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PubMed2001

Speciation of low molecular weight Al complexes in serum of CAPD patients.

Speciation of LMW--Al complexes was performed in human serum of six continuous ambulatory peritoneal dialysis (CAPD) patients in order to investigate the individual variability in the percentage and the composition of LMW--Al species. The total concentration of Al in serum ranged from 10 to 120 ng ml(-1). The samples with high total concentration of Al were analysed directly, while those of low total Al concentration were spiked with Al(3+). Spiked and non-spiked samples (100--120 ng ml(-1) of total Al) were microultrafiltered through a membrane filter (cut-off 30,000 Da) to separate Al-transferrin from LMW-Al complexes. On an anion-exchange fast protein liquid chromatography (FPLC) column, 0.2 ml of filtrate was injected. An aqueous -- 4 mol l(-1) NH(4)NO(3) linear gradient elution was applied for 10 min to separate LMW--Al complexes. Fractions of 0.2 ml collected throughout the chromatographic run were diluted 1:1 with water and Al determined 'off line' by electrothermal atomic absorption spectrometry (ETAAS). The characterisation of LMW-Al species eluted under the chromatographic peaks was performed also by electrospray tandem mass spectrometric (ES-MS-MS) analysis. It was found experimentally that the percentage of LMW--Al species in spiked and non-spiked serum ranged from 25 to 50% (in one non-spiked sample 100%). The following LMW--Al species were separated and identified during the chromatographic run: Al-phosphate and a mixture of Al-citrate and ternary Al-citrate--phosphate complexes. It was found experimentally that the distribution of these species varied among particular patients. Similar distribution of LMW--Al species was found in spiked serum of healthy volunteers.

Aluminum Compounds↗
PubMed2002

A novel herpes simplex virus type 1 transcript (AL-RNA) antisense to the 5' end of the latency-associated transcript produces a protein in infected rabbits.

Following primary ocular infection, herpes simplex virus type 1 (HSV-1) establishes a lifelong latent infection in sensory neurons of the trigeminal ganglia. Latency-associated transcript (LAT), the only known viral gene abundantly transcribed during HSV-1 neuronal latency, is required for high levels of reactivation. Recently we showed that three different mutants that do not alter the LAT promoter but contain deletions within the 5' end of the primary LAT transcript affect viral virulence (G. C. Perng et al., J. Virol. 75:9018-9028, 2001). In contrast, in LAT-null mutants viral virulence appears unaltered (T. M. Block et al., Virology 192:618-630, 1993; D. C. Bloom et al., J. Virol. 68:1283-1292, 1994; J. M. Hill et al., Virology 174:117-125, 1990; G. C. Perng et al., J. Virol. 68:8045-8055, 1994; F. Sedarati, K. M. Izumi, E. K. Wagner, and J. G. Stevens, J. Virol. 63:4455-4458, 1989). We therefore hypothesized that the 5' end of LAT and/or an as yet unidentified gene that overlaps part of this region is involved in viral virulence. We report here on the discovery and initial characterization of a novel HSV-1 RNA consistent with such a putative gene. The novel RNA was antisense to the 5' end of LAT and was designated AL-RNA (anti-LAT sense RNA). The AL-RNA overlapped the core LAT promoter and the first 158 nucleotides of the 5' end of the primary LAT transcript. AL-RNA was detected in extracts from neuron-like cells (PC-12) infected with wild-type HSV-1 but not in cells infected with a mutant with the AL region deleted. The deletions in each of the above three mutants with altered virulence encompass the 5' end of the AL-RNA, and these mutants cannot transcribe AL. This supports the hypothesis that the AL gene may play a role in viral virulence. Based on comparison to the corresponding genomic sequence, the AL-RNA did not appear to be spliced. The AL-RNA was polyadenylated and contained an open reading frame capable of encoding a protein 56 amino acids in length with a predicted molecular mass of 6.8 kDa. Sera from three of three rabbits infected with wild-type HSV-1 but not sera from any of three rabbits infected with a mutant with the AL-RNA region deleted recognized the Escherichia coli recombinantly expressed AL open reading frame on Western blots. In addition, four of six rabbits infected with wild-type virus developed enzyme-linked immunosorbent assay titers against one or more AL synthetic peptides. These results suggest that an AL protein is produced in vivo.

