Vanadium Uptake Research Articles

Electron paramagnetic resonance studies and effects of vanadium in Saccharomyces cerevisiae

Vanadium uptake by whole cells and isolated cell walls of the yeast Saccharomyces cerevisiae was studied. When orthovanadate was added to wild-type S. cerevisiae cells growing in rich medium, growth was inhibited as a function of the VO4(3-) concentration and the growth was completely arrested at a concentration of 20 mM of VO4(3-) in YEPD. Electron paramagnetic resonance (EPR) spectroscopy was used to obtain structural and dynamic information about the cell-associated paramagnetic vanadyl ion. The presence of EPR signals indicated that vanadate was reduced by whole cells to the vanadyl ion. On the contrary, no EPR signals were detected after interaction of vanadate with isolated cell walls. A 'mobile' and an 'immobile' species associated in cells with small chelates and with macromolecular sites, respectively, were identified. The value of rational correlation time tau r indicated the relative motional freedom at the macromolecular site. A strongly 'immobilized' vanadyl species bound to polar sites mainly through coulombic attractions was detected after interaction of VO2+ ions with isolated cell walls.

A new experimental system of using fertile chick eggs to evaluate vanadium absorption and antidotal effectiveness to prevent vanadium uptake

To establish the absorption of vanadium compounds such as vanadium chloride, vanadyl sulfate, and sodium metavanadate and to find effective chelating and reducing agents to cope with the absorption and uptake of vanadium compounds by embryonic chicks, aqueous vanadium solutions with or without chelating and reducing agent solutions were introduced into the air sacs of 14-day-old fertile chick eggs. After incubation of a further 5 days, mortality, embryonic weight, and vanadium content in the legs and toes were measured. Vanadium concentration in the legs and toes increased linearly as the administration of vanadium compounds increased and can be used as an index for vanadium absorption. Vanadium accumulation in the legs and toes, embryonic growth, and mortality showed no essential differences among VCl 3, VOSO 4, and NaVO 3. Among 19 antidotal substances tested, deferoxamine mesylate was the most effective, and Xylenol Orange, EDTA, and basophenathroline were secondarily effective to prevent vanadium uptake. Tiron could not prevent absorption from VOSO 4 as effectively as NaVO 3. Deferoxamine was the most effective in decreasing the death rate and increasing embryonic growth. Tiron was secondarily effective when excessive Tiron was administered. Antidotal effectiveness of deferoxamine was observed when it was simultaneously administered with vanadium compounds. Deferoxamine and VOSO 4 formed an equimolar complex that is unabsorbable. These results are comparable with the results shown in previous reports using rats and mice. The present experimental system using fertile chick eggs had advantages in the examination of mineral absorption and in the screening for effective antidotes from the viewpoints of ease of experimental procedure and animal welfare in comparison with conventional methods using laboratory animals.

Vanadium bioaccumulation inPisum sativum seedlings

Vanadium bioaccumulation calculated as the ratio of its content in plant biomass to that in the substrate (Vbi-index) was studied in pea. Vbi was on average 11.275, 11.770 and 13.153 in the roots, and 0.809, 0.467 and 0.749 in the shoots of the cultivars Opal, Laser and Ramir, respectively. This indicates cultivar differences in vanadium uptake, and low translocation rates from roots to shoots. Vanadium (3 to 30 mg 1-1) decreased shoot and root fresh and dry masses of the three cultivars. Seedlings of the cv. Opal were the most susceptible to higher concentrations of vanadium (20 to 30 mg 1-1), whereas seedlings of cv. Laser were the most resistant.

