Plant iron status regulates ammonium-use efficiency through protein N-glycosylation.

Improving nitrogen-use efficiency is an important path toward enhancing crop yield and alleviating the environmental impacts of fertilizer use. Ammonium (NH4+) is the energetically preferred inorganic N source for plants. The interaction of NH4+ with other nutrients is a chief determinant of ammonium-use efficiency (AUE) and of the tipping point toward ammonium toxicity, but these interactions have remained ill-defined. Here, we report that iron (Fe) accumulation is a critical factor determining AUE and have identified a substance that can enhance AUE by manipulating Fe availability. Fe accumulation under NH4+ nutrition induces NH4+ efflux in the root system, reducing both growth and AUE in Arabidopsis (Arabidopsis thaliana). Low external availability of Fe and a low plant Fe status substantially enhance protein N-glycosylation through a Vitamin C1-independent pathway, thereby reducing NH4+ efflux to increase AUE during the vegetative stage in Arabidopsis under elevated NH4+ supply. We confirm the validity of the iron-ammonium interaction in the important crop species lettuce (Lactuca sativa). We further show that dolomite can act as an effective substrate to subdue Fe accumulation under NH4+ nutrition by reducing the expression of Low Phosphate Root 2 and acidification of the rhizosphere. Our findings present a strategy to improve AUE and reveal the underlying molecular-physiological mechanism.

Interaction of ammonium nutrition with essential mineral cations.

Plant growth and development depend on sufficient nutrient availability in soils. Agricultural soils are generally nitrogen (N) deficient, and thus soils need to be supplemented with fertilizers. Ammonium (NH4+) is a major inorganic N source. However, at high concentrations, NH4+ becomes a stressor that inhibits plant growth. The cause of NH4+ stress or toxicity is multifactorial, but the interaction of NH4+ with other nutrients is among the main determinants of plants' sensitivity towards high NH4+ supply. In addition, NH4+ uptake and assimilation provoke the acidification of the cell external medium (apoplast/rhizosphere), which has a clear impact on nutrient availability. This review summarizes current knowledge, at both the physiological and the molecular level, of the interaction of NH4+ nutrition with essential mineral elements that are absorbed as cations, both macronutrients (K+, Ca2+, Mg2+) and micronutrients (Fe2+/3+, Mn2+, Cu+/2+, Zn2+, Ni2+). We hypothesize that considering these nutritional interactions, and soil pH, when formulating fertilizers may be key in order to boost the use of NH4+-based fertilizers, which have less environmental impact compared with nitrate-based ones. In addition, we are convinced that better understanding of these interactions will help to identify novel targets with the potential to improve crop productivity.

Multichannel Topological Kondo Effect.

A Coulomb blockaded M-Majorana island coupled to normal metal leads realizes a novel type of Kondo effect where the effective impurity "spin" transforms under the orthogonal group SO(M). The impurity spin stems from the nonlocal topological ground state degeneracy of the island and thus the effect is known as the topological Kondo effect. We introduce a physically motivated N-channel generalization of the topological Kondo model. Starting from the simplest case N=2, we conjecture a stable intermediate coupling fixed point and evaluate the resulting low-temperature impurity entropy. The impurity entropy indicates that an emergent Fibonacci anyon can be realized in the N=2 model. We also map the case N=2, M=4 to the conventional four-channel Kondo model and find the conductance at the intermediate fixed point. By using the perturbative renormalization group, we also analyze the large-N limit, where the fixed point moves to weak coupling. In the isotropic limit, we find an intermediate stable fixed point, which is stable to "exchange" coupling anisotropies, but unstable to channel anisotropy. We evaluate the fixed point impurity entropy and conductance to obtain experimentally observable signatures of our results. In the large-N limit, we evaluate the full crossover function describing the temperature-dependent conductance.

Endovascular Treatment Failure of Renal Arteriovenous Malformation due to an Extrarenal Feeding Artery: A Case Report.

