Al Uptake Research Articles

The effect of pH on the kinetics of intra- and extracellular uptake of Al in Fontinalis antipyretica: changes in the cellular contents of K, Mg, and Ca.

The effect of acidity on the accumulation of Al in the aquatic bryophyte Fontinalis antipyretica was studied. The main interest of this study was in characterizing the relationship between the two parameters, as Al is typically mobilized in acidic environments, where it becomes extremely toxic. With this aim, a series of laboratory experiments were carried out where samples of F. antipyretica were held in tanks of water with different concentrations of Al (0.1-3 mg L(-1)) and levels of acidity (pH 3-5. 8). The incubation time varied between 1 and 24 h. In general, the greatest accumulations of both intra- and extracellular Al were found at a pH of 4.4. With the results obtained, the kinetics of both intra- and extracellular Al uptake was characterized, and models constructed for different combinations of Al and acidity. The study was completed by examining the relationship between the pH of the holding water and bioaccumulation of Al and the variation in concentration of cations essential to plant life, which are also indicators of changes in cellular physiology (K, Mg, Ca). In general, losses of these elements were found at intra- and extracellular locations, especially at high pH.

Bioavailability of Al in alum‐treated drinking water

In healthy people, Al uptake from alum‐treated water is low.Several epidemiological studies have associated aluminum (Al) in drinking water with the incidence of Alzheimer's disease, despite the fact that water provides a relatively minor proportion of intake compared with other dietary sources. For Al from alum‐treated drinking water to contribute markedly to blood Al, it would have to be much more bioavailable, i.e., more readily taken up from the gut into the bloodstream, than Al from food. The relative bioavailabilities of Al naturally present in food and in alum‐treated drinking water (ATW) were determined using 29 healthy volunteers who drank, during two‐day periods, ATW or pure water, with and without citrate, while on a controlled diet. Only 1–2 percent of the daily intake of Al came from ATW and only 0.3–0.4 percent of the Al in ATW was absorbed by the body—the same percentage as that absorbed from food. It was estimated that drinking 1.6 L/d of ATW containing 140 μg/L Al would contribute only 0.4–1.1 percent of the lifetime body burden of Al.

Effect of Aluminum and Silicon in Solution on the Growth of Rice (Oryza sativa L.) uspension Cells

Cells of two indica rice (Oryza sativa L.) varieties, one aluminum-tolerant (IAC3), and the other aluminum-sensitive (IR45), were grown in suspension culture in a medium with or without Al (0-800 µM), Si (0-2,000 µM), or Al and Si in combination as well as in R2 medium as control. The influence of Al or Si on cell growth was evaluated based on the growth of the cells in the treatment medium as well as in the R2 medium and compared with the effect on rice seedlings. Similar responses were observed for the cells and the seedlings; Al treatment resulted in a significant reduction of cell growth in both varieties, and the growth was reduced with the increase of the Al uptake by the cells. IAC3 was more tolerant to Al and it absorbed more Al than IR45. On the contrary, Si alone had almost no effect or exerted a negligible effect on the cell growth in both varieties and Si was hardly absorbed by the cells. There was a slight alleviative effect of Si on Al toxicity in the suspension cells of IR45, whereas, a considerable ameliorative effect in the seedlings. The content of total Al and of AI insoluble in citric acid in the cells were higher in the sole Al (800 µM) treatment than in the Al-Si combination treatment. This tendency was also observed in aluminon staining. The differences in the alleviative effects of Si and the uptake of Al and Si between the suspension cells and seedlings may have resulted from the presence of roots and morphological differences in the apoplastic tissues.

