Magnesium in biology

Magnesium is an essential element in biological systems. Magnesium occurs typically as the Mg²⁺ ion. It is an essential mineral nutrient (i.e., element) for life^[1][2][3][4] and is present in every cell type in every organism. For example, adenosine triphosphate (ATP), the main source of energy in cells, must bind to a magnesium ion in order to be biologically active. What is called ATP is often actually Mg-ATP.^[5] As such, magnesium plays a role in the stability of all polyphosphate compounds in the cells, including those associated with the synthesis of DNA and RNA.

Over 300 enzymes require the presence of magnesium ions for their catalytic action, including all enzymes utilizing or synthesizing ATP, or those that use other nucleotides to synthesize DNA and RNA.^[6]

In plants, magnesium is necessary for synthesis of chlorophyll and photosynthesis.

Function

A balance of magnesium is vital to the well-being of all organisms. Magnesium is a relatively abundant ion in Earth's crust and mantle and is highly bioavailable in the hydrosphere. This availability, in combination with a useful and very unusual chemistry, may have led to its utilization in evolution as an ion for signaling, enzyme activation, and catalysis. However, the unusual nature of ionic magnesium has also led to a major challenge in the use of the ion in biological systems. Biological membranes are impermeable to magnesium (and other ions), so transport proteins must facilitate the flow of magnesium, both into and out of cells and intracellular compartments.

Human health

Inadequate magnesium intake frequently causes muscle

) is rare, and is more common as a drug side-effect (such as chronic alcohol or diuretic use) than from low food intake per se, but it can occur in people fed intravenously for extended periods of time.

The most common symptom of excess oral magnesium intake is

is very rare. Infants, which have less ability to excrete excess magnesium even when healthy, should not be given magnesium supplements, except under a physician's care.

) is erratic and of poorer efficiency, since it depends on the neutralization and solution of the salt by the acid of the stomach, which may not be (and usually is not) complete.

In 2021, magnesium salts were the 211th most commonly prescribed medication in the United States, with more than 2 million prescriptions.[11]^[12]

Nerve conduction

Magnesium can affect muscle relaxation through direct action on cell membranes. Mg²⁺ ions close certain types of

Hypertension

Intravenous magnesium sulphate is used in treating pre-eclampsia.^[15] For other than pregnancy-related hypertension, a meta-analysis of 22 clinical trials with dose ranges of 120 to 973 mg/day and a mean dose of 410 mg, concluded that magnesium supplementation had a small but statistically significant effect, lowering systolic blood pressure by 3–4 mm Hg and diastolic blood pressure by 2–3 mm Hg. The effect was larger when the dose was more than 370 mg/day.^[16]

Diabetes and glucose tolerance

Higher dietary intakes of magnesium correspond to lower diabetes incidence.^[17] For people with diabetes or at high risk of diabetes, magnesium supplementation lowers fasting glucose.^[18]

Mitochondria

Magnesium is essential as part of the process that generates adenosine triphosphate.^[19][20]

Mitochondria are often referred to as the "powerhouses of the cell" because their primary role is generating energy for cellular processes. They achieve this by breaking down nutrients, primarily glucose, through a series of chemical reactions known as cellular respiration. This process ultimately produces adenosine triphosphate (ATP), the cell's main energy currency.

Vitamin D

Magnesium and vitamin D have a synergistic relationship in the body, meaning they work together to optimize each other's functions:^[21][22]

• Magnesium activates vitamin D
• Vitamin D influences magnesium absorption.
• Bone health: They play crucial roles in calcium absorption and bone metabolism.
• Muscle function: They contribute to muscle contraction and relaxation, impacting physical performance and overall well-being.
• Immune function: They support a healthy immune system and may help reduce inflammation.

Overall, maintaining adequate levels of both magnesium and vitamin D is essential for optimal health and well-being.

