Aluminum and low pH effects on translatable RNA population from bean calli

Summary We have reproduced in vitro aluminium toxicity on bean calli for the purpose of analyzing how gene expression is modified by aluminum ions (Al). We have used three different media. L3m with reduced Ca and P_i concentration and a pH of 5.7; L3m4, similar, but with a pH of 4.0; and L3m4Al with the same composition and pH as L3m4, but with Al salt (AlCl₃) (500 mg/l) added. We cultured genotypically identical calli for 24 h and 1 month in the three media. Total RNA was obtained from all the calli and in vitro translated. The polypeptides obtained were resolved by two-dimensional polyacrylamide gel electrophoresis (2-D-PAGE) and compared. After the 24 h of treatment the three patterns were similar and only quantitative differences between L3m4Al-cultured and calli cultured in the two other media were detected. These differences disappeared after one month of treatment and new spots were detected in 2-D-PAGE of L3m4- and L3m4Al-cultured calli, but not in L3m. The differences observed after the 24-h treatment could be due to the ageing of the calli rather than to Al toxicity, and those described at 1 month seemed to be mostly related to pH. We suggest that Al does not specifically affect gene expression. The induced changes appeared later in time and were mainly related to low pH; only one polypeptide was associated with Al after the 1-month treatment.     

The role of the plasmalemma in metal tolerance in angiosperms

Evidence for the role of the plasmalemma in metal tolerance of metal resistant ecotypes, cultivars and clones is presented. A range of tolerance mechanisms involving the plasmalemma are discussed including alterations to protein carrier and channel function and synthesis, efflux pumps and maintenance of plasmalemma integrity. Specific examples of such alterations from the literature on Al, As and Cu tolerance, where the plasmalemma has been shown to have a role in tolerance are considered. Tolerance by alterations to plasmalemma function in tolerant ecotypes may also rely on internal metal detoxification mechanisms constitutive in tolerant and non-tolerant plants.     

Heme oxygenase induction

The effect of repeated parenteral administration of aluminum (Al) was investigated to determine if a relationship exists between the severity of anemia and increase in hepatic heme oxygenase activity. Female Swiss Webster mice were dosed for 11 d with 50 mg Al/kg, as Al lactate, and sodium lactate was given to control mice. On d 12, hematocrit, hemoglobin, blood smears, hepatic heme oxygenase activity, and cytochrome P450 levels were assessed. Significant decreases in hematocrit (39.1±0.7 vs 43.1±0.3% in controls) and hemoglobin (13.1±0.4 vs 14.2±0.2 g/dL in controls) were produced by Al administration. Blood smears from Al-treated mice consistently showed smaller, more irregular red cells. Cytochrome P450 content was significantly decreased (0.443±0.043 vs 0.665±0.055 nmol/mg) whereas hepatic heme oxygenase activity was significantly increased (2.75±0.34 vs 1.66±0.20 nmol/mg/h) in Al-treated animals. The production of mild anemia by parenteral aluminum correlated significantly with the increase in heme oxygenase activity, which, although only 66% greater than in control, preceded a significant loss of cytochrome P450. The increased heme oxygenase activity, with subsequent increased destruction of heme and/or heme proteins is discussed as a possible mechanism for the microcytic, hypochromic anemia associated with Al overload.     

Influence of aluminum in nutrient solutions on chemical composition in upland rice cultivars

Summary Aluminum toxicity is an important growth limiting factor for upland rice production on oxisols of cerrado region in Brazil. Data related to the effect of Al on uptake of nutrients for rice crop are limited. The effect of five Al concentrations (0, 10, 20, 40 and 60 ppm) in culture solution on the chemical composition of 30 upland rice cultivars was studied.Aluminum concentration and content in plant tissues were increased with higher levels of Al in all cultivar. In the roots Al content was higher as compared with the tops. Critical toxic level of Al in the tops of 21 days old plants varied from 100 to 417 ppm depending on the cultivars. Rice cultivars responded differently to Al treatments with respect to nutrients uptake. Increased Al concentrations in the solution exerted an inhibiting effect on the concentrations and contents of N, P, K, Ca, Mg, S, Na, Zn, Fe, Mn, B and Cu. Thus the inhibition was more effective for macronutrients in the plant tops in following order: Mg>Ca>P>K>N>S>Na. Whereas for micronutrients it was in the order of Mn>Zn>Fe>Cu>B. Morphological, physiological and biochemical effects of Al, toxicity responsible for the reduction in plant nutrient uptake, are discussed.     

