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1.
Cadmium accumulation in the chloroplast of Euglena gracilis   总被引:5,自引:0,他引:5  
Intracellular distribution of Cd, cysteine, glutathione, and Cd-induced thiol peptides in Euglena gracilis cultured under photoheterotrophic conditions was studied. After 3 days of culture with 0.2 m M CdCl2, 62% of the Cd accumulated by cells was equally distributed between the cytosolic and chloroplastic fractions. However, after 8 days, metal content increased in the crude chloroplastic fraction to 40% of total and decreased to 19% in the cytosol; in Percoll-purified chloroplasts the estimated content of Cd raised to 62%. Accumulation of Cd in chloroplasts could be mediated by a transporter of free Cd2+, since uptake of added CdCl2 in isolated chloroplasts exhibited a hyperbolic type of kinetics with a Km of 57 µ M and Vmax of 3.7 nmol (mg protein)−1 min−1. The contents of cysteine and glutathione markedly increased in both chloroplasts (7–19 times) and cytosol (4–9 times) by exposure to Cd2+, although they were always higher in the cytosol. Thiol-containing peptides induced by Cd were mainly located in the cytosol after 3 days, and in the chloroplasts after 8 days of culture. The data suggested that Cd was compartmentalized into chloroplasts in a process that may involve the transport of free Cd and the participation of thiol-peptides.  相似文献   

2.
Field studies have shown that the addition of Zn to Cd-containing soils can help reduce accumulation of Cd in crop plants. To understand the mechanisms involved, this study used 109Cd and 65Zn to examine the transport interactions of Zn and Cd at the root cell plasma membrane of bread wheat ( Triticum aestivum L.) and durum wheat ( Triticum turgidum L. var. durum ). Results showed that Cd2+ uptake was inhibited by Zn2+ and Zn2+ uptake was inhibited by Cd2+. Concentration-dependent uptake of both Cd2+ and Zn2+ consisted of a combination of linear binding by cell walls and saturable, Michaelis-Menten influx across the plasma membrane. Saturable influx data from experiments with and without 10 µm concentrations of the corresponding inhibiting ion were converted to double reciprocal plots. The results revealed a competitive interaction between Cd2+ and Zn2+, confirming that Cd2+ and Zn2+ share a common transport system at the root cell plasma membrane in both bread and durum wheat. The study suggests that breeding or agronomic strategies that aim to decrease Cd uptake or increase Zn uptake must take into account the potential accompanying change in transport of the competing ion.  相似文献   

3.
Effects of mixtures of chloride salts of cadmium, copper and zinc on survival, whole body residues, and histopathology of mummichog, Fundulus heteroclitus (L.), were investigated in synthetic sea water at 20‰ salinity and 20°C. Mixtures of Cu2+ and Zn2+ as indicated by 96 h bioassay studies produced more deaths than expected on the basis of toxicities of individual components. Concentrations of Cd2+ not ordinarily lethal exerted a negative effect on survival of fish intoxicated by salts of copper, zinc, or both.
Atomic absorption determinations of Cd, Cu, and Zn residues in mummichog which survived 96 h exposures to each of these toxicants provided useful indices of total body burdens for these metals. Residues from survivors held in mixtures, especially Cd2+ and Zn2+ mixtures, did not conform to patterns observed for single elements. Whole body aggregates of Cd, Cu, and Zn from dead mummichogs were of limited worth owing to possible accumulation of these metals from the medium after death.
Renal and lateral line canal lesions were noted in all fish subjected to copper concentrations of 1 mg/1 and higher. Renal lesions observed in fish immersed in mixtures of Cu2+ and Cd2+ assumed a damage pattern characteristic of Cd2+; with mixtures of Cu2+ and Zn2+, lesion were typical of Cu2+-induced damage. Lesions induced in lateral line epithelium by Cu2+ were not affected by either Cd2+ or Zn2+. Epithelia lining the oral cavity were necrotized by the caustic action of high levels of Zn2+ (60 mg/1) and of Cu2+ (8 mg/1).  相似文献   

