Structural Approach to Understanding the Formation of Amorphous Metal Hydroxides.

This study investigates the formation of amorphous tetravalent metal hydroxides, M(OH)4, based on the structural analysis by small- and wide-angle X-ray scattering (SWAXS) and on the electrical potential charge near the surface of M(OH)4 particles. The amorphous zirconium hydroxide solid phases that aged in NaCl and CaCl2 solutions at 25 °C exhibited a hierarchical structure consisting of primary particles of a few nanometers in size and their aggregates more than 100 nm in size. The SWAXS profiles suggested that the size of the primary particles depends on the ionic strength and electrolytes in the sample solutions. The smaller size of the primary particles observed in solutions with higher ionic strength can be explained by the thinner electrical double layer. Additionally, we focused on the ζ potentials of M(OH)4 suspensions in NaCl, NaNO3, and CaCl2 solutions. With the aid of reference systems of metal oxides, MO2, it was found that the ζ potentials were well interpreted by a traditional surface ionization and complexation model, and the size distributions of large aggregates were explained by the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory with the ζ potential values. The present study suggests the formation mechanism of amorphous metal hydroxides through a combination of structural analysis and investigation of electrical potentials.

Functional roles of ALMT-type anion channels in malate-induced stomatal closure in tomato and Arabidopsis.

Guard-cell-type aluminium-activated malate transporters (ALMTs) are involved in stomatal closure by exporting anions from guard cells. However, their physiological and electrophysiological functions are yet to be explored. Here, we analysed the physiological and electrophysiological properties of the ALMT channels in Arabidopsis and tomato (Solanum lycopersicum). SlALMT11 was specifically expressed in tomato guard cells. External malate-induced stomatal closure was impaired in ALMT-suppressed lines of tomato and Arabidopsis, although abscisic acid did not influence the stomatal response in SlALMT11-knock-down tomato lines. Electrophysiological analyses in Xenopus oocytes showed that SlALMT11 and AtALMT12/QUAC1 exhibited characteristic bell-shaped current-voltage patterns dependent on extracellular malate, fumarate, and citrate. Both ALMTs could transport malate, fumarate, and succinate, but not citrate, suggesting that the guard-cell-type ALMTs are dicarboxylic anion channels activated by extracellular organic acids. The truncation of acidic amino acids, Asp or Glu, from the C-terminal end of SlALMT11 or AtALMT12/QUAC1 led to the disappearance of the bell-shaped current-voltage patterns. Our findings establish that malate-activated stomatal closure is mediated by guard-cell-type ALMT channels that require an acidic amino acid in the C-terminus as a candidate voltage sensor in both tomato and Arabidopsis.

Sorption of Cs+ and Eu3+ ions onto sedimentary rock in the presence of gamma-irradiated humic acid.

The influence of humic acid (HA) and its radiological degradation on the sorption of Cs+ and Eu3+ by sedimentary rock (obtained from the Horonobe Underground Research Laboratory in Japan) was investigated to understand the sorption process of metal ions and humic substances. Aldrich HA solution was gamma-irradiated assuming a strong radiation from a highly radioactive waste to be disposed of in deep geological formations. Batch sorption experiments were performed to evaluate the effect of gamma-irradiated HA on the sorption of Cs+ and Eu3+ ions. The addition of non-irradiated HA weakened the Eu sorption because of the lower sorption of the negatively charged Eu-HA complexes compared with free Eu ions. The sorption of Cs ions was barely affected by the presence of HA and its gamma irradiation. The concentration ratio of metal complexed and non-complexed species in the solid and liquid phases was evaluated by sequential filtration and chemical equilibrium calculations. The ratios were low in both phases for Cs and supported the minimal contribution of HA to Cs sorption. However, the concentration ratio for Eu3+ in the liquid phase was high, indicating that the complexing ability of HA to Eu3+ was higher than that of HA to Cs+.

