Fe Deficiency Research Articles

Application of fluorescent transients to indicate nutrient deficiencies in a microalga Nannochloropsis oceanica

Here we studied the effects of nutrient deficiency, focusing on Ca, N, S, Mg, Fe, on photosynthetic performance of Nannochloropsis oceanica to determine the abilities of fluorescence transients to detect nutrient limitation. We conducted a two-level (replete/deplete) fully factorial experiment for each of 5 nutrients and found different responses to nutrient limitation. A potential indicator of N limitation was trapped energy per reaction center (TRO/RC), as the synthesis of photosynthetic reaction center (RC) declined under N deficiency and eventually the ratio of TRO/RC increased. Photosystem II performance measured by performance index (PIABS) was not compromised under Fe, S and Mg deficiency, whereas the impact of Ca and N was critical. Although interactive nutrient interactions on photosynthetic parameters were observed, relationships were established between net reaction closure (MO) and Mg; dissipated energy flux per RC (DIO/RC) and S; and average quantum yield of photochemistry (ΦPav) and Ca.

Fe deficiency-induced ethylene synthesis confers resistance to Botrytis cinerea.

Although iron (Fe) deficiency is an adverse condition to growth and development of plants, it increases the resistance to pathogens. How Fe deficiency induces the resistance to pathogens is still unclear. Here, we reveal that the inoculation of Botrytis cinerea activates the Fe deficiency response of plants, which further induces ethylene synthesis and then resistance to B. cinerea. FIT and bHLH Ib are a pair of bHLH transcription factors, which control the Fe deficiency response. Both the Fe deficiency-induced ethylene synthesis and resistance are blocked in fit-2 and bhlh4x-1 (a quadruple mutant for four bHLH Ib members). SAM1 and SAM2, twoethylene synthesis-associated genes, are induced by Fe deficiency in a FIT-bHLH Ib-dependent manner. Moreover, SAM1 and SAM2 are required for the increased ethylene and resistance to B. cinerea under Fe-deficient conditions. Our findings suggest that the FIT-bHLH Ib module activates the expression of SAM1 and SAM2, thereby inducing ethylene synthesis and resistance to B. cinerea. This study uncovers that Fe signaling also functions as a part of the plant immune system against pathogens.

Iron doses on growth and gas exchange of dwarf cashew seedlings

Cashew plants have shown, a few days after planting in the field, interveinal chlorosis in young leaves and, as the symptoms become worse, the leaves are completely chlorotic, a nutritional disorder that is related to iron (Fe) deficiency. Thus, the objective was to evaluate the growth and physiological responses of grafted seedlings of dwarf cashew as a function of Fe doses. The experiment was conducted in a greenhouse, in a completely randomized design, with four replicates. Treatments consisted of five doses of Fe (0; 2.5; 5; 7.5 and 10 mg L−1), using iron sulfate (20% Fe) as source. The following parameters were evaluated: growth variables – height, number of leaves, leaf area, stem diameter and dry matter (roots, shoots and total); and physiological variables – photosynthesis (A), stomatal conductance (gs), transpiration (E), water use efficiency (WUE), instantaneous carboxylation efficiency (A/Ci), photosynthetic pigments and relative chlorophyll index. Fe deficiency affected the photosynthetic process, causing significant reductions in the evaluated characteristics, indicating the need for its adequate supply for the growth of dwarf cashew plants.

The low ferric chelate reductase activity and high apoplastic pH in leaves cause iron deficiency chlorosis in ‘Huangguan’ pears grafted onto quince A grown in calcareous soil

Quince (Cydonia oblonga Mill.) is a dwarfing rootstock often used in pear cultivation. However, the pear cultivar ‘Huangguan’ (Pyrus bretschneideri Rehd. cv) grafted onto quince A (HG-QA) suffered iron (Fe) deficiency chlorosis in the calcareous soils of North China, while ‘Huangguan’ grafted onto Pyrus betulifolia (HG-PB) did not. We hypothesized that the higher leaf apoplastic pH of HG-QA than HG-PB causes Fe deficiency chlorosis by restricting Fe transportation within leaves. Three-year-old rootstocks quince A and Pyrus betulifolia and the combinations HG-QA and HG-PB were grown in the same orchard in a calcareous soil. Newly expanded leaves were analysed for Fe related properties. Micro X-ray fluorescence analysis was used for Fe mapping within the individual leaves. The extractable Fe(II) concentrations in quince A and HG-QA leaves were much lower than those in Pyrus betulifolia and HG-PB, even though the total leaf Fe concentrations were similar. More Fe was located near the leaf midrib in quince A and HG-QA than in Pyrus betulifolia and HG-PB. These were correlated with the lower ferric chelate reductase (FCR) activity in the chlorotic leaves of the quince A rootstock than Pyrus betulifolia and the lower FCR activity and higher apoplastic pH in the chlorotic leaves of the HG-QA rootstock-scion combination than HG-PB. In conclusion, the reduced Fe availability within the leaves caused by the lower FCR activity and higher apoplastic pH compared with those of HG-PB led to HG-QA leaf chlorosis in calcareous soils. This result implies that rootstocks are involved in the regulation of leaf Fe utilization by scions.