4.
Sugar beets ( Beta vulgaris L. cv. Monohill) grown in a complete nutrient solution, were treated with Cd2+ (5 or 50 μ M ) and/or EDTA (10 or 100 μ M ) in different combinations. The Cd contents of five-week-old roots and shoots were determined by atomic absorption spectrophotometry, and the sucrose, glucose and fructose contents were measured enzymatically. The Cd2+ uptake in both roots and shoots shows a linear relationship to the concentration of free Cd2+ in the nutrient solution. This uptake is diminished in the presence of EDTA, suggesting that the Cd-EDTA complex is unable to penetrate the membranes. The contents of glucose, fructose and sucrose in both roots and shoots decrease with increasing uptake of free Cd2+. This may be a secondary effect caused by the inhibition of photosynthesis in the presence of Cd2+. EDTA reduces the inhibition of Cd2+ on sugar formation and accumulation. In the presence of EDTA alone the sugar content increases somewhat. EDTA slightly influences the dry weights of whole plants. The ratio roots:whole plants increases. Cd2+ (≤ 50 μ M ) increases the dry matter portion of roots by ca 30%, but not that of shoots.  相似文献   

5.
The uptake of Cd2+ by excised roots of Tamarix aphylla (L.) Karst, was investigated using roots of hydroponically grown plants. The concentration isotherm of Cd2+ uptake approached saturation with a single phase hyperbola. The time course of Cd2+ absorption was generally hyperbolic, with an apparent linear section between 2 and 30 min. The temperature response varied among different temperature ranges: a Q10 of approximately 1.9 was found between 10 and 20°C, but at higher and lower temperatures Q10 values were only 1–1.3. It is concluded that Cd2+ uptake by the roots of T. aphylla at moderate temperatures is mediated by a metabolic process, combined with a passive influx component that becomes dominant at higher and lower temperatures. The distribution of the absorption sites for Cd2+ and for Fe2+ along the roots of T. aphylla was also investigated. Cadmium uptake showed no apparent pattern, whereas a distinct pattern of uptake was observed for Fe2+, with the highest rates at the root tip. Iron absorption was stimulated in the presence of nutrients, whereas that of Cd2+ was inhibited. Adsorption and absorption of Cd2+ were strongly inhibited by Ca2+ and by Mg2+, but were unaffected by Fe2+. Monovalent ions (Na+, K+, Li+) also reduced Cd2+ absorption, but to a lesser extent than Ca2+ and Mg2+. Uptake of Cd+ was reduced at lower pH of the medium. The importance of interfering cations for Cd2+ tolerance of T. aphylla is emphasized.  相似文献   

6.
Transpiration rates of young Tamarix aphylla (L.) Karst, plants grown in hydroponics were measured under NaCl- and Cd(NO3)2-stress. Transpiration rates were negatively correlated with the relative humidity of the ambient air at all NaCl concentrations investigated. Low and intermediate concentrations of Cd2+ (45 and 90 μ M , respectively) in the medium caused an increase in transpiration rates. This was particularly pronounced at low levels of relative humidity. At 180 μ M Cd2+, transpiration rates dropped, probably as a result of root damage due to Cd2+ toxicity. Since the transpiration rates differed by a factor of ca 3 between day and night, it is concluded that the stomata did not lose their ability to regulate transpiration under the influence of NaCl or of Cd(NO3)2. The transpiration behaviour of T. aphylla indicates that the effect of water vapour pressure (presented as relative humidity) on the degree of stomatal opening is small. Under conditions of ample water supply transpiration follows the evaporative demand of the ambient air and is influenced by the water uptake capacity of the root system as well as by other environmental factors, e.g. light.  相似文献   

