Mechanism for the Uptake of Zinc by Fontinalis antipyretica

The rate of uptake, the effects of carrier ions, temperature, light intensity and dinitrophenol (DNP) upon the uptake of zinc (using zinc-65 as tracer) by Fontinalis antipyretica were investigated. The absorption medium contained 0.5 mW CaSO₄ and the pH was kept constant using boric acid and sodium hydroxide as buffer. About 50 per cent of the zinc absorbed at equilibrium was taken up in the first half hour, Analysis by semi-log plot procedures showed that, at least, three sections may be distinguished in the uptake curve, suggesting that three successive processes (stages) were involved. The first stage was very short, and not influenced by temperature, light intensity and DNP. The second stage, lasting no more than 90 minutes, mi very slightly affected by the same three factors. In this stage freshly killed plants absorb more zinc than living material. The third stage, lasting several days, was very slow and was light, temperature and DNP dependent. Based on these findings, a mechanism for zinc uptake is proposed.     

Efficient Zn and Pb uptake by filamentous fungus Paecilomyces marquandii with engagement of metal hydrocarbonates precipitation

Zinc and lead biosorption by living non-growing filamentous fungus Paecilomyces marquandii was examined for its potential application in heavy metals elimination from contaminated areas. Metal uptake by the studied fungus was pH dependent and reached the level of 308 mg of Zn²⁺ g⁻¹ and 505 mg of Pb²⁺ g⁻¹ at pH of 7.5 caused by microprecipitation in slightly alkaline environment. All other metal studies were cultivated with unregulated pH yielding the maximum of 186.2 mg of Zn²⁺ g⁻¹ and 305.8 mg of Pb²⁺ g⁻¹. Interestingly, zinc binding by mycelium increased intensively after 15 h of incubation, whereas the lead concentration in biomass extended gradually and proportionally to the initial concentration and the time of contact. The study showed that thermal pretreatment of mycelium led to a decline in metal uptake, especially in the case of zinc. The mycelium slightly digested by the cell wall lytic enzyme complex, could adsorb lead twice as well after 2 h of exposure whereas zinc loading did not differ from the metal uptake by mycelia without any digestion procedure. The release of potassium ions from the mycelium, concomitant with lead uptake was observed suggesting ion exchange participation in lead binding. Energy-dispersive X-ray analysis, X-ray diffraction and FTIR spectroscopy revealed the presence of both metals hydrocarbonates on the mycelium surface. Additionally, the contribution of carboxyl and amide groups, originating from the mycelium, in metal binding was confirmed by FTIR analysis.The obtained results suggest that the effective metals uptake by P. marquandii was due to a combined mechanism with a dominant role of metabolism dependent microprecipitation.     

Rb+ uptake by isolated pea mesophyll protoplasts in light and darkness

Rb⁺ uptake into protoplasts isolated from the mesophyll of Pisum sativum L. cv. Dan has been followed at intervals of a few minutes in the light and in the dark. The progress curve for uptake in the dark decreased in slope after about 7 min; in the light, by contrast, the slope increased. This effect was more pronounced at pH 7 than at pH 5.5. The pH profile for uptake in the dark rose with increasing pH: in the light the profile flattened, or even fell somewhat, between pH 5.5 and pH 6.5, then rose again. In the dark the proton uncoupler carbonyl cyanide m-chlorphenylhydrazone (CCCP) had little or no effect, either at pH 5.5 or at pH 7.4; in the light CCCP was strongly inhibitory, particularly at pH 7.4. Increasing concentrations of CCCP produced progressively more and more severe inhibition in the light, but in the dark produced a slight rise in uptake. The ATPase inhibitors quercetin, rutin and diethyl-stilbestrol, as well as arsenate, all depressed uptake in the light, particularly at higher pH Dark uptake was sensitive only at pH 5.5, not at pH 7.4. In marked contrast to the case of methyl-3 glucose, where protoplasts which were switched from light to dark took up sugar at the accelerated light rate for the first 7 min in the dark, a switch to darkness produced a Rb⁺ uptake rate below that for protoplasts held continuously in the dark. It is inferred that the mechanism of Rb⁺ uptake does not involve proton cotransport. Information regarding the membrane potential was obtained by following the distribution of tetraphenyl phosphonium (TPP⁺) between protoplasts and medium. The potential was more negative in the light than in the dark. It was also more negative at pH 7 than at pH 5 both in the light and in the dark. Treatment with CCCP produced no appreciable depolarization within the first 20 min, indicating thet the CCCP inhibition of Rb⁺ uptake in the light cannot be ascribed to a reduction in potential. An ATP-fueled K⁺ porter, or K⁺-H⁺ antiporter, seems the most likely explanation. The maintenance of the rising pH profile in the dark, despite the presence of a CCCP concentration which drastically inhibits light uptake, suggests that the profile does not depend on the operation of the proton pump.     