Apoplast utilisation of nanohaematite initiates parallel suppression of RIBA1 and FRO1&3 in Cucumis sativus

Nanoscale Fe containing particles can penetrate the root apoplast. Nevertheless, cell wall size exclusion questions that for Fe mobilisation, a close contact between the membrane integrating FERRIC REDUCTASE OXIDASE (FRO) enzymes and Fe containing particles is required. Haematite nanoparticle suspension, size of 10–20 nm, characterized by 57Fe Mössbauer spectroscopy, TEM, ICP and SAED was subjected to Fe utilisation by the flavin secreting model plant cucumber (Cucumis sativus). Alterations in the structure and distribution of the particles were revealed by 57Fe Mössbauer spectroscopy, HRTEM and EDS element mapping. Biological utilisation of Fe resulted in a suppression of Fe deficiency responses (expression of CsFRO 1, 2 &3 and RIBOFLAVIN A1; CsRIBA1 genes and root ferric chelate reductase activity). Haematite nanoparticles were stacked in the middle lamella of the apoplast. Fe mobilisation is evidenced by the reduction in the particle size. Fe release from nanoparticles does not require a contact with the plasma membrane. Parallel suppression in the CsFRO 1&3 and CsRIBA1 transcript amounts support that flavin biosynthesis is an inclusive Fe deficiency response involved in the reduction-based Fe utilisation of Cucumis sativus roots. CsFRO2 is suggested to play a role in the intracellular Fe homeostasis.

Carbon and Iron Uptake by Phytoplankton in the Amundsen Sea, Antarctica.

Freshwater components in the Southern Ocean, whether sea ice meltwater or meteoric water, influence the growth of phytoplankton by affecting water stability and supplying dissolved iron (DFe). In addition, melting sea ice stimulates phytoplankton blooms by providing ice algae. In this study, sea ice meltwater and meteoric water in the Amundsen Sea (AS) were differentiated by their stable oxygen isotopic compositions (δ18O), while the phytoplankton carbon fixation rate (CFR) and iron uptake rate (FeUR) values were determined using the 14C and 55Fe tracer assays, respectively. Our results showed that FeUR exhibits a significant positive response only to sea ice meltwater, suggesting that DFe and algae provided by sea ice melting may be the main cause. In addition, the CFR had a slightly positive response to the freshwater input and a stronger correlation with the phytoplankton biomass, suggesting that the freshwater input may have enhanced the CFR through the algae released from sea ice melting. The FeUR normalized to the phytoplankton biomass was significantly positively correlated with the mixed layer depth, suggesting that water stability regulates the phytoplankton growth and the resulting Fe demand. A higher Fe demand per unit of carbon fixation during sea ice formation leads to a higher Fe/C ratio in phytoplankton. Although no significant correlations were observed between the FeUR, CFR, and meteoric water, meteoric water may have an effect on larger phytoplankton sensitive to Fe deficiencies. The results of culture experiments with DFe addition showed that the added Fe significantly enhanced the Fe uptake, carbon fixation, and Fe/C ratio of the cells, especially for micro-phytoplankton. The more pronounced response of micro-phytoplankton means that the meteoric water input may affect the efficiency of carbon export. Our study provides the first measurements of phytoplankton Fe quotas in the AS in austral late summer and early autumn, providing insights into how meteoric water and sea ice meltwater affect seasonal changes in Antarctic ecosystems.

Integration of Transcriptome and Metabolome Analyses Reveals the Mechanistic Basis for Cadmium Accumulation in Maize.