7.
Toxicities of cadmium (Cd) and zinc (Zn) to the green alga Selenastrum capricornutum Printz were determined over 72 h in defined synthetic media buffered by citrate (FRAQCIT ; [citrate] = 100 μM or 5 μM) or nitrilotriacetate (FRAQNTA ; [NTA] = 5 μM). Algal sensitivity to free Cd2+ or free Zn2+ in FRAQCIT was much higher than in FRAQNTA. In parallel experiments, short-term intracellular uptake of radiolabeled 109Cd was measured as a function of time (0–30 min) in FRAQCIT and FRAQNTA; for a given free Cd2+ concentration (8, 250, or 610 nM), intracellular accumulation of Cd was consistently higher in FRAQCIT than in FRAQNTA. Under the same conditions, the alga accumulated 14C-labeled citrate almost linearly over a 2-h period. Loss of 109Cd from algal cells that had been prelabeled with the radionuclide occurred slowly, and the loss rate was insensitive to the presence or absence of citrate, indicating that the overall permeability of the algal membrane to Cd was unaffected by citrate. The enhanced bioavailability of Cd in the presence of citrate could be explained by membrane transport of a charged Cd–citrate complex, presumably by accidental transport.  相似文献   

8.
Characterization of phytochelatin synthase from tomato   总被引:11,自引:0,他引:11  
The enzyme that synthesizes Cd-binding phytochelatins (PCs), PC synthase, has been studied in tomato ( Lycopersicon esculentum ) cell cultures and plants. This enzyme transfers γ-GluCys from GSH or PC to either GSH or an existing polymer of (γ-GluCys)nGly. PC synthase from tomato requires GSH or PCs as substrates but cannot utilise γ-GluCys or GSSG. PC synthase is activated both in vivo and in vitro by a variety of heavy metal ions, including Cd2+, Ag+, Cu2+, Au+, Zn2+, Fe2+, Hg2+ and Pb2+. In crude protein extracts from tomato cells the enzyme has an apparent Km of 7.7 m M for GSH in the presence of 0.5 m M Cd2+, and exhibits maximum activity at pH 8.0 and 35°C. PC synthase is present in tomato cells grown in the absence of Cd. The level of enzyme activity is regulated during the cell culture cycle, with the highest activity occurring 3 days after subculture. Cadmium-resistant tomato cells growing in medium containing 6 m M CdCl2 have a 65% increase in PC synthase activity compared to unselected cells. PC synthase is also present in roots and stems of tomato plants, but not in leaves or fruits. The distribution of the enzyme in tomato plants and regulation of PC synthase activity in tomato cells indicate that PC synthase, and PCs, may have additional functions in plant metabolism that are not directly related to the formation of Cd-PC complexes in response to cadmium.  相似文献   

9.
Pb and Cd uptake in rice roots   总被引:9,自引:0,他引:9  
Pb and Cd are heavy metal pollutants that inhibit plant growth. Using a cultivated rice variety (Dongjin, Oryza sativa L.), we studied how the transport and toxicity of Pb2+ and Cd2+ are affected by the presence of K+, Ca2+ or Mg2+. K+ had a little effect on uptake or toxicity of Pb2+ and Cd2+. Ca2+ or Mg2+ blocked both Cd2+ transport into rice roots and Cd2+ toxicity on root growth, which suggested that their detoxification effect is directly related to their blocking of entry of the heavy metals. Similarly, Ca2+ blocked both Pb2+ transport into the root and Pb2+ toxicity on root growth. The protective effect of Ca2+ on Pb2+ toxicity may be related to its inhibition of the heavy metal accumulation in the root tip, a potential target site of Pb2+ toxicity. Mg2+ did not ameliorate the Pb2+ toxicity on root growth as much as Ca2+ did, although it decreased Pb2+ uptake into roots similarly as Ca2+ did. These results suggest that the protective effect of Ca2+ on Pb2+ toxicity may involve multiple mechanisms including competition at the entry level, and that Pb2+ and Cd2+ may compete with divalent cations for transport into roots of rice plants.  相似文献   

10.
Excretion of minerals by the NaCl-resistant and comparatively cadmium-resistant tree Tamarix aphylla (L.) Karst, was investigated. Cd2+ was excreted by plants exposed for 1–10 days to 9 or 45 μ M Cd2+ solutions. Excretion of this toxic ion increased considerably with time but was less than 5% of the quantities that had been accumulated in the shoots. Excretion of Na+ and Cl was positively correlated with NaCl concentration (1.5, 10, 50 m M ) of the medium. The Na+/Cl ratios of the excrete were positively correlated with the concentration of the treatment solution. Ca2+ excretion decreased with increasing NaCl concentrations of the solution. Excretion of K+ and Mg2+ was only little affected by NaCl. Excretion of Li+ occurred whenever this element was supplied in the uptake solution; daily excretion rates of Li+ increased with time. The ecological significance of excretion is discussed in relation to the low selectivity of the mechanism in T. aphylla .  相似文献   