Physiological Role of Aerobic Fermentation Constitutively Expressed in an Aluminum-Tolerant Cell Line of Tobacco (Nicotiana tabacum).

Aluminum (Al)-tolerant tobacco cell line ALT301 derived from SL (wild-type) hardly exhibits Al-triggered reactive oxygen species (ROS) compared with SL. Molecular mechanism leading to this phenotype was investigated comparatively with SL. Under normal growth condition, metabolome data suggested the activation of glycolysis and lactate fermentation but the repression of the tricarboxylic acid (TCA) cycle in ALT301, namely aerobic fermentation, which seemed to be transcriptionally controlled partly by higher expression of genes encoding lactate dehydrogenase and pyruvate dehydrogenase kinase. Microarray and gene ontology analyses revealed the upregulation of the gene encoding related to APETALA2.3 (RAP2.3)-like protein, one of the group VII ethylene response factors (ERFVIIs), in ALT301. ERFVII transcription factors are known to be key regulators for hypoxia response that promotes substrate-level ATP production by glycolysis and fermentation. ERFVIIs are degraded under normoxia by the N-end rule pathway of proteolysis depending on both oxygen and nitric oxide (NO), and NO is produced mainly by nitrate reductase (NR) in plants. In ALT301, levels of the NR gene expression (NIA2), NR activity and NO production were all lower compared with SL. Consistently, the known effects of NO on respiratory pathways were also repressed in ALT301. Under Al-treatment condition, NO level increased in both lines but was lower in ALT301. These results suggest that the upregulation of the RAP2.3-like gene and the downregulation of the NIA2 gene and resultant NO depletion in ALT301 coordinately enhance aerobic fermentation, which seems to be related to a higher capacity to prevent ROS production in mitochondria under Al stress.

Radiocaesium accumulation capacity of epiphytic lichens and adjacent barks collected at the perimeter boundary site of the Fukushima Dai-ichi Nuclear Power Station.

We investigated the radiocaesium content of nine epiphytic foliose lichens species and the adjacent barks of Zelkova serrata (Ulmaceae, "Japanese elm") and Cerasus sp. (Rosaceae, "Cherry tree") at the boundary of the Fukushima Dai-ichi Nuclear Power Station six years after the accident in 2011. Caesium-137 activities per unit area (the 137Cs-inventory) were determined to compare radiocaesium retentions of lichens (65 specimens) and barks (44 specimens) under the same growth conditions. The 137Cs-inventory of lichens collected from Zelkova serrata and Cerasus sp. were respectively 7.9- and 3.8-times greater than the adjacent barks. Furthermore, we examined the radiocaesium distribution within these samples using autoradiography and on the surfaces with an electron probe micro analyzer (EPMA). Autoradiographic results showed strong local spotting and heterogeneous distributions of radioactivity in both the lichen and bark samples, although the intensities were lower in the barks. The electron microscopy analysis demonstrated that particulates with similar sizes and compositions were distributed on the surfaces of the samples. We therefore concluded that the lichens and barks could capture fine particles, including radiocaesium particles. In addition, radioactivity was distributed more towards the inwards of the lichen samples than the peripheries. This suggests that lichen can retain 137Cs that is chemically immobilised in particulates intracellularly, unlike bark.

Gamma-irradiation-induced molecular-weight distribution and complexation affinity of humic acid with Cs+, Sr2+, and Eu3.

Solutions of humic acid (HA) were irradiated with 0, 1, 5, 10, 50, and 100 kGy of gamma irradiation using a 60Co source. The non-irradiated and irradiated HA molecules were fractionated by ultrafiltration into four categories: > 100, 50-100, 10-50, and < 10 kDa. Total organic carbon measurements and potentiometric titration analysis suggested that (1) some gamma-irradiated HA molecules were degraded into smaller molecules and (2) radiolytic degradation caused phenolic -OH became the predominant functional group in the small molecular-weight fractions of HA. The effect of absorbed dose of gamma rays on the distributions of Cs+, Sr2+, and Eu3+ ions in the molecular-weight fractions of the metal-HA systems was examined to discuss the complexation affinity. The metal ions were distributed in the smaller molecular-weight fractions at different doses, which corresponded to the degradation of HA molecules. For a predetermined absorbed dose, Cs+ ions did not change the molecular-weight distribution of the total organic carbon content of the degraded HA molecules. Conversely, the Sr2+ and Eu3+ ions redistributed organic carbon toward the larger molecular-weight fractions.

