Effects of chromium compounds on plasma membrane Mg2+-ATPase activity of BHK cells.

An ATPase activity stimulated by divalent ions (Mg²⁺, Ca²⁺, Mn²⁺, Zn²⁺) has been observed in intact hamster fibroblasts cultured in vitro (BHK line). Such activity has been determined by the incubation (30 min at 37°C) of washed cell suspensions (about 1 mg of proteins) in a medium containing 100 mM NaCl, 20 mM KCl, 15 mM Tris—HCl (pH 7.4), 10 mM NaHCO₃, 5 mM glucose and equimolar concentrations of ATP and divalent cation. Mg²⁺-ATPase activity is insensitive to ouabain and lacks specificity towards nucleoside triphosphate substrates. AMP and ADP are not hydrolyzed under these conditions. Apparent K_m of 0.76 mM and V_max of 1.46 μmol Pi · mg proteins^?1 · h^?1 have been calculated for Mg-ATP complex. This ATPase is an ectoenzyme, therefore its activity could be used as a suitable index of the action of chemicals like chromium compounds known for their cytotoxic effects on membrane functions.Salts of trivalent (CrCl₃) and hexavalent (K₂Cr₂O₇) chromium at concentrations ranging from 1 mM to 5 mM inhibit Mg²⁺-ATPase. The inhibition by K₂Cr₂O₇ is observed after pretreatment of the cells with this compound followed by its absence from the assay medium “per se” for Mg²⁺-ATPase, and it is referred to the alterations of membrane bound enzyme structures by the oxidizing hexavalent chromium. The inhibition by CrCl₃ is mainly evident when this compound is present in the incubation medium, and is referred to the interaction of trivalent chromium with Mg²⁺-ATP as it is partially reversed by increasing Mg²⁺-ATP concentration.     

Magnesium deficiency results in an increased formation of osteoclasts

Magnesium (Mg²⁺) deficiency is a frequently occurring disorder that leads to loss of bone mass, abnormal bone growth and skeletal weakness. It is not clear whether Mg²⁺ deficiency affects the formation and/or activity of osteoclasts. We evaluated the effect of Mg²⁺ restriction on these parameters. Bone marrow cells from long bone and jaw of mice were seeded on plastic and on bone in medium containing different concentrations of Mg²⁺ (0.8 mM which is 100% of the normal value, 0.4, 0.08 and 0 mM). The effect of Mg²⁺ deficiency was evaluated on osteoclast precursors for their viability after 3 days and proliferation rate after 3 and 6 days, as was mRNA expression of osteoclastogenesis-related genes and Mg²⁺-related genes. After 6 days of incubation, the number of tartrate resistant acid phosphatase-positive (TRACP⁺) multinucleated cells was determined, and the TRACP activity of the medium was measured. Osteoclastic activity was assessed at 8 days by resorption pit analysis. Mg²⁺ deficiency resulted in increased numbers of osteoclast-like cells, a phenomenon found for both types of marrow. Mg²⁺ deficiency had no effect on cell viability and proliferation. Increased osteoclastogenesis due to Mg²⁺ deficiency was reflected in higher expression of osteoclast-related genes. However, resorption per osteoclast and TRACP activity were lower in the absence of Mg²⁺. In conclusion, Mg²⁺ deficiency augmented osteoclastogenesis but appeared to inhibit the activity of these cells. Together, our in vitro data suggest that altered osteoclast numbers and activity may contribute to the skeletal phenotype as seen in Mg²⁺ deficient patients.     

Correlated effects of external magnesium on cation content and DNA synthesis in culture chicken embryo fibroblasts.

Depletion of Mg²⁺ in the growth medium for chicken embryo fibroblasts produces a large decrease in DNA synthesis as measured by ³H-thymidine incorporation, and concomitant decreases in cellular K⁺ and Mg²⁺ and increases in Na⁺ and Ca²⁺. In cells grown in media containing 0.2 mM Ca²⁺, graded reduction of Mg²⁺ from 0.8 mM (control) to 0.016 mM produced graded decreases in DNA synthesis to 10% of control at 0.016 mM Mg²⁺. Concomitantly, cell cations showed graded changes, Na⁺ increasing to 227%, K⁺ decreasing to 52.5%, Mg²⁺ decreasing to 57.5% and Ca²⁺ increasing to 153.5% of control. The effects of Mg²⁺ depletion on DNA synthesis and cell cation content exhibited a dependence on Ca²⁺ concentration, the effects being larger at low Ca²⁺ concentration. Use of inorganic pyrophosphate in the growth medium as a selective complexor of Mg²⁺ caused a marked decrease in DNA synthesis which was accompanied by changes in cellular cation content similar to those produced by direct Mg²⁺ depletion. The effects of Mg²⁺ depletion on cell cation content are explainable in terms of changes in membrane permeability caused by rapid external surface exchange of bound divalent cations. Among the several interpretations of the data in terms of possible mechanisms by which changes in external Mg²⁺ concentration may affect cell metabolism, the most consistent with known properties of the system is the concept of a central role for intracellular free Mg²⁺ in the coordinate control of growth and metabolism in animal cells.     