UPTAKE OF CADMIUM BY FRESHWATER GREEN ALGAE: EFFECTS OF PH AND AQUATIC HUMIC SUBSTANCES1

The effects of humic substances and low pH on short‐term Cd uptake by Pseudokirchneriella subcapitata (Korshikov) Hindak and Chlamydomonas reinhardtii Dang were investigated under defined exposure conditions. The uptake experiments were run in the presence of either a synthetic organic ligand (nitrilotriacetate) or natural organic ligands (Suwannee River fulvic or humic acid). An ion‐exchange method was used to measure the free Cd²⁺ concentrations in the exposure solutions. At pH 5, measured free Cd²⁺ concentrations agreed with estimations made using the geochemical equilibrium model WHAM, but at pH 7 the model overestimated complexation by both Suwannee River fulvic and humic acids compared with the ion‐exchange measurements. Consistent with the metal internalization step being rate limiting for overall short‐term uptake, intracellular Cd uptake was linear for exposure times less than 20 min at pH 5 or pH 7 for both algal species. After taking into account complexation of Cd in solution, Suwannee River humic substances had no additional effects on cadmium uptake at pH 7, as would be predicted by the free ion model. This absence of effects other than complexation persisted at pH 5, where the tendency of humic substances to adsorb to the algal cell surface is favored. Changes in pH strongly influenced Cd uptake, with the intracellular flux of Cd being at least 20 times lower at pH 5 than at pH 7 for P. subcapitata. Our results support models such as the free ion model or the biotic ligand model, in which humic substances act indirectly on Cd uptake by reducing the bioavailability of Cd by complexation in solution.     

Accumulation of zinc and cadmium by Cytophaga johnsonae

Passive and active accumulation of zinc and cadmium by a common soil and freshwater bacterium, Cytophaga johnsonae, was studied using a radio-tracer batch distribution technique. The effects of variation of pH (3–10), as well as of ionic strength (0.007 and 0.07 m) on passive accumulation of the metals were examined. For both zinc and cadmium, accumulation was mainly due to passive processes, such as surface adsorption and/or diffusion into the periplasm. However, at low zinc concentrations, accumulation increased when glucose was added, suggesting an active uptake; at higher zinc concentrations such uptake was not detected, probably because it was masked by the stronger sorption properties of the cell wall. Adsorption of the metals was pH dependent: at higher ionic strength, accumulation was enhanced at pH values above 7; at lower ionic strength, adsorption differed and was markedly higher, with increased accumulation between pH 5 and 8.     

Cadmium uptake in Elodea canadensis leaves and its interference with extra‐ and intra‐cellular pH

This study investigated cadmium (Cd) uptake in Elodea canadensis shoots under different photosynthetic conditions, and its effects on internal (cytosolic) and external pH. The plants were grown under photosynthetic (light) or non‐photosynthetic (dark or in the presence of a photosynthetic inhibitor) conditions in the presence or absence of CdCl₂ (0.5 μm ) in a medium with a starting pH of 5.0. The pH‐sensitive dye BCECF‐AM was used to monitor cytosolic pH changes in the leaves. Cadmium uptake in protoplasts and leaves was detected with a Cd‐specific fluorescent dye, Leadmium Green AM, and with atomic absorption spectrophotometry. During cultivation for 3 days without Cd, shoots of E. canadensis increased the pH of the surrounding water, irrespective of the photosynthetic conditions. This medium alkalisation was higher in the presence of CdCl₂. Moreover, the presence of Cd also increased the cation exchange capacity of the shoots. The total Cd uptake by E. canadensis shoots was independent of photosynthetic conditions. Protoplasts from plants exposed to 0.5 μm CdCl₂ for 3 days did not exhibit significant change in cytosolic [Cd²⁺] or pH. However, exposure to CdCl₂ for 7 days resulted in increased cytosolic [Cd²⁺] as well as pH. The results suggest that E. canadensis subjected to a low CdCl₂ concentration initially sequesters Cd into the apoplasm, but under prolonged exposure, Cd is transported into the cytosol and subsequently alters cytosolic pH. In contrast, addition of 10–50 μm CdCl₂ directly to protoplasts resulted in immediate uptake of Cd into the cytosol.     