Testosterone

It is theorized that the process of making testosterone from cholesterol, needs magnesium to function properly.^[23]

Studies have shown that significant gains in testosterone occur after taking 8-10 mg magnesium/kg body weight/day.^[24][25]

Dietary recommendations

The U.S. Institute of Medicine (IOM) updated Estimated Average Requirements (EARs) and

Reference Daily Intake of magnesium^[27]

Age	Male	Female	Pregnancy	Lactation
Birth to 6 months	30 mg*	30 mg*
7–12 months	75 mg*	75 mg*
1–3 years	80 mg	80 mg
4–8 years	130 mg	130 mg
9–13 years	240 mg	240 mg
14–18 years	410 mg	360 mg	400 mg	360 mg
19–30 years	400 mg	310 mg	350 mg	310 mg
31–50 years	420 mg	320 mg	360 mg	320 mg
51+ years	420 mg	320 mg

* = Adequate intake

The European Food Safety Authority (EFSA) refers to the collective set of information as Dietary Reference Values, with Population Reference Intake (PRI) instead of RDA, and Average Requirement instead of EAR. AI and UL defined the same as in United States. For women and men ages 18 and older the AIs are set at 300 and 350 mg/day, respectively. AIs for pregnancy and lactation are also 300 mg/day. For children ages 1–17 years the AIs increase with age from 170 to 250 mg/day. These AIs are lower than the U.S. RDAs.^[28] The European Food Safety Authority reviewed the same safety question and set its UL at 250 mg/day - lower than the U.S. value.^[29] The magnesium UL is unique in that it is lower than some of the RDAs. It applies to intake from a pharmacological agent or dietary supplement only, and does not include intake from food and water.

Labeling

For U.S. food and dietary supplement labeling purposes the amount in a serving is expressed as a percent of daily value (%DV). For magnesium labeling purposes 100% of the daily value was 400 mg, but as of May 27, 2016, it was revised to 420 mg to bring it into agreement with the RDA.^[30][31] A table of the old and new adult Daily Values is provided at Reference Daily Intake.

Food sources

Although many foods contain magnesium, it is usually found in low levels. As with most nutrients, daily needs for magnesium are unlikely to be met by one serving of any single food. Eating a wide variety of fruits, vegetables, and grains will help ensure adequate intake of magnesium.

Because magnesium readily dissolves in water, refined foods, which are often processed or cooked in water and dried, in general, are poor sources of the nutrient. For example,

whole-wheat bread

has twice as much magnesium as white bread because the magnesium-rich germ and bran are removed when white flour is processed. The table of food sources of magnesium suggests many dietary sources of magnesium.

"soft" water

contains less of the ion. Dietary surveys do not assess magnesium intake from water, which may lead to underestimating total magnesium intake and its variability.

Too much magnesium may make it difficult for the body to absorb

). However, as noted, symptoms of low magnesium from pure dietary deficiency are thought to be rarely encountered.

Following are some foods and the amount of magnesium in them:[33]

Biological range, distribution, and regulation

In

).

In plants, and more recently in animals, magnesium has been recognized as an important signaling ion, both activating and mediating many biochemical reactions. The best example of this is perhaps the regulation of carbon fixation in chloroplasts in the Calvin cycle.^[42][43]

Magnesium is very important in cellular function. Deficiency of the

Plants deficient in magnesium show stress responses. The first observable signs of both magnesium starvation and overexposure in plants is a decrease in the rate of photosynthesis. This is due to the central position of the Mg²⁺ ion in the chlorophyll molecule. The later effects of magnesium deficiency on plants are a significant reduction in growth and reproductive viability.^[4] Magnesium can also be toxic to plants, although this is typically seen only in drought conditions.^[47][48]

In animals, magnesium deficiency (

Overexposure to magnesium may be toxic to individual cells, though these effects have been difficult to show experimentally.^[citation needed] Hypermagnesemia, an overabundance of magnesium in the blood, is usually caused by loss of kidney function. Healthy animals rapidly excrete excess magnesium in the urine and stool.^[54] Urinary magnesium is called magnesuria. Characteristic concentrations of magnesium in model organisms are: in E. coli 30-100mM (bound), 0.01-1mM (free), in budding yeast 50mM, in mammalian cell 10mM (bound), 0.5mM (free) and in blood plasma 1mM.^[55]

Biological chemistry

Mg²⁺ is the fourth-most-abundant metal ion in cells (per moles) and the most abundant free divalent cation — as a result, it is deeply and intrinsically woven into cellular metabolism. Indeed, Mg²⁺-dependent enzymes appear in virtually every metabolic pathway: Specific binding of Mg²⁺ to biological membranes is frequently observed, Mg²⁺ is also used as a signalling molecule, and much of nucleic acid biochemistry requires Mg²⁺, including all reactions that require release of energy from ATP.^[56][57][43] In nucleotides, the triple-phosphate moiety of the compound is invariably stabilized by association with Mg²⁺ in all enzymatic processes.