Renal arteriovenous malformation (RAVM) is a rare pathology. It may present with heamturia, hypertension, and congestive heart failure. Digital subtraction angiography (DSA) is the standard diagnostic choice, and endovascular embolization is a preferred procedure of management in most cases. The feeding branches of RAVM are reported to originate from renal arteries. In this report, a 43-year-old female with recurrent massive hematuria and left flank pain was described. Renal angiography revealed double renal arteries supplying the left kidney and multiple renal arteriovenous fistula formation around the renal pelvis. Embolization with coils and gelfoam was performed after which her hematuria subsided. One month later, the patient was readmitted to our hospital due to the relapse of massive hematuria following heavy physical activities. DSA found another feeding artery of the RAVM originating from the aorta around the 4th lumbar vertebra. After embolization of this arterial feeder, hematuria settled. There was no recurrence during a 10-month follow-up. To our knowledge, this is the first case of RAVM with an extrarenal feeding artery, and omission of this scenario can lead to treatment failure.

OsEIL1 protects rice growth under NH4+ nutrition by regulating OsVTC1-3-dependent N-glycosylation and root NH4+ efflux.

Rice is known for its superior adaptation to ammonium (NH4+ ) as a nitrogen source. Compared to many other cereals, it displays lower NH4+ efflux in roots and higher nitrogen-use efficiency on NH4+ . A critical role for GDP-mannose pyrophosphorylase (VTC1) in controlling root NH4+ fluxes was previously documented in Arabidopsis, but the molecular pathways involved in regulating VTC1-dependent NH4+ efflux remain unclear. Here, we report that ETHYLENE-INSENSITIVE3-LIKE1 (OsEIL1) acts as a key transcription factor regulating OsVTC1-3-dependent NH4+ efflux and protein N-glycosylation in rice grown under NH4+ nutrition. We show that OsEIL1 in rice plays a contrasting role to Arabidopsis-homologous ETHYLENE-INSENSITIVE3 (AtEIN3) and maintains rice growth under NH4+ by stabilizing protein N-glycosylation and reducing root NH4+ efflux. OsEIL1 constrains NH4+ efflux by activation of OsVTC1-3, but not OsVTC1-1 or OsVTC1-8. OsEIL1 binds directly to the promoter EIN3-binding site (EBS) of OsVTC1-3 in vitro and in vivo and acts to increase the transcription of OsVTC1-3. Our work demonstrates an important link between excessive root NH4+ efflux and OsVTC1-3-mediated protein N-glycosylation in rice grown under NH4+ nutrition and identifies OsEIL1 as a direct genetic regulator of OsVTC1-3 expression.

Hem-o-Lok clip migration into renal pelvis and stone formation as a long-term complication following laparoscopic pyelolithotomy: a case report and literature review.

BACKGROUND: Hem-o-Lok clips (HOLCs) are widely used in minimal access urological operations due to the advantage of vascular control and suture stabilization. In rare cases, however, they can develop problems themselves. Migration of HOLCs into the collecting system is a fairly rare complication after laparoscopic pyelolithotomy. To date, only two cases were reported in the literature. CASE PRESENTATION: This article describes a case of 51-year-old man with a complaint of left flank pain. He had a medical history of ipsilateral retroperitoneal laparoscopic pyelolithotomy at another hospital 8 years ago. Non-contrast CT scan demonstrated a renal stone in the left ureteropelvic junction complicated by mild hydronephrosis. A straight foreign body was found near the renal pelvis, with part of it wedging into renal pelvic wall. A percutaneous nephrolithotomy (PNL) was performed for this patient. After some fragmentation, a HOLC was found in the kernel of the stone. With an alligator plier, the clip was totally removed out of the collecting system. The postoperative period and follow-up were uneventful. CONCLUSIONS: HOLC migration into renal pelvis is a rare complication following laparoscopic pyelolithotomy. It could act as nidus for stone formation under extended exposure to urine. Using HOLCs to stabilize the anastomotic suture near renal pelvis should be avoided to prevent this complication. Instead, knotting is a better choice under such condition. The secondary calculi and dislodged HOLCs can be removed through PNL by an alligator plier after laser lithotripsy.

WRKY46 promotes ammonium tolerance in Arabidopsis by repressing NUDX9 and indole-3-acetic acid-conjugating genes and by inhibiting ammonium efflux in the root elongation zone.