Amino Acid Sequence↗
PubMed2001

Distribution and mobility of aluminium in an Al-accumulating plant, Fagopyrum esculentum Moench.

Buckwheat (Fagopyrum esculentum Moench. cv. Jianxi) accumulates high concentrations of Al in the leaves without showing any toxicity. To understand the accumulation mechanism of Al in buckwheat, the distribution and mobility of Al in buckwheat were investigated. Relatively long-term treatment (28 d) with Al led to a decrease in Al concentration from old to young leaves, while a short-term (1 d) exposure to Al resulted in a uniform distribution of Al in the leaves. When the fourth leaf was wrapped inside a transparent plastic bag to suppress transpiration, the Al concentration of this leaf was only one-quarter of that in the corresponding leaf without wrapping. Within a leaf, the Al concentration at the margins was much higher than that in the centre. These results indicate that Al distribution in the leaves is controlled by both rate and duration of transpiration. The mobility of Al between old and new leaves was studied by first growing plants in a solution with Al, followed by culture in a solution without Al. The Al content in the two new leaves appeared after removal of external Al was very low, whereas that in the old leaves did not decrease but continued to increase. The increased Al content was found to be translocated from Al remaining in the roots. It is concluded that Al is not mobile once it is accumulated in the leaf.

Adaptation, Physiological↗
PubMed2004

Interactive effects of Al, Ca and other cations on root elongation of rice cultivars under low pH.

BACKGROUND AND AIMS: As with other crop species, Al tolerance in rice (Oryza sativa) is widely different among cultivars, and the mechanism for tolerance is unknown. The Ca2+-displacement hypothesis, that is, Al displaces Ca2+ from critical sites in the root apoplast, was predicted to be the essential mechanism for causing Al toxicity in rice cultivars. If displacement of Ca is an essential cause of Al toxicity in rice, Al toxicity may show the same trend as toxicities of elements such as Sr and Ba that are effective in displacing Ca. METHODS: The interactive effects of Al, Ca, Sr and Ba on root elongation of rice cultivars with different Al tolerances were evaluated in hydroponic culture. Al and Ca accumulation in root tips was also investigated. KEY RESULTS AND CONCLUSIONS: Not only Al but also Sr and Ba applications inhibited root growth of rice cultivars under low Ca conditions. As expected, rice cultivars more tolerant of Sr and Ba were also tolerant of Al (japonica > indica). Although Mg application did not affect Sr or Ba toxicity, Mg alleviated Al toxicity to the same level as Ca application. In addition, Ca application decreased the Al content in root tips without displacement. These results suggest that Ca does not have a specific, irreplaceable role in Al toxicity, unlike Sr and Ba toxicities. Alleviation of Al toxicity with increasing concentrations of Ca in rice cultivars is due to increased ionic strength, not due to decreased Al activity. The difference in Al tolerance between indica and japonica cultivars disappears under high ionic strength conditions, suggesting that different electrochemical characteristics of root-tip cells are related to the significant difference in Al tolerance under low ionic strength conditions.

Aluminum↗
PubMed2004

Molecular mapping of a gene responsible for Al-activated secretion of citrate in barley.

Aluminium (Al) toxicity is an important limitation to barley (Hordeum vulgare L.) on acid soil. Al-resistant cultivars of barley detoxify Al externally by secreting citrate from the roots. To link the genetics and physiology of Al resistance in barley, genes controlling Al resistance and Al-activated secretion of citrate were mapped. An analysis of Al-induced root growth inhibition from 100 F2 seedlings derived from an Al-resistant cultivar (Murasakimochi) and an Al-sensitive cultivar (Morex) showed that a gene associated with Al resistance is localized on chromosome 4H, tightly linked to microsatellite marker Bmag353. Quantitative trait locus (QTL) analysis from 59 F4 seedlings derived from an F3 plant heterozygous at the region of Al resistance on chromosome 4H showed that a gene responsible for the Al-activated secretion of citrate was also tightly linked to microsatellite marker Bmag353. This QTL explained more than 50% of the phenotypic variation in citrate secretion in this population. These results indicate that the gene controlling Al resistance on barley chromosome 4H is identical to that for Al-activated secretion of citrate and that the secretion of citrate is one of the mechanisms of Al resistance in barley. The identification of the microsatellite marker associated with both Al resistance and citrate secretion provides a valuable tool for marker-assisted selection of Al-resistant lines.