Chlorophyll

In photosynthetic organisms, Mg²⁺ has the additional vital role of being the coordinating ion in the chlorophyll molecule. This role was discovered by Richard Willstätter, who received the Nobel Prize in Chemistry 1915 for the purification and structure of chlorophyll binding with sixth number of carbon

Enzymes

The chemistry of the Mg²⁺ ion, as applied to enzymes, uses the full range of this ion's unusual reaction chemistry to fulfill a range of functions.^{[56][58][59][60]} Mg²⁺ interacts with substrates, enzymes, and occasionally both (Mg²⁺ may form part of the active site). In general, Mg²⁺ interacts with substrates through inner sphere coordination, stabilising anions or reactive intermediates, also including binding to ATP and activating the molecule to nucleophilic attack. When interacting with enzymes and other proteins, Mg²⁺ may bind using inner or outer sphere coordination, to either alter the conformation of the enzyme or take part in the chemistry of the catalytic reaction. In either case, because Mg²⁺ is only rarely fully dehydrated during ligand binding, it may be a water molecule associated with the Mg²⁺ that is important rather than the ion itself. The Lewis acidity of Mg²⁺ (pK_a 11.4) is used to allow both hydrolysis and condensation reactions (most common ones being phosphate ester hydrolysis and phosphoryl transfer) that would otherwise require pH values greatly removed from physiological values.

Essential role in the biological activity of ATP

ATP (adenosine triphosphate), the main source of energy in cells, must be bound to a magnesium ion in order to be biologically active. What is called ATP is often actually Mg-ATP.^[5]

Nucleic acids

).

Magnesium ions can be critical in maintaining the positional integrity of closely clustered phosphate groups. These clusters appear in numerous and distinct parts of the cell nucleus and cytoplasm. For instance, hexahydrated Mg²⁺ ions bind in the deep major groove and at the outer mouth of A-form nucleic acid duplexes.^[63]

Cell membranes and walls

Biological

Proteins

The Mg²⁺ ion tends to bind only weakly to

(e.g., ATP), but also, what is more important, it is buffered by storage of Mg²⁺ in intracellular compartments. The transport of Mg²⁺ between intracellular compartments may be a major part of regulating enzyme activity. The interaction of Mg²⁺ with proteins must also be considered for the transport of the ion across biological membranes.

Manganese

In biological systems, only

prefers Mn²⁺.

Importance in drug binding

An article[65] investigating the structural basis of interactions between clinically relevant antibiotics and the 50S ribosome appeared in Nature in October 2001. High-resolution X-ray crystallography established that these antibiotics associate only with the 23S rRNA of a ribosomal subunit, and no interactions are formed with a subunit's protein portion. The article stresses that the results show "the importance of putative Mg²⁺ ions for the binding of some drugs".

Measuring magnesium in biological samples

By radioactive isotopes

The use of radioactive tracer elements in ion uptake assays allows the calculation of km, Ki and Vmax and determines the initial change in the ion content of the cells. ²⁸Mg decays by the emission of a high-energy beta or gamma particle, which can be measured using a scintillation counter. However, the radioactive half-life of ²⁸Mg, the most stable of the radioactive magnesium isotopes, is only 21 hours. This severely restricts the experiments involving the nuclide. Also, since 1990, no facility has routinely produced ²⁸Mg, and the price per mCi is now predicted to be approximately US$30,000.^[66] The chemical nature of Mg²⁺ is such that it is closely approximated by few other cations.^[67] However, Co²⁺, Mn²⁺ and Ni²⁺ have been used successfully to mimic the properties of Mg²⁺ in some enzyme reactions, and radioactive forms of these elements have been employed successfully in cation transport studies. The difficulty of using metal ion replacement in the study of enzyme function is that the relationship between the enzyme activities with the replacement ion compared to the original is very difficult to ascertain.^[67]

