Manganese Toxicity Symptoms Research Articles

Magnetic Resonance Imaging and Manganism: A Narrative Review and Laboratory Recommendations.

In recent years, a series of articles has been published concerning magnetic resonance imaging (MRI) studies in a group of patients exposed to manganism, specifically factory workers, welders, and individuals with liver diseases, as well as those abusing home-produced ephedrone. Some potential symptoms of manganese toxicity include motor disturbances, neurocognitive problems, sleep disorders, and psychosocial changes. Despite various publications on MRI research in individuals with an elevated risk of manganism, there is a noticeable absence of a comprehensive review in this field. The detection of the accumulation of manganese in the brain through MRI can confirm the diagnosis and guide appropriate treatment. Due to the high cost of determining manganese ion levels in biological material, an additional aim of the manuscript was to identify simple medical laboratory parameters that, when performed concurrently with MRI, could assist in the diagnosis of manganism. Among these types of parameters are the levels of bilirubin, magnesium, liver enzymes, creatinine, hemoglobin, and hematocrit.

Physiological highlights of manganese toxicity symptoms in soybean plants: Mn toxicity responses

Manganese (Mn) is an essential element for plants; however, high concentrations in certain soil conditions can cause toxicity symptoms in the plant tissue. Here, we describe Mn toxicity symptoms and Mn toxicity responses in soybean plants. Soybean plants exposed to excess Mn showed reductions in the CO2 assimilation rate and stomatal conductance, which in turn resulted in decreased shoot biomass. Furthermore, peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) activity were higher in plants grown with the highest Mn concentration. The Mn doses increased the activity of antioxidant enzymes such as CAT, POD, and SOD. The toxicity symptoms presented by the leaves included hypertrophying of the adaxial epidermis and the formation of necrotic areas with purple-colored veins. Dramatic movement of calcium from the healthy region to the purple-colored necrotic region was observed, as was the exit of potassium from the necrotic area to the healthy region of the tissue. The high activities of POD and SOD in the presence of high Mn compartmented in the roots was the main physiological responses at high Mn uptake by soybean plants.

The effect of silicon on the symptoms of manganese toxicity in maize plants

The effect of exogenously applied silicon (Si) on plant growth, lipid peroxidation, total phenolic compounds and non-protein thiols was studied in two maize varieties (Zea mays L. vars. Kneja 605, 434) differing in sensitivity to excess manganese (Mn). Based on the density of brown spots per leaf area and relative shoot weight (RSW) used to define Mn tolerance var. Kneja 434 was found to be more Mn-tolerant than Kneja 605. The lipid peroxidation level and total phenolic compounds were enhanced with increasing Mn concentration in the nutrient solution. In addition, the Mn-sensitive var. Kneja 605 with markedly expressed first visible Mn toxicity symptoms had higher levels of total phenolic acids than var. Kneja 434 thus supporting the hypothesis that a stimulating effect of Mn on phenol content reflected rather a stress response to Mn excess than a tolerance mechanism. In contrast, non-protein SH content increased to a higher extent in the Mn-tolerant var. Kneja 434. The increased amount of non-protein SH compounds was accompanied by a much stronger oxidative stress in the Mn-sensitive plants when compared with the Mn-tolerant variety, thus suggesting that non-protein SH compounds may play a role in Mn tolerance in maize. The addition of silicon (Si) reduced the density of brown spots per leaf area as well as lipid peroxidation level and improved plant growth in Mn-treated plants.

Eficiência do fosfato natural de Gafsa associado à calagem e gesso e sintomas nutricionais da alfafa, <em>Medicago sativa</em> L.