Aluminum uptake and aluminum-induced rapid root growth inhibition of rice seedlings

Aluminum (Al) inhibits root growth in acidic soil, but the site of action of Al remains unclear. We investigated whether the rate of Al accumulation correlates to Al-indeced rapid root growth inhibition in rice seedlings (Oryza sativa L. cv. Youngnam). Growth of roots was significantly inhibited by 100 μM AICI3, as early as 1 h after the treatment. The inhibition of root growth was strongly dependent on Al concentration (l50 = 20 (μM) and Al-exposure time (l50 = 23 min at 25 μM Al) in a solution of 10 mM KCI and 1 mM CaCl2 buffered by 10 mM Mes/KOH (pH 4.5). Using ICPES, massive uptake of Al by roots was observed even at 15 min treatment of 25 μM Al. The kinetics of Al uptake by the roots closely corresponded to the inhibitory effects of Al on root growth. When the roots of seedlings were exposed to 50 (μM Al for 1 h, then sectioned and stained with hematoxylin, all cell types of the roots showed the presence of Al in the cytoplasm. These results indicate that Al was rapidly taken up into the root cells and thereby reduced root growth.

Capacity for aluminium uptake depends on brefeldin A-sensitive membrane traffic in tobacco ( Nicotiana tabacum L. cv. BY-2) cells

The relationship between cellular growth and aluminium (Al) uptake was examined by applying brefeldin A, a vesicle transport inhibitor, to cultured tobacco (Nicotiana tabacum L. cv. BY-2) cells. Cultured cells almost completely lost the capacity for Al uptake when pre-incubated for 1–3 h in a minimal medium. Pre-incubation also diminished subsequent growth in a culture medium. However, competency for Al uptake (20 μm, pH 4.5) was sustained in a dose-dependent and reversible manner when cells were treated with brefeldin A (10 μm), an inhibitor of Golgi-mediated secretion, prior to and during the incubation in minimal medium.

Aluminum enhances iron uptake and expression of neurofibrillary tangle protein in neuroblastoma cells.

Aluminum (Al) and iron (Fe) have been implicated as playing a toxic role in the pathologic lesions of Alzheimer's disease. In the following report we describe the uptake and toxicity of Al, the effect of Al on Fe uptake, and the expression of neurofibrillary tangle (NFT) protein in murine neuroblastoma cells (Neuro 2A). Significant cell Al uptake and inhibition of cell growth were seen in Neuro 2A cells at 24, 48, 72, and 96 h after plating in medium containing Al transferrin (Al-Tf) and Al citrate. Al-loaded Neuro 2A cells showed increased rates of 59Fe and 125I-Tf uptake and total cellular Fe content at 24, 48, 72, and 96 h after plating compared with control cultures. Significant increases in NFT protein staining were detected in Al-exposed cells at 72 and 96 h in culture compared with controls. The intensity of NFT staining in Al-loaded cells was directly proportional to the time in culture. There was no difference in malonyldialdehyde levels measured in control versus Al-loaded Neuro 2A cells. These results suggest that the accumulation of Al in Neuro 2A cells resulted in increased uptake of Fe, inhibition of cell growth, and expression of NFT protein, partially mimicking the pathological hallmarks of Alzheimer's disease. This model system may also be applicable for Al-induced dialysis dementia, because the Al concentrations at which cell toxicity occurred can be found in dialysis patients.

Early effects of aluminium on nutrient (K, Ca, and Mg) status of different root zones of two rice cultivars

Effects of aluminium on nutrient (K, Ca, and Mg) status of different root zones were evaluated in two rice cultivars with high (IR45) and low (BG35) Al sensitivity. Roots of the two cultivars were exposed to 140 μM AlCl3 at pH 4.1 for 24 h. The Al accumulation in IR45 was higher than in BG35 in all the root zones. The uptake of Al in apex and middle‐root zone was higher than in the basal zone of both cultivars. The enhanced Al uptake in root apical and middle zones of IR45 induced drastical changes in Ca and Mg concentrations. As these changes occurred without any Al‐growth inhibition, it is suggested that disturbances of these nutrients are the primary lesion of Al in IR45. The results further indicated that competitive interactions between Al and Mg in the Al‐sensitive cultivar have an important role for Al tolerance in rice plants.