Vanadium uptake by yeast cells

During incubation with vanadyl, Saccharomyces cerevisiae yeast cells were able to accumulate millimolar concentrations of this divalent cation within an intracellular compartment. The intracellular vanadyl ions were bound to low molecular weight substances. This was indicated by th isotorpic nature of the electron paramagnetic resonance (EPR) spectra of the respective samples. Accumulation of intracellular vanadyl was dependent on presence of glucose during incubation. It could be inhibited by various di- and trivalent metal cations. Of these cations lanthanum displayed the strongest inhibitory action. If yeast cells were exposed to more than 50 μM vanadyl sulfate at a pH higher than 4.0, a potassium loss into the medium was detected. The magnitude of this potassium loss suggests a damage of the plasma membrane caused by vanadyl. Upon addition of vanadate to yeast cells surface-bound vanadyl was detectable after several minutes by EPR. This could be the consequence of extracellular reduction of vanadate to vanadyl. The reduction was followed by a slow accumulation of intracellular vanadium, which could be inhibited by lanthanum or phosphate. Therefore, permeation of vanadyl into the cells can be assumed as one mechanism of vanadium accumulation by yeast during incubation with vanadate.

Speciation of vanadium present in a model yeast system

Yeast cells were used as a model system for the investigation and identification of toxic forms of vanadium obtained on dosing a nutrient medium with various known vanadium species. Total vanadium uptake by the yeast cells was in the region of 10 p.p.m. when the nutrient medium was dosed with 200 p.p.m. of the toxic species VV prepared as a V2O5-NaOH solution. No cell growth was observed in the nutrient medium when the concentrations were above 200 p.p.m. However, vanadium was found to accumulate in the yeast cells to a much greater extent when the nutrient medium was dosed with solutions of the less toxic form VIV. Total vanadium in the cells was determined using flame atomic absorption spectrometry.

Vanadium uptake by higher plants: Some recent developments

The occurrence of vanadium in the biosphere, and the possible roles this element may play in the metabolism of living organisms, especially higher plants, are discussed. The aqueous chemistry of the element is reviewed, and the chemical properties of the element are related to those of soils and plants. Evidence is present for a biotransformation of vanadium from vanadate (VO 3 (-) ) to vanadyl (VO(2+)) during uptake by plants, based on tissue analysis and ESR spectra. The significance of this process on the potential impact of vanadium in the biosphere is discussed.

The acid promoted disproportionation of a vanadium(IV) phenolate: implications for vanadium uptake in tunicates

Under anaerobic conditions VIVO(salen)(salen =N,N′-ethylenebis-salicylideneaminato) undergoes an acid promoted disproportionation to yield a VIII(salen) species and VVO(salen)+ which upon addition of chloride ion react via back electron transfer to yield VIVO(salen) and VIVCl2(salen).

Physiological Significance of Vanadium Uptake during N<sub>2</sub> and NC<sub>3</sub><sup>-</sup> Metabolism in Various Strains of a N<sub>2</sub>-Fixing Cyanobacterium <italic>Nostoc muscorum</italic>

Physiological Significance of Vanadium Uptake during N<sub>2</sub> and NC<sub>3</sub><sup>-</sup> Metabolism in Various Strains of a N<sub>2</sub>-Fixing Cyanobacterium <italic>Nostoc muscorum</italic>

Vanadium uptake by higher plants

Vanadium uptake by higher plants

Uptake, assimilation, and excretion of vanadium in the shrimp, Lysmata seticaudata (Risso), and the crab, Carcinus maenas (L.)

Shrimps, Lysmata seticaudata (Risso). and crabs, Carcinus maenas (L.) took up 48V from water relatively slowly reaching concentration factors of ≈ 10 1 after an exposure of 3 wk. Vanadium uptake by non-moulting shrimps was independent of temperature between 13 and 24dgC. Moulting, the frequency of which increased with temperature, had a strong effect, however, on the uptake of this metal. Both increased salinity and vanadium levels in sea water tended to decrease vanadium accumulation by shrimps. Vanadium-48 uptake from water in hepatopancreas and gill of shrimps was much more rapid than that in same tissues of crabs; stable vanadium concentrations in these tissues indicated a similar trend although the differences were less pronounced. The large fraction of 48V and vanadium found in exoskeleton of both species suggests the importance of physical adsorption in the uptake process. Contaminated shrimps eliminated vanadium at rates which depend on temperature but are independent of either salinity or whole body stable vanadium levels. The fact that moulting greatly accelerated vanadium depuration underscores the important rôle played by crustacean exuviation in the marine biogeochemistry of this metal. Significantly high assimilation (≈ 30%) and retention of ingested vanadium as well as differences noted between in situ vanadium concentration factors and those based on direct uptake from water, lead to the conclusion that the food pathway is of major importance in the bioaccumulation of this metal in shrimps and crabs under natural conditions.