Effect of gamma-irradiation on complexation of humic substances with divalent calcium ion.

The effect of gamma-irradiation doses of 0, 10, 100, and 500 kGy at the dose rates of 1 or 0.1 kGy/h on the molecular and chemical properties of humic substances (HS) were investigated using total organic carbon measurements, UV-Vis spectrometry, 13C nuclear magnetic resonance, and acid-base titration. A possible mechanism of the radiolysis on HS was also speculated. The complexation ability of irradiated HS with Ca2+ ions was studied using a Ca ion-selective electrode. The apparent formation constants of the Ca-HS complexes increased as the irradiation dose increased, and this was attributed to the relative increase in the ratio of phenolic -OH to carboxylic groups of HS. The contribution of the phenolic -OH groups to Ca-HS complexes was suppressed at pH 5 owing to its high acid dissociation constants. In addition, the radiation dose rates of 1 and 0.1 kGy/h did not significantly affect the properties of HS and the apparent formation constants of the Ca-HS complexes.

Fabrication of a Phosphate Ion Selective Electrode Based on Modified Molybdenum Metal.

A phosphate ion-selective electrode using molybdenum metal was constructed. The modified molybdenum electrode responded to HPO42- in the presence of molybdenum dioxide and molybdophosphate (PMo12O403-) on the surface. The electrode exhibited a linear response to HPO42- in the concentration range between 1.0 × 10-5 and 1.0 × 10-1 M (mol dm-3) in the pH range from 8.0 to 9.5 with a detection limit of 1.0 × 10-6 M. The sensor showed near Nernstian characteristics (27.8 ± 0.5 mV dec-1) at pH 9.0. Since the responding potential was attributed to the activity of HPO42-, the potential at a given concentration of phosphate depended on the pH. The electrode indicated a good selectivity with respect to other common anions such as NO3-, SO42-, Cl-, HCO3- and CH3COO-. The modified molybdenum electrode can be continuously used for over a 1 month with good reproducibility. The feasibility of the electrochemical sensor was proved by successful for the detection of phosphate in real samples.

The EQ-5D-5L in patients admitted to a hospital in Japan with recent spinal cord injury: a descriptive study.

STUDY DESIGN: Descriptive study. OBJECTIVE: To demonstrate Euro Quality of Life 5-dimensional 5-level (EQ-5D-5L) by severity level at the acute stage and discharge in patients with traumatic spinal cord injury (SCI). SETTING: Spinal Injuries Center, Fukuoka, Japan. METHODS: Patients with traumatic SCI who completed the EQ-5D-5L instrument at the acute stage and discharge were divided into four groups according to severity (severity group G1; C1-C4 ASIA Impairment Scale (AIS) A, B, and C, G2; C5-C8 AIS A, B, and C, G3; T1-S5 AIS A, B, and C, G4; all AIS D). All data were extracted from the Japan single-center study for spinal cord injury database (JSSCI-DB). RESULTS: Data were collected from 139 individuals at the acute stage and 164 individuals at discharge. In the comparison of utility score by severity in acute stage and discharge, G3 was significantly higher in discharge (0.325 versus 0.580). Utility scores by degree of severity were significantly higher in group G4 than those of G1, G2, and G3 at the acute stage. Utility scores at discharge were significantly higher in groups G3 and G4 than in G1, and there was a significant difference between groups G4 and G2. CONCLUSIONS: At each stage, the utility scores of group G4 were significantly higher than those of groups G1 and G2. Altogether, the utility scores for hospitalized patients with traumatic SCI that were indicated in this study will serve as basic data that can be used while performing spinal regeneration medical procedures in the future.