Acquisition of aluminum tolerance in Saccharomyces cerevisiae by expression of the BCB or NtGDI1 gene derived from plants

Eleven aluminum stress-induced genes derived from plants (wheat, Arabidopsis and tobacco) were introduced into Saccharomyces cerevisiae to test if expression of these genes confers Al tolerance. Al sensitivity tests showed that expression of two genes, either an Arabidopsis gene for blue copper binding protein ( BCB), or a tobacco gene for the GDP dissociation inhibitor ( NtGDI1), conferred Al tolerance. Determinations of total content and localization of Al ions in these transformants suggested that the BCB gene product functions in restricting Al uptake, while expression of the NtGDI1 gene promotes release of Al ions after uptake.

Acquisition of aluminum tolerance in Saccharomyces cerevisiae by expression of the BCB or NtGDI1 gene derived from plants.

Eleven aluminum stress-induced genes derived from plants (wheat, Arabidopsis and tobacco) were introduced into Saccharomyces cerevisiae to test if expression of these genes confers Al tolerance. Al sensitivity tests showed that expression of two genes, either an Arabidopsis gene for blue copper binding protein (BCB), or a tobacco gene for the GDP dissociation inhibitor (NtGDI1), conferred Al tolerance. Determinations of total content and localization of Al ions in these transformants suggested that the BCB gene product functions in restricting Al uptake, while expression of the NtGDI1 gene promotes release of Al ions after uptake.

Does aluminium affect root growth of maize through interaction with the cell wall – plasma membrane – cytoskeleton continuum?

The mechanism of aluminium-induced inhibition of root elongation is still not well understood. It is a matter of debate whether the primary lesions of Al toxicity are apoplastic or symplastic. The present paper summarises experimental evidence which offers new avenues in the understanding of Al toxicity and resistance in maize. Application of Al for 1 h to individual 1 mm sections of the root apex only inhibited root elongation if applied to the first 3 apical mm. The most Al-sensitive apical root zone appeared to be the 1–2 mm segment. Aluminium-induced prominent alterations in both the microtubular (disintegration) and the actin cytoskeleton (altered polymerisation patterns) were found especially in the apical 1–2 mm zone using monoclonal antibodies. Since accumulation of Al in the root apoplast is dependent on the properties of the pectic matrix, we investigated whether Al uptake and toxicity could be modulated by changing the pectin content of the cell walls through pre-treatment of intact maize plants with 150 mM NaCl for 5 days. NaCl-adapted plants with higher pectin content accumulated more Al in their root apices and they were more Al-sensitive as indicated by more severe inhibition of root elongation and enhanced callose induction by Al. This special role of the pectic matrix of the cell walls in the modulation of Al toxicity is also indicated by a close positive correlation between pectin, Al, and Al-induced callose contents of 1 mm root segments along the 5 mm root apex. On the basis of the presented data we suggest that the rapid disorganisation of the cytoskeleton leading to root growth inhibition may be mediated by interaction of Al with the apoplastic side of the cell wall – plasma membrane – cytoskeleton continuum.

Effects of nitrogen source and aluminum on growth of tropical tree seedlings adapted to low pH soils

The effects of N-source and Al on the growth of seedlings of Melastoma malabathricum, Acacia mangium, and Melaleuca cajuputi, which are tropical woody plants and are very tolerant to Al, and barley (Hordeum vulgare), which is a typical Al-sensitive plant, were investigated. The Al and N treatments consisted of the application of either 0 or 0.5 mM Al, and 2 mM NH4 + or N03 -, respectively. Growth of the tropical plants was enhanced by Al and NH4 application. In all the plant species, the pH of the culture solution decreased and the concentrations of soluble Al and P increased with the + NH4 treatment, which positively affected the growth of the tropical plant species. Excised roots of M. malabathricum dissolved insoluble Al with NH4 application and absorbed Al mainly from root tips. Al did not affect the leaf N concentration except in the case of barley. Roots of M. cajuputi exuded a large amount of citrate, which slightly increased by the + Al treatment. In A. mangium, the reactivity of soluble Al to PCV (pyrocatecholviolet) decreased in the culture solution of the + Al + NH4. treatment and Al concentration of roots in this treatment was very low. Roots of M. malabathricum released H+ along with Al uptake as well as NH4 + uptake. It is concluded that Al and NH4 + exert beneficial effects on the growth of tropical tree seedlings.