Effects of pH on ammonium uptake by Typha latifolia L.

The effects of solution pH on NH₄⁺ uptake kinetics and net H⁺ extrusion by Typha latifolia L. were studied during short-term (days) and long-term (weeks) exposure to pH in the range of pH 3.5–8.0. The NH₄⁺ uptake kinetics were estimated from depletion curves using a modified Michaelis-Menten model. T. latifolia was able to grow in solution culture with NH₄⁺ as the sole N source and to withstand a low medium pH for short periods (days). With prolonged exposure (weeks) to pH 3.5, however, the plants showed severe symptoms of stress and stopped growing. The solution pH affected NH₄⁺ uptake kinetics. The affinity for NH₄⁺, as quantified by the half saturation constant (K_1/2) and C_min (the NH₄⁺ concentration at which uptake ceases), decreased with pH. K_1/2 was increased from 7.1 to 19.2 mmol m^?3 and C_min from 2.0 to 5.7 mmol m^?3 by lowering the pH in steps from 8.0 to 3.5. V_max was, however, largely unaffected by pH (～22 μmol h^?1 g^?1 root dry weight). Under prolonged exposure to constant pH, growth rates were highest at PH 5.0 and 6.5. At pH 8.0 growth was slightly depressed and at pH 3.5 growth completely stopped. NH₄⁺ uptake kinetics were similar at pH 5.0, 6.5 and 8.0 whereas at pH 3.5 NH₄⁺ uptake almost completely stopped. The ratio between net H⁺ extrusion and NH₄⁺ uptake decreased significantly at low pH. The adverse effects of low pH on NH₄⁺ uptake kinetics are probably a consequence of a reduced H⁺-ATPase activity and/or an increased re-entry of H⁺ at low pH, and the associated decrease in the electrochemical gradient across the plasma membranes of the root cells.     

Mechanism of Zinc Uptake in Bean (Phaseolus vulgaris) Tissues

Uptake of micronutrient zinc by intact leaves, enzymically isolated leaf cells, leaf disks, excised roots, and stem-callus tissue of two field bean cultivars 'Saginaw’ and ‘Sanilac’) was studied using radio-isotope tracer technique. Radio-phosphorus absorption by these tissues was also followed under comparable experimental conditions. A rapid absorption of the micronutrient and strong dependency on external zinc concentration and pH were revealed. Absorption of zinc was not inhibited by respiratory inhibitors (dinitrophenol, azide, cyanide, and amytal), and was not light or temperature dependent. Q₁₀ values for zinc uptake ranged between 1 and 1.2. Uptake of phosphate, on the other hand, was temperature and light dependent and drastically reduced by the presence of metabolic inhibitors. Differences in responses to respiratory inhibitors, temperature, pH, light and darkness, and kinetic data, strongly suggest that zinc uptake in bean tissues occurs primarily by a passive mechanism, involving possibly a physical or physiochemical binding of the micronutrient ions to the cell wall and free space components, and a passive diffusion into the interior of the cell.     

Nystatin affects zinc uptake in human fibroblasts

The mechanism(s) by which zinc is transported into cells has not been identified. Since zinc uptake is inhibited by reducing the temperature, zinc uptake may depend on the movement of plasma membrane micoenvironments, such as endocytosis or potocytosis. We investigated the potential role of potocytosis in cellular zinc uptake by incubating normal and acrodermatitis enteropathica fibroblasts with nystatin, a sterol-binding drug previously shown to inhibit potocytosis. Zinc uptake was determined during initial rates of uptake (10 min) following incubation of the fibroblasts in 50 μg nystatin/mL or 0.1% dimethyl-sulfoxide for 10 min at 37°C. The cells were then incubated with 1 to 30 μM ⁶⁵zinc. Michaelis-Menten kinetics were observed for zinc uptake. Nystatin inhibited zinc uptake in both the normal and AE fibroblasts. Reduced cellular uptake of zinc was associated with its internalization, not its external binding. In normal fibroblasts, nystatin significantly reduced theK _m 56% and theV _max 69%. In the AE fibroblasts, nystatin treatment significantly reduced theV _max 59%, but did not significantly affect theK _m. The AE mutation alone affected theV _max for cellular zinc uptake. The control AE fibroblasts exhibited a 40% reduction inV _max compared to control normal fibroblasts. We conclude that nystatin exerts its effect on zinc uptake by reducing the velocity at which zinc traverses the cell membrane, possibly through potocytosis. Furthermore, the AE mutation also effects zinc transport by reducing zinc transport.     