Vanadium transfer in the mussel Mytilus galloprovincialis

Radiotracers were used to study processes controlling the accumulation and elimination of vanadium in the Mediterranean mussel Mytilus galloprovincialis. Vanadium uptake rates varied inversely with both salinity and vanadium concentration in water, but were independent of temperature. After a 3 wk exposure to 48V, the highest concentration factors were found in the byssus (≈1900) with much lower values computed for shell (≈ 70) and soft tissues (≈5). More than 90% of the total 48V accumulated was fixed to shell, suggesting that uptake is primarily a result of surface sorption processes. Much of the vanadium in shell was firmly bound to the periostracum and was not easily removed by acid leaching. Food-chain experiments indicated that the assimilation coefficient for ingested vanadium is low (≈7%) and that the assimilated fraction is rapidly excreted from the mussel. These findings coupled with knowledge of in situ and experimentally-derived vanadium concentration-factors have allowed a preliminary assessment of the relative importance of the food and water pathways in the contamination of mussels under conditions of acute and chronic exposure. Contaminated mussels transferred to clean sea water lost 48V at rates that depended upon temperature but were largely unaffected by either salinity or by vanadium levels in mussel tissues. Total vanadium depuration was slow and was governed by loss from a slowly-exchanging compartment with a characteristic half-time of about 100 d. Individual mussel tissues were analyzed for stable vanadium and the possibility of using these tissues, particularly the byssus, as bioindicators of ambient vanadium levels in the marine environment is also discussed.

Vanadium Uptake by Plants

The kinetics of vanadium absorption by excised barley (Hordeum vulgare L., cv. Eire) roots were investigated with respect to ionic species of V in solution, time and concentration dependence, Ca sensitivity, and interaction with various anions, cations, and pH levels. The role of metabolism in V absorption was also studied using anaerobic treatment (N(2) gas) and chemical inhibitors (NaN(3), KCN, or 2,4-dinitrophenol). Approximately one-third of the labeled V initially taken up by excised roots was desorbed to a constant level after 45 min in unlabeled V solutions. The rate of absorption of labeled V from 5 mum NH(4)VO(3) solutions containing 0.5 mm CaSO(4) was constant for at least 3 hours. Omission of Ca resulted in a 72% reduction in V uptake when compared to controls with 0.5 mm CaSO(4). The rate of uptake of V was highest at pH 4 but dropped to a very low level at pH 10. It was relatively constant between the pH levels of 5 and 8 at which the VO(3) (-) ion is the predominant ionic species in solution. The rate of absorption of V was followed as a function of concentrations from 0.5 to 100 mum NH(4)VO(3). It was found to be a linear function of concentration and did not follow saturation kinetics. Absorption experiments carried out with labeled V from either N(a)VO(3) or NH(4)VO(3) sources gave similar results. No anion studied (i.e. HPO(4) (2-), HAsO(4) (2-), MoO(4) (2-), SeO(4) (2-), SeO(3) (2-), CrO(4) (2-), BO(3) (3-), No(3) (-), and Cl(-)) interfered appreciably (i.e. less than 30% inhibition) with the absorption of labeled V. Anaerobic treatment of absorption solution with N(2) gas did not inhibit V absorption by excised roots. The results obtained using chemical inhibitors were not consistent. It was concluded that V is not actively absorbed by excised barley roots.