Adaptation, Physiological↗
PubMed1999

[The clinico-pathological findings of the patients grouped as respiratory motor paralysis preceded type of ALS].

We reported five autopsied patients grouped as respiratory motor paralysis preceded type of ALS (R-ALS) classified as one clinical type of ALS from the patients living beyond respiratory failure reported in the previous paper, in which ALS the ontogenetically new motor functions in the "first motor system" proposed by Holstege involved first. The neuropathological changes of five patients were not limited in the degeneration of conventional "motor system" such as corticospinal tract and spinal and cranial motoneurons, but extended into the realm of "non-motor system", which could show the anterolateral myelin pallor in spinal cord by myelin staining, and detect the fibrillary gliosis of the anterior commissural area, the spinal grey matter of intemediate zone and anterior horn in all patients, and of medullary reticular formation in three one by Holzer staining. These pathological lesions could be included in the "first motor system". Considered from this study of the clinico-pathological findings of R-ALS based on "a new view of ALS", which respiratory failure in ALS is not terminus in ALS and total course of ALS might be TLS, it might be concluded that the clinico-pathologically involved initial lesions of ALS might be in the "first motor system", and include not only degenerations of "motor system", but also those of "non-motor system", which is the basically pathological lesions in ALS. Furthermore, the hitherto clinico-pathological ALS findings, which respiratory failure in ALS is terminus in ALS, could be included in this group, and showed as a part of ALS discussed from this study. Total clinico-pathological on ALS from the initial ones (R-type) to the advanced ones (TLS) including ALS-dementia should be considered further based on "the second and the third motor systems in addition to the first one".

Adult↗
PubMed2004

Modeling and electrokinetic evidences on the processes of the Al(III) sorption continuum in SiO2(s) suspension.

Reactions of Al(III) at the interface between SiO2(s) and aqueous solution were characteristically and quantitatively studied using electrophoretic methods and applying a surface complexation/precipitation model (SCM/SPM). The surface and bulk properties of Al(III)/SiO2 suspensions were determined as functions of pH and initial Al(III) concentration. Simulated modeling results indicate that the SCM, accounting for the adsorption mechanism, predicts sorption data for low surface coverage only reasonably well. Al(III) hydrolysis and surface hydroxide precipitation must be invoked as the Al(III) concentration and/or pH progressively increase. Accordingly, the three processes in the Al(III) sorption continuum, from adsorption through hydrolysis to surface precipitation, could be identified by the divergence between the SCM/SPM predictions and the experimental data. SiO2(s) suspensions with low Al(III) concentrations (1 x 10(-4) and 1 x 10(-5) M) exhibit electrophoretic behavior similar to that of a pure SiO2(s) system. In Al(III)/SiO2 systems with high Al concentrations of 1 x 10(-3), 5 x 10(-3) and 1 x 10(-2) M, three charge reversals (CR) are observed, separately representing, in order of increasing pH, the point of zero charge (PZC) on the SiO2 substrate (CR1), the onset of the surface precipitation of Al hydroxide (CR2), and at a high pH, the PZC of the Al(OH)3 coating (CR3). Furthermore, in the 1 x 10(-3) M Al(III)/SiO2(s) system, CR2 is consistent with the modeling results of SCM/SPM and provides evidence that Al(III) forms a surface precipitate on SiO2(s) at pH above 4. SiO2(s) dissolution was slightly inhibited when Al(III) was adsorbed onto the surface of SiO2(s), as compared to the dissolution that occurs in a pure SiO2(s) suspension system. Al hydroxide surface precipitation dramatically reduced the dissolution of SiO2(s) because the Al hydroxide passive film inhibited the corrosion of the SiO2(s) surface by OH- ions.

Adsorption↗
PubMed2001

Probing the role of calmodulin in Al toxicity in maize.