Ammonium (NH4+ ) is toxic to root growth in most plants, even at moderate concentrations. Transcriptional regulation is one of the most important mechanisms in the response of plants to NH4+ toxicity, but the nature of the involvement of transcription factors (TFs) in this regulation remains unclear. Here, RNA-seq analysis was performed on Arabidopsis roots to screen for ammonium-responsive TFs. WRKY46, the member of the WRKY transcription factor family most responsive to NH4+ , was selected. We defined the role of WRKY46 using mutation and overexpression assays, and characterized the regulation of NUDX9 and indole-3-acetic acid (IAA)-conjugating genes by WRKY46 via yeast one-hybrid and electrophoretic mobility shift assays and chromatin immunoprecipitation-quantitative real-time polymerase chain reaction (ChIP-qPCR). Knockout of WRKY46 increased, while overexpression of WRKY46 decreased, NH4+ -suppression of the primary root. WRKY46 is shown to directly bind to the promoters of the NUDX9 and IAA-conjugating genes (GH3.1, GH3.6, UGT75D1, UGT84B2) and to inhibit their transcription, thus positively regulating free IAA content and stabilizing protein N-glycosylation, leading to an inhibition of NH4+ efflux in the root elongation zone (EZ). We identify TF involvement in the regulation of NH4+ efflux in the EZ, and show that WRKY46 inhibits NH4+ efflux by negative regulation of NUDX9 and IAA-conjugating genes.

TaANR1-TaBG1 and TaWabi5-TaNRT2s/NARs Link ABA Metabolism and Nitrate Acquisition in Wheat Roots.

Nitrate is the preferred form of nitrogen for most plants, acting both as a nutrient and a signaling molecule. However, the components and regulatory factors governing nitrate uptake in bread wheat (Triticum aestivum), one of the world's most important crop species, have remained unclear, largely due to the complexity of its hexaploid genome. Here, based on recently released whole-genome information for bread wheat, the high-affinity nitrate transporter2 (NRT2) and the nitrate-assimilation-related (NAR) gene family are characterized. We show that abscisic acid (ABA)- Glc ester deconjugation is stimulated in bread wheat roots by nitrate resupply following nitrate withdrawal, leading to enhanced root-tissue ABA accumulation, and that this enhancement, in turn, affects the expression of root-type NRT2/NAR genes. TaANR1 is shown to regulate nitrate-mediated ABA accumulation by directly activating TaBG1, while TaWabi5 is involved in ABA-mediated NO3 - induction of NRT2/NAR genes. Building on previous evidence establishing ABA involvement in the developmental response to high-nitrate stress, our study suggests that ABA also contributes to the optimization of nitrate uptake by regulating the expression of NRT2/NAR genes under limited nitrate supply, offering a new target for improvement of nitrate absorption in crops.

Induction of S-nitrosoglutathione reductase protects root growth from ammonium toxicity by regulating potassium homeostasis in Arabidopsis and rice.

Ammonium (NH4+) is toxic to root growth in most plants already at moderate levels of supply, but mechanisms of root growth tolerance to NH4+ remain poorly understood. Here, we report that high levels of NH4+ induce nitric oxide (NO) accumulation, while inhibiting potassium (K+) acquisition via SNO1 (sensitive to nitric oxide 1)/SOS4 (salt overly sensitive 4), leading to the arrest of primary root growth. High levels of NH4+ also stimulated the accumulation of GSNOR (S-nitrosoglutathione reductase) in roots. GSNOR overexpression improved root tolerance to NH4+. Loss of GSNOR further induced NO accumulation, increased SNO1/SOS4 activity, and reduced K+ levels in root tissue, enhancing root growth sensitivity to NH4+. Moreover, the GSNOR-like gene, OsGSNOR, is also required for NH4+ tolerance in rice. Immunoblotting showed that the NH4+-induced GSNOR protein accumulation was abolished in the VTC1- (vitamin C1) defective mutant vtc1-1, which is hypersensititive to NH4+ toxicity. GSNOR overexpression enhanced vtc1-1 root tolerance to NH4+. Our findings suggest that induction of GSNOR increases NH4+ tolerance in Arabidopsis roots by counteracting NO-mediated suppression of tissue K+, which depends on VTC1 function.

