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Al Content (al + content)
Selected AbstractsSpatially resolved X-ray diffraction as a tool for strain analysis in laterally modulated epitaxial structuresCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2009A. Wierzbicka Abstract Spatially resolved X-ray diffraction (SRXRD) is applied for micro-imaging of strain in laterally modulated epitaxial structures. In GaAs layers grown by liquid phase epitaxial lateral overgrowth (ELO) on SiO2 -masked GaAs substrates a downward tilt of ELO wings caused by their interaction with the mask is observed. The distribution of the tilt magnitude across the wings width is determined with ,m-scale spatial resolution. This allows measuring of the shape of the lattice planes in individual ELO stripes. If a large area of the sample is studied the X-ray imaging provides precise information on the tilt of an individual wing and its distribution. In heteroepitaxial GaSb/GaAs ELO layers local mosaicity in the wing area is found. By the SRXRD the size of microblocks and their relative misorientation were analyzed. Finally, the SRXRD technique was applied to study distribution of localized strain in AlGaN epilayers grown by MOVPE on bulk GaN substrates with AlN mask. X-ray mapping proves that by mask patterning strain in AlGaN layer can be easily engineered, which opens a way to produce thicker, crack-free AlGaN layers with a higher Al content needed in GaN-based laser diodes. All these examples show that high spatial and angular resolutions offered by SRXRD makes the technique a powerful tool to study local lattice distortions in semiconductor microstructures. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Aluminum Content in Foods and Beverages Consumed in the Spanish DietJOURNAL OF FOOD SCIENCE, Issue 2 2000F.F. López ABSTRACT: A reliable and rapid method for determining aluminum content in foods and beverages was developed using electrothermal atomization-atomic absorption spectrometry (ETA-AAS) using previous optimization of the time-temperature program for the graphite furnace. The samples were subjected to acid mineralization with HNO3 and V2O5. The technique used slurries for assay in samples of dairy products. The detection limit was 4.0 pg. The mean recovery obtained ranged from 98.5% to 99.0%. The variation coefficient ranged from 3.2% to 5.2%. The results obtained ranged from 1.362 to 6.610 ,g/g in seafood, 0.171 to 29.688 ,g/g in vegetables, 19.560 to 70.100 ,g/g in olive oil, 0.424 to 6.430 ,g/g in dairy products and 25.600 to 58.057 ,g/g in stimulant drinks and infusions. This study contributes new data on the Al content of a variety of foods and beverages in Spain and such data are important for composition tables. The higher presence corresponded to seafood, vegetables and dairy products. Their contribution to Al dietary intake were estimated. [source] Electrolytic Synthesis of Al-Doped ZnO Nanopowders With Low Electrical ResistivityJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2010Takeshi Takaki Al-doped ZnO (AZO) nanopowders with different Al content were fabricated by a galvanostatic electrolytic method. The electrical resistivities were measured by a cell method, which reached its minimum (28 ,·cm) at 0.93 at.% of Al with its grain size of ,30 nm. Microstructures of powders were characterized by X-ray diffraction and transmission electron microscopy (TEM), which showed a decrease in grain size with the increase of Al content. In addition, the distributions of Al and the chemical bonding nature of Al atoms were examined by STEM-EDS and by X-ray photoelectron spectra, respectively, which suggested the substituational incorporation of Al atom into the ZnO lattice. Absorption properties were investigated for wavelength ranging from 250 to 2500 nm, which showed that the film coated with AZO nanopowders exhibited a rapid decrease in transmittance below 370 nm to ,0% and beyond 1250 nm to ,40% (at 2000 nm). [source] Forming Al2O3,Al Composites with Controlled Compositions by Reactive Metal Penetration of Dense Aluminosilicate PreformsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2000William G. Fahrenholtz Alumina,Al composites with controlled compositions containing 17 to 31 vol% Al were formed by reactive metal penetration (RMP) of molten Al into dense aluminosilicate preforms. A reaction model has been developed to accurately predict composite Al content from the SiO2:Al2O3 ratio of the preform. The model was tested and validated by comparing predicted composite compositions to those