Identification of brain ecto-apyrase as a phosphoprotein

The divalent cation requirements of NOS activity in bovine retina homogenate supernatant were investigated. Supernatants were assayed under standard conditions (in mM: EDTA 0.45, Ca²⁺ 0.25, Mg²⁺ 4.0). In order to investigate the enzyme's dependence on divalent cations, the tissue homogenate was depleted of di- and trivalent cations by passing it over a cation-exchange column (Chelex 100). Surprisingly, NOS activity was 50-100% higher in this preparation. However, addition of either EDTA (33 M) or EGTA (1 mM) almost fully inhibited NOS activity, suggesting a requirement for residual divalent metal cation(s). Phenanthroline or iminodiacetic acid at low concentrations had little effect on activity, suggesting no requirement for Fe²⁺, Zn²⁺ or Cu²⁺. Ca²⁺ had a moderate stimulatory effect, with an optimum activity around 0.01 mM. Mg²⁺ or Mn²⁺ had little effect at concentrations < 0.25 mM. However, in the presence of EDTA, Mn²⁺ or Ca²⁺ markedly stimulated NOS activity with the optimum at 0.1 mM. At high concentrations (> 0.1-0.2 mM), all divalent cations tested (Ba²⁺, Zn²⁺, Co²⁺, Mn²⁺, Mg²⁺, Ca²⁺), as well as La³⁺, dose-dependently inhibited NOS activity. We propose that retinal NOS requires low concentrations of naturally occurring divalent metal ions, most probably Ca²⁺, for optimal activity and is inhibited by high di- and trivalent metal concentrations, probably by competition with Ca²⁺.     

Mg<Superscript>2+ </Superscript>Decreases Arrhenius Energies of Activation for High Temperature Catalysis of Phosphatases in <Emphasis Type="Italic">Thermoactinomyces vulgaris</Emphasis>

The nonspecific acid and alkaline phosphatases of Thermoactinomyces vulgaris were found to be optimally active at 65°C and 70°C, respectively, indicating the thermophilic nature of these enzymes in this obligate thermophile. Mg²⁺, when added in the assay mixture (in the form of MgCl₂), increased the specific activities of these enzymes without affecting their respective temperature optima. This divalent cation decreased the Arrhenius energies of activation (E _A ) of both acid and alkaline phosphatases, as substantiated by Mg²⁺-dependent decrease in the slopes of their Arrhenius plots, which were found to be linear. Thus, Mg²⁺-dependent stimulation of high temperature catalysis of T. vulgaris phosphatases appeared to be accomplished by the decrease in their E _A values by this divalent cation, and such unique feature of these enzymes might be associated with their evolutionary adaptation in this thermophilic actinomycete to support its growth at elevated temperatures. The catalytic role of Mg²⁺ in enhancing the phosphatase activities was specified by the fact that this metal ion was able to recover the enzyme activities inhibited by dialysis and EDTA.     

Effect of multiplication stimulating activity (MSA) on intracellular cAMP levels and adenylate cyclase activity in chick embryo fibroblasts.

Stimulation of hamster lymph node cells, splenocytes and thymocytes by the mitogen phytohemagglutinin-P (PHA) was found to be greatly enhanced by addition of 1–10 mM LiCl to the cultures. Lithium enhanced stimulation, as determined by [³H]TdR incorporation, only if added within the first 24 h of culture. The enhancing effect of lithium was specific for this monovalent cation since equivalent concentrations of KCl or NaCl did not induce a similar effect on [³H]TdR incorporation. The divalent cations Mg²⁺ (1–10 mM) and Ca²⁺ (1-1.6 mM), also had an enhancing effect on PHA stimulation. However, addition of Li⁺ to cultures enhanced with Mg²⁺ and/or Ca²⁺ led to an additional potentiation of the response to PHA. These results suggest that Li⁺ modifies a unique early event during stimulation of lymphoid cells by this mitogen.     