By fluorescent indicators

A number of chelators of divalent cations have different fluorescence spectra in the bound and unbound states.^[68] Chelators for Ca²⁺ are well established, have high affinity for the cation, and low interference from other ions. Mg²⁺ chelators lag behind and the major fluorescence dye for Mg²⁺ (mag-fura 2^[69]) actually has a higher affinity for Ca²⁺.^[70] This limits the application of this dye to cell types where the resting level of Ca²⁺ is < 1 μM and does not vary with the experimental conditions under which Mg²⁺ is to be measured. Recently, Otten et al. (2001) have described work into a new class of compounds that may prove more useful, having significantly better binding affinities for Mg²⁺.^[71] The use of the fluorescent dyes is limited to measuring the free Mg²⁺. If the ion concentration is buffered by the cell by chelation or removal to subcellular compartments, the measured rate of uptake will give only minimum values of km and Vmax.

By electrophysiology

First, ion-specific microelectrodes can be used to measure the internal free ion concentration of cells and organelles. The major advantages are that readings can be made from cells over relatively long periods of time, and that unlike dyes very little extra ion buffering capacity is added to the cells.^[72]

Second, the technique of two-electrode voltage-clamp allows the direct measurement of the ion flux across the membrane of a cell.^[73] The membrane is held at an electric potential and the responding current is measured. All ions passing across the membrane contribute to the measured current.

Third, the technique of patch-clamp uses isolated sections of natural or artificial membrane in much the same manner as voltage-clamp but without the secondary effects of a cellular system. Under ideal conditions the conductance of individual channels can be quantified. This methodology gives the most direct measurement of the action of ion channels.^[73]

By absorption spectroscopy

Flame atomic absorption spectroscopy (AAS) determines the total magnesium content of a biological sample.^[68] This method is destructive; biological samples must be broken down in concentrated acids to avoid clogging the fine nebulising apparatus. Beyond this, the only limitation is that samples must be in a volume of approximately 2 mL and at a concentration range of 0.1 – 0.4 μmol/L for optimum accuracy. As this technique cannot distinguish between Mg²⁺ already present in the cell and that taken up during the experiment, only content not uptaken can be quantified.

Inductively coupled plasma (ICP) using either the mass spectrometry (MS) or atomic emission spectroscopy (AES) modifications also allows the determination of the total ion content of biological samples.^[74] These techniques are more sensitive than flame AAS and are capable of measuring the quantities of multiple ions simultaneously. However, they are also significantly more expensive.

Magnesium transport

The chemical and biochemical properties of Mg²⁺ present the cellular system with a significant challenge when transporting the ion across biological membranes. The dogma of ion transport states that the transporter recognises the ion then progressively removes the water of hydration, removing most or all of the water at a selective pore before releasing the ion on the far side of the membrane.^[75] Due to the properties of Mg²⁺, large volume change from hydrated to bare ion, high energy of hydration and very low rate of ligand exchange in the inner coordination sphere, these steps are probably more difficult than for most other ions. To date, only the ZntA protein of Paramecium has been shown to be a Mg²⁺ channel.^[76] The mechanisms of Mg²⁺ transport by the remaining proteins are beginning to be uncovered with the first three-dimensional structure of a Mg²⁺ transport complex being solved in 2004.^[77]

The

Due to the strength of the inner sphere complexation between Mg²⁺ and any ligand, multiple simultaneous interactions with the transport protein at this level might significantly retard the ion in the transport pore. Hence, it is possible that much of the hydration water is retained during transport, allowing the weaker (but still specific) outer sphere coordination.

In spite of the mechanistic difficulty, Mg²⁺ must be transported across membranes, and a large number of Mg²⁺ fluxes across membranes from a variety of systems have been described.[78] However, only a small selection of Mg²⁺ transporters have been characterised at the molecular level.

Ligand ion channel blockade

.

Plant physiology of magnesium

The previous sections have dealt in detail with the chemical and biochemical aspects of Mg²⁺ and its transport across cellular membranes. This section will apply this knowledge to aspects of whole plant physiology, in an attempt to show how these processes interact with the larger and more complex environment of the multicellular organism.