This experiment was carried out in glasshouse, Alfalfa, Medicago sativa L. (Poaceae), was cultivated in Typical Mapluolox soil. The study aimed at evaluating the agronomic efficiency index (AEI) of Gafsa phosphate (GP) and of GP with gypsum application before and after liming compared to triple superphosphate (TS), at the rates of 50, 100 and 200 mg P dm -3 , as well as relating soil nutrients with the treatments and with the nutrient symptoms. Three sowings were made. All GP combinations presented a very low AEI during the first sowing and high in third sowing. A higher soil phosphorus concentration was obtained with GP than TS only after ultimate harvest. Liming before or after phosphate fertilization had similar responses on soil phosphorus concentration. Phosphorus deficiency occasioned reduced growth and purple stem. Symptoms of manganese toxicity were characterized by a yellow and purple color in the leave borders. The efficiency of GP increased with the time.

Responses of two closely related oak species, Quercus robur and Q. petraea, to excess manganese concentrations in the rooting medium

Quercus robur (L.) and Q. petraea (Matt.) Liebl. are European oak species that often grow in forest soils with high soluble manganese (Mn2+) concentrations. We tested the effects of Mn2+ at concentrations of 0.0024 mM (control), 0.24 mM (typical of acidic forest soils) and 1.2 mM (typical of forest soils under strongly reducing conditions) on the growth, tissue anatomy, foliar element concentrations, subcellular element distribution and gas exchange of solution-cultured seedlings. At the highest Mn2+ concentration, seedlings were grown with and without an elevated concentration (1.2 mM) of magnesium (Mg2+). At 0.24 mM Mn2+, foliar Mn concentrations were higher than observed in the field. Vacuoles of the leaf epidermis and mesophyll were the main sites of manganese accumulation. High nutrient solution Mn2+ concentration significantly lowered foliar iron (Fe) and Mg concentrations. Elevated Mg2+ concentration raised the foliar Mg concentrations to control values, but Fe concentrations and gas exchange remained depressed. In seedlings grown in the 1.2 mM Mn2+ treatment without elevated Mg2+ damage to the phloem of the petioles and a reduction in root mass were observed in both species. The effects on shoot and root growth were greatest in Q. petraea. Alleviation of manganese toxicity symptoms by Mg2+ in Q. petraea was less effective than in Q. robur. Our results suggest that the soil solution Mn2+ concentrations that occur in European oak forests are unlikely to affect the distribution and performance of Q. robur and Q. petraea in the field.

Response of subterranean clover, balansa clover, and gland clover to lime when grown in mixtures on an acid soil

This study compared the relative tolerances of subterranean clover (Trifolium subterraneum L.), balansa clover (T. michelianum Savi.), and gland clover (T. glanduliferum Boiss.) to acid soil conditions. Seed yield, seedling density, herbage production, N2 fixation, and herbage mineral composition of the 3 legumes were assessed when grown on an acid soil (pHCa of 4.3 and 15% exchangeable Al [0–0.10 m]) with and without the addition of lime (CaCO3). Annual legume species were sown in a mixed sward together with burr medic (Medicago polymorpha L.), and in mixtures with either lucerne (Medicago sativa L.), chicory (Cichorium intybus L.), or phalaris (Phalaris aquatica L.). Due to drier than average seasonal conditions, none of the perennial species persisted beyond the first summer. Lime increased the herbage production of annual legumes by 18–22% and total pasture production by 14% in both 2002 and 2003. Subterranean clover was the most tolerant of the annual legumes to acid soil conditions, showing no visible toxicity symptoms and no response to lime in terms of seed yield. In contrast, both balansa and gland clovers exhibited visual symptoms of manganese toxicity in the absence of lime, with Mn concentrations in the shoots of 817 mg/kg and 626 mg/kg, respectively. Both species responded positively to lime with seed yields increasing by 45% and 124%, respectively. Lime increased the proportion of herbage N derived from N2 fixation by subterranean clover from 29 to 40% and by gland clover from 30 to 43%. Lime had no effect on the proportion of N2 fixed by balansa clover (29–31%), suggesting a suboptimal symbiosis of rhizobia with that species. Adding chicory or phalaris to the pasture mix increased sward herbage production in the establishment year by 39% and 21%, respectively. Based on leaf symptoms and herbage yield responses to lime, Mn toxicity was present in lucerne with tissue levels of up to 916 mg/kg, but no symptoms were observed in chicory (1129 mg/kg) or phalaris (403 mg/kg). Chicory and phalaris were more tolerant of acidity and high levels of Mn than lucerne, gland clover, and balansa clover. The study highlighted the value of the small-seeded annual legumes, balansa clover and gland clover, to the production of mixed pasture swards even in drier than average seasonal conditions. Although more sensitive to acid soils than subterranean clover, they set a greater number of seeds and, in the case of balansa clover, a greater weight of seed under moisture stress in the establishment year than the larger seeded subterranean clover.