measured for RMP composites made from preforms of known compositions. Aluminosilicate preforms containing 28.1, 39.0, and 54.1 wt% SiO2 were reacted with Al to produce composites with 17, 25, and 31 vol% Al, respectively. These values compare favorably to Al contents of 17.7, 22.7, and 28.6 vol% Al predicted using the reaction model. The differences between predicted and measured values are attributed to the presence of porosity and Si in the composites, as well as impurities in the SiO2 glass phase and porosity in the preforms, none of which is specifically accounted for in the reaction model. [source] The role that bond coat depletion of aluminum has on the lifetime of APS-TBC under oxidizing conditionsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 7 2008D. Renusch Abstract Bond coat oxidation as well as bond coat depletion of Al are still believed to be a major degradation mechanism with respect to the lifetime of thermal barrier coating (TBC) systems. In this study the top coat lifetime is described as being limited by both bond coat depletion of Al and mechanical failure of the top coat. The empirical results are introduced by considering three spallation cases, namely, Al depletion failure, thermal fatigue failure, and thermal aging failure. Al depletion failure occurs when the Al content within the bond coat reaches a critical value. In this paper bond coat depletion of Al is modeled by considering the diffusion of Al into both the thermally grown oxide (TGO) and substrate. The diffusion model results are compared to Al concentration profiles measured with an electron beam microprobe. These measured results are from oxidized air plasma sprayed TBC systems (APS-TBC) with vacuum plasma sprayed (VPS) bond coats for exposures up to 5000 h in the temperature range of 950,1100,°C. This paper focuses on the Al depletion failure and how it relates to top coat spallation. [source] Spectral reflectance-compositional properties of spinels and chromites: Implications for planetary remote sensing and geothermometryMETEORITICS & PLANETARY SCIENCE, Issue 4 2004Edward A. Cloutis These two groups of minerals are spectrally distinct, which relates largely to differences in the types of major cations present. Both exhibit a number of absorption features in the 0.3,26 ,m region that show systematic variations with composition and can be used to quantify or constrain certain compositional parameters, such as cation abundances, and site occupancies. For spinels, the best correlations exist between Fe2+ content and wavelength positions of the 0.46, 0.93, 2.8, Restrahelen, 12.3, 16.2, and 17.5 ,m absorption features, Al and Fe3+ content with the wavelength position of the 0.93 ,m absorption feature, and Cr content from the depth of the absorption band near 0.55 ,m. For chromites, the best correlations exist between Cr content and wavelength positions of the 0.49, 0.59, 2, 17.5, and 23 ,m absorption features, Fe2+ and Mg contents with the wavelength position of the 1.3 ,m absorption feature, and Al content with the wavelength position of the 2 ,m absorption feature. At shorter wavelengths, spinels and chromites are most readily distinguished by the wavelength position of the absorption band in the 2 ,m region (<2.1 ,m for spinels, >2.1 ,m for chromite), while at longer wavelengths, spectral differences are more pronounced. The importance of being able to derive compositional information for spinels and chromites from spectral analysis stems from the relationship between composition and petrogenetic conditions (pressure, temperature, oxygen fugacity) and the widespread presence of spinels and chromites in the inner solar system. When coupled with the ability to derive compositional information for mafic silicates from spectral analysis, this opens up the possibility of deriving petrogenetic information for remote spinel- and chromite-bearing targets from analysis of their reflectance spectra. [source] Spatially resolved cathodoluminescence study on AlGaN layer fabricated by air-bridged lateral epitaxial growthPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2004Akihiko Ishibashi Abstract Structural properties of AlGaN layer on the GaN seed layer fabricated by air-bridged lateral epitaxial growth (ABLEG) have been studied by spatially resolved cathodoluminescence (CL) microscopy. The cross-sectional spatially resolved CL images of the ABLEG-AlGaN layer reveal that there are roughly three regions which have different main CL peaks. This result suggests that there are roughly three regions with the different Al contents. Before coalescence of the overgrown AlGaN wings, there are two regions of Al content, such as about 6.5, 10.6%. On the other hand, after coalescence of the wings, the Al content of the AlGaN layer becomes uniform (Al content = 8.9%). These results suggest that the facet growth of the overgrown AlGaN wings causes the modulation of Al content in the ABLEG-AlGaN layer. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Atmospheric-pressure MOVPE growth of In-rich InAlNPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008Y. Houchin Abstract This paper reports the atmospheric-pressure MOVPE growth of In-rich InAlN. All InAlN films prepared here (Al content:0, 0.43) do not show phase separation. The incorporation of Al in InAlN is decreased with increasing growth temperature. A decrease in Al content is also observed for films grown at a position farther from the up-stream end of the susceptor. The marked decrease in the Al content along the gas flow direction seems to be caused by the shortage of TMA supply at the downstream by the parasitic reaction of TMA. A single-crystalline InAlN film with an Al content of 0-0.43 is successfully grown by adjusting growth temperature and TMA/(TMI+TMA) molar ratio. FWHM of X-ray rocking curve for InAlN is increased with increasing Al content. The carrier concentrations in InAlN films are comparable to that in InN (1-5 × 1019 cm,3). All the single-crystalline InAlN films with an Al content of 0-0.3 show a photoluminescence at room temperature. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Transport properties in n-type AlGaN/AlN/GaN-superlatticesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008J. Hertkorn Abstract In order to improve the lateral conductivity in optoelectronic devices, we have investigated Si-doped AlGaN/AlN/GaN-superlattices. As a first step we performed calculations of the band structure of Al-GaN/AlN/GaN modulation doped multi heterostructures. Based on these results we worked on optimizing the growth of low Al content (xAl, 20%) superlattices by MOVPE. Several tens of abrupt and graded AlGaN/AlN/GaN-layer pairs could be grown crack-free on 2 ,m thick n-GaN layers deposited on sapphire substrates with AlN nucleation. By Van-der-Pauw Hall measurements, we determined that the lateral conductivity of a 1.5 ,m thick superlattice structure is a factor of four higher than in highly n-doped bulk material with comparable thickness without compromising too much the vertical conductivity as confirmed by two step TLM-measurements. At 4K we could demonstrate an extremely high effective mobility of 18760 cm2/Vs at n=2×1014 cm,2 (R=1.6,/®), a clear verification of our excellent crystal quality. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spectroscopic studies of the infrared emission from Tm doped AlxGa1,xN thin filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005E. Nyein Abstract The infrared (IR) emission properties of in-situ Tm doped AlxGa1,xN thin films (0 , x , 1) prepared by solid-source molecular-beam epitaxy were investigated. All samples exhibited 1.48 µm photoluminescence (PL) from the 3H4,3F4 transition of Tm3+. The absolute intensity of the 1.48 µm PL varied strongly with Al content and reached a maximum for Al0.81Ga0.19N:Tm. The integrated 1.48 (m PL from Al0.81Ga0.19N:Tm was weakly temperature dependent and decreased by less than a factor of two between 15 K and 300 K. The PL lifetime of the 3H4 state decreased only slightly from ,102 (s to ,86 (s for the same temperature range. The results suggest that non-radiative decay processes in the 3H4 level are small in Al0.81Ga0.19N:Tm, which is supported by the well-known energy-gap law for multiphonon relaxations. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetic and XPS studies on TbNi5,xAlx systemPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004E. Burzo Abstract Magnetic measurements were performed on TbNi5,xAlx system, in the temperature range 1.7,300 K. At T = 1.7 K the saturation magnetizations are smaller than gJJ value of Tb. The nickel moments at 0 K, determined by band structure calculations are antiparallely oriented to Tb one and decrease in magnitude, being essentially null for TbNi3Al2 sample. The effective nickel moments vary from 2.10 ,B (x = 0) to , 1.10 ,B (x = 2). The XPS studies show that the Ni2p core level lines are similar to those of pure Ni, although the intensities of Ni 6 eV satellite decrease. The valence band spectra suggest an increase of the Ni3d,Al3p hybridization, when increasing Al content, in agreement with band structure calculations. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Thick crack-free AlGaN films deposited by facet-controlled epitaxial lateral overgrowthPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003R. Liu Abstract Thick crack-free AlGaN films have been grown on inclined-facet GaN templates. Light emitting diodes with , = 323 nm has been achieved on these epilayers. The GaN template was grown at a low temperature in order to obtain triangle-facet growth fronts. Subsequent growth of AlGaN on this template involving a lateral overgrowth process exhibits interesting properties. The microstructure and optical characterizations were done using transmission electron microscopy and cathodoluminescence. At the AlGaN/GaN interface, a high density of dislocations was created due to lattice mismatch strain. Another unexpected set of triangular boundaries was observed inside the AlGaN layer, which grew without any change of the growth parameters. These boundaries were found to arise from domains grown in different directions. Mono-chromatic cathodoluminescence images indicate that Al content is different between the vertically-grown and the laterally-grown domains, suggesting that lattice mismatch strain exists between them. Dislocations were created at these mismatched boundaries to relax the strain. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Al14Ba8La26.3Ru18Sr53.7O167: a variant of cubic perovskite with isolated RuO6 unitsACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2010F. J. Zúñiga The crystal structure of the title aluminium barium lanthanum ruthenium strontium oxide has been solved and refined using neutron powder diffraction to establish the parameters of the oxygen sublattice and then single-crystal X-ray diffraction data for the final refinement. The structure is a cubic modification of the perovskite ABO3 structure type. The refined composition is Ba0.167La0.548Sr1.118Ru0.377Al0.290O3.480, and with respect to the basic perovskite structure type it might be written as (Ba8La13.68Sr34.32)(Al13.92La12.64Ru18.08Sr19.36)O192,x, with x = 24.96. The metal atoms lie on special positions. The A -type sites are occupied by Ba, La and Sr. The Ba atoms are located in a regular cuboctahedral environment, whereas the La and Sr atoms share the same positions with an irregular coordination of O atoms. The B -type sites are divided between two different Wyckoff positions occupied by Ru/Al and La/Sr. Only Al and Ru occupy sites close to the ideal perovskite positions, while La and Sr move away from these positions toward the (111) planes with high Al content. The structure contains isolated RuO6 octahedra, which form tetrahedral substructural units. [source] Synthetic hydrotalcites from different routes and their application as catalysts and gas adsorbents: a reviewAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 9 2009M. R. Othman Abstract In this paper, widely accepted methods of hydrotalcite preparation such as co-precipitation, urea hydrolysis, hydrothermal, sol,gel, microwave irradiation, steam activation and solvothermal have been selected and reviewed. Our review indicates that the nature of the divalent cations, the synthesis method, the calcination temperature and the nature of the interlayer species are determinant factors in shaping the surface properties of the layered double hydoxides. The basic strength of the surface base site and structural changes produced in the mixed oxides can be adjusted conveniently by varying the Al content during the synthesis. The combination of sol,gel with microwave irradiation during the gelling and crystallization steps has also been found to increase the surface area of the hydrotalcite-like compound. Copyright © 2009 John Wiley & Sons, Ltd. [source] Melt,wall rock interaction in the mantle shown by silicate melt inclusions in peridotite xenoliths from the central Pannonian Basin (western Hungary)ISLAND ARC, Issue 2 2009Csaba Szabó Abstract In this paper we present a detailed textural and geochemical study of two equigranular textured amphibole-bearing spinel lherzolite xenoliths from Szigliget, Bakony,Balaton Highland Volcanic Field (BBHVF, western Hungary) containing abundant primary silicate melt inclusions (SMIs) in clinopyroxene rims and secondary SMIs in orthopyroxene (and rarely spinel) along healed fractures. The SMIs are dominantly composed of silicate glass and CO2 -rich bubbles. Clinopyroxene and orthopyroxene are zoned in both studied xenoliths, especially with respect to Fe, Mg, Na, and Al contents. Cores of clinopyroxenes in