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81.
We report on the synthesis, characterization and photophysical properties of a new symmetrically tetra substituted {at non-peripheral positions with tetra(1,1′-bi-binaphtoxy)} phthalocyanines containing H2, Mg(II), Al(III)Cl, Si(IV)Cl2 in the central cavity. The synthesized compounds were characterized by the elemental analyses, UV-Vis, FT-IR and 1H NMR spectroscopies. The fluorescence quantum yields, triplet quantum yields and lifetimes of the newly synthesized H2, Mg, Al, and Si phthalocyanines were explored. Triplet quantum yields ranged from 0.24 to 0.54. The triplet lifetime for the silicon phthalocyanine derivative was the highest ever reported for a phthalocyanine (∼3.5 ms). 相似文献
82.
M. D. Vázquez 《Plant biology (Stuttgart, Germany)》2002,4(2):234-249
Abstract: Ultrastructural studies, together with X-ray microanalytical, immunocytochemical and cytochemical analysis performed in root tips of Al-resistant (C-525 M) and Al-sensitive (Adour 250, HS 7777 and BR 201 F) maize plants ( Zea mays L.), after 96 h exposure to 20 μM Al, showed qualitatively similar results in the four cultivars.
Al was identified in electron-opaque precipitates, which were insoluble even in EDTA chelate. They also contained an elevated proportion of P and also of K and Ca, some traces of Mn, Fe and Zn and sometimes of Mg. This elemental composition is similar to that described for phytin (Al-phytin), and the precipitates were localized in the two principal extraplasmatic compartments: cell walls and vacuoles. Al-phytin was detected in swollen areas of cell walls in membraneous concentric configurations, resembling myelin figures, probably rich in phosphatidyl inositol, which also intervene in the vacuolar internalization of Al-phytin and are similar to a peculiar form of endocytosis (not previously described). Abnormal apoplastic protuberances containing abundant electron-opaque Al-phytin deposits, agglutinated by callose (immunocytochemically identified), were shown in cortex cells with high mitotic activity (around 1 - 1.5 mm from cap root). Al-hyperaccumulator cells parallel to the root axis were correlated with longitudinal lysigenous intercellular spaces after cell death and dissolution (lysigeny). Indicators of activated lysigeny, as low levels of Al and callose (in agreement with other authors) and high levels of phosphoinositides, can mark Al-resistant genotypes, contrary to Al-sensitive genotypes, probably derived from a partially activated or even inactivated lysigeny.
The lysigeny of Al hyperaccumulator cells constitutes new ultrastructural evidence of an Al exclusion mechanism, supporting biochemical results reported by other investigators. 相似文献
Al was identified in electron-opaque precipitates, which were insoluble even in EDTA chelate. They also contained an elevated proportion of P and also of K and Ca, some traces of Mn, Fe and Zn and sometimes of Mg. This elemental composition is similar to that described for phytin (Al-phytin), and the precipitates were localized in the two principal extraplasmatic compartments: cell walls and vacuoles. Al-phytin was detected in swollen areas of cell walls in membraneous concentric configurations, resembling myelin figures, probably rich in phosphatidyl inositol, which also intervene in the vacuolar internalization of Al-phytin and are similar to a peculiar form of endocytosis (not previously described). Abnormal apoplastic protuberances containing abundant electron-opaque Al-phytin deposits, agglutinated by callose (immunocytochemically identified), were shown in cortex cells with high mitotic activity (around 1 - 1.5 mm from cap root). Al-hyperaccumulator cells parallel to the root axis were correlated with longitudinal lysigenous intercellular spaces after cell death and dissolution (lysigeny). Indicators of activated lysigeny, as low levels of Al and callose (in agreement with other authors) and high levels of phosphoinositides, can mark Al-resistant genotypes, contrary to Al-sensitive genotypes, probably derived from a partially activated or even inactivated lysigeny.
The lysigeny of Al hyperaccumulator cells constitutes new ultrastructural evidence of an Al exclusion mechanism, supporting biochemical results reported by other investigators. 相似文献
83.
Plants growing in acid soils suffer both phosphorus (P) deficiency and aluminum (Al) toxicity stresses. Selection of genotypes for adaptation to either P deficiency or Al toxicity has sometimes been unsuccessful because these two soil factors often interact. Two experiments were conducted to evaluate eight cowpea genotypes for Al resistance and to study the combined effect of P deficiency and Al toxicity stress on growth, P uptake, and organic acid anion exudation of two genotypes of contrasting Al resistance selected from the first experiment. Relative root inhibition by 30 μM Al ranged from 14% to 60% and differed significantly among the genotypes. Al significantly induced callose formation, particularly in Al-sensitive genotypes. P accumulation was significantly reduced (28% and 95%) by Al application for both the Al-resistant and the Al-sensitive genotypes. Al supply significantly enhanced malate release of root apices of both genotypes. However, the exudation rate was significantly higher in the Al-resistant genotype. P deprivation induced an enhanced malate exudation in the presence of Al only in the Al-resistant genotype IT89KD-391. Citrate exudation rate of the root apices was lower than malate exudation by a factor of about 10, and was primarily enhanced by P deficiency in both genotypes. Al treatment further enhanced citrate exudation in P-sufficient, but not in P-deficient plants. The level of citrate exudation was consistently higher in the Al-resistant genotype IT89KD-391 particularly in presence of Al.It is concluded that the Al-resistant genotype is better adapted to acid Al-toxic and P-deficient soils than the Al-sensitive genotype since both malate and citrate exudation were more enhanced by combined Al and P-deficiency stresses. 相似文献
84.