Characterization of cell surface material removed by water and NaCl washing ofParacoccus denitrificans grown under conditions of divalent cation deficiency and sufficiency

Paracoccus denitrificans grown on complex medium deficient in Mg²⁺ and Ca²⁺ are rendered lysozyme susceptible by washing with NaCl, whereas cells grown in a succinate-salts medium (Mg²⁺ and Ca²⁺ sufficient) or complex medium supplemented with Mg²⁺+Ca²⁺ are not. The material released by water washing of cells grown on complex medium and complex medium supplemented with Mg²⁺ and Ca²⁺ was characterized by a high protein content. There was a high lipid: protein ratio and an appreciable amount of 3-deoxyoctulosonic acid in the material released by NaCl washing of cells grown under all conditions, indicating release of outer membrane material. The lipid ornithine: lipid phosphorous ratios of NaCl wash from cells grown on complex medium and complex medium supplemented with Mg²⁺ and Ca²⁺ were 0.54 and 0.34, respectively. Although NaCl washing removed outer membrane material from cells grown under all conditions, only divalent cation deficient cells were rendered lysozyme susceptible. This might be explained by the increased outer membrane ornithine-containing lipid to phospholipid ratio in these cells yielding a more permeable outer membrane.     

Interaction of Anions and Cations in Regulating Energy Distribution between the Two Photosystems

Cations such as Mg²⁺ regulate spillover of absorbed excitation energy mainly in favour of photosystem (PS) 2. Effect of low concentration (<10 mM) of the monovalent cation Na⁺ on chlorophyll (Chl) a fluorescence was completely overridden by divalent cation Mg²⁺ (5 mM). Based on Chl a fluorescence yield and 77 K emission measurements, we revealed the role and effectiveness of anions (Cl^-, SO₄ ^2-, PO₄ ^3-) in lowering the Mg²⁺-induced PS2 fluorescence. The higher the valency of the anion, the lesser was the expression of Mg²⁺ effect. Anions may thus overcome Mg²⁺ effects up to certain extent in a valency dependent manner, thereby diverting more energy to PS1 even in the presence of MgCl₂. They may do so by reversing Mg²⁺-induced changes.     

Accumulation of magnesium ions during fermentative metabolism in Saccharomyces cerevisiae

When cells of Saccharomyces cerevisiae were grown aerobically under glucose-repressed conditions, ethanol production displayed a hyperbolic relationship over a limited range of magnesium concentrations up to around 0.5 mM. A similar relationship existed between available Mg²⁺ and ethanol yield, but over a narrower range of Mg²⁺ concentrations. Cellular demand for Mg²⁺ during fermentation was reflected in the accumulation patterns of Mg²⁺ by yeast cells from the growth medium. Entry of cells into the stationary growth phase and the time of maximum ethanol and minimum sugar concentration correlated with a period of maximum Mg²⁺ transport by yeast cells. The timing of Mg²⁺ transport fluxes by S. cerevisiae is potentially useful when conditioning yeast seed inocula prior to alcohol fermentations. Received 04 March 1996/ Accepted in revised form 21 August 1996     

Effects of Ca and Mg on Growth and Calcification of the Coccolithophorid Pleurochrysis haptonemofera: Ca Requirement for Cell Division in Coccolith-Bearing Cells and for Normal Coccolith Formation with Acidic Polysaccharides

The effects of Ca²⁺ and Mg²⁺ on cellular growth and calcification in Pleurochrysis haptonemofera were investigated. In the presence of a normal concentration of Mg²⁺, coccolith-bearing cells (C-cells) required more than 0.5 mM Ca²⁺ for growth, while naked cells could grow even with 0.5 mM Ca²⁺. The calcification rate of C-cells, which was determined using decalcified cells, was significantly repressed with less than or equal to 0.5 mM Ca²⁺. Although the calcification rate did not change so much with 5–30 mM Ca²⁺, it decreased with higher concentrations of Ca²⁺, as well as C-cell-specific growth repression. Under these conditions, Ca²⁺ affected the rate of coccolith formation, but neither the coccolith morphology nor total amounts and ratios of divalent cations and acidic polysaccharides (Ph-PS-1, -2, and -3) were included in coccoliths. These findings suggest that sufficient calcification is required for the division of C-cells. Under low Ca²⁺ and high Mg²⁺ conditions, coccoliths with an abnormal morphology, having immature shield elements, were synthesized. Composition analysis of the coccoliths revealed high Mg/Ca and low Ph-PS-2/(Ph-PS-1 and -3) ratios, as compared with those under low Ca²⁺ and normal Mg²⁺ conditions, suggesting that the abnormal morphology is due to a change in the crystal type and/or acidic polysaccharide composition.     