Structural Approach to Understanding the Solubility of Metal Hydroxides.

We report the hierarchical structure of zirconium hydroxide after aging at different temperatures to elucidate the factors governing zirconium solubility in aqueous solutions. Zirconium hydroxide solid phases after aging at 25, 40, 60, and 90 °C under acidic to alkaline conditions were investigated using extended X-ray absorption fine structure (EXAFS), wide- and small-angle X-ray scattering (WAXS and SAXS), and transmission electron microscopy (TEM) techniques to reveal the bulk and surface structures of the solid phases from the nanoscale to sub-microscale. After aging at 25 °C, the fundamental building unit of the solid phase was considered to be tetrameric and dimeric hydroxide species. These polynuclear species formed amorphous primary particles that are approximately 3 nm in size, which in turn formed aggregates that are hundreds of nanometers in size. This hierarchical structure was found to be stable up to 60 °C under acidic and neutral conditions and up to 40 °C under alkaline conditions. After aging at 90 °C under acidic conditions and at 60 and 90 °C under alkaline conditions, the WAXS and EXAFS measurements suggested the crystallization of the solid phase. The SAXS profiles and TEM observations supported the existence of crystallized large particles about 60 nm in size, and the appearance of the Guinier region in the SAXS profiles indicated that the crystallization of the amorphous primary particles leads to the reduction of the size of the large aggregates. The transformation of the solid-phase structure by temperature was discussed in relation to the solubility product to understand the solubility-limiting solid phase. The solubility of zirconium hydroxide after aging at different temperatures was governed not only by the size of the amorphous primary particles or crystallized large particles but also by their surface configuration.

Parents' perceptions of their spouses' parenting and infant temperament as predictors of parenting and coparenting.

The present study examined how mothers' and fathers' perceptions of each others' parenting competence and infant temperament interact to predict each parent's individual behaviors during coparenting (involvement, support, and warmth) and their dyadic child-centered coparenting behavior. Data were obtained from a longitudinal study of 125 families in central Texas over their first 2 years of parenthood. Ratings of infants' temperament were obtained when infants were 6 weeks old. Each parents' perceptions of their spouse's parenting were coded from a couple interaction task when infants were 8 months old, and parents' coparenting behaviors were coded from triadic (mother-father-child) interactions obtained when children were 24 months old. Parents' perceptions of their spouse's parenting at 8 months interacted with their infants' temperament to predict their later warmth and dyadic child-centered coparenting. High maternal perceptions of fathers' parenting predicted high levels of father warmth and high levels of dyadic child-centered coparenting when infant temperamental reactivity was high. In contrast, high paternal perceptions of mothers' parenting marginally predicted high levels of mother warmth and high dyadic child-centered coparenting when infant temperamental reactivity was low. Parents' individual warmth and fathers' involvement and support were also associated with dyadic child-centered coparenting. This study should help researchers further understand how parents' attitudes toward each other's parenting interact with their infants' temperament qualities across the early years of parenthood to influence the quality of their dyadic coparenting. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

AtALMT3 is Involved in Malate Efflux Induced by Phosphorus Deficiency in Arabidopsis thaliana Root Hairs.

