms did not affect iron reduction capacity in the SHB rhizosphere under iron deficiency conditions, but it increased iron reduction capacity in the SHB rhizosphere under iron abundance conditions. Nevertheless, inoculation treatments generally decreased SHB iron uptake from the medium. Ex vitro, inoculation with a consortium of iron-reducing microorganisms did not affect iron reduction capacity in the SHB rhizosphere. In all experiments, the inoculation treatment did not increase leaf active iron concentration. Altogether, our results suggest that inoculation with iron-reducing microorganisms is not a viable alternative for enhancing SHB iron nutrition.

Crosstalk between Gibberellin Signaling and Iron Uptake in Plants: An Achilles’ Heel for Modern Cereal Varieties?

Plants utilize sophisticated morphological and physiological mechanisms to acquire iron from soil. In this issue of Developmental Cell,Wild et al. (2016) find that the hormone signal gibberellic acid is key in integrating these responses, raising questions about the impact of altering GA responses in modern cereal varieties on iron acquisition.

Burkholderia phytofirmans Inoculation-Induced Changes on the Shoot Cell Anatomy and Iron Accumulation Reveal Novel Components of Arabidopsis-Endophyte Interaction that Can Benefit Downstream Biomass Deconstruction.

It is known that plant growth promoting bacteria (PGPB) elicit positive effects on plant growth and biomass yield. However, the actual mechanism behind the plant-PGPB interaction is poorly understood, and the literature is scarce regarding the thermochemical pretreatability and enzymatic degradability of biomass derived from PGPB-inoculated plants. Most recent transcriptional analyses of PGPB strain Burkholderia phytofirmans PsJN inoculating potato in literature and Arabidopsis in our present study have revealed the expression of genes for ferritin and the biosynthesis and transport of siderophores (i.e., the molecules with high affinity for iron), respectively. The expression of such genes in the shoots of PsJN-inoculated plants prompted us to propose that PsJN-inoculation can improve the host plant's iron uptake and accumulation, which facilitates the downstream plant biomass pretreatment and conversion to simple sugars. In this study, we employed B. phytofirmans PsJN to inoculate the Arabidopsis thaliana plants, and conducted the first investigation for its effects on the biomass yield, the anatomical organization of stems, the iron accumulation, and the pretreatment and enzymatic hydrolysis of harvested biomass. The results showed that the strain PsJN stimulated plant growth in the earlier period of plant development and enlarged the cell size of stem piths, and it also indeed enhanced the essential metals uptake and accumulation in host plants. Moreover, we found that the PsJN-inoculated plant biomass released more glucose and xylose after hot water pretreatment and subsequent co-saccharification, which provided a novel insight into development of lignocellulosic biofuels from renewable biomass resources.

Cytochrome b5 Reductase 1 Triggers Serial Reactions that Lead to Iron Uptake in Plants

Rhizosphere acidification is essential for iron (Fe) uptake into plant roots. Plasma membrane (PM) H+-ATPases play key roles in rhizosphere acidification. However, it is not fully understood how PM H+-ATPase activity is regulated to enhance root Fe uptake under Fe-deficient conditions. Here, we present evidence that cytochrome b5 reductase 1 (CBR1) increases the levels of unsaturated fatty acids, which stimulate PM H+-ATPase activity and thus lead to rhizosphere acidification. CBR1-overexpressing (CBR1-OX) Arabidopsis thaliana plants had higher levels of unsaturated fatty acids (18:2 and 18:3), higher PM H+-ATPase activity, and lower rhizosphere pH than wild-type plants. By contrast, cbr1 loss-of-function mutant plants showed lower levels of unsaturated fatty acids and lower PM H+-ATPase activity but higher rhizosphere pH. Reduced PM H+-ATPase activity in cbr1 could be restored in vitro by addition of unsaturated fatty acids. Transcript levels of CBR1, fatty acids desaturase2 (FAD2), and fatty acids desaturase3 (FAD3) were increased under Fe-deficient conditions. We propose that CBR1 has a crucial role in increasing the levels of unsaturated fatty acids, which activate the PM H+-ATPase and thus reduce rhizosphere pH. This reaction cascade ultimately promotes root Fe uptake.

Getting to the root of plant iron uptake and cell-cell transport: Polarity matters!

Plasma membrane proteins play pivotal roles in mediating responses to endogenous and environmental cues. Regulation of membrane protein levels and establishment of polarity are fundamental for many cellular processes. In plants, IRON-REGULATED TRANSPORTER 1 (IRT1) is the major root iron transporter but is also responsible for the absorption of other divalent metals such as manganese, zinc and cobalt. We recently uncovered that IRT1 is polarly localized to the outer plasma membrane domain of plant root epidermal cells upon depletion of its secondary metal substrates. The endosome-recruited FYVE1 protein interacts with IRT1 in the endocytic pathway and plays a crucial role in the establishment of IRT1 polarity, likely through its recycling to the cell surface. Our work sheds light on the mechanisms of radial transport of nutrients across the different cell types of plant roots toward the vascular tissues and raises interesting parallel with iron transport in mammals.