The role of calmodulin on Al toxicity was studied in two maize (Zea mays L.) inbred lines, Cat 100-6 (Al-tolerant) and S 1587-17 (Al-sensitive). Increasing levels of Al induced the release of malate at similar rate by roots of both genotypes, while the exudation of citrate, a stronger Al-binding compound, was 3.5 times higher in Cat 100-6 seedlings exposed to 16.2x10(-6) Al(3+) activity. The calmodulin inhibitor trifluoperazine significantly reduced the root growth in both genotypes, mimicking the main effect of Al. However, when Cat 100-6 and S 1587-17 seedlings were challenged with Al in conjunction with trifluoperazine, no further reduction in root growth or any other effect of Al toxicity was observed. The rate of Al-induced citrate exudation by both genotypes was not affected by treatment with trifluoperazine or calmidazolium, another calmodulin inhibitor. The Al(3+) interaction with cytoplasmic CaM was estimated using models for the binding of Al(3+) and Mg(2+) with CaM and physiological concentrations of citrate, CaM, InsP(3), ATP, ADP, Al(3+) and Mg(2+). In this simulation, Al(3+) associated with citrate and InsP(3), but not with CaM. We conclude that calmodulin is not relevant to the physiological processes leading to the Al tolerance in maize, nor is it a primary target for Al toxicity.

Adaptation, Physiological↗
PubMed1997

Direct Evaluation of the Ca2+-Displacement Hypothesis for Al Toxicity.

One explanation for Al toxicity in plants suggests that Al displaces Ca2+ from critical sites in the apoplasm. We evaluated the Ca2+-displacement hypothesis directly using near-isogenic lines of wheat (Triticum aestivum L.) that differ in Al tolerance at a single locus. We measured both the growth and total accumulation (apoplasmic plus symplasmic) of 45Ca and Al into roots that had been exposed to Al alone or to Al with other cations. Root growth in the Al-sensitive line was found to be severely inhibited by low activities of Al, even though Ca2+ accumulation was relatively unaffected. In solutions containing the same activity of the Al3+ and Ca2+ ions as above, but also including either 3.0 mM Mg2+, 3.0 mM Sr2+, or 30 mM Na+, growth improved, whereas 45Ca2+ accumulation was significantly decreased. Since most of the 45Ca2+ accumulated by roots during short-term treatments will reside in the apoplasm, these results indicate that displacement of Ca2+ from the apoplasm by Al cannot account for the Al-induced inhibition of root growth and, therefore, do not support the Ca2+-displacement hypothesis for Al toxicity. We also show that total accumulation of Al by root apices is greater in the Al-sensitive genotype than the Al-tolerant genotype and suggest that cation amelioration of Al toxicity is caused by the reduction in Al accumulation.

Journal Article↗
PubMed2005

Comparison of water-soluble and exchangeable forms of Al in acid forest soils.

Soil acidification promotes Al release from minerals and parent bedrocks; it also affects Al mobilization and speciation. Speciation of KCl extractable and water-extractable Al in forest soils was done by means of HPLC/IC method. Species Al3+ were the most abundant Al forms in the KCl extracts (around 93%). Prevailing Al forms (more than 70%) in aqueous extracts were Al(X)1+, [i.e., Al(OH)2+, Al(SO4)+, AlF2+, Al(oxalate)+, Al(H-citrate)+, etc.] species. It is assumed that most of KCl and water-extractable Al is bound in soil sorption complex (i.e., highly dispersed colloidal fraction of the soil solid phase creating negative charge) where majority of Al exists in the form of Al3+ species. The ECEC values, total carbon content and parameters related to soil organic matter composition (N and S content) have apparent effect on Al speciation. The most toxic Al3+ species are more concentrated in the B horizons compared to the A and E horizons. Aqueous extracts simulate Al release to soil solution under normal conditions; it can thus exhibit the actual Al toxicity. On the other hand, KCl extraction describes a potential threat for case of strong disturbance of natural soil conditions.

Journal Article↗
PubMed2005

Phytoremediation of effluents from aluminum smelters: a study of Al retention in mesocosms containing aquatic plants.