Long non-coding RNA-H19 stimulates osteogenic differentiation of bone marrow mesenchymal stem cells via the microRNA-149/SDF-1 axis.

Bone defects resulting from non-union fractures or tumour resections are common clinical problems. Long non-coding RNAs (lncRNAs) are reported to play vital roles in stem cell differentiation. The aim of this study was to elucidate the role of lncRNA-H19 in osteogenic differentiation of bone marrow mesenchymal stem cells (BMMSCs). Following the establishment of an osteogenic differentiation model in rats, the expression of H19, microRNA-149 (miR-149) and stromal cell-derived factor-1 (SDF-1) was measured by RT-qPCR. Thereafter, BMMSCs were isolated from rats and treated with a series of mimic, inhibitor or siRNA. SDF-1 expression, alkaline phosphatase (ALP) activity and osteocalcin (OCN) content were detected. The mineralized and calcified nodules were assessed by alizarin red S and Von Kossa staining. BMMSC surface markers were detected by flow cytometry. Western blot analysis was used to measure the expression of ALP, OCN, runt-related transcription factor 2 (RUNX2) and osterix (OSX) proteins. Lastly, dual-luciferase reporter gene assay and RNA immunoprecipitation were applied to verify the relationship of H19, miR-149 and SDF-1. Overexpressed H19 and SDF-1 and poorly expressed miR-149 were found in rats with osteogenic differentiation. H19 increased SDF-1 expression by binding to miR-149. H19 enhanced ALP activity, OCN content, calcium deposit and ALP, OCN, RUNX2 and OSX protein expression of BMMSCS by up-regulating SDF-1 via binding to miR-149. Taken together, up-regulated H19 could promote the osteogenic differentiation of BMMSCs by increasing SDF-1 via miR-149.

Endogenous ABA alleviates rice ammonium toxicity by reducing ROS and free ammonium via regulation of the SAPK9-bZIP20 pathway.

Ammonium (NH4+) is one of the principal nitrogen (N) sources in soils, but is typically toxic already at intermediate concentrations. The phytohormone abscisic acid (ABA) plays a pivotal role in responses to environmental stresses. However, the role of ABA under high-NH4+ stress in rice (Oryza sativa L.) is only marginally understood. Here, we report that elevated NH4+ can significantly accelerate tissue ABA accumulation. Mutants with high (Osaba8ox) and low levels of ABA (Osphs3-1) exhibit elevated tolerance or sensitivity to high-NH4+ stress, respectively. Furthermore, ABA can decrease NH4+-induced oxidative damage and tissue NH4+ accumulation by enhancing antioxidant and glutamine synthetase (GS)/glutamate synthetasae (GOGAT) enzyme activities. Using RNA sequencing and quantitative real-time PCR approaches, we ascertain that two genes, OsSAPK9 and OsbZIP20, are induced both by high NH4+ and by ABA. Our data indicate that OsSAPK9 interacts with OsbZIP20, and can phosphorylate OsbZIP20 and activate its function. When OsSAPK9 or OsbZIP20 are knocked out in rice, ABA-mediated antioxidant and GS/GOGAT activity enhancement under high-NH4+ stress disappear, and the two mutants are more sensitive to high-NH4+ stress compared with their wild types. Taken together, our results suggest that ABA plays a positive role in regulating the OsSAPK9-OsbZIP20 pathway in rice to increase tolerance to high-NH4+ stress.

Hypermethylation of microRNA-149 activates SDF-1/CXCR4 to promote osteogenic differentiation of mesenchymal stem cells.