Cadmium (Cd) pollution in soil has become a major environmental issue worldwide. However, the underlying molecular mechanism of low grain-Cd accumulation (GCA) in maize is still largely unknown. Herein, we report the mechanistic basis for low GCA in maize by a multiomics approach. The low GCA genotype L63 showed normal vacuolar formation and a lower capacity of xylem loading of Cd than the high-accumulator L42 under Cd stress. Transcriptomic sequencing identified 84 low-GCA-associated genes which are mainly involved in the S-adenosylmethionine (SAM) cycle, metal transport, and vacuolar sequestration. A metabolome analysis revealed that L63 plants had a more active SAM cycle and a greater capacity for terpenoid synthesis and phenylalanine metabolism than L42. Combining the analysis of transcriptome and metabolome characterized several genes as key genes involved in the determination of Cd accumulation. Our study identifies a mechanistic basis for low Cd accumulation in maize grains and provides candidate genes for genetic improvement of crops.

The bHLH Transcription Factor OsbHLH057 Regulates Iron Homeostasis in Rice

Many basic Helix-Loop-Helix (bHLH) transcription factors precisely regulate the expression of Fe uptake and translocation genes to control iron (Fe) homeostasis, as both Fe deficiency and toxicity impair plant growth and development. In rice, three clade IVc bHLH transcription factors have been characterised as positively regulating Fe-deficiency response genes. However, the function of OsbHLH057, another clade IVc bHLH transcription factor, in regulating Fe homeostasis is unknown. Here, we report that OsbHLH057 is involved in regulating Fe homeostasis in rice. OsbHLH057 was highly expressed in the leaf blades and lowly expressed in the roots; it was mainly expressed in the stele and highly expressed in the lateral roots. In addition, OsbHLH057 was slightly induced by Fe deficiency in the shoots on the first day but was not affected by Fe availability in the roots. OsbHLH057 localised in the nucleus exhibited transcriptional activation activity. Under Fe-sufficient conditions, OsbHLH057 knockout or overexpression lines increased or decreased the shoot Fe concentration and the expression of several Fe homeostasis-related genes, respectively. Under Fe-deficient conditions, plants with an OsbHLH057 mutation showed susceptibility to Fe deficiency and accumulated lower Fe concentrations in the shoot compared with the wild type. Unexpectedly, the OsbHLH057-overexpressing lines had reduced tolerance to Fe deficiency. These results indicate that OsbHLH057 plays a positive role in regulating Fe homeostasis, at least under Fe-sufficient conditions.

FeCl3 and Fe2(SO4)3 differentially reduce Cd uptake and accumulation in Polish wheat (Triticum polonicum L.) seedlings by exporting Cd from roots and limiting Cd binding in the root cell walls

Wheat grown in cadmium (Cd)-contaminated soils easily accumulates more Cd in edible parts than the Chinese safety limit (0.1 mg/kg). FeCl3 and Fe2(SO4)3 have been used to extract Cd from Cd-contaminated soils. Thus, we hypothesized that FeCl3 and Fe2(SO4)3, used as iron (Fe) fertilizers, can reduce Cd uptake and accumulation in wheat. Here, a hydroponic experiment was performed with three FeCl3 and Fe2(SO4)3 concentrations under 80 μM CdCl2 stress on dwarf Polish wheat (Triticum polonicum L., 2n = 4x = 28, AABB) seedlings. Compared with Fe deficiency, FeCl3 and Fe2(SO4)3 additions competitively reduced Cd concentrations. The reductions were not associated with changes in dry weight and root morphological parameters. FeCl3 and Fe2(SO4)3 additions reduced Cd concentrations in the following order from smallest to largest reduction: 25 μM Fe2(SO4)3 < 200 μM FeCl3 < 50 μM FeCl3 < 100 μM Fe2(SO4)3. Investigation of subcellular distributions showed that the four Fe fertilizers differentially reduced Cd binding in the root cell walls and enhanced root sucrose and trehalose. Cd chemical form analysis revealed that Fe fertilizer addition also differentially reduced root FE, FW, and FNaCl. Transcriptomic analysis revealed that addition of FeCl3 and Fe2(SO4)3 differentially up-regulated several genes that hydrolyze cell wall polysaccharides and metal transporter genes for Cd uptake (IRT1 and CAX19) and export (ZIP1, ABCG11, ABCG14, ABCG28, ABCG37, ABCG44, and ABCG48) reducing Cd uptake and accumulation. Our results demonstrated that FeCl3 and Fe2(SO4)3 can reduce Cd accumulation in wheat, and 50 μM FeCl3 is the most effective treatment.