Implication of distinct proteins in cadmium uptake and transport by intestinal cells HT-29

The mechanisms of intestinal absorption have not been clearly elucidated for cadmium, a toxic metal. In this work, we show the implication of distinct proteins in cadmium transport, and the transport step where these proteins are involved. We first validated the HT-29 model by evaluating nontoxic doses of cadmium (ranging from 1 to 20 μmol/L), and by quantifying metal uptake and transepithelial transport. The time-course of 1 μmol/L cadmium uptake at pH 7.5 showed three steps: a rapid one during the first 4 min, probably due to cadmium binding to the membrane; a slower one, characterized by K _m of 1.65±0.54 μmol/L and V _max of 3.9±0.3 pmol/min per mg protein; and a third, corresponding to slow accumulation that was not equilibrated even after 48 h of cadmium exposure. Intracellular metallothionein content following 1 or 5 μmol/L cadmium exposure showed a significant increase after 6 h of exposure, and was not equilibrated even after 72 h, allowing cadmium accumulation. After 24 h of exposure, metallothionein content was 5-fold, 14-fold, 26-fold, and 50-fold, respectively, for cells grown in the presence of 1, 5, 10, and 20 μmol/L cadmium, compared to control cells. The second step of uptake, characterized by carrier-mediated transport, was markedly increased at pH 5.5, compared to pH 7.5, and strongly inhibited by the metabolic inhibitor dinitrophenol. Moreover Nramp2 transporter cDNA was present in HT-29 cells. These data suggest the involvement of a proton-coupled transporter, which may be the divalent cation transporter Nramp2 (natural resistance-associated macrophage protein 2). Cadmium uptake was also inhibited by copper, zinc, and para-chloromercuribenzenesulfonate (pCMBS), but not by verapamil or ouabain. Taken together, our results indicate that cadmium could enter HT-29 cell by Nramp2 proton-coupled active transport and by diffusion, and accumulates in the cell as long as it binds to metallothionein. Cadmium toxicity could depend partly on the activity of Nramp2, and partly on metallothionein content. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interactions between a soil fungus,Trichoderma harzianum,and IIb metals—adsorption to mycelium and production of complexing metabolites

Fungi are capable of accumulating metals and, in soil, such accumulation may influence metal speciation and transport. The interactions between a common soil fungus, Trichoderma harzianum, and IIb elements were studied in the present investigation. The accumulation of the metals zinc, cadmium and mercury by starved and non-starved mycelium at different pH was determined by a batch technique using radioactive tracers; uptake of the metals was found to be large, with respective distribution coefficients of about 10^3.5, 10^2.5 and 10^4.0 for zinc, cadmium and mercury, respectively. Metal accumulation by a starved system was largely independent of pH in the range 3–9, where in a non-starved system an increased accumulation of zinc (at 10^– m) was observed at low pH (3–5). Potentiometric titrations performed on the two systems revealed significant differences in acid capacities, i.e. values close to zero for the starved system and 500–800 meq kg^– for the non-starved system. The maximum metal uptake was at least 50 mmol kg^– at pH 6.5 (calculated from adsorption isotherms). The present findings suggests that in the non-starved system a metabolite is produced and then released when the pH is within a certain range.     

Heavy metal biosorption by fungal mycelial by-products: mechanisms and influence of pH

Summary Mycelial wastes of Rhizopus arrhizus, used in fermentation industries to produce lipases, were studied for their ability to absorb various heavy metal ions (Ni, Zn, Cd and Pb). Chelation of all these ions occurs by a chemical, equilibrated and saturatable mechanism, following the Langmuir adsorption model. Data transformation allowed us to calculate maximum uptake and dissociation constants of the sorption reaction. We also investigated the influence of pH on metal accumulation. Sorption capacity variations between different biosorbent types (Rhizopus, Mucor, Penicillium, and Aspergillus), could be related to their acidity. pH neutralisation during the sorption reaction considerably enhanced zinc chelation (up to 56 mg/g). Previous NaOH treatment of mycelial wastes also increased their capacity for metal sorption. We report R. arrhizus metal uptake curves versus pH, using a pH-stat system. Optimal adsorption was achieved at neutral pH for nickel and zinc, pH 5.0 for lead, and inhibition of chelation was observed when the pH decreased. These results illustrate the importance of pH during the adsorption process, indicating a competitive mechanism for chelation between heavy metal ions and protons at cell wall adsorption sites. Correspondence to: J.-C. Roux     