Nutritional requirements and interactions

Mg²⁺ is essential for plant growth and is present in higher plants in amounts on the order of 80 μmol g⁻¹ dry weight.[4] The amounts of Mg²⁺ vary in different parts of the plant and are dependent upon nutritional status. In times of plenty, excess Mg²⁺ may be stored in vascular cells (Stelzer et al., 1990;^[40] and in times of starvation Mg²⁺ is redistributed, in many plants, from older to newer leaves.^[4][79]

Mg²⁺ is taken up into plants via the roots. Interactions with other cations in the

Mg²⁺ binds relatively weakly to these charges, and can be displaced by other cations, impeding uptake and causing deficiency in the plant.

Within individual plant cells, the Mg²⁺ requirements are largely the same as for all cellular life; Mg²⁺ is used to stabilise membranes, is vital to the utilisation of ATP, is extensively involved in the nucleic acid biochemistry, and is a cofactor for many enzymes (including the ribosome). Also, Mg²⁺ is the coordinating ion in the chlorophyll molecule. It is the intracellular compartmentalisation of Mg²⁺ in plant cells that leads to additional complexity. Four compartments within the plant cell have reported interactions with Mg²⁺. Initially, Mg²⁺ will enter the cell into the cytoplasm (by an as yet unidentified system), but free Mg²⁺ concentrations in this compartment are tightly regulated at relatively low levels (≈2 mmol/L) and so any excess Mg²⁺ is either quickly exported or stored in the second intracellular compartment, the vacuole.[82] The requirement for Mg²⁺ in mitochondria has been demonstrated in yeast^[83] and it seems highly likely that the same will apply in plants. The chloroplasts also require significant amounts of internal Mg²⁺, and low concentrations of cytoplasmic Mg²⁺.^[84][85] In addition, it seems likely that the other subcellular organelles (e.g., Golgi, endoplasmic reticulum, etc.) also require Mg²⁺.

Distributing magnesium ions within the plant

Once in the cytoplasmic space of root cells Mg²⁺, along with the other cations, is probably transported radially into the stele and the vascular tissue.^[86] From the cells surrounding the xylem the ions are released or pumped into the xylem and carried up through the plant. In the case of Mg²⁺, which is highly mobile in both the xylem and phloem,^[87] the ions will be transported to the top of the plant and back down again in a continuous cycle of replenishment. Hence, uptake and release from vascular cells is probably a key part of whole plant Mg²⁺ homeostasis. Figure 1 shows how few processes have been connected to their molecular mechanisms (only vacuolar uptake has been associated with a transport protein, AtMHX).

The diagram shows a schematic of a plant and the putative processes of Mg²⁺ transport at the root and leaf where Mg²⁺ is loaded and unloaded from the vascular tissues.

(9) is unknown. Mg²⁺ may return to the roots in the phloem sap.

When a Mg²⁺ ion has been absorbed by a cell requiring it for metabolic processes, it is generally assumed that the ion stays in that cell for as long as the cell is active.^[4] In vascular cells, this is not always the case; in times of plenty, Mg²⁺ is stored in the vacuole, takes no part in the day-to-day metabolic processes of the cell (Stelzer et al., 1990), and is released at need. But for most cells it is death by senescence or injury that releases Mg²⁺ and many of the other ionic constituents, recycling them into healthy parts of the plant. In addition, when Mg²⁺ in the environment is limiting, some species are able to mobilise Mg²⁺ from older tissues.^[79] These processes involve the release of Mg²⁺ from its bound and stored states and its transport back into the vascular tissue, where it can be distributed to the rest of the plant. In times of growth and development, Mg²⁺ is also remobilised within the plant as source and sink relationships change.^[4]

The homeostasis of Mg²⁺ within single plant cells is maintained by processes occurring at the plasma membrane and at the vacuole membrane (see Figure 2). The major driving force for the translocation of ions in plant cells is ΔpH.^[88] H⁺-ATPases pump H⁺ ions against their concentration gradient to maintain the pH differential that can be used for the transport of other ions and molecules. H⁺ ions are pumped out of the cytoplasm into the extracellular space or into the vacuole. The entry of Mg²⁺ into cells may occur through one of two pathways, via channels using the ΔΨ (negative inside) across this membrane or by symport with H⁺ ions. To transport the Mg²⁺ ion into the vacuole requires a Mg²⁺/H⁺ antiport transporter (such as AtMHX). The H⁺-ATPases are dependent on Mg²⁺ (bound to ATP) for activity, so that Mg²⁺ is required to maintain its own homeostasis.