The aim of this work was to investigate as to how neurons and glial cells separated from the brain cortex respond to oxidative
stress induced by aluminum. Female SD rats were exposed to aluminum at the dose level of 100 mg/kg b.w. for 8 weeks. Neuronal
and glial cell-enriched fractions were obtained from rat cerebral cortex by sieving the trypsinated homogenate through a series
of nylon meshes, followed by centrifugation on ficoll density gradient. Total glutathione content, glutathione peroxidase
(GPx), glutathione reductase (GR), and glutathione-s-transferase (GST) along with antioxidant enzymes superoxide dismutase
(SOD), catalase were estimated in neuronal and glial-enriched fractions in both control (N-c and G-c) and aluminum exposed
animals (N-a and G-a). Secondary products of lipid peroxidation that is MDA levels were estimated by measuring the (TBARS)
levels. Our results indicate that TBARS levels were significantly higher in glial cell fraction of unexposed controls (Gc)
than the neuronal cells (Nc). Correspondingly the glial cells had higher levels of GSH, GSSG, GPx and GST where as neurons
had higher levels of catalase, SOD and GR. Following aluminum exposures significant increase in the TBARS levels was observed
in neurons as compared to glial cells which also showed a significant decrease in SOD and catalase activity. The decrease
in the TBARS levels in the glial cells could be related to the increase in the GSH levels, GR activity, and GST activity which
were found to be increased in glial enriched fractions following aluminum exposure. The increase in activity of various enzymes
viz GR, GST in glial cells as compared to neurons suggests that glial cells are actively involved in glutathione homeostasis.
Our conclusion is that glial and neurons isolated from rat cerebral cortex show a varied pattern of important antioxidant
enzymes and glial cells are more capable of handling the oxidative stress conditions. 相似文献
85.
Aluminum (Al3+) has been recognized as a main toxic factor in crop production in acid lands. Phosphatidic acid (PA) is emerging as an important
lipid signaling molecule and has been implicated in various stress-signaling pathways in plants. In this paper, we focus on
how PA generation is affected by Al3+ using Coffea arabica suspension cells. We pre-labeled cells with [32P]orthophosphate (32Pi) and assayed for 32P-PA formation in response to Al3+. Treating cells for 15 min with either AlCl3 or Al(NO3)3 inhibited the formation of PA. In order to test how Al3+ affected PA signaling, we used the peptide mastoparan-7 (mas-7), which is known as a very potent stimulator of PA formation.
The Al3+ inhibited mas-7 induction of PA response, both before and after Al3+ incubation. The PA involved in signaling is generated by two distinct phospholipid signaling pathways, via phospholipase
D (PLD; EC: 3.1.4.4) or via Phospholipase C (PLC; EC: 3.1.4.3), and diacylglycerol kinase (DGK; EC 2.7.1.107). By labeling
with 32Pi for short periods of time, we found that PA formation was inhibited almost 30% when the cells were incubated with AlCl3 suggesting the involvement of the PLC/DGK pathway. Incubation of cells with PLC inhibitor, U73122, affected PA formation,
like AlCl3 did. PLD in vivo activation by mas-7 was reduced by Al3+. These results suggest that PA formation was prevented through the inhibition of the PLC activity, and it provides the first
evidence for the role of Al toxicity on PA production. 相似文献
86.
We demonstrated that magnesium (Mg) can alleviate aluminum (Al) toxicity in rice bean [Vigna umbellata (Thunb.) Ohwi & Ohashi] more effectively than is expected from a non-specific cation response. Micromolar concentrations of Mg alleviated the inhibition of root growth by Al but not by lanthanum, and neither strontium nor barium at the micromolar level alleviates Al toxicity. Aluminum also induced citrate efflux from rice bean roots, and this response was stimulated by inclusion of 10 microM Mg in the treatment solution. The increase in the Al-induced citrate efflux by Mg paralleled the improvement in root growth, suggesting that the ameliorative effect of Mg might be related to greater citrate efflux. Vanadate (an effective H+-ATPase inhibitor) decreased the Al-induced citrate efflux, while addition of Mg partly restored the efflux. Mg addition also increased the activity of Al-reduced plasma membrane H+-ATPase, as well as helping to maintain the Mg and calcium contents in root apices. We propose that the addition of Mg to the toxic Al treatment helps maintain the tissue Mg content and the activity of the plasma membrane H+-ATPase. These changes enhanced the Al-dependent efflux of citrate which provided extra protection from Al stress. 相似文献
87.