both xenoliths show trace element distribution close to primitive mantle. Rims of clinopyroxenes are enriched in Th, U, light rare earth elements (LREEs) and medium REEs (MREEs). Amphiboles in the Szg08 xenolith exhibit elevated Rb, Ba, Nb, Ta, LREE, and MREE contents. The composition of silicate glass in the SMIs covers a wide range from the basaltic trachyandesite and andesite to phonolitic compositions. The glasses are particularly rich in P2O5. Both primary and secondary SMIs are strongly enriched in incompatible trace elements (mostly U, Th, La, Zr) and display a slight negative Hf anomaly. The development of zoned pyroxenes, as well as the entrapment of primary SMIs in the clinopyroxene rims, happened after partial melting and subsequent crystallization of clinopyroxenes, most probably due to an interaction between hot volatile-bearing evolved melt and mantle wall-rocks. This silicate melt filled microfractures in orthopyroxenes (and rarely spinels) resulting in secondary SMIs. [source] Forming Al2O3,Al Composites with Controlled Compositions by Reactive Metal Penetration of Dense Aluminosilicate PreformsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2000William G. Fahrenholtz Alumina,Al composites with controlled compositions containing 17 to 31 vol% Al were formed by reactive metal penetration (RMP) of molten Al into dense aluminosilicate preforms. A reaction model has been developed to accurately predict composite Al content from the SiO2:Al2O3 ratio of the preform. The model was tested and validated by comparing predicted composite compositions to those measured for RMP composites made from preforms of known compositions. Aluminosilicate preforms containing 28.1, 39.0, and 54.1 wt% SiO2 were reacted with Al to produce composites with 17, 25, and 31 vol% Al, respectively. These values compare favorably to Al contents of 17.7, 22.7, and 28.6 vol% Al predicted using the reaction model. The differences between predicted and measured values are attributed to the presence of porosity and Si in the composites, as well as impurities in the SiO2 glass phase and porosity in the preforms, none of which is specifically accounted for in the reaction model. [source] Geochemical characterization of moldavites from a new locality, the Cheb Basin, Czech RepublicMETEORITICS & PLANETARY SCIENCE, Issue 3 2008anda Detailed comparison of the Cheb Basin moldavites with moldavites from other substrewn fields in both major and trace element composition shows that the Cheb Basin is a separate substrewn field. The geochemical data obtained are discussed with respect to the source materials and processes leading to formation of moldavites. The data show that three groups of Cheb Basin moldavites exist. Ten samples of group 1 are characterized by the lowest content of Al, Fe, Na, and other elements representing phyllosilicate minerals, and by high Ca + Mg contents related probably to carbonates. They resemble the "poisonous green" moldavites, a subgroup of the Southern Bohemian moldavites. Seven samples of group 2 and 6 samples of group 3 are similar to typical moldavites of the Southern Bohemian substrewn field. These two groups differ from each other mainly in Al contents; with higher contents of Al and the elements associated with phyllosilicate minerals (namely Ba and Sr), group 3 also resembles the Moravian moldavites. Significant positive correlations between K, Ca, Mg, and Mn found in group 2 of the Cheb Basin moldavites and the enrichment in these elements observed generally in all moldavites, as well as other facts, e.g., high K/Na and K/Rb ratios and the reduced conditions during formation of moldavites, have been attributed to possible contribution to the moldavite source materials of the ash produced by burning of vegetation and soil organic matter present at the pre-impact area. [source] Oxalate exudation into the root-tip water free space confers protection from aluminum toxicity and allows aluminum accumulation in the symplast in buckwheat (Fagopyrum esculentum)NEW PHYTOLOGIST, Issue 2 2010Benjamin Klug Summary ,A better understanding of aluminum (Al) uptake and transport is expected to contribute to unravel the apparent contradiction between Al exclusion and Al accumulation in buckwheat. ,We studied the effect of Al supply on the root-tip Al and oxalate concentrations of the apoplastic water free space fluid (WFSF) and the symplast as affected by temperature, oxalate supply and the anion-channel blocker phenylglyoxal (PG). ,Aluminum supply rapidly activated the release of oxalate to the WFSF to