Influence of aluminum on motility and swarming of Pseudomonas sp. and Arthrobacter sp.

The effect of Al on the motility and the swarming of Pseudomonas sp. and Arthrobacter sp. was investigated. pH calibration curves were determined in semi-solid agar which enabled us to distinguish between the effects of aluminum and protons. Motility of the bacteria was distinctly influenced by Al but this effect could be attributed to the increased acidity accompanying Al addition. The swarming of Pseudomonas sp. is reported for the first time. The swarming ability decreased with both Al and HCl addition to the medium but the obstruction due to aluminum was significantly stronger than the influence of HCl.     

Long-term trends in soil solution and stream water chemistry at the Hubbard Brook Experimental Forest: relationship with landscape position

In acid-sensitive watersheds of the northeastern US, decreases in SO₂ emissions and atmospheric deposition of sulfur have not been accompanied by marked changes in pH and acid neutralizing capacity (ANC). To better understand this phenomenon, we investigated the long-term trends in soil solution (1984–1998) and stream water (1982–2000) chemistry along a natural soil catena at the Hubbard Brook Experimental Forest, New Hampshire, USA. Significant declines in strong acid anion concentrations were accompanied by declines in base cation concentrations in soil solutions draining the Oa and Bs soil horizons at all elevations. The magnitude of change varied with position in the landscape. Recovery, as indicated by increasing ANC (mean 2.38µEqL^–1year^–1) and decreasing concentrations of inorganic monomeric Al (mean 1.03µmolL^–1year^–1), was confined to solutions draining the Bs horizon at mid-to-higher elevations. However, persistently low Ca²⁺/Al_i ratios (<1) in Bs soil solutions at these sites may be evidence of continuing Al stress to trees. In Bs soil solution at a lower elevation site and in Oa soil solutions at all sites, declines in base cations (mean 3.71µEqL^–1year^–1) were either similar to or exceeded declines in strong acid anions (mean 3.25µEqL^–1year^–1) resulting in no change in ANC. Changes in the chemistry of stream water reflected changes in soil solutions, with the greatest improvement in ANC occurring at high elevation and the rate of increase decreasing with decreases in elevation. The pH of soil solutions and stream waters either declined or did not change significantly. Therefore pH-buffering processes, including hydrolysis of Al and possibly the deprotonation of organic acids, have prevented increases in drainage water pH despite considerable reductions in inputs of strong acids.     

Effects of acute and chronic coingestion of AlCl3 with citrate or polyphenolic acids on tissue retention and distribution of aluminum in rats

Aluminum (Al) is toxic to certain biological systems and has been implicated as a neurotoxic agent in the pathogenesis of Alzheimer’s disease. Intestinal absorption of Al is very low (0.1%), but many organic dietary components are potential chelators of Al and may enhance its absorption and tissue distribution. We examined the effects of acute and chronic coingestion of AlCl₃ with different polyphenolic acids on Al retention and compared to citrate in rats. In experiment 1, animals fasted for 14 h were dosed orally with demineralized water, Al chloride, Al chloride plus sodium citrate, or Al chloride plus a polyphenol acid. Blood samples were taken before and 2 h after the gavage and animals were killed 6 h later. In experiment 2, the rats were adapted on a purified diet for 1 wk and received the following for 4 wk in their experimental diets: AlCl₃, except group 1, plus citrate or a polyphenol acid, except groups 1 and 2. Animals were killed and blood and tissues were sampled. In experiment 1, citrate highly enhanced Al absorption and its tissue retention. Gallic and chlorogenic acids significantly increased tibia and kidney Al levels compared to the Al group. In experiment 2, Al levels in the urine were significantly increased in all the Al groups compared to the control group. Significantly higher Al levels in the tibia, kidney, and brain were observed in the citrate group and a significant increase in brain Al level was also noted in the chlorogenic acid group compared to AlCl₃ group. This may suggest a possible relation structure-activity of polyphenol acids. However, further studies are necessary to better understand the influence of polyphenol acids on Al metabolism, in particular that of chlorogenic acid.     