Four mesocosms were exposed to circumneutral and aluminum (Al)-rich wastewater during two successive summers (2000, 2001). The goals of the study were to measure the bioaccumulation of dissolved Al by the aquatic plants Typha latifolia, Lemna minor, Nuphar variegatum and Potamogeton epihydrus, and to evaluate their importance in the retention of Al by the mesocosms. In 2000, inlet concentrations of total monomeric Al were reduced by 56% and 29% at the Arvida and Laterrière mesocosms, respectively, whereas in 2001 inlet dissolved Al concentrations in the inlet decreased by 40% and 33%. L. minor had the highest Al uptake rate (0.8--17 mg Al g(-1)d(-1)). However, because T. latifolia (cattails) yielded the highest biomass, it was responsible for 99% of the Al uptake, largely in its root tissue. In 2001, Al uptake by macrophytes accounted for 2--4% and 15--54% of the total Al retained by the Laterrière and Arvida mesocosms, respectively. In the Laterrière mesocosms, Al uptake by cattails could account for 12% and 18% of the dissolved Al retained by both mesocosms. In contrast, dissolved Al was not significantly reduced in the Arvida enclosures, yet cattails did accumulate Al in their roots. Further research is needed to identify the species community composition that would optimize dissolved Al retention.

Aluminum↗
PubMed2005

Aluminum fractions in root tips of slash pine and loblolly pine families differing in Al resistance.

Aluminum (Al) distribution among several cellular fractions was investigated in root tips of seedlings of one Al-resistant and one Al-sensitive family of slash pine (Pinus elliottii Engelm.) and loblolly pine (Pinus taeda L.) grown in nutrient solution containing 100 microM AlCl3 (pH 4) for 167 h. Aluminum present in 5-mm-long root tips was fractionated into cell-wall-labile (desorbed in 0.5 mM citric acid), cell-wall-bound (retained after filtering disrupted cells through 20-microm mesh) and symplasmic (filtrate following cell disruption) fractions. When averaged across both species, 12% of Al absorbed by root tips appeared in the symplasmic fraction and 88% in the apoplasmic fraction (55% as cell-wall-labile, and 33% as cell-wall-bound). On a fresh mass basis, total Al in root tips was lower in loblolly pine than in slash pine, lower in the Al-resistant slash pine family than in the Al-sensitive slash pine family, and lower in the Al-resistant families than in the Al-sensitive families across species. Although the data support the hypothesis that Al-resistant plants limit Al uptake to root apices, they do not exclude other mechanisms of Al resistance. Differential Al resistance between the species and between slash pine families may also be associated with the size of the total non-labile and cell-wall-labile Al fractions, respectively. We were unable to identify the basis for differential Al resistance in loblolly pine.

Aluminum↗
PubMed1997

Water Transport Properties of Roots and Root Cortical Cells in Proton- and Al-Stressed Maize Varieties.

Root and root cell pressure-probe techniques were used to investigate the possible relationship between Al- or H+-induced alterations of the hydraulic conductivity of root cells (LPc) and whole-root water conductivity (LPr) in maize (Zea mays L.) plants. To distinguish between H+ and Al effects two varieties that differ in H+ and Al tolerance were assayed. Based on root elongation rates after 24 h in nutrient solution of pH 6.0, pH 4.5, or pH 4.5 plus 50 [mu]M Al, the variety Adour 250 was found to be H+-sensitive and Al-tolerant, whereas the variety BR 201 F was found to be H+-tolerant but Al-sensitive. No Al-induced decrease of root pressure and root cell turgor was observed in Al-sensitive BR 201 F, indicating that Al toxicity did not cause a general breakdown of membrane integrity and that ion pumping to the stele was maintained. Al reduced LPc more than LPr in Al-sensitive BR 201 F. Proton toxicity in Adour 250 affected LPr more than LPc. In this Al-tolerant variety LPc was increased by Al. Nevertheless, this positive effect on LPc did not render higher LPr values. In conclusion, there were no direct relationships between Al- or H+-induced decreases of LPr and the effects on LPc. To our knowledge, this is the first time that the influence of H+ and Al on root and root cell water relations has been directly measured by pressure-probe techniques.

Journal Article↗
PubMed2003

Toxicity of Al to Desulfovibrio desulfuricans.