Under phosphorus (P)-deficient conditions, organic acid secretion from roots plays an important role in P mobilization from insoluble P in the soil. In this study, we characterized AtALMT3, a homolog of the Arabidopsis thaliana aluminum-activated malate transporter family gene. Among the 14 AtALMT family genes, only AtALMT3 was significantly up-regulated in P-deficient roots. AtALMT3 promoter::ß-glucuronidase is expressed in the epidermis in roots, especially in root hair cells. AtALMT3 protein was localized in the plasma membrane and in small vesicles. Fluorescence of AtALMT3::GFP was not observed on the vacuole membrane of protoplast after lysis, indicating that AtALMT3 localizes mainly in the plasma membrane. Compared with the wild-type (WT) line, malate exudation in the AtALMT3-knockdown line (atalmt3-1) and overexpression line (atalmt3-2) under P deficiency were, respectively, 37% and 126%. In contrast, no significant difference was found in citrate exudation among these lines. The complementation of the atalmt3-1 line with AtALMT3 recovered the malate exudation to the level of the WT. Taken together, these results suggest that AtALMT3 localized in root hair membranes is involved in malate efflux in response to P deficiency.

Comparison of human papillomavirus genotyping and cytology triage, COMPACT Study: Design, methods and baseline results in 14 642 women.

Although cytology-based screening programs have significantly reduced mortality and morbidity from cervical cancer, the global consensus is that primary human papillomavirus (HPV) testing for cervical screening increases detection of high-grade cervical intraepithelial neoplasia (CIN) and invasive cancer. However, the optimal triage strategy for HPV-positive women to avoid over-referral to colposcopy may be setting specific. As Japan requires data that have been generated domestically to modify screening guidelines, we conducted a 3-year prospective study, COMparison of HPV genotyping And Cytology Triage (COMPACT), to evaluate the potential role of HPV16/18 partial genotyping and cytology for primary HPV screening. In total, 14 642 women aged 20 to 69 years undergoing routine screening at 3 centers in Hokkaido were enrolled. Conventional cytology and HPV testing were carried out. Women with abnormal cytology or HPV16/18 positivity underwent colposcopy. Those with 12 other high-risk (hr) HPV types underwent repeat cytology after 6 months. Primary study endpoints were detection of high-grade cervical disease defined as CIN2/CIN3 or greater as determined by consensus pathology. Prevalence of cytological abnormalities was 2.4%. hrHPV, HPV 16, and HPV 18 were detected in 4.6%, 0.9%, and 0.3% of women, respectively. HPV16/18 were detected in all (8/8) invasive cervical cancers and in all (2/2) adenocarcinomas in situ. Both cytological abnormalities and hrHPV positivity declined with increasing age. This is the first Japanese study to investigate the role of partial genotyping and cytology in an HPV-based screening program. Results should help policy-makers develop guidelines for future cervical screening programs and management of cervical abnormalities based on HPV genotype.

Aluminium-induced cell death requires upregulation of NtVPE1 gene coding vacuolar processing enzyme in tobacco (Nicotiana tabacum L.).

Cell death mechanism triggered by aluminium (Al) ion was investigated at root apex of tobacco (cultivar Bright Yellow) and in cultured tobacco cell line BY-2 derived from Bright Yellow, focusing on VPE genes (NtVPE1a, NtVPE1b, NtVPE2, NtVPE3). Cell death was detected as a loss of integrity of the plasma membrane by vital staining with fluorescein diacetate (in root apex) and Evans blue (in BY-2), respectively. At root apex, the upregulation of gene expression of VPE1a and VPE1b was observed significantly after 9h of Al exposure in parallel with an enhancement of cell death, while the upregulation of VPE2 and VPE3 were observed later. Similarly, in BY-2 cells, the upregulation of VPE1a and VPE1b and the enhancement of cell death were synchronously observed after 3-h exposure to Al, while the upregulation of VPE2 and VPE3 occurred later. RNA interference (RNAi) lines of each of the VPEs were constructed in BY-2 cells. Comparative studies between wild-type and the RNAi lines indicated that both Al-enhanced VPE activity and Al-induced cell death were significantly suppressed in the RNAi lines of VPE1 (dual suppressor of VPE1a and VPE1b), but not in the RNAi lines of VPE2 and that of VPE3. Taken together, we conclude that the upregulation of VPE1 gene expression and following enhancement of VPE activity under Al stress cause cell death in actively growing or elongating cells of tobacco.