Uptake of Aluminium by the root tips of an Al-sensitive and Al-tolerant cultivar of Zea mays

Uptake and compartmentation of Al in the roots tips were investigated in two corn ( Zea mays L.) cultivars (HS7777 single sensitive hybrid and C525-M single tolerant hybrid). Seedlings were grown for 24 h in nutrient solution at pH 4.4 characterized by low ionic strength (2,06 μM) and low Al 3+ activity (10.3 μM). The root elongation decreased strongly for the sensitive cultivar. There were no differences in the contents of total Al in the entire roots between cultivars. Nonexchangeable-Al and exchangeable-Al contents were higher in the root tips of HS7777. The sensitive cultivar also showed higher total and exchangeable-Al contents in excised root tips in 180 min of Al uptake. Al uptake for both cultivars increased in solution containing 0.1 mM of 2,4-dinitrophenol. Al contents were higher for the tolerant cultivar.

Effect of fluoride and phosphate on yield and mineral composition of barley grown on three soils

In a greenhouse experiment, the effect of fluoride (F) and phosphorus (P) addition on the growth and mineral composition of barley (Hordeum vulgare L.) was studied in three different soils, Cahaba sandy loam (acid), Weld loam (neutral), and Haverson silty loam (alkaline calcareous). Four levels of F [0, 100, 400, and 1,000 mg kg‐1 soil as hydrogen fluoride (HF)] and three levels of P [50, 150, and 550 mg kg‐1 soil as phosphoric acid (H3PO4)] were used. The effect of P addition on the native soil F and the capacity of soil to sorb added F was investigated. Addition of P released some of the native F from the soil samples that did not receive any F. The amount of F released ranged from 0.135 to 1.860 mg kg‐1 soil. The amount of F released from the soils decreased with increasing P addition. Most of F added was sorbed by the soil solid phase. The amount of F sorbed ranged between 74.0% and 96.3% of the added F. For both the acid and neutral soils, increasing P addition increased F sorption at all F levels. In the case of alkaline soil, however, this effect was only clear at the low F level. The formation of insoluble F minerals may be enhanced by the addition of P to the soils. In the greenhouse experiment, F addition had a negative effect on dry matter yield (DMY) of barley grown on the acid and neutral soil while no effect was observed for the alkaline soil. These results may reflect the effect of F addition on the solubility of aluminum (Al) and other metals in the soils. On the other hand, increasing F addition from 50 to 550 mg kg‐1 soil had no clear effect on DMY of plants in the three soils. The study also included the effect of F and P addition on their uptake by plants. Generally, addition of P depressed F uptake by plants grown on the three soils. On the other hand, increasing F addition depressed P uptake for the acid soil while no clear trend was observed for the neutral and alkaline soil. A significant positive effect of F addition on Al uptake was observed for both the acid and neutral soils. A highly significant correlation of 0.87 and 0.60 was obtained between soil extractable F and Al uptake for the acid and neutral soil, respectively. Addition of F to the alkaline soil resulted in minor increases in Al uptake. The effect of P addition, at different levels of F, on Al uptake was investigated for the three soils. For the acid soil, significant decrease in Al uptake was observed only at the highest F level. The effect of P addition on Al uptake was not clear in the other two soils.

P-Cresol, a uremic compound, enhances the uptake of aluminum in hepatocytes.