Effect of Iron Application on Rice Plants in Improving Grain Nutritional Quality in Northeastern of Thailand

Iron (Fe) deficiency in humans caused by inadequate dietary intake is a global nutritional problem. The field experiments in this paper were conducted in the same paddy field over two consecutive years during the dry seasons of 2017 and 2018. The aims of the experiments were to evaluate the effects of iron application methods (soil or foliar alone and a combination of soil + foliar) on the Fe content in brown rice grain and to compare the grain yields of three rice cultivars, namely Chinat1 (poor Fe grain concentration), Riceberry and Tubtim Chumpae (rich Fe grain concentration). The results show that all iron application methods significantly increase the iron content of brown rice grains in comparison with non-iron application in two cropping years. The iron application to the soil combined with foliar gave the highest iron content in the brown rice grain. However, the responses to the iron application methods were different among rice cultivars. The highest grain iron contents of Chainat1 and Riceberry were shown in the combination of soil and foliar application, whereas Tubtim Chumpae had the highest grain iron content in the foliar application alone. The differences in grain yield were affected by the rice cultivar, but not by iron application methods. The Chainat1 produced the highest grain yield. In addition, Chainat1 had the strongest correlation between brown rice grain iron content and grain yield for both cropping years.

Iron counteracts zinc-induced toxicity in soybeans

Zinc (Zn) and iron (Fe) are essential micronutrients for all living organisms and the major targets for crop biofortification. However, when acquired in excess quantities, Zn and Fe can be toxic to plants. In this study, we examined the interaction between Zn and Fe in soybean plants under various Zn and Fe treatments. While the level of Zn accumulation increased with increasing Zn supplies, Zn content greatly decreased with rising Fe supplies. Moreover, Zn uptake rates were negatively correlated with Fe supplies. However, Fe accumulation was not greatly affected by elevating Zn supplies. Excess Zn supplies were found to induce typical Fe deficiency symptoms under low Fe conditions, which can be counteracted by increasing Fe supplies. Interestingly, leaf chlorosis caused by excess Zn and low Fe supplies was not directly associated with reduced total Fe content but likely associated with deleterious effects of excess Zn. The combination of high Zn and low Fe greatly activates FRO2 and FIT1 gene expression in soybean roots. Besides, Zn-Fe interaction influences the activities of antioxidative enzymes as well as the uptake, accumulation, and homeostasis of other essential micronutrients, such as copper and manganese in soybean plants. These findings provide new perspectives on Zn and Fe interaction and on heavy metal-induced Fe deficiency-like symptoms.

Molecular cloning and functional characterization of MhHEC2-like genes in Malus halliana reveals it enhances Fe (iron) deficiency tolerance.

The basic helix-loop-helix (bHLH) family, as one of the largest families of transcription factors (TFs) in plants, plays crucial roles in regulating growth, development, and abiotic stress responses. However, studies on the association of the bHLH genes with apple iron (Fe) deficiency are limited. Here, multiple bHLH genes that responded to Fe deficiency were selected for quantitative real-time PCR in Malus halliana. The results showed that the expression of HEC2-like gene exerted more values compared to other genes under Fe deficiency stress, but the mechanism by which it regulates Fe deficiency stress is unclear. Subsequently, MhHEC2-like gene (ID: 103,455,961) was cloned from M. halliana for functional identification. We found that both transgenic Arabidopsis thaliana and tobacco displayed less chlorosis and more robust growth than wild-type (WT) controls under Fe deficiency stress. At the same time, the overexpressed apple calli grew prominently larger and better under Fe deficiency compared to the wild type. On the other hand, physiological index measurements revealed that overexpressed MhHEC2-like gene enhanced tolerance to Fe deficiency stress in A. thaliana and tobacco by promoting the synthesis of photosynthetic pigments, improving antioxidant enzyme activity, and enhancing Fe reduction, and strengthened tolerance to Fe deficiency stress in apple calli by reducing pH, boosting Fe reduction, and increasing antioxidant enzyme activity. To sum up, the overexpression of MhHEC2-like gene strengthened tolerance to Fe deficiency stress in Arabidopsis thaliana, tobacco, and apple calli.

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.

Latent heat thermal storage of solid-state phase transition in thermally stabilized hexagonal FeS

Large amounts of heat are required in areas such as food processing and textile industries to maintain equipment in the medium-temperature zone 393–573 K. However, thermal storage materials that work at this temperature are rare. Hexagonal iron sulfide FeS exhibits a solid-state phase transition at 420 K, accompanied by a high entropy change. The quenched FeS is unstable when subjected to a thermal cycling test, and the related entropy change declines. A secondary hexagonal phase with Fe deficiency was confirmed by neutron powder diffractions. Annealing FeS at temperatures slightly higher than Tt can accelerate the formation of the secondary phase. Once the sample is stabilized, the entropy change is no longer changeable. The thermally stabilized FeS sample exhibits a relatively high thermal storage density up to 136 J/cm3. This work suggests a new solid candidate for the application of solid-state phase transition latent heat energy storage in the medium-temperature region.