Bacillus subtilis Cells Lacking Penicillin-Binding Protein 1 Require Increased Levels of Divalent Cations for Growth

Bacillus subtilis strains lacking penicillin-binding protein 1 (PBP1), encoded by ponA, required greater amounts of Mg²⁺ or Ca²⁺ for vegetative growth or spore outgrowth than the wild-type strain and strains lacking other high-molecular-weight (HMW) PBPs. Growth of ponA cells in a medium low in Mg²⁺ also resulted in greatly increased cell bending compared to wild-type cells or cells lacking other HMW PBPs. The addition of high levels of Mg²⁺ to growth media eliminated these phenotypes of a ponA mutant. In contrast to the effects of divalent cations, NaCl did not restore ponA cell growth in a divalent-cation-deficient medium. Surprisingly, wild-type cells swelled and then lysed during both vegetative growth and spore outgrowth when 500 mM NaCl was included in a divalent-cation-deficient medium. Again, Mg²⁺ addition was sufficient to allow normal vegetative growth and spore outgrowth of both wild-type and ponA cells in a medium with 500 mM NaCl. These studies demonstrate that (i) while HMW PBPs possess largely redundant functions in rich medium, when divalent cations are limiting, PBP1 is required for cell growth and spore outgrowth; and (ii) high levels of NaCl induce cell lysis in media deficient in divalent cations during both vegetative growth and spore outgrowth.     

Leucocyte locomotion and chemotaxis : The influence of divalent cations and cation ionophores

Human blood neutrophil leucocytes and monocytes incubated in the absence of Ca²⁺ and Mg²⁺ showed reduced, but still substantial migration into micropore filters towards chemotactic agents, compared with cells migrating in a divalent cation-rich medium. This reduction in migration could be reversed by adding low doses of divalent cation ionophores (X537A or A23187) to the Ca²⁺- and Mg²⁺-free medium which suggests that migrating leucocytes in media depleted of extracellular divalent cations can make use of intracellular divalent cations and that the intracellular cation exchange necessary for locomotion is facilitated by the ionophores. At higher doses, the ionophores inhibited locomotion, as did procaine which reduces membrane permeability to cations. Little effect of K⁺ depletion or of ouabain on leucocyte locomotion was noted.     

Demonstration of two stable potential states of plasmalemma ofChara without tonoplast

Summary The tonoplast of cells ofChara australis was removed by replacement of the cell sap with a medium containing 5 mM EGTA (ethyleneglycol-bis-(-aminoethyl ether) N, N-tetraacetic acid). Such cells without tonoplast could generate an action potential of rectangular shape. In the present paper characteristics of the action potential were studied under various external ionic conditions.Action potentials could be elicited without refractory period and the peak of the action potential was constant among action potentials.Duration of the action potential decreased under repeated excitations, but recovered after pause. Increase in concentrations of alkali metal cations, Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺, resulted in prolongation of the action potential.At proper concentrations of monovalent cations the membrane potential could stay either at the resting level or at the depolarized level and could be shifted reversibly from the former level to the latter one orvice versa by applying outward or inward current. Further increase in concentrations of monovalent cations resulted in arrest of the membrane potential at the depolirized level. The critical concentrations of the monovalent cations to hold the membrane potential at the depolarized level were about 10 mM irrespective of the cation species.Divalent cations, Ca²⁺, Mg²⁺, Sr²⁺, Ni²⁺ and Mn²⁺, added to the bathing medium suppressed the effect of monovalent cations to prolong the action potential.Ca²⁺ and Mg²⁺ added to the bathing medium caused repolarization of the plasmalemma which had been depolarized by application of high concentrations of K⁺ to the bathing medium. The antagonism between monovalent and divalent cations on the state of the plasmalemma ofChara cells was discussed based on the two stable states hypothesis proposed by Tasaki (Tasaki, I. 1968. Nerve Excitation. Charles C. Thomas, Springfield, Illinois).     