In the end-stage renal disease patient, certain uremic compounds could influence the cellular accumulation of aluminum (Al). In this study, we examined the effect of 15 uremic ultrafiltrate fractions obtained by HPLC on the uptake and toxicity of Al in mouse hepatocytes (MH) in culture, a model system in which Al is taken up bound to transferrin (Tf). Uremic fractions 4 to 8, 12, 14, and 15 increased cellular Al uptake and aspartate aminotransferase release and decreased cell growth when Tf-Al, not Al citrate, was added to culture media. Compounds that have been extracted previously from these ultrafiltrate fractions (p-cresol, xanthine, tryptophan, hippuric acid, and o-hydroxyhippuric acid) were then tested for their effect on Al uptake and toxicity in MH at concentrations found in uremic serum. Significant Al uptake by MH was observed only when p-cresol was added together with Tf-Al. Time-response curves showed increased Al uptake and toxicity at p-cresol concentrations of 3 mg/dl in culture media. Dose-response curves confirmed that Al uptake and cell toxicity were proportional to p-cresol from 1.5 mg/dl to 3 mg/dl in culture media. p-Cresol was not toxic to MH in the absence of Tf-Al in media. p-Cresol increased Tf-associated Al uptake only because there was no effect on Al uptake when Al citrate was substituted, and studies with Tf-I125-Al in the presence of this compound showed increased Tf-I125 taken up by MH. p-Cresol did not increase Tf saturation with Al. p-Cresol also increased Tf-Al uptake in Friend erythroleukemia and neuroblastoma cells in culture. Our studies suggest that p-cresol and uremic fractions 4 to 8, 12, 14, and 15 increase the uptake and toxicity of Al in cultured MH. These compounds may play a role in the accumulation and toxicity of Al in the liver of end-stage renal disease patients and possibly in all cells that express Tf receptors.

Effect of corncob compost on plant growth in an acid red soil

A comparison of corncob compost with lime on plant growth was studied in acid red soil with pH of 4.07. Lettuce, pea, and corn were selected as test plants for their varying tolerance to acid soil. The pot experiment compared six soil treatments and a check. Soil amendments were 1, 2, and 4 cmol calcium carbonate (CaCO3) kg‐1 and 5, 10, and 20 g corncob compost kg‐1 soil. Results showed higher manganese (Mn) than aluminum (Al) content of the shoot in all check group plants. Reduced shoot Mn content increased shoot dry weight in all test plants, regardless of acid soil tolerance or soil treatment. The higher the test plant resistance to soil acidity, the weaker the detoxification effect of corncob compost was on Al uptake when compared with the check group. Liming was more effective at reducing shoot Mn content than corncob compost with the exception of the more acidity sensitive lettuce. Shoot phosphorus (P) content, however, increased with corncob compost from enhanced organic matter rates. Corncob compost treatments significantly increased shoot dry weight over liming in the acid soil. This study demonstrated an environmentally acceptable use for an agricultural waste.

The influence of dissolved silicate on the physiological chemistry of aluminium, studied in humans using tracer 26Al and accelerator mass spectrometry

Trace quantities of aluminium, spiked with 26Al, were administered twice, to each of two subjects, in citrate-containing drinks (4 or 50 mmol/l). Silicate (0.5 mmol/l), in the form of a Si-rich natural mineral water, was added to the dose on the second occasion for each subject. Al-uptake and excretion were determined from AMS measurement of 26Al in blood plasma (whole plasma and the low molecular weight fraction) and urine for up to 7 days. Citrate markedly enhanced Al uptake, as previously observed. A major effect of silicate was to enhance the rate of Al elimination, probably through an increase in the LMW plasma fraction (5% with no Si; 7.5% with Si). Aluminium uptake appeared to be only slightly affected by Si, and showed opposite effects depending on citrate concentration. With low citrate, Si marginally increased Al uptake, whilst with high citrate, Al uptake appeared to be reduced by the presence of Si.

Aluminum and Phosphorus Interactions in Mycorrhizal and Nonmycorrhizal Highbush Blueberry Plantlets

Aluminum (Al) and phosphorus (P) interactions were investigated in mycorrhizal (M) and nonmycorrhizal (NM) highbush blueberry (Vaccinium corymbosum L.) plantlets in a factorial experiment. The toxic effects of Al on highbush blueberry were characterized by decreased shoot, root, and total plant dry mass. Many of the negative effects of Al on plant root, shoot, and total dry matter production were reversed by foliar P and N application, indicating P or N uptake were limited by high Al concentration. However, Al-mediated growth reduction in P-stressed plants indicated that the restriction of P uptake by high Al may not have been the only mechanism for Al toxicity in this experiment. Root Al and P concentration were negatively correlated in NM but not M plantlets, suggesting mycorrhizal infection may alter P uptake processes. Al uptake was also affected by mycorrhizal infection, with more Al accumulating in M plantlet roots and leaves. Correlations among foliar ion concentrations were also affected by mycorrhizal fungal infection.