Identification of iron and zinc responsive genes in pearl millet using genome-wide RNA-sequencing approach

Pearl millet (Pennisetum glaucum L.), an important source of iron (Fe) and zinc (Zn) for millions of families in dryland tropics, helps in eradicating micronutrient malnutrition. The crop is rich in Fe and Zn, therefore, identification of the key genes operating the mineral pathways is an important step to accelerate the development of biofortified cultivars. In a first-of-its-kind experiment, leaf and root samples of a pearl millet inbred ICMB 1505 were exposed to combinations of Fe and Zn stress conditions using the hydroponics method, and a whole-genome transcriptome assay was carried out to characterize the differentially expressed genes (DEGs) and pathways. A total of 37,093 DEGs under different combinations of stress conditions were identified, of which, 7,023 and 9,996 DEGs were reported in the leaf and root stress treatments, respectively. Among the 10,194 unique DEGs, 8,605 were annotated to cellular, biological, and molecular functions and 458 DEGs were assigned to 39 pathways. The results revealed the expression of major genes related to the mugineic acid pathway, phytohormones, chlorophyll biosynthesis, photosynthesis, and carbohydrate metabolism during Fe and Zn stress. The cross-talks between the Fe and Zn provided information on their dual and opposite regulation of key uptake and transporter genes under Fe and Zn deficiency. SNP haplotypes in rice, maize, sorghum, and foxtail millet as well as in Arabidopsis using pearl millet Fe and Zn responsive genes could be used for designing the markers in staple crops. Our results will assist in developing Fe and Zn-efficient pearl millet varieties in biofortification breeding programs and precision delivery mechanisms to ameliorate malnutrition in South Asia and Sub-Saharan Africa.

The ferroxidases LPR1 and LPR2 control iron translocation in the xylem of Arabidopsis plants

Iron (Fe) deficiency is common in agricultural crops and affects millions of people worldwide. Translocation of Fe in the xylem is a key step for Fe distribution in plants. The mechanism controlling this process remains largely unknown. Here, we report that two Arabidopsis ferroxidases, LPR1 and LPR2, play a crucial and redundant role in controlling Fe translocation in the xylem. LPR1 and LPR2 are mainly localized in the cell walls of xylem vessels and the surrounding cells in roots, leaves, and stems. Knockout of both LPR1 and LPR2 increased the proportion of Fe(II) in the xylem sap, and caused Fe deposition along the vascular bundles especially in the petioles and main veins of leaves, which was alleviated by blocking blue light. The lpr1 lpr2 double mutant displayed constitutive expression of Fe deficiency response genes and overaccumulation of Fe in the roots and mature leaves under Fe-sufficient supply, but Fe deficiency chlorosis in the new leaves and inflorescences under low Fe supply. Moreover, the lpr1 lpr2 double mutant showed lower Fe concentrations in the xylem and phloem saps, and impaired 57Fe translocation along the xylem. In vitro assays showed that Fe(III)-citrate, the main form of Fe in xylem sap, is easily photoreduced to Fe(II)-citrate, which is unstable and prone to adsorption by cell walls. Taken together, these results indicate that LPR1 and LPR2 are required to oxidize Fe(II) and maintain Fe(III)-citrate stability and mobility during xylem translocation against photoreduction. Our study not only uncovers an essential physiological role of LPR1 and LPR2 but also reveals a new mechanism by which plants maintain Fe mobility during long-distance translocation in the xylem.

A tale of two metals: Biofortification of rice grains with iron and zinc.