The toxicity of Al to Desulfovibrio desulfuricans G20 was assessed over a period of 8 weeks in a modified lactate C medium buffered at four initial pHs (5.0, 6.5, 7.2, and 8.3) and treated with five levels of added Al (0, 0.01, 0.1, 1.0, and 10 mM). At pH 5, cell population densities decreased significantly and any effect of Al was negligible compared to that of the pH. At pHs 6.5 and 7.2, the cell population densities increased by 30-fold during the first few days and then remained stable for soluble-Al concentrations of <5 x 10(-5) M. In treatments having total-Al concentrations of > or =1 mM, soluble-Al concentrations exceeded 5 x 10(-5) M and limited cell population growth substantially and proportionally. At pH 8.3, soluble-Al concentrations were below the 5 x 10(-5) M toxicity threshold and cell population density increases of 20- to 40-fold were observed. An apparent cell population response to added Al at pH 8.3 was attributed to the presence of large, spirilloidal bacteria (accounting for as much as 80% of the cells at the 10 mM added Al level). Calculations of soluble-Al speciation for the pH 6.5 and 7.2 treatments that showed Al toxicity suggested the possible presence of the Al(13)O(4)(OH)(24)(H(2)O)(12)(7+) "tridecamer" cation and an inverse correlation of the tridecamer concentration and the cell population density. Analysis by (27)Al nuclear magnetic resonance spectroscopy, however, yielded no evidence of this species in freshly prepared samples or those taken 800 days after inoculation. Exclusion of the tridecamer species from the aqueous speciation calculations at pHs 6.5 and 7.2 yielded inverse correlations of the neutral Al(OH)(3) and anionic Al(OH)(4)(-) monomeric species with cell population density, suggesting that one or both of these ions bear primary responsibility for the toxicity observed.

Aluminum↗
PubMed2006

Evaluating controlling factors to Al(i)/(Ca + Mg) molar ratio in acidic soil water, southern and southwestern China: multivariate approach.

Al(i)/(Ca + Mg) molar ratio in soil water has been used as an indicator to the effects of acid deposition on terrestrial ecosystems. However, the main factors controlling this ratio have not been well documented in southern and southwestern China. In this study, we presented the variation in inorganic aluminum (Al(i)) and Al(i)/(Ca + Mg) molar ratio in different sites and soil horizons based on two to three years monitoring data, and evaluated the main factors controlling Al(i)/(Ca + Mg) molar ratio using principle component analysis (PCA) and partial least square (PLS) regression. Monitoring data showed although Al(i)/(Ca + Mg) molar ratios in most soil water were lower than assumed critical 1.0, higher molar ratios were found in some soil water at TSP and LXH site. Besides acid loading, both soil properties and soil water chemistry affected the value of Al(i)/(Ca + Mg) molar ratio in soil water. Partial least square (PLS) indicated that they had different relative importance in different soil horizons. In A-horizon, soil aluminum saturation (AlS) had higher influence on Al(i)/(Ca + Mg) molar ratio than soil water chemistry did; higher soil aluminum saturation (AlS) led to higher Al(i)/(Ca + Mg) molar ratio in soil water. In the deeper horizons (i.e., B(1)-, B(2)- and BC-horizon), inorganic aluminum (Al(i)) in soil water had more and more important role in regulating Al(i)/(Ca + Mg) molar ratio. On regional scale, soil aluminum saturation (AlS) as well as cation exchange capacity (CEC) was the dominant factor controlling Al(i)/(Ca + Mg) molar ratio. This should be paid enough attention on when making regional acid rain control policy in China.

Acids↗
PubMed1999

Linking Intermetallics and Zintl Compounds: An Investigation of Ternary Trielides (Al, Ga, In) Forming the NaZn(13) Structure Type.