A multidrug and toxic compound extrusion transporter mediates berberine accumulation into vacuoles in Coptis japonica.

Plants produce a large variety of alkaloids, which have diverse chemical structures and biological activities. Many of these alkaloids accumulate in vacuoles. Although some membrane proteins on tonoplasts have been identified as alkaloid uptake transporters, few have been characterized to date, and relatively little is known about the mechanisms underlying alkaloid transport and accumulation in plant cells. Berberine is a model alkaloid. Although all genes involved in berberine biosynthesis, as well as the master regulator, have been identified, the gene responsible for the final accumulation of berberine at tonoplasts has not been determined. This study showed that a multidrug and toxic compound extrusion protein 1 (CjMATE1) may act as a berberine transporter in cultured Coptis japonica cells. CjMATE1 was found to localize at tonoplasts in C. japonica cells and, in intact plants, to be expressed preferentially in rhizomes, the site of abundant berberine accumulation. Cellular transport analysis using a yeast expression system showed that CjMATE1 could transport berberine. Expression analysis showed that RNAi suppression of CjbHLH1, a master transcription factor of the berberine biosynthetic pathway, markedly reduced the expression of CjMATE1 in a manner similar to the suppression of berberine biosynthetic genes. These results strongly suggest that CjMATE1 is the transporter that mediates berberine accumulation in vacuoles.

Interaction of rare earth elements and components of the Horonobe deep groundwater.

To better understand the migration behavior of minor actinides in deep groundwater, the interactions between doped rare earth elements (REEs) and components of Horonobe deep groundwater were investigated. Approximately 10 ppb of the REEs, i.e. Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Tm, and Yb were doped into a groundwater sample collected from a packed section in a borehole drilled at 140 m depth in the experiment drift of Horonobe Underground Research Laboratory in Hokkaido, Japan. The groundwater sample was sequentially filtered with a 0.2 µm pore filter, and 10 kDa, 3 kDa and 1 kDa nominal molecular weight limit (NMWL) ultrafilters with conditions kept inert. Next, the filtrate solutions were analyzed with inductively coupled plasma mass spectrometry (ICP-MS) to determine the concentrations of the REEs retained in solution at each filtration step, while the used filters were analyzed through neutron activation analysis (NAA) and TOF-SIMS element mapping to determine the amounts and chemical species of the trapped fractions of REEs on each filter. A strong relationship between the ratios of REEs retained in the filtrate solutions and the ionic radii of the associated REEs was observed; i.e. smaller REEs occur in larger proportions dissolved in the solution phase under the conditions of the Horonobe groundwater. The NAA and TOF-SIMS analyses revealed that portions of the REEs were trapped by the 0.2 µm pore filter as REE phosphates, which correspond to the species predicted to be predominant by chemical equilibrium calculations for the conditions of the Horonobe groundwater. Additionally, small portions of colloidal REEs were trapped by the 10 kDa and 3 kDa NMWL ultrafilters. These results suggest that phosphate anions play an important role in the chemical behavior of REEs in saline (seawater-based) groundwater, which may be useful for predicting the migration behavior of trivalent actinides released from radioactive waste repositories in the far future.

Two Members of the Aluminum-Activated Malate Transporter Family, SlALMT4 and SlALMT5, are Expressed during Fruit Development, and the Overexpression of SlALMT5 Alters Organic Acid Contents in Seeds in Tomato (Solanum lycopersicum).