11.
Abstract Uptake of Cd2+ into Cd-resistant cells was approximately four times lower than in Cd-sensitive cells of Saccharomyces cerevisiae . Binding of Cd2+ to the yeast cells increased during incubation of the cells in the presence of Cd2+. The increase in the binding was much higher for wild-type cells than for Cd-resistant cells. This increased binding is ascribed to permeabilization of part of the cells. There is no single relation between the relative rate of K+ efflux and the cellular Cd content as has been found previously for wild-type cells. The rates of K+ efflux were much less than those found for the wild-type cells. Only with short incubation periods of the cells with Cd2+ was the same dependence found between the efflux of K+ and the cellular Cd content for both types of cell. The discrepancies found after extended incubation of the cells with Cd2+ are ascribed to the fact that Cd-provoked K+ release proceeds via an all-or-nothing process and that K+ released from permeabilized cells can be reaccumulated in still intact cells. The latter proceeds more efficiently in Cd-resistant cells than in wild-type cells.  相似文献   

12.
Sunflower seedlings ( Helianthus annuus hybrid Select) were grown in a complete nutrient solution in the absence or presence of Cd2+ (10 and 20 μM). Analyses were performed to establish whether there was a differential effect of Cd2+ on mature and young leaves. After 7 d the growth parameters as well as the leaf area had decreased in both mature and young leaves. Accumulation of Cd2+ in the roots exceeded that in the shoots. Seedlings treated with Cd2+ exhibited reduced contents of chlorophyll and CO2 assimilation rate, with a greater decrease in young leaves. The photochemical efficiency of photosystem II (PSII) was not altered by Cd2+ treatment in either mature or young leaves, although during steady-state photosynthesis in young leaves there was a significant alteration in the following parameters: quantum yield of electron transport by PSII (ΦPSII), photochemical quenching ( q P), non-photochemical quenching ( q NP), and excitation capture efficiency of PSII (Φexc).  相似文献   

13.
Seedlings of spring wheat ( Triticum aestivum L. cv. Svenno) were cultivated at 20°C in continuous light or darkness with the roots in nutrient solutions for six days. The plants were starved for K+ during different periods of time to produce plants with various K+ status. In one cultivation light-grown plants were pretreated in darkness, and vice versa, before the uptake experiment. In all experiments, roots were put in a complete nutrient medium containing 2.0 m M K+ radiolabelled with 86Rb. The uptake time was varied (5, 60 or 120 min).
The K+ concentration in the roots, [K+]root, increased during the course of the uptake experiments, especially in light and at initially low [K+]root, At the same time K+ (86Rb) influx in the roots decreased. The simoidal relationship obtained between K+ (86Rb) influx and [K+]root was affected by these changes, and Hill plots gave various Hill coefficients, nH, depending on the duration of the uptake experiments. nH from three apparently straight line segments of the same plot, in different [K+]root - intervals, indicated a falling degree of interaction between the binding sites as [K+]root increased. For the dark-grown plants negative cooperativity could not be demonstrated.  相似文献   

14.
Sugar-beet plants ( Beta vulgaris L. cv. Monohill) were cultivated for 4 weeks in a complete nutrient solution. Indirect effects of cadmium were studied by adding 5, 10 or 20 μ M CdCl2 to the culture medium while direct effects were determined by adding 1, 5, 20, 50 or 2 000 μ M CdCl2 to the assay media. The photosynthetic properties were characterized by measurement of CO2 fixation in intact plants, fluorescence emission by intact leaves and isolated chloroplasts, photosystem (PS) I and PSII mediated electron transport of isolated chloroplasts, and CO2-dependent O2 evolution by protoplasts. When directly applied to isolated leaves, protoplasts and chloroplasts. Cd2+ impeded CO2 fixation without affecting the rates of electron transport of PSI or PSII or the rate of dark respiration. When Cd2+ was applied through the culture medium the capacity for, and the maximal quantum yield of CO2 assimilation by intact plants both decreased. This was associated with: (1) decreased total as well as effective chlorophyll content (PSII antennae size), (2) decreased coupling of electron transport in isolated chloroplasts, (3) perturbed carbon reduction cycle as indicated by fluorescence measurements. Also, protoplasts isolated from leaves of Cd2+-cultivated plants showed an increased rate of dark respiration.  相似文献   