Kinetics and mechanism of tolerance induction on acclimation ofVillorita cyprinoides (Hanley) to copper and zinc

The typical euryhaline clamVillorita cyprinoides (Hanley) was acclimated to copper and zinc at salinity 13 × 10⁻³ and < 1 × 10⁻³ (fresh water). Acclimation enhanced the lethal tolerance, as denoted by dose-survival curves, which was more pronounced after zinc acclimation. In fresh water copper acclimation sensitized the organisms. The copper accumulation trend was significantly changed consequent to metal acclimation, especially after zinc acclimation, indicating some tissue metal regulatory effect. Acclimation to copper equiped the organism to survive for longer periods with increased body burden of copper, while zinc acclimation supressed the uptake of the more toxic ion copper. The earlier report of increased uptake of zinc by this organism during combined exposure with copper is corelated in the present context. The role of metallothionein like protein in providing protection against metal toxicity, the environmental implication of acclimation phenomena are indicated     

Zinc biosorption from aqueous solution by a halotolerant cyanobacterium Aphanothece halophytica

We have investigated the characteristics of zinc biosorption by Aphanothece halophytica. Zinc could be rapidly taken up from aqueous solution by the cells with an equilibrium being reached within 15 min of incubation with 100 mg L⁻¹ ZnCl₂. The adsorbed zinc was desorbed by treatment with 10 mM EDTA. The presence of glucose, carbonyl cyanide m-chlorophenylhydrazone (CCCP), and N,N′-dicyclohexylcarbodiimide (DCCD) did not affect the uptake of zinc. The specific uptake of zinc increased at low cell concentration and decreased when cell concentration exceeded 0.2 g L⁻¹. The binding of zinc followed Langmuir isotherm kinetics with a maximum zinc binding capacity of 133 mg g⁻¹ and an apparent zinc binding constant of 28 mg L⁻¹. The presence of an equimolar concentration of Mn²⁺, Mg²⁺, Co²⁺, K⁺, or Na⁺ had no effect on zinc biosorption, whereas Ca²⁺, Hg²⁺, and Pb²⁺ showed an inhibitory effect. The biosorption of zinc was low at a pH range from 4 to 6, but increased progressively at pH 6.5 and 7. Received: 12 December 2001 / Accepted: 11 January 2002     

Zinc uptake by isolated rat hepatocytes

Isolated rat hepatocytes were used to investigate the uptake of zinc at early exposure times. Hepatocytes were incubated with ⁶⁵Zn (1–500 μM) and samples were withdrawn at times ranging from 25 s to 60 min. A biphasic pattern of uptake was observed with a rapid first phase of uptake followed by a slower second phase. The relationship between velocity of uptake and substrate concentration for the first phase was nonlinear, while that of the second phase was linear. The presence of 10 μM cadmium produced a decrease in the velocity of uptake of only the first phase. This suggests that the first phase is at least partly carrier mediated, while there is no indication of involvement of a carrier in the second phase. KCN (1 mM) and carbonyl cyanide m-chlorophenylhydrazone (2 μM), did not cause any change in the uptake of ⁶⁵Zn (1 μM), which suggests that there is no active component in the uptake of zinc.     

The effect of the acrodermatitis enteropathica mutation on zinc uptake in human fibroblasts

The acrodermatitis enteropathica (AE) mutation affects intestinal zinc absorption. Our goal was to determine whether the AE mutation affects zinc uptake in human fibroblasts. Zinc uptake was determined during initial rates of uptake (10 min) following incubation in HEPES/saline buffer. Zinc uptake (from 0.25 to 1 μM) into normal fibroblasts was significantly greater than into the AE fibroblasts (p<0.05). In order to identify factors that may alter cellular zinc uptake and be affected by the AE mutation, zinc uptake in the presence of albumin or bicarbonate was measured. Albumin restricted zinc uptake in both normal and AE fibroblasts, whereas bicarbonate stimulated zinc uptake in the normal fibroblasts. The effect of bicarbonate on zinc uptake in the AE fibroblasts was significantly reduced in both the Pronase-sensitive and Pronase-resistant compartments. Following loading of the fibroblasts with 1 μM zinc for 60 min, zinc efflux and retention were measured. The AE mutation did not affect zinc retention compared to normal fibroblasts. We conclude that the AE mutation affects both zinc binding to the cell surface and its translocation across the plasma membrane into the cell, possibly mediated through a defective anionic exchange mechanism.     