The aluminum-activated malate transporter (ALMT) family of proteins transports malate and/or inorganic anions across plant membranes. To demonstrate the possible role of ALMT genes in tomato fruit development, we focused on SlALMT4 and SlALMT5, the two major genes expressed during fruit development. Predicted proteins were classified into clade 2 of the family, many members of which localize to endomembranes. Tissue-specific gene expression was determined using transgenic tomato expressing the ß-glucuronidase reporter gene controlled by their own promoters. Both the genes were expressed in vascular bundles connecting to developing seeds in fruit and in the embryo of mature seeds. Further, SlALMT5 was expressed in embryo in developing seeds in fruit. Subcellular localization of both proteins to the endoplasmic reticulum (ER) was established by transiently expressing the green fluorescent protein fusions in plant protoplasts. SlALMT5 probably localized to other endomembranes as well. Localization of SlALMT5 to the ER was also confirmed by immunoblot analysis. The transport function of both SlALMT proteins was investigated electrophysiologically in Xenopus oocytes. SlALMT5 transported malate and inorganic anions such as nitrate and chloride, but not citrate. SlALMT4 also transported malate, but the results were less consistent perhaps because it did not localize strongly to the plasma membrane. To elucidate the physiological role of SlALMT5 further, we overexpressed SlALMT5 in tomato. Compared with the wild type, overexpressors exhibited higher malate and citrate contents in mature seeds, but not in fruit. We conclude that the malate transport function of SlALMT5 expressed in developing fruit influences the organic acid contents in mature seeds.

A Dicarboxylate Transporter, LjALMT4, Mainly Expressed in Nodules of Lotus japonicus.

Legume plants can establish symbiosis with soil bacteria called rhizobia to obtain nitrogen as a nutrient directly from atmospheric N2 via symbiotic nitrogen fixation. Legumes and rhizobia form nodules, symbiotic organs in which fixed-nitrogen and photosynthetic products are exchanged between rhizobia and plant cells. The photosynthetic products supplied to rhizobia are thought to be dicarboxylates but little is known about the movement of dicarboxylates in the nodules. In terms of dicarboxylate transporters, an aluminum-activated malate transporter (ALMT) family is a strong candidate responsible for the membrane transport of carboxylates in nodules. Among the seven ALMT genes in the Lotus japonicus genome, only one, LjALMT4, shows a high expression in the nodules. LjALMT4 showed transport activity in a Xenopus oocyte system, with LjALMT4 mediating the efflux of dicarboxylates including malate, succinate, and fumarate, but not tricarboxylates such as citrate. LjALMT4 also mediated the influx of several inorganic anions. Organ-specific gene expression analysis showed LjALMT4 mRNA mainly in the parenchyma cells of nodule vascular bundles. These results suggest that LjALMT4 may not be involved in the direct supply of dicarboxylates to rhizobia in infected cells but is responsible for supplying malate as well as several anions necessary for symbiotic nitrogen fixation, via nodule vasculatures.

A chimeric protein of aluminum-activated malate transporter generated from wheat and Arabidopsis shows enhanced response to trivalent cations.

TaALMT1 from wheat (Triticum aestivum) and AtALMT1 from Arabidopsis thaliana encode aluminum (Al)-activated malate transporters, which confer acid-soil tolerance by releasing malate from roots. Chimeric proteins from TaALMT1 and AtALMT1 (Ta::At, At::Ta) were previously analyzed in Xenopus laevis oocytes. Those studies showed that Al could activate malate efflux from the Ta::At chimera but not from At::Ta. Here, functions of TaALMT1, AtALMT1 and the chimeric protein Ta::At were compared in cultured tobacco BY-2 cells. We focused on the sensitivity and specificity of their activation by trivalent cations. The activation of malate efflux by Al was at least two-fold greater in the chimera than the native proteins. All proteins were also activated by lanthanides (erbium, ytterbium, gadolinium, and lanthanum), but the chimera again released more malate than TaALMT1 or AtALMT1. In Xenopus oocytes, Al, ytterbium, and erbium activated inward currents from the native TaALMT1 and the chimeric protein, but gadolinium only activated currents from the chimera. Lanthanum inhibited currents from both proteins. These results demonstrated that function of the chimera protein was altered compared to the native proteins and was more responsive to a range of trivalent cations when expressed in plant cells.