Super-high-affinity binding site for [3H]diazepam in the presence of Co2+, Ni2+, Cu2+, OR Zn2+

Chloride salts of Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Cr³⁺, Mn²⁺, Fe²⁺, and Fe³⁺ had no effect on [³H]diazepam binding. Chloride salts of Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ increased [³H]diazepam binding by 34 to 68% in a concentration-dependent fashion. Since these divalent cations potentiated the GABA-enhanced [³H]diazepam binding and the effect of each divalent cation was nearly additive with GABA, these cations probably act at a site different from the GABA recognition site in the benzodiazepine-receptor complex. Scatchard plots of [³H]diazepam binding without an effective divalent cation showed a single class of binding, with a Kd value of 5.3 mM. In the presence of 1 mM Co²⁺, Ni²⁺, Cu²⁺, or Zn²⁺, two distinct binding sites were evident with apparent Kd values of 1.0 nM and 5.7 nM. The higher-affinity binding was not detected in the absence of an effective divalent cation and is probably a novel, super-high-affinity binding site.     

Calcium and magnesium effect on divalent cation deficientHydrilla verticillata thylakoid electron transport activity

The role of divalent cations like magnesium (Mg²⁺) and calcium (Ca²⁺) was irrvestigated on energy distribution process ofHydrilla verticillata thylakoids. Effect of these cations was tested on relative quantum yield of photosystem (PS) II catalyzed electron transport activity, room and liquid nitrogen temperature fluorescence emission properties and thylakoid light scattering characteristics. The electron transport activity was found to be stimulated in the presence of these cations in a light intensity independent manner. The concentration of cation required for maximum stimulation was nearly 10–12 mM. Comparatively, Ca²⁺ was more effective than Mg²⁺. Cation induced stimulation in electron transport activity was not accompanied by increase in chlorophylla fluorescence intensity either at room (25°C) or liquid nitrogen (77°K) temperatures. Furthermore, 540 nm absorption and 90° light scattering properties of thylakoids remained insensitive towards divalent cations. These facts together suggest that divalent cations inHydrilla thylakoids are not effective in supporting the excitation distribution between the interacting photosystem complexes.     

Nutrients determine the spatial architecture of Paracoccus sp. biofilm

Bacterial biofilms adapt and shape their structure in response to varied environmental conditions. A statistical methodology was adopted in this study to empirically investigate the influence of nutrients on biofilm structural parameters deduced from confocal scanning laser microscope images of Paracoccus sp.W1b, a denitrifying bacterium. High concentrations of succinate, Mg⁺⁺, Ca⁺⁺, and Mn⁺⁺ were shown to enhance biofilm formation whereas higher concentration of iron decreased biofilm formation. Biofilm formed at high succinate was uneven with high surface to biovolume ratio. Higher Mg⁺⁺ or Ca⁺⁺ concentrations induced cohesion of biofilm cells, but contrasting biofilm architectures were detected. Biofilm with subpopulation of pillar-like protruding cells was distributed on a mosaic form of monolayer cells in medium with 10 mM Mg⁺⁺. 10 mM Ca⁺⁺ induced a dense confluent biofilm. Denitrification activity was significantly increased in the Mg⁺⁺- and Ca⁺⁺-induced biofilms. Chelator treatment of various biofilm ages indicated that divalent cations are important in the initial stages of biofilm formation.     

Regulation of divalent cations of the membrane-bound pyrophosphatase of Rhodospirillum rubrum,as shown by the hydrolysis of tripositive-pyrophosphate complexes

Tripositive-pyrophosphate [M(III)-PPi] complexes were used to investigate the role of free divalent cations on the membrane-bound pyrophosphatase. Divalent cations remain free and the M(III)-PPi complexes were employed as substrates. Formation of a La-PPi complex was studied by fluorescence, and the fact that Zn²⁺ and Mg²⁺ remain free in the solution was validated. Hydrolysis of La-PPi is stimulated by the presence of fixed concentrations of free Mg²⁺ or Zn²⁺ and this stimulation depends on the concentration of the cations when the La-PPi complex is fixed. The divalent cation stimulation order is Zn²⁺ > Co²⁺ > Mg²⁺ > Mn²⁺ > Ca²⁺ (at 0.5 mm of free cation). With different M(III)-PPi complexes, Zn²⁺ produces the same K _m, for all the complexes and Mg²⁺ stimulates with a different K _m. The results suggest that both Mg²⁺ and Zn²⁺ activate the membrane-bound pyrophosphatase but through different mechanisms.     