Iron (Fe) and zinc (Zn) are essential micronutrients needed by virtually all living organisms, including plants and humans, for proper growth and development. Due to its capacity to easily exchange electrons, Fe is important for electron transport in mitochondria and chloroplasts. Fe is also necessary for chlorophyll synthesis. Zn is a cofactor for several proteins, including Zn-finger transcription factors and redox metabolism enzymes such as copper/Zn superoxide dismutases. In humans, Fe participates in oxygen transport, electron transport, and cell division whereas Zn is involved in nucleic acid metabolism, apoptosis, immunity, and reproduction. Rice (Oryza sativa L.) is one of the major staple food crops, feeding over half of the world's population. However, Fe and Zn concentrations are low in rice grains, especially in the endosperm, which is consumed as white rice. Populations relying heavily on rice and other cereals are prone to Fe and Zn deficiency. One of the most cost-effective solutions to this problem is biofortification, which increases the nutritional value of crops, mainly in their edible organs, without yield reductions. In recent years, several approaches were applied to enhance the accumulation of Fe and Zn in rice seeds, especially in the endosperm. Here, we summarize these attempts involving transgenics and mutant lines, which resulted in Fe and/or Zn biofortification in rice grains. We review rice plant manipulations using ferritin genes, metal transporters, changes in the nicotianamine/phytosiderophore pathway (including biosynthetic genes and transporters), regulators of Fe deficiency responses, and other mutants/overexpressing lines used in gene characterization that resulted in Fe/Zn concentration changes in seeds. This review also discusses research gaps and proposes possible future directions that could be important to increase the concentration and bioavailability of Fe and Zn in rice seeds without the accumulation of deleterious elements. We also emphasize the need for a better understanding of metal homeostasis in rice, the importance of evaluating yield components of plants containing transgenes/mutations under field conditions, and the potential of identifying genes that can be manipulated by gene editing and other nontransgenic approaches.

Hydrogen sulfide and nitric oxide regulate the adaptation to iron deficiency through affecting Fe homeostasis and thiol redox modification in Glycine max seedlings

Iron (Fe) is a vital microelement required for the growth and development of plants. Hydrogen sulfide (H2S) and nitric oxide (NO), as messenger molecules, participated in the regulation of plant physiological processes. Here, we studied the interaction effects of H2S and NO on the adaptation to Fe deficiency in Glycine max L. Physiological, biochemical and molecular approaches were conducted to analyze the role of H2S and NO in regulating the adaptation to Fe deficiency in soybean. We found that H2S and NO had obvious rescuing function on the Fe deficiency-induced the plant growth inhibition, which was significantly correlated with the increase in Fe content in the leaves, stems, and roots of soybean. Meanwhile, H+-flux, ferric chelate reductase (FCR) activity, and root apoplast Fe content were significantly affected by H2S and NO. Under Fe deficiency conditions NO and H2S regulated the expression of genes related to Fe homeostasis. Moreover, photosynthesis (Pn) and photosystem II (PSII) efficiency were enhanced by H2S and NO, and thiol redox modification was important for regulating the adaptation of Fe deficiency. The aforementioned affirmative influences caused by H2S and NO were also totally reversed by cPTIO (a NO scavenger). Our results suggested that H2S might act upstream of NO in response to Fe deficiency by affecting the Fe homeostasis enzyme activities and gene expression, and by promoting Fe accumulation in plant tissues as well as by enhancing thiol redox modification and photosynthesis in soybean plants.

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.

The vacuolar transporter LaMTP8.1 detoxifies manganese in leaves of Lupinus albus.

Manganese (Mn) is an essential microelement, but overaccumulation is harmful to many plant species. Most plants have similar minimal Mn requirements, but the tolerance to elevated Mn varies considerably. Mobilization of phosphate (P) by plant roots leads to increased Mn uptake, and shoot Mn levels have been reported to serve as an indicator for P mobilization efficiency in the presence of P deficiency. White lupin (Lupinus albus L.) mobilizes P and Mn with outstanding efficiency due to the formation of determinate cluster roots that release carboxylates. The high Mn tolerance of L. albus goes along with shoot Mn accumulation, but the molecular basis of this detoxification mechanism has been unknown. In this study, we identify LaMTP8.1 as the transporter mediating vacuolar sequestration of Mn in the shoot of white lupin. The function of Mn transport was demonstrated by yeast complementation analysis, in which LaMTP8.1 detoxified Mn in pmr1∆ mutant cells upon elevated Mn supply. In addition, LaMTP8.1 also functioned as an iron (Fe) transporter in yeast assays. The expression of LaMTP8.1 was particularly high in old leaves under high Mn stress. However, low P availability per se did not result in transcriptional upregulation of LaMTP8.1. Moreover, LaMTP8.1 expression was strongly upregulated under Fe deficiency, where it was accompanied by Mn accumulation, indicating a role in the interaction of these micronutrients in L. albus. In conclusion, the tonoplast-localized Mn transporter LaMTP8.1 mediates Mn detoxification in leaf vacuoles, providing a mechanistic explanation for the high Mn accumulation and Mn tolerance in this species.