MicroRNAs (miRs) involve in osteogenic differentiation and osteogenic potential of mesenchymal stem cells (MSCs). Accordingly, the present study aimed to further uncover role miR-149 plays in osteogenic differentiation of MSCs with the involvement of the stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor-4 (CXCR4) pathway. Initially, the osteogenic differentiation model was induced. Next, the positive expression of STRO-1 in periosteum, alkaline phosphatase (ALP) activity, osteocalcin (OCN) protein content, and the calcium deposition in MSCs were determined. MSCs were treated with DNA methyltransferase inhibitor 5-aza-CdR, SDF-1 neutralizing antibody, or CXCR4 antagonist AMD3100 to investigate their roles in osteogenic differentiation; with the expression of CD44, CD90, CD14, and CD45 detected. Furthermore, the levels of SDF-1 and CXCR4, and the genes related to stemness (Nanog, Oct-4, and Sox-2) were measured to explore the effects of miR-149. The obtained data revealed the upregulation of STRO-1 in the periosteum. miR-149 could specifically bind to SDF-1. Besides, increased miR-149 methylation, higher ALP activity and OCN content, decreased positive rates of CD44 and CD90, and increased positive rates of CD14 and CD45 were found in osteogenic differentiation of MSCs. Subsequently, 5-Aza-CdR treatment reversed the above-mentioned effects. MSCs were finally treated with SDF-1 neutralizing antibody or AMD3100 to decrease Nanog, Oct-4, and Sox-2 expression. Taken together these results, miR-149 hypermethylation has the potential to activate the SDF-1/CXCR4 pathway and further promote osteogenic differentiation of MSCs.

GNAS knockdown suppresses osteogenic differentiation of mesenchymal stem cells via activation of Hippo signaling pathway.

Bone marrow-derived mesenchymal stem cells (BMSCs) are a suitable option for cell-based tissue engineering therapies due to their ability to renew and differentiate into multiple different tissue types, such as bone. Over the last decade, the effect of GNAS on the regulation of osteoblast differentiation has attracted great attention. Herein, this study aimed to explore the role of GNAS in osteogenic differentiation of MSCs. A total of 85 GNASf/f male mice were selected for animal experiments and 10 GNASf/f male mice for BMSC isolation to conduct cell experiments. The mice and BMSCs were treated with Verteporfin (a Hippo signaling pathway inhibitor) to inhibit the Hippo signaling pathway or recombinant adenovirus-expressing Cre to knockout the GNAS expression. Next, computed tomography scan, Von Kossa staining, and alizarin red staining were performed to detect osteogenic differentiation ability. Moreover, immunohistochemistry and alkaline phosphatase (ALP) staining were used to assess the expression of Oc and Osx in femur tissues and ALP activity. At last, the expression of GNAS, osteogenic markers, and factors related to the Hippo signaling pathway was evaluated. Initially, the results displayed successful knockout of the GNAS gene from mice and BMSCs. Moreover, the data indicated that GNAS knockout inhibits expression of Oc, Osx, ALP, BMP-2, and Runx2, and ALP activity. Additionally, GNAS knockout promotes activation of the Hippo signaling pathway, so as to repress osteogenic differentiation. Collectively, depleted GNAS exerts an inhibitory role in osteogenic differentiation of MSCs by activating Hippo signaling pathway, providing a candidate mediator for osteoporosis.

The Arabidopsis AMOT1/EIN3 gene plays an important role in the amelioration of ammonium toxicity.

Ammonium (NH4+) toxicity inhibits shoot growth in Arabidopsis, but the underlying mechanisms remain poorly characterized. Here, we show that a novel Arabidopsis mutant, ammonium tolerance 1 (amot1), exhibits enhanced shoot growth tolerance to NH4+. Molecular cloning revealed that amot1 is a new allele of EIN3, a key regulator of ethylene responses. The amot1 mutant and the allelic ein3-1 mutants show greater NH4+ tolerance than the wild type. Moreover, transgenic plants overexpressing EIN3 (EIN3ox) are more sensitive to NH4+ toxicity The ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) increases shoot sensitivity to NH4+, whereas the ethylene perception inhibitor Ag+ decreases sensitivity. NH4+ induces ACC and ethylene accumulation. Furthermore, ethylene-insensitive mutants such as etr1-3 and ein3eil1 display enhanced NH4+ tolerance. In contrast, the ethylene overproduction mutant eto1-1 exhibits decreased ammonium tolerance. AMOT1/EIN3 positively regulates shoot ROS accumulation, leading to oxidative stress under NH4+ stress, a trait that may be related to increased expression of peroxidase-encoding genes. These findings demonstrate the role of AMOT1/EIN3 in NH4+ tolerance and confirm the strong link between NH4+ toxicity symptoms and the accumulation of hydrogen peroxide.