Aluminum-induced cell death of barley-root border cells is correlated with peroxidase- and oxalate oxidase-mediated hydrogen peroxide production

The function of root border cells (RBC) during aluminum (Al) stress and the involvement of oxalate oxidase, peroxidase and H₂O₂ generation in Al toxicity were studied in barley roots. Our results suggest that RBC effectively protect the barley root tip from Al relative to the situation in roots cultivated in hydroponics where RBC are not sustained in the area surrounding the root tip. The removal of RBC from Al-treated roots increased root growth inhibition, Al and Evans blue uptake, inhibition of RBC production, the level of dead RBC, peroxidase and oxalate oxidase activity and the production of H₂O₂. Our results suggest that even though RBC actively produce active oxygen species during Al stress, their role in the protection of root tips against Al toxicity is to chelate Al in their dead cell body.     

Reverse genetic analysis of the glutathione metabolic pathway suggests a novel role of<Emphasis Type="Italic"> PHGPX</Emphasis> and<Emphasis Type="Italic"> URE2</Emphasis> genes in aluminum resistance in<Emphasis Type="Italic"> Saccharomyces cerevisiae</Emphasis>

We have taken a systematic genetic approach to study the potential role of glutathione metabolism in aluminum (Al) toxicity and resistance, using disruption mutants available in Saccharomyces cerevisiae. Yeast disruption mutants defective in phospholipid hydroperoxide glutathione peroxidases (PHGPX; phgpx1 , phgpx2 , and phgpx3), were tested for their sensitivity to Al. The triple mutant, phgpx1 /2/3, was more sensitive to Al (55% reduction in growth at 300 M Al) than any single phgpx mutant, indicating that the PHGPX genes may collectively contribute to Al resistance. The hypersensitivity of phgpx3 to Al was overcome by complementation with PHGPX3, and all PHGPX genes showed increased expression in response to Al in the wild-type strain (YPH250), with maximum induction of approximately 2.5-fold for PHGPX3. Both phgpx3 and phgpx1/2/3 mutants were sensitive to oxidative stress (exposure to H₂O₂ or diamide). Lipid peroxidation was also increased in the phgpx1/2/3 mutant compared to the parental strain. Disruption mutants defective in genes for glutathione S-transferases (GSTs) (gtt1 and gtt2), glutathione biosynthesis (gsh1 and gsh2), glutathione reductase (glr1) and a glutathione transporter (opt1) did not show hypersensitivity to Al relative to the parental strain BY4741. Interestingly, a strain deleted for URE2, a gene which encodes a prion precursor with homology to GSTs, also showed hypersensitivity to Al. The hypersensitivity of the ure2 mutant could be overcome by complementation with URE2. Expression of URE2 in the parental strain increased approximately 2-fold in response to exposure to 100 M Al. Intracellular oxidation levels in the ure2 mutant showed a 2-fold (non-stressed) and 3-fold (when exposed-to 2 mM H₂O₂) increase compared to BY4741; however, the ure2 mutant showed no change in lipid peroxidation compared to the control. The phgpx1/2/3 and ure2 mutants both showed increased accumulation of Al. These findings suggest the involvement of PHGPX genes and a novel role of URE2 in Al toxicity/resistance in S. cerevisiae.Communicated by D.Y. Thomas     

Bone aluminum uptake in uremic rats receiving intraperitoneal iron

To assess the effect of concomitant iron and aluminum loads on bone aluminum accumulation and on the response to the deferoxamine test in rats with the same aluminum surcharge, Wistar rats with chronic renal failure were divided into three groups: iron-overloaded rats (N=6) (intraperitoneal iron); iron-depleted rats (N=6) (blood withdrawal two to three times per week); control rats (N=4) (no manipulation). All groups received intraperitoneal aluminum simultaneously. After 6 wk, a deferoxamine challenge test was performed. Thereafter, bone aluminum and iron were measured. The iron-overloaded rats showed higher bone iron content (iron overloaded: 147.7±55.4 μg/g; iron depleted: 7.9±1.0, and controls 13.3±9.9 μg/g, p<0.010) and lower bone aluminum content (iron overloaded: 14.2±4.0 μg/g; iron depleted: 70.9±35.1 μg/g; controls: 72.7±28.3 μg/g p<0.005). No differences were found between the iron-depleted and control rats. After the deferoxamine infusion, the iron-depleted rats tended to have higher serum aluminum increments (p=NS) and higher urinary aluminum excretion (p<0.012, p<0.020) than control rats despite similar amounts of aluminum in bone of the two groups. Aluminum bone accumulation was minor if iron and aluminum loads were given concomitantly. The iron depletion influenced the results of the deferoxamine challenge test in rats with similar bone aluminum burden.