establish a 1 : 1 Al to oxalate ratio. In the symplast, the Al concentration was 100 times higher than in the external solution, and the Al to oxalate ratio was 1 : 2. Loading and unloading of Al, but not of oxalate, into and from the symplast were reduced at low temperature and are thus under metabolic control. Application of PG reduced the constitutive and the Al-enhanced WFSF oxalate concentrations and enhanced Al-induced root-growth inhibition. Unlike a 1 : 3 Al to oxalate ratio, a 1 : 1 ratio ameliorated only partly Al-induced root-growth inhibition without affecting root-tip Al contents or WFSF Al concentrations. ,We present a hypothesis with an Al oxalate (Ox)+ plasma-membrane transporter in the root cortex and a xylem-loading Al citrate (Cit)n, transporter in the xylem parenchyma cells as key elements of Al accumulation in buckwheat. [source] Spatially resolved cathodoluminescence study on AlGaN layer fabricated by air-bridged lateral epitaxial growthPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2004Akihiko Ishibashi Abstract Structural properties of AlGaN layer on the GaN seed layer fabricated by air-bridged lateral epitaxial growth (ABLEG) have been studied by spatially resolved cathodoluminescence (CL) microscopy. The cross-sectional spatially resolved CL images of the ABLEG-AlGaN layer reveal that there are roughly three regions which have different main CL peaks. This result suggests that there are roughly three regions with the different Al contents. Before coalescence of the overgrown AlGaN wings, there are two regions of Al content, such as about 6.5, 10.6%. On the other hand, after coalescence of the wings, the Al content of the AlGaN layer becomes uniform (Al content = 8.9%). These results suggest that the facet growth of the overgrown AlGaN wings causes the modulation of Al content in the ABLEG-AlGaN layer. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effects of Al composition on luminescence properties of europium implanted AlxGa1,xN (0 , x , 1)PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003Y. Nakanishi Abstract Europium (Eu) ions are introduced into AlxGa1,xN (0 , x , 1) by implantation to investigate the effect of Al composition on the luminescence properties. For all samples with Al contents between 0 and 100%, strong and sharp red emission peaks related to the 4f,4f intra transitions of Eu3+ are observed around 600 , 660 nm at room temperature. The intensity of the Eu3+ -related luminescence increases with increasing Al contents, and the photoluminescence of 5D0,7F2 transition related to Eu3+ shows strongest intensity at Al = 50%. The intensity is 100 times stronger than that of Eu in GaN, and several times stronger than that of near-band-edge emission for un-doped GaN. These results suggest that the luminescence property of Eu3+ can be dramatically improved by using Al0.5Ga0.5N as a host material. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effect of boron on the expression of aluminium toxicity in Phaseolus vulgarisPHYSIOLOGIA PLANTARUM, Issue 2 2007Angelika Stass The interaction of boron (B) and aluminium (Al) was investigated in 5-day-old seedlings of soybean cv. Maple Arrow. Al treatment inhibited root elongation and callose formation in root tips particularly after 4-h Al treatment. After 10 and 24 h, both parameters indicated increasing recovery from Al stress. B deficiency aggravated Al toxicity compared with B sufficiency. B deficiency did lead to an increase in unmethylated pectin in the first 3 mm of the root tip. This increase in potential binding sites is reflected in generally higher Al contents in root tips of B-deficient plants. A fractionated extraction of Al from the root tips showed that citrate-exchangeable and non-exchangeable Al steeply increased up to 4 h, but then decreased after 10- and 24-h Al treatment faster in B-sufficient than in B-deficient plants. This decrease of Al contents can be explained by an Al-enhanced release of citrate from the root tips after 10-h Al treatment. However, the citrate exudation rate was the same (after 10 h) or even lower (after 24 h) in B-sufficient plants and thus cannot explain the faster decrease in Al contents of the root tips compared with the B-deficient plants. We, therefore, propose that under B deficiency, Al is more strongly bound by the pectic network of the cell wall of the root tips, which delays or prevents the recovery from initial Al stress through exudation of citrate, and thus explains the greater Al sensitivity of B-deficient common bean roots. [source] | |||||||||||||||||||