A schematic of a plant cell is shown including the four major compartments currently recognised as interacting with Mg²⁺. H⁺-ATPases maintain a constant ΔpH across the plasma membrane and the vacuole membrane. Mg²⁺ is transported into the vacuole using the energy of ΔpH (in A. thaliana by AtMHX). Transport of Mg²⁺ into cells may use either the negative ΔΨ or the ΔpH. The transport of Mg²⁺ into mitochondria probably uses ΔΨ as in the mitochondria of yeast, and it is likely that chloroplasts take Mg²⁺ by a similar system. The mechanism and the molecular basis for the release of Mg²⁺ from vacuoles and from the cell is not known. Likewise, the light-regulated Mg²⁺ concentration changes in chloroplasts are not fully understood, but do require the transport of H⁺ ions across the thylakoid membrane.

Magnesium, chloroplasts and photosynthesis

Mg²⁺ is the coordinating metal ion in the chlorophyll molecule, and in plants where the ion is in high supply about 6% of the total Mg²⁺ is bound to chlorophyll.^[4][89][90] Thylakoid stacking is stabilised by Mg²⁺ and is important for the efficiency of photosynthesis, allowing phase transitions to occur.^[91]

Mg²⁺ is probably taken up into chloroplasts to the greatest extent during the light-induced development from proplastid to chloroplast or etioplast to chloroplast. At these times, the synthesis of chlorophyll and the biogenesis of the thylakoid membrane stacks absolutely require the divalent cation.^[92][93]

Whether Mg²⁺ is able to move into and out of chloroplasts after this initial developmental phase has been the subject of several conflicting reports. Deshaies et al. (1984) found that Mg²⁺ did move in and out of isolated chloroplasts from young pea plants,^[94] but Gupta and Berkowitz (1989) were unable to reproduce the result using older spinach chloroplasts.^[95] Deshaies et al. had stated in their paper that older pea chloroplasts showed less significant changes in Mg²⁺ content than those used to form their conclusions. The relative proportion of immature chloroplasts present in the preparations may explain these observations.

The metabolic state of the chloroplast changes considerably between night and day. During the day, the chloroplast is actively harvesting the energy of light and converting it into chemical energy. The activation of the metabolic pathways involved comes from the changes in the chemical nature of the stroma on the addition of light. H⁺ is pumped out of the stroma (into both the cytoplasm and the lumen) leading to an alkaline pH.^[96][97] Mg²⁺ (along with K⁺) is released from the lumen into the stroma, in an electroneutralisation process to balance the flow of H⁺.^{[98][99][100][101]} Finally, thiol groups on enzymes are reduced by a change in the redox state of the stroma.^[102] Examples of enzymes activated in response to these changes are fructose 1,6-bisphosphatase, sedoheptulose bisphosphatase and ribulose-1,5-bisphosphate carboxylase.^[4][59][102] During the dark period, if these enzymes were active a wasteful cycling of products and substrates would occur.

Two major classes of the enzymes that interact with Mg²⁺ in the stroma during the light phase can be identified.^[59] Firstly, enzymes in the glycolytic pathway most often interact with two atoms of Mg²⁺. The first atom is as an allosteric modulator of the enzymes' activity, while the second forms part of the active site and is directly involved in the catalytic reaction. The second class of enzymes includes those where the Mg²⁺ is complexed to nucleotide di- and tri-phosphates (ADP and ATP), and the chemical change involves phosphoryl transfer. Mg²⁺ may also serve in a structural maintenance role in these enzymes (e.g., enolase).