The Influence of Different Knowledge-Driven Methods on Landslide Susceptibility Mapping: A Case Study in the Changbai Mountain Area, Northeast China.

Landslides are one of the most frequent geomorphic hazards, and they often result in the loss of property and human life in the Changbai Mountain area (CMA), Northeast China. The objective of this study was to produce and compare landslide susceptibility maps for the CMA using an information content model (ICM) with three knowledge-driven methods (the artificial hierarchy process with the ICM (AHP-ICM), the entropy weight method with the ICM (EWM-ICM), and the rough set with the ICM (RS-ICM)) and to explore the influence of different knowledge-driven methods for a series of parameters on the accuracy of landslide susceptibility mapping (LSM). In this research, the landslide inventory data (145 landslides) were randomly divided into a training dataset: 70% (81 landslides) were used for training the models and 30% (35 landslides) were used for validation. In addition, 13 layers of landslide conditioning factors, namely, altitude, slope gradient, slope aspect, lithology, distance to faults, distance to roads, distance to rivers, annual precipitation, land type, normalized difference vegetation index (NDVI), topographic wetness index (TWI), plan curvature, and profile curvature, were taken as independent, causal predictors. Landslide susceptibility maps were developed using the ICM, RS-ICM, AHP-ICM, and EWM-ICM, in which weights were assigned to every conditioning factor. The resultant susceptibility was validated using the area under the ROC curve (AUC) method. The success accuracies of the landslide susceptibility maps produced by the ICM, RS-ICM, AHP-ICM, and EWM-ICM methods were 0.931, 0.939, 0.912, and 0.883, respectively, with prediction accuracy rates of 0.926, 0.927, 0.917, and 0.878 for the ICM, RS-ICM, AHP-ICM, and EWM-ICM, respectively. Hence, it can be concluded that the four models used in this study gave close results, with the RS-ICM exhibiting the best performance in landslide susceptibility mapping.

Excess iron stress reduces root tip zone growth through nitric oxide-mediated repression of potassium homeostasis in Arabidopsis.

The root tip zone is regarded as the principal action site for iron (Fe) toxicity and is more sensitive than other root zones, but the mechanism underpinning this remains largely unknown. We explored the mechanism underpinning the higher sensitivity at the Arabidopsis root tip and elucidated the role of nitric oxide (NO) using NO-related mutants and pharmacological methods. Higher Fe sensitivity of the root tip is associated with reduced potassium (K+ ) retention. NO in root tips is increased significantly above levels elsewhere in the root and is involved in the arrest of primary root tip zone growth under excess Fe, at least in part related to NO-induced K+ loss via SNO1 (sensitive to nitric oxide 1)/SOS4 (salt overly sensitive 4) and reduced root tip zone cell viability. Moreover, ethylene can antagonize excess Fe-inhibited root growth and K+ efflux, in part by the control of root tip NO levels. We conclude that excess Fe attenuates root growth by effecting an increase in root tip zone NO, and that this attenuation is related to NO-mediated alterations in K+ homeostasis, partly via SNO1/SOS4.

Auxin Resistant1 and PIN-FORMED2 Protect Lateral Root Formation in Arabidopsis under Iron Stress.

A stunted root system is a significant symptom of iron (Fe) toxicity, yet little is known about the effects of excess Fe on lateral root (LR) development. In this work, we show that excess Fe has different effects on LR development in different portions of the Arabidopsis (Arabidopsis thaliana) root system and that inhibitory effects on the LR initiation are only seen in roots newly formed during excess Fe exposure. We show that root tip contact with Fe is both necessary and sufficient for LR inhibition and that the auxin, but not abscisic acid, pathway is engaged centrally in the initial stages of excess Fe exposure. Furthermore, Fe stress significantly reduced PIN-FORMED2 (PIN2)-green fluorescent protein (GFP) expression in root tips, and pin2-1 mutants exhibited significantly fewer LR initiation events under excess Fe than the wild type. Exogenous application of both Fe and glutathione together increased PIN2-GFP expression and the number of LR initiation events compared with Fe treatment alone. The ethylene inhibitor aminoethoxyvinyl-glycine intensified Fe-dependent inhibition of LR formation in the wild type, and this inhibition was significantly reduced in the ethylene overproduction mutant ethylene overproducer1-1. We show that Auxin Resistant1 (AUX1) is a critical component in the mediation of endogenous ethylene effects on LR formation under excess Fe stress. Our findings demonstrate the relationship between excess Fe-dependent PIN2 expression and LR formation and the potential role of AUX1 in ethylene-mediated LR tolerance and suggest that AUX1 and PIN2 protect LR formation in Arabidopsis during the early stages of Fe stress.