Aluminum toxicity in acid soils severely limits crop productivity through inhibition of root growth and, consequently, shoot
development. Several Arabidopsis mutants were previously identified as having roots with Al hypersensitivity, suggesting that these represent deleterious
mutations affecting genes required for either Al tolerance or resistance mechanisms. For this report, the als1-1 mutant was chosen for further characterization. The phenotype of als1-1 is most obviously presented in Al challenged roots, as evidenced by exaggerated root growth inhibition in conjunction with
increased expression of Al-responsive genes compared to wt. Using a map-based cloning approach, the als1-1 mutation was isolated and found to represent a deleterious amino acid substitution in a previously uncharacterized half type
ABC transporter, At5g39040, which is expressed in a non-Al dependent manner in all organs tested. GUS-dependent analyses revealed that ALS1 expression is primarily localized to the root tip and the vasculature throughout the plant. Concomitant with this, an ALS1:
GFP fusion accumulates at the vacuolar membrane of root cells, indicating that ALS1 may be important for intracellular movement
of some substrate, possibly chelated Al, as part of a mechanism of Al sequestration. 相似文献
88.
Peptides with the ability to specifically bind aluminum would potentially be of great use in the fields of biochemistry and environmental chemistry. Unfortunately no such peptides are known. An aluminum-specific peptide may be used as an in vivo chelator, for metalloprotein design, for understanding metal-ion induced folding and metal-ion trafficking, and as an environmental sensor to monitor metal pollution in the environment. Plants genetically engineered to produce an aluminum binding peptide might be useful in environmental remediation in areas of high free aluminum ion concentration. In this paper, which is the theoretical complement to the experimental work, we analyzed crystallographic structures of EF-hands bound to various metals in order to determine the ligand distances and identities to compare to metal-ion size, charge, electronegativity, and coordination number and performed energy minimization calculations to identify possible mutations. We then constructed various mutant sequences in silico in an isolated EF-hand from troponin C and analyzed their binding behavior using molecular mechanics for binding to Tb(3+) as compared to Al(3+). As a result of these analyses we were able to isolate some characteristics that could lead to mutant peptides with enhanced aluminum activity that we plan to test experimentally in the future. We also performed metal-ion binding studies with the isolated EF-hand used in the computational work to examine the ability of Al(3+) and comparative metals to bind the peptide. In competition studies, the peptide demonstrated preference for Tb(3+) over Al(3+). 相似文献
89.
Suzuki T Tamura S Nakanishi H Tashiro M Nishizawa NK Yoshimura E 《Biological trace element research》2007,120(1-3):257-263
The budding yeast Saccharomyces cerevisiae secretes 2-isopropylmalic acid (2-iPMA), an intermediate in leucine biosynthesis. Because 2-iPMA binds Al(III) in the culture
medium, it is thought to reduce toxicity by Al(III). The effects of 2-iPMA and malic acid (MA) on Al toxicity were investigated
in a medium with a low pH and low concentrations of phosphates and magnesium. The reduction in the growth of S. cerevisiae observed in the presence of 100 μM Al(III) ions was relieved more by the addition of 1.0 mM 2-iPMA than by 1.0 mM MA, indicating
that 2-iPMA possesses superior Al(III)-ion detoxification ability. Investigations using the wild type and the Δleu4 and Δleu9 mutant strains indicated that secretion of a sufficient level of 2-iPMA was required to enhance the Al tolerance. It is thought
that 2-iPMA secreted from the yeast cells chelates Al ions and prevents them from entering the cells, resulting in Al tolerance.
Suzuki and Tamura contributed equally to this work. 相似文献
90.
Effects of both chronic aluminum (Al) exposure and partial hepatectomy on iron (Fe) homeostasis were studied. Male Wistar
rats were intraperitoneally administered either 27 mg Al/kg body weight (as aluminum hydroxide) or the vehicle saline, three
times a week for 3 mo. After this time, half of the rats of each group was sham operated (SH) and the other half was partially
hepatectomized (PH). Animals of the four experimental groups (vehicle+SH [SH]; Al+SH; vehicle+PH [PH], and Al+PH) were killed
48h after the surgical procedure. Serum, hepatic, and intestinal Al levels were found to be increased both for Al+SH and Al+PH.
The serum Fe concentration and transferrin saturation percentage were significantly diminished in the rats of the Al+PH group,
thus showing interaction between Al administration and PH. The 50Fe mucosal-to-serosal transport, studied in the intestinal loop in situ, was not affected by Al or PH. The malregulation of intestinal Fe absorption in Al exposure and/or PH when the serum Fe concentration
was diminished could be the result of the increased lipid peroxidation (thiobarbituric acid-reactive substances [TBARS]) observed
in this tissue. Mucosal TBARS were increased by Al exposure (+26%) and PH (+37%) and interaction between Al and PH was observed
(+44%). These results show that when liver surgery is performed after prolonged Al exposure, it leads to impairment of Fe
homeostasis. We underline the importance of the exposure to Al, a potentially toxic element, in the study of risk assessment
in patients who must be submitted to major liver resection. 相似文献