NUTRITIONAL REQUIREMENTS FOR SEXUAL REPRODUCTION IN MESOTAENIUM KRAMSTAI (CHLOROPHYTA) 1

Optimum conditions for conjugation in the heterothallic saccoderm desmid Mesotaenium kramstai Lemmer-mann have been determined. In culture, cells acquired the ability to form gamete pairs just prior to the onset of stationary phase after sufficient nitrate had been depleted from the medium. The appearance of potential gametes was delayed by increasing the concentration of KNO₃ When cells of both mating types were harvested from 15 to 18 day old cultures, washed, resuspended in fresh medium, and mixed, approximately 50 percent of the cells paired (measured three days after mixing) in a medium containing 0.13 mM or less KNO₃. At greater concentrations, fewer pairs formed; no pairs formed in medium containing 0.5 mM KNO₃. Conjugation was not inhibited by other macronutrients. Calcium and magnesium were essential for maximum conjugation. Although Ca²⁺ and Mg²⁺ contentrations of 0.05 mM and 0. I mM, respectively, were sufficient for optimum growth, maximum conjugation required more than 10 times these values. Few gamete pairs formed when either Ca²⁺ or Mg²⁺ was omitted from the medium, no pairing occurred when both Ca²⁺ and Mg²⁺ were omitted.     

Insulin action in isolated fat cells: II. Effects of divalent cations on stimulation by insulin of protein synthesis,on inhibition of lipolysis by insulin,and on the binding of 125I-labelled insulin to isolated fat cells

The effects of omission of Ca²⁺ and Mg²⁺ from the incubation medium on three aspects of insulin action in isolated fat cells have been investigated. In the (Ca²⁺ + Mg²⁺)-free incubation medium incorporation of L-[¹⁴C]leucine into fat cell protein was reduced in the absence of insulin. Insulin stimulated L-[¹⁴C]-leucine incorporation only in the presence of added CaCl₂ or MgCl₂. Incubation of the cells in the (Ca²⁺ + Mg²⁺)-free medium reduced but did not abolish the ability of adrenaline to stimulate lipolysis or the ability of insulin to inhibit the adrenaline-stimulated lipolysis. Specific binding of ¹²⁵I-labelled insulin to the fat cells was reduced in the absence of Ca²⁺ and Mg²⁺ but was not abolished, even in the presence of EDTA. Ca²⁺ was routinely the most effective divalent cation in supporting these aspects of insulin action, but similar responses were obtained with Mg²⁺, Sr²⁺ and Ba²⁺.Since insulin still binds to the cells under conditions in which some of the cellular effects of the hormone are abolished, it is suggested that divalent cations may have a role, either direct or indirect, in the processes linking the insulin-insulin receptor complex to certain effector systems in the cells. It is tentatively suggested that this action occurs at the level of the fat cell plasma membrane.     

Arabidopsis Transporter MGT6 Mediates Magnesium Uptake and Is Required for Growth under Magnesium Limitation

Although magnesium (Mg²⁺) is the most abundant divalent cation in plant cells, little is known about the mechanism of Mg²⁺ uptake by plant roots. Here, we report a key function of Magnesium Transport6 (MGT6)/Mitochondrial RNA Splicing2-4 in Mg²⁺ uptake and low-Mg²⁺ tolerance in Arabidopsis thaliana. MGT6 is expressed mainly in plant aerial tissues when Mg²⁺ levels are high in the soil or growth medium. Its expression is highly induced in the roots during Mg²⁺ deficiency, suggesting a role for MGT6 in response to the low-Mg²⁺ status in roots. Silencing of MGT6 in transgenic plants by RNA interference (RNAi) resulted in growth retardation under the low-Mg²⁺ condition, and the phenotype was restored to normal growth after RNAi plants were transferred to Mg²⁺-sufficient medium. RNAi plants contained lower levels of Mg²⁺ compared with wild-type plants under low Mg²⁺ but not under Mg²⁺-sufficient conditions. Further analysis indicated that MGT6 was localized in the plasma membrane and played a key role in Mg²⁺ uptake by roots under Mg²⁺ limitation. We conclude that MGT6 mediates Mg²⁺ uptake in roots and is required for plant adaptation to a low-Mg²⁺ environment.