Ethylene is critical to the maintenance of primary root growth and Fe homeostasis under Fe stress in Arabidopsis.

Iron (Fe) is an essential microelement but is highly toxic when in excess. The response of plant roots to Fe toxicity and the nature of the regulatory pathways engaged are poorly understood. Here, we examined the response to excess Fe exposure in Arabidopsis wild type and ethylene mutants with a focus on primary root growth and the role of ethylene. We showed that excess Fe arrested primary root growth by decreasing both cell elongation and division, and principally resulteds from direct external Fe contact at the root tip. Pronounced ethylene, but not abscisic acid, evolution was associated with excess Fe exposure. Ethylene antagonists intensified root growth inhibition in the wild type, while the inhibition was significantly reduced in ethylene-overproduction mutants. We showed that ethylene plays a positive role in tissue Fe homeostasis, even in the absence of iron-plaque formation. Ethylene reduced Fe concentrations in the stele, xylem, and shoot. Furthermore, ethylene increased the expression of genes encoding Fe-sequestering ferritins. Additionally, ethylene significantly enhanced root K(+) status and upregulated K(+)-transporter (HAK5) expression. Our findings highlight the important role of ethylene in tissue Fe and K homeostasis and primary root growth under Fe stress in Arabidopsis.

[Study on Differential Optical Absorption Spectroscopy Data Processing Based on Chirp-Z Transformation].

Differential optical absorption spectroscopy (DOAS) is a commonly used atmospheric pollution monitoring method. Denoising of monitoring spectral data will improve the inversion accuracy. Fourier transform filtering method is effectively capable of filtering out the noise in the spectral data. But the algorithm itself can introduce errors. In this paper, a chirp-z transform method is put forward. By means of the local thinning of Fourier transform spectrum, it can retain the denoising effect of Fourier transform and compensate the error of the algorithm, which will further improve the inversion accuracy. The paper study on the concentration retrieving of SO2 and NO2. The results show that simple division causes bigger error and is not very stable. Chirp-z transform is proved to be more accurate than Fourier transform. Results of the frequency spectrum analysis show that Fourier transform cannot solve the distortion and weakening problems of characteristic absorption spectrum. Chirp-z transform shows ability in fine refactoring of specific frequency spectrum.

Physiological and molecular mechanisms of plant-root responses to iron toxicity.

The chemical form and physiological activity of iron (Fe) in soil are dependent on soil pH and redox potential (Eh), and Fe levels in soils are frequently elevated to the point of causing Fe toxicity in plants, with inhibition of normal physiological activities and of growth and development. In this review, we describe how iron toxicity triggers important physiological changes, including nitric-oxide (NO)-mediated potassium (K+) efflux at the tips of roots and accumulation of reactive oxygen species (ROS) and reactive nitrogen (RNS) in roots, resulting in physiological stress. We focus on the root system, as the first point of contact with Fe in soil, and describe the key processes engaged in Fe transport, distribution, binding, and other mechanisms that are drawn upon to defend against high-Fe stress. We describe the root-system regulation of key physiological processes and of morphological development through signaling substances such as ethylene, auxin, reactive oxygen species, and nitric oxide, and discuss gene-expression responses under high Fe. We especially focus on studies on the physiological and molecular mechanisms in rice and Arabidopsis under high Fe, hoping to provide a valuable theoretical basis for improving the ability of crop roots to adapt to soil Fe toxicity.