EFFECT OF DIMETHYL SULFOXIDE ON ZINC65 UPTAKE,RESPIRATION, AND RNA AND PROTEIN METABOLISM IN BEAN (PHASEOLUS VULGARIS) TISSUES

The effect of dimethyl sulfoxide (DMSO) on zinc⁶⁵ uptake, respiration, RNA, and protein metabolism in various tissues of two bean (Phaseolus vulgaris L.) cultivars showing differential growth responses to zinc has been studied. At a concentration of 1%, DMSO stimulated zinc uptake in excised roots, stem-callus tissue, leaf disks, and enzymically isolated leaf cells, but did not significantly alter the uptake and incorporation of C¹⁴-uracil into RNA and C¹⁴-methionine into protein, although a slight inhibition was discernible in some tissues. At a higher concentration (10%) DMSO increased Zn⁶⁵ uptake in excise roots incubated for 2 hr; however, at the same concentration, C¹⁴-uracil and C¹⁴-methionine uptake and incorporation were considerably inhibited in all the tissues. Oxygen uptake as measured with Warburg manometers was impaired, and the inhibition showed a time and concentration dependency. The fact that DMSO inhibited respiration and RNA and protein metabolism, while at the same concentration zinc uptake was increased, suggests that zinc uptake in beans is primarily a non-metabolic process. The possible mechanisms of DMSO action are discussed in the light of its reported effects on membrane permeability and cell metabolism.     

Zinc transport by respiratory epithelial cells and interaction with iron homeostasis

Despite recurrent exposure to zinc through inhalation of ambient air pollution particles, relatively little information is known about the homeostasis of this metal in respiratory epithelial cells. We describe zinc uptake and release by respiratory epithelial cells and test the postulate that Zn²⁺ transport interacts with iron homeostasis in these same cells. Zn²⁺ uptake after 4 and 8 h of exposure to zinc sulfate was concentration- and time-dependent. A majority of Zn²⁺ release occurred in the 4 h immediately following cell exposure to ZnSO₄. Regarding metal importers, mRNA for Zip1 and Zip2 showed no change after respiratory epithelial cell exposure to zinc while mRNA for divalent metal transporter (DMT)1 increased. Western blot assay for DMT1 protein supported an elevated expression of this transport protein following zinc exposure. RT-PCR confirmed mRNA for the metal exporters ZnT1 and ZnT4 with the former increasing after ZnSO₄. Cell concentrations of ferritin increased with zinc exposure while oxidative stress, measured as lipid peroxides, was decreased supporting an anti-oxidant function for Zn²⁺. Increased DMT1 expression, following pre-incubations of respiratory epithelial cells with TNF-α, IFN-γ, and endotoxin, was associated with significantly decreased intracellular zinc transport. Finally, incubations of respiratory epithelial cells with both zinc sulfate and ferric ammonium citrate resulted in elevated intracellular concentrations of both metals. We conclude that exposure to zinc increases iron uptake by respiratory epithelial cells. Elevations in cell iron can possibly affect an increased expression of DMT1 and ferritin which function to diminish oxidative stress. Comparable to other metal exposures, changes in iron homeostasis may contribute to the biological effects of zinc in specific cells and tissues.     

INFLUENCE OF THE CLAY TYPES ILLITE AND MONTMORILLONITE ON THE UPTAKE OF65 Zn BY SCENEDESMUS OBLIQUUS.

SUMMARY

The stimulatory effect of the clays illite and montmorillonite on zinc uptake by Scenedesmus obliquus is discussed. The competitive effects of hydrogen, phosphate, magnesium and copper ions on zinc uptake are illustrated. This competition is reduced in the presence of illite and montmorillonite and zinc uptake is stimulated. Ferrous ions have no effect on zinc uptake, while calcium ions antagonize zinc uptake at high concentrations. The latter effect was remarkable in the presence of montmorillonite.