15.
Heavy metal loads in forest soils have been increasing over time due to atmospheric inputs. Accumulation in the upper soil layers could affect establishment of seedlings and forest regeneration. Mediterranean species show a high initial root development, allowing seedlings to reach the moisture of deeper soil layers. In the present work seedlings of stone pine ( Pinus pinea L.) and maritime pine ( Pinus pinaster Ait.), were grown in culture solution supplied with 0.0, 0.1, 1 or 5 μ M CdSO4 or with 1 μ M CdSO4 and 1 μ M CuSO4 combined. In both species tap-root elongation was drastically reduced in the 5 μ M Cd2+ and in the (Cd2++ Cu2+) treatments. A supply of 0.1 or 1 μ M Cd2+, however, enhanced root elongation in Pinus pinea without significantly influencing root elongation in Pinus pinaster . In both species the root density (weight per unit length) and the width of the cortex increased in response to Cd2+ exposure. In Pinus pinaster the mitotic index decreased at the higher Cd2+ concentrations and when Cd2+ and Cu2+ were combined. The data suggest that cell elongation is more sensitive to Cd2+ than cell division. The number and length of the lateral roots were also affected by Cd2+ treatment to a higher degree in Pinus pinaster than in Pinus pinea, reflecting the different Cd- tolerance of the two species.  相似文献   

16.
A factorial culture experiment was designed to investigate the influence of light regimes and of some metal chelators on the accumulation of cadmium by Lemna gibba L. The plants were grown in a complete nutrient solution containing Cd2+ concentrations ranging from 0 to 27 μ M with or without EDTA, ethylenediamine-N,N'- bis -( o -hydroxyphenylacetic acid) (EDDHA) or salicylic acid. Each experiment was run for eight days in 18 h:6 h light:dark or continuous light. An increase in the Cd2+ concentration in plants and a simultaneous drop in accumulation efficiency (ratio of Cd2+ concentration in plants to the initial Cd2+ concentration in the nutrient solution) with increasing ambient Cd2+ levels was best represented by regression power curves. At the lowest Cd2+ concentration which caused a significant decrease in the relative growth rate of duckweed, there was a decrease in manganese and zinc and an increase in the iron level in the plants. EDDHA and EDTA protected in some cases against the toxic action of cadmium without preventing its uptake by plants. It was thus observed that 9 μ M or higher levels of Cd2+ were toxic to Lemna gibba depending on the chelator and light regime. Duckweed grown in continuous light produced, in general, more dry matter and hence accumulated more cadmium.  相似文献   

17.
Abstract: We have used the human sympathetic neuronal line SH-SY5Y to investigate the effects of hypoxia on noradrenaline (NA) release evoked by either raised [K+]o (100 m M ) or the nicotinic acetylcholine receptor (nAChR) agonist dimethylphenylpiperazinium iodide (DMPP). NA release was monitored by loading cells with [3H]NA and collecting effluent fractions from perfused cells kept in a sealed perifusion chamber. Cells were challenged twice with either stimulus and release was expressed as that evoked by the second challenge as a fraction of that evoked by the first. K+-evoked release was unaffected by hypoxia (P o 2≅ 30–38 mm Hg), but release evoked by DMPP was significantly increased. For both stimuli, replacement of Ca2+o with 1 m M EGTA abolished NA release. K+-evoked release was also dramatically reduced in the presence of 200 µ M Cd2+ to block voltage-gated Ca2+ channels, but DMPP-evoked release was less affected. In hypoxia, DMPP-evoked Cd2+-resistant NA release was dramatically increased. Our findings indicate that hypoxia increases NA release evoked from SH-SY5Y cells in response to nAChR activation by increasing Ca2+ influx through the nAChR pore, or by activating an unidentified Cd2+-resistant Ca2+-influx pathway. As acetylcholine is the endogenous transmitter at sympathetic ganglia, these findings may have important implications for sympathetic activity under hypoxic conditions.  相似文献   