A populous group of ternary trielide rich (Al, Ga, In) intermetallics forming the NaZn(13) structure type has been synthesized from stoichiometric combinations of the elements in an arc melter. These ternary compounds have the general formula AM(x)()T(13)(-)(x)(), where A = Ba, Sr, La, Eu, M = Cu and Ag, and T = Al, Ga, and In, with 5 </= x </= 6.5, and have been structurally characterized by both powder and single-crystal X-ray diffraction. Furthermore, magnetic susceptibility, electrical resistivity, XPS, and EDS measurements are reported for some of the samples. Single-crystal X-ray diffraction experiments on BaCu(5)Al(8) (BaCu(5.10(7))Al(7.90(7)), cubic, a = 12.205(4) Å, Z = 8) and EuCu(6.5)Al(6.5) (EuCu(6.41(5))Al(6.59(5)), cubic, a = 11.928(1) Å, Z = 8) indicate that the quasi-infinite three-dimensional [Cu(x)()Al(13)(-)(x)()] framework involves mostly Cu atoms centering icosahedra, with its vertexes randomly occupied by the remaining Cu and Al atoms. On the other hand, when M = Ag, Al shows a greater tendency to occupy the center of the icosahedra. A systematic study of the compositional variation in BaCu(x)()Al(13)(-)(x)() demonstrates that the NaZn(13) type phase exists within a narrow range of x between five and six. To examine the role of the cation A in stabilizing this structure, quaternary phases, e.g., BaSrAg(12)Al(14) (BaSrAg(12.0(1))Al(14.0(1)), cubic, a = 12.689(1) Å, Z = 4) and SrCeCu(12)Al(14) (SrCeCu(11.74(2))Al(14.26(2)), cubic, a = 11.938(1) Å, Z = 4), were prepared and characterized. Extended Hückel calculations on these ternary aluminides demonstrate how the tuning of the system's stoichiometry maximizes the bonding within the atom-centered icosahedral framework. These calculations also address the substitution pattern of M and T within the [M(x)()T(13)(-)(x)()] network. Tight-binding LMTO calculations have also been applied to examine the charge-density and electron-localization functions (ELF) in this structure for different electron counts in order to address the nature of chemical bonding in these phases. One important conclusion from the theoretical results is that the NaZn(13) type phases show optimal stability for 40-42 valence electrons for the [M(x)()T(13)(-)(x)()] framework.

Journal Article↗
PubMed2001

Characterization of agglutinin-like sequence genes from non-albicans Candida and phylogenetic analysis of the ALS family.

The ALS (agglutinin-like sequence) gene family of Candida albicans encodes cell-surface glycoproteins implicated in adhesion of the organism to host surfaces. Southern blot analysis with ALS-specific probes suggested the presence of ALS gene families in C. dubliniensis and C. tropicalis; three partial ALS genes were isolated from each organism. Northern blot analysis demonstrated that mechanisms governing expression of ALS genes in C. albicans and C. dubliniensis are different. Western blots with an anti-Als serum showed that cross-reactive proteins are linked by beta 1,6-glucan in the cell wall of each non-albicans Candida, suggesting similar cell wall architecture and conserved processing of Als proteins in these organisms. Although an ALS family is present in each organism, phylogenetic analysis of the C. albicans, C. dubliniensis, and C. tropicalis ALS genes indicated that, within each species, sequence diversification is extensive and unique ALS sequences have arisen. Phylogenetic analysis of the ALS and SAP (secreted aspartyl proteinase) families show that the ALS family is younger than the SAP family. ALS genes in C. albicans, C. dubliniensis, and C. tropicalis tend to be located on chromosomes that also encode genes from the SAP family, yet the two families have unexpectedly different evolutionary histories. Homologous recombination between the tandem repeat sequences present in ALS genes could explain the different histories for co-localized genes in a predominantly clonal organism like C. albicans.

Agglutinins↗
PubMed2001

A patch-clamp study on the physiology of aluminum toxicity and aluminum tolerance in maize. Identification and characterization of Al(3+)-induced anion channels.

The presence of Al(3+) in the rhizosphere induces citrate efflux from the root apex of the Al-tolerant maize (Zea mays) hybrid South American 3, consequently chelating and reducing the activity of toxic Al(3+) at the root surface. Because citrate is released from root apical cells as the deprotonated anion, we used the patch-clamp technique in protoplasts isolated from the terminal 5 mm of the root to study the plasma membrane ion transporters that could be involved in Al-tolerance and Al-toxicity responses. Acidification of the extracellular environment stimulated inward K(+) currents while inhibiting outward K(+) currents. Addition of extracellular Al(3+) inhibited the remaining K(+) outward currents, blocked the K(+) inward current, and caused the activation of an inward Cl(-) current (anion efflux). Studies with excised membrane patches revealed the existence of Al-dependent anion channels, which were highly selective for anions over cations. Our success in activating this channel with extracellular Al(3+) in membrane patches excised prior to any Al(3+) exposure indicates that the machinery required for Al(3+) activation of this channel, and consequently the whole root Al(3+) response, is localized to the root-cell plasma membrane. This Al(3+)-activated anion channel may also be permeable to organic acids, thus mediating the Al-tolerance response (i.e. Al-induced organic acid exudation) observed in intact maize root apices.

Aluminum↗