Hydrolysed wool: a novel soil amendment for zinc and iron biofortification of wheat

Biofortification—with either the application of zinc and iron fertilizer or the application of amendments to increase their bioavailability in soil—is a possible strategy to tackle worldwide micronutrient malnutrition. We investigated the effect of hydrolysed wool on the uptake of zinc and iron by wheat (Triticum aestivum var. Greina). We performed pot experiments in which either hydrolysed wool or mineral fertilizer of the same elemental composition was incorporated into a loamy-sand collected from an agricultural field. Zinc grain concentrations were 37.7 mg kg−1 (control), 45.5 mg kg−1 (mineral fertilization) and 54.1 mg kg−1 (hydrolysed wool). In addition, hydrolysed wool application increased grain yield 2-fold and grain protein content 1.5-fold, compared with 1.4-fold and 1.3-fold, respectively, by the mineral fertilizer. We propose that hydrolysed wool could be used to supplement other fertilizers, enhancing the latter with an easily available N source as well as promoting zinc and iron uptake in plants.

The Iron Assimilatory Protein, FEA1, from Chlamydomonas reinhardtii Facilitates Iron-Specific Metal Uptake in Yeast and Plants.

We demonstrate that the unique green algal iron assimilatory protein, FEA1, is able to complement the Arabidopsis iron-transporter mutant, irt1, as well as enhance iron accumulation in FEA1 expressing wild-type plants. Expression of the FEA1 protein reduced iron-deficient growth phenotypes when plants were grown under iron limiting conditions and enhanced iron accumulation up to fivefold relative to wild-type plants when grown in iron sufficient media. Using yeast iron-uptake mutants, we demonstrate that the FEA1 protein specifically facilitates the uptake of the ferrous form of iron. Significantly, the FEA1 protein does not increase sensitivity to toxic concentrations of competing, non-ferrous metals nor facilitate their (cadmium) accumulation. These results indicate that the FEA1 protein is iron specific consistent with the observation the FEA1 protein is overexpressed in cadmium stressed algae presumably to facilitate iron uptake. We propose that the FEA1 iron assimilatory protein has ideal characteristics for the iron biofortification of crops and/or for facilitated iron uptake in plants when they are grown in low iron, high pH soils, or soils that may be contaminated with heavy metals.

Effect of Nostoc sp. on soil characteristics, plant growth and nutrient uptake

The arid desert area is expanding by 6 million ha year−1. Nostoc, a terrestrial cyanobacterium, is known as a pioneer organism which can photosynthesize, fix atmospheric nitrogen, and secrete polysaccharides. In order to explore the potential of Nostoc as a countermeasure to soil desertification, we have investigated the effects of Nostoc on the chemical and physical properties of soil and on plant growth in outdoor and laboratory experiments. The effect of Nostoc on soil properties, when applied on the surface of soil in plastic containers, was determined after cultivation for 90 days outdoors. Its effect on plant growth and nutrient uptake was determined by growing Nostoc with Komatsuna (Brassica rapa var. peruviridis) on a soil-less culture in a plastic petri dish incubated inside a growth chamber for 14 days. Two colonies of Nostoc with different shapes were also examined for their tolerance to dryness and salinity. Nostoc application resulted in an increase in the organic carbon and nitrogen content of the surface soil and enhanced plant growth and plant iron uptake, but soil temperature and moisture were maintained. Spherical-shaped Nostoc showed a higher tolerance to dryness and salinity than irregular-shaped Nostoc, and the former was able to rectify problematic soil better than the latter. The results indicate that the application of Nostoc to soil has a potential for increasing soil organic matter and reclaiming degraded soil ecosystems.

Mining iron: Iron uptake and transport in plants

Iron uptake in plants is highly regulated in order to supply amounts sufficient for optimal growth while preventing excess accumulation. In response to iron deficiency, plants induce either reduction-based or chelation-based mechanisms to enhance iron uptake from the soil. Genes involved in each mechanism have been identified from various model plants including Arabidopsis and rice. Iron transport within plants is also tightly controlled. New information has emerged on transporters that play a role in xylem loading and phloem loading/unloading of iron, and on the iron chelators involved in iron homeostasis. Some of the components regulating iron deficiency responses also have been elucidated, demonstrating that iron dependent gene regulation occurs at both the transcriptional and post-transcriptional levels.