18.
The inhibitory action of divalent cations on the Ca2+-ATPase activity of a plasma membrane-rich microsome fraction isolated from the roots of barley ( Hordeum vulgare L. cv. Conquest) was investigated. Using electron paramagnetic resonance spectroscopy to measure cation-induced changes in membrane lipid properties, it was demonstrated that certain divalent cations (Ca2+, Cd2+, UO2+2) inhibit the Ca2+ ATP-ase by restriction of lipid polar head group mobility and not by alteration of membrane surface potential. Monovalent cations which stimulate the Ca2+-ATPase of barley roots (Na+, K+, ethanolamine HCl) can also reverse the Ca2+-ATPase inhibition by Cd2+. The degree of Na+ reversal of Cd2+-induced Ca2+-ATPase inhibition was influenced by the nature of the anion.  相似文献   

19.
Some classes of marine phytoplankton are believed to be more tolerant of high concentrations of trace metals than others, but the results of experimental tests of this hypothesis are ambiguous. Eleven species of phytoplankton representing five classes were grown in Aquil medium containing Cd concentrations between 10−8 and 10−5 M ([Cd2+]= 10−9.85 to 10−6.84 M), and growth rates and intracellular concentrations of Cd, C, N, and S were measured. The mean Cd2+ concentration (pCd50) that reduced the growth rate of each species to 50% of its maximum varied by 2.5 orders of magnitude, from 10−6.23 for Emiliania huxleyi to 10−8.79 for Synechococcus sp. Taxonomic trends in Cd resistance were not apparent in these data. Cadmium quotas (mol Cd·L−1 cell volume) were lowest in species of Bacillariophyceae (ANOVA, P < 0.001), suggesting that they might regulate Cd transport differently than other taxa. Cellular S:C molar ratios increased in four of seven phytoplankton grown at high pCd (7.37–6.84) compared to low Cd ion concentrations (no added Cd), a result of increases in S·L−1 cell volume. Nitrogen:carbon molar ratios were also higher in Cd-exposed phytoplankton, as changes in N and S were highly correlated ( r = 0.98, P < 0.0001). In two species that were examined, S:C ratios increased as a linear function of increasing Cd concentration. The results demonstrate large variability in Cd resistance among phytoplankton that is primarily a function of interspecific differences in Cd detoxification.  相似文献   

20.
Pyoverdine (PvdI) is the major siderophore secreted by Pseudomonas aeruginosa PAOI in order to get access to iron. After being loaded with iron in the extracellular medium, PvdI is transported across the bacterial outer membrane by the transporter, FpvAI. We used the spectral properties of PvdI to show that in addition to Fe3+, this siderophore also chelates, but with lower efficiencies, all the 16 metals used in our screening. Afterwards, FpvAI at the cell surface binds Ag+, Al3+, Cd2+, Co2+, Cu2+, Fe3+, Ga3+, Hg2+, Mn2+, Ni2+ or Zn2+ in complex with PvdI. We used Inductively Coupled Plasma-Atomic Emission Spectrometry to monitor metal uptake in P. aeruginosa : TonB-dependent uptake, in the presence of PvdI, was only efficient for Fe3+. Cu2+, Ga3+, Mn2+ and Ni2+ were also transported into the cell but with lower uptake rates. The presence of Al3+, Cu2+, Ga3+, Mn2+, Ni2+ and Zn2+ in the extracellular medium induced PvdI production in P. aeruginosa . All these data allow a better understanding of the behaviour of the PvdI uptake pathway in the presence of metals other than iron: FpvAI at the cell surface has broad metal specificity at the binding stage and it is highly selective for Fe3+ only during the uptake process.  相似文献   

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