Magnesium stress

Plant stress responses can be observed in plants that are under- or over-supplied with Mg²⁺. The first observable signs of Mg²⁺ stress in plants for both starvation and toxicity is a depression of the rate of photosynthesis, it is presumed because of the strong relationships between Mg²⁺ and chloroplasts/chlorophyll. In pine trees, even before the visible appearance of yellowing and necrotic spots, the photosynthetic efficiency of the needles drops markedly.^[79] In Mg²⁺ deficiency, reported secondary effects include carbohydrate immobility, loss of RNA transcription and loss of protein synthesis.^[103] However, due to the mobility of Mg²⁺ within the plant, the deficiency phenotype may be present only in the older parts of the plant. For example, in Pinus radiata starved of Mg²⁺, one of the earliest identifying signs is the chlorosis in the needles on the lower branches of the tree. This is because Mg²⁺ has been recovered from these tissues and moved to growing (green) needles higher in the tree.^[79]

A Mg²⁺ deficit can be caused by the lack of the ion in the media (soil), but more commonly comes from inhibition of its uptake.^[4] Mg²⁺ binds quite weakly to the negatively charged groups in the root cell walls, so that excesses of other cations such as K⁺, NH₄⁺, Ca²⁺, and Mn²⁺ can all impede uptake.(Kurvits and Kirkby, 1980;^[80] In acid soils Al³⁺ is a particularly strong inhibitor of Mg²⁺ uptake.^[104][105] The inhibition by Al³⁺ and Mn²⁺ is more severe than can be explained by simple displacement, hence it is possible that these ions bind to the Mg²⁺ uptake system directly.^[4] In bacteria and yeast, such binding by Mn²⁺ has already been observed. Stress responses in the plant develop as cellular processes halt due to a lack of Mg²⁺ (e.g. maintenance of ΔpH across the plasma and vacuole membranes). In Mg²⁺-starved plants under low light conditions, the percentage of Mg²⁺ bound to chlorophyll has been recorded at 50%.^[106] Presumably, this imbalance has detrimental effects on other cellular processes.

Mg²⁺ toxicity stress is more difficult to develop. When Mg²⁺ is plentiful, in general the plants take up the ion and store it (Stelzer et al., 1990). However, if this is followed by drought then ionic concentrations within the cell can increase dramatically. High cytoplasmic Mg²⁺ concentrations block a K⁺ channel in the inner envelope membrane of the chloroplast, in turn inhibiting the removal of H⁺ ions from the chloroplast stroma. This leads to an acidification of the stroma that inactivates key enzymes in

See also

• Biology and pharmacology of chemical elements
• Calcium in biology – Use of calcium by organisms
• Iodine in biology – Use of Iodine by organisms
• Ion channels
   – Pore-forming membrane proteinPages displaying short descriptions of redirect targets
• Magnesium deficiency (agriculture)
• Magnesium deficiency (medicine)
   – Condition of low level of magnesium in the bodyPages displaying short descriptions of redirect targets
• Myers' cocktail – Questionable IV vitamin alternative therapy
• Osteoporosis – Skeletal disorder
• Potassium in biology – Use of Potassium by organisms
• Selenium in biology – Use of Selenium by organisms
• Sodium in biology – Use of Sodium by organisms

Notes

References

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• Findling, R. L.; Maxwell, K; Scotese-Wojtila, L; Huang, J; Yamashita, T; Wiznitzer, M (1997). "High-dose pyridoxine and magnesium administration in children with autistic disorder: an absence of salutary effects in a double-blind, placebo-controlled study". J Autism Dev Disord. 27 (4): 467–478.
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• Tolbert, L.; Haigler, T; Waits, MM; Dennis, T (1993). "Brief report: lack of response in an autistic population to a low dose clinical trial of pyridoxine plus magnesium". J Autism Dev Disord. 23 (1): 193–199.
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• Mousain-Bosc M, Roche M, Polge A, Pradal-Prat D, Rapin J, Bali JP (Mar 2006). "Improvement of neurobehavioral disorders in children supplemented with magnesium-vitamin B6. I. Attention deficit hyperactivity disorders". Magnes. Res. 19 (1): 46–52.
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External links

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• Magnesium Deficiency
• List of foods rich in Magnesium
• The Magnesium Website- Includes full text papers and textbook chapters by leading magnesium authorities Mildred Seelig, Jean Durlach, Burton M. Altura and Bella T. Altura. Links to over 300 articles discussing magnesium and magnesium deficiency.
• Dietary Reference Intake
• Healing Thresholds - description of research studies regarding supplementation with magnesium and other therapies for autism