Uptake of Al across the plasma membrane of plant cells

Measurements of intracellular, cytosolic Al are plagued with technical difficulties. An accurate quantification of Al uptake into the cytosol relies on the effectiveness of the methods that desorb Al bound to the cell wall. However, published desorption methods are not completely effective in removing cell wall Al. Using giant algal cells of Chara corallina, where a physical separation of the cell wall and the cytosol can be achieved surgically, it was shown that up to 99.99% of the total cellular Al accumulates in the cell wall. Even when 95% of total Al present in intact cells was desorbed, still over 20 times more Al was left in the cell wall than in the cytosol. Therefore, without physical separation of the cell wall and the cytosol, minute amounts of cytosolic Al need to be measured in the considerably larger background of the cell wall Al. Consequently, up to several orders of magnitude lower uptake rates of Al were measured across the plasma membrane of intact Chara cells in comparison to currently available values on higher plant cells (Triticum aestivum, t Glycine max, Phaseolus vulgaris), where at least some of the cell wall Al was attributed to the intracellular, cytosolic Al. Uptake of Al across the plasma membrane of Chara cells occurs without a delay at a very low rate that is directly proportional to Al concentration in the uptake medium. Moreover, residual Al left in the cell wall after desorption can be taken up into the cytosol of Chara cells during subsequent growth in the artificial pond water. For measuring Al uptake into roots of higher plants, the Secondary Ion Mass Spectrometry is the best available technique because it appears to overestimate the cytosolic Al to the lower extent than any other currently used analytical method for determination of Al.

Influence of silicon pretreatment on aluminium toxicity in maize roots

The influence of Si pretreatment on Al toxicity in an Al sensitive maize variety (Zea mays L. var. BR 201 F) was investigated using root elongation rates (RER) and hematoxylin staining as stress indicators. Plants pretreated with 1 mt M Si (+ Si) and then exposed for 24 h to Al in nutrient solution without concurrent Si supply in the rooting medium exhibited higher RER than plants that were not pretreated with Si (-Si). The ameliorative effect of Si was due to lower Al uptake and to the exclusion of Al from the root tips in + Si plants. Lower Al uptake in + Si plants was not a consequence of decreased Al availability in the bulk solution. The possible mechanisms of Si-induced increase of Al resistance are discussed

Spatial variation in the kinetics of aluminium (Al) uptake in roots of wheat ( Triticum aestivum L.) exhibiting differential resistance to Al. Evidence for metabolism-dependent exclusion of Al

Summary We have investigated the kinetics of Al uptake into various root segments and have compared uptake between two wheat (Triticum aestivum L.) cultivars that differ in their ability to resist Al toxicity. Following 60 and 180 min of exposure to Al, we found no differences in total Al accumulation between root tips (0–5 mm) and more mature root regions (5–10 and 10–20 mm). However, when roots were exposed to Al and subsequently desorbed in citric acid to remove exchangeable Al in the cell wall and in NH4Cl to remove the mucilage, non-exchangeable Al levels in root tips were 33 to 37% greater than in mature root regions. When the rate of accumulation of non-exchangeable Al in 20 mm root tips between an Al-resistant cultivar (PT 741) and an Al-sensitive cultivar (Neepawa) was compared, no differences were observed. When the same comparison was made in 5 mm root tips, the rate of Al accumulation in the Al-sensitive cultivar was nearly twice that in the Al-resistant cultivar. Furthermore, the rate of Al uptake in the Al-resistant cultivar increased dramatically in the presence of the metabolic inhibitor and protonophore, DNP, while DNP had little effect on uptake in the sensitive cultivar. This effect of DNP was also specific to root tip tissue. Our results support the hypothesis that DNP inhibits an Al exclusion mechanism operating at the plasma membrane in Al-resistant cultivars.