Uptake and translocation of manganese in seedlings of two varieties of Douglas fir (Pseudotsuga menziesii var. viridis and glauca)

Douglas fir (Pseudotsuga menziesii) variety glauca (DFG) but not the variety viridis (DFV) showed symptoms of manganese (Mn) toxicity in some field sites. We hypothesized that these two varieties differed in Mn metabolism. To test this hypothesis, biomass partitioning, Mn concentrations, subcellular localization and 54Mn-transport were investigated. Total Mn uptake was three-times higher in DFG than in DFV. DFV retained > 90% of 54Mn in roots, whereas > 60% was transported to the shoot in DFG. The epidermis was probably the most efficient Mn barrier since DFV contained lower Mn concentrations in cortical cells and vacuoles of roots than DFG. In both varieties, xylem loading was restricted and phloem transport was low. However, sieve cells still contained high Mn concentrations. DFV displayed higher biomass production and higher shoot : root ratios than DFG. Our results clearly show that both varieties of Douglas fir differ significantly in Mn-uptake and allocation patterns rendering DFG more vulnerable to Mn toxicity.

The Effects of Root Zone Temperature and Limestone on pH and Electrical Conductivity on New Guinea Impatiens `Celebration Orange'

The purpose of this experiment was to examine the effects of various root-zone temperatures and pH on Impatiens ×hybrida, New Guinea impatiens `Celebration Orange.' Greenhouse growers need to be cognizant of the root-zone medium pH, as New Guinea impatiens are sensitive to nutrient toxicities at low pH. It is thought that limestone at low root-zone medium temperatures is not quickly activated, leading to toxicities. The objectives of this project were to determine: the effect of root-zone medium pH on foliar symptoms of iron and manganese toxicity; and the effective rates and grind size of limestone on root-zone medium pH. Various rates of limestone and different grind sizes were incorporated into a sphagnum peat moss-based medium at a range of temperatures. This experiment used a two-way thermogradient plate to maintain varying, but stable root-zone medium temperatures, ranging from 12 to 42 °C. Plant growth as well as root-zone medium pH was monitored. Changes in root-zone medium pH were monitored over time. Results indicated that the addition of moderate or high rates of limestone, 6 or 3 kg·m-3, provided stable root-zone media pH over the course of time. Both limestone grind sizes at 325 and 100–200 mesh provided satisfactory starting and ending pH values for healthy New Guinea impatiens growth, especially between the root-zone temperatures of 30 and 18 °C. Higher and lower temperature extremes inhibited root growth, resulting in lower quality plants.

Genotypes of lucerne ( Medicago sativa L.) show differential tolerance to manganese deficiency and toxicity when grown in bauxite residue sand

The physical and chemical characteristics of bauxite residue sand (BRS) affect the availability of a number of nutrients to plants, especially manganese (Mn). Lucerne (Medicago sativa L.) has been chosen as a BRS revegetation species because of its deep-rooting habit and tendency to tolerate moderately alkaline and saline soils, even though it is still prone to Mn deficiency stress. Sixteen commercially available lucerne genotypes were grown in BRS after addition of 5, 50 or 500 μg Mn g−1 BRS in a glasshouse. Manganese deficiency and toxicity symptoms were observed in 5 and 500 μg g−1 treatments, respectively. Symptom expression varied in severity between genotypes. Relative tolerance to Mn deficiency was defined by shoot dry weight at 5 μg Mn g−1 as a percentage of shoot dry weight at 50 μg Mn g−1. Salado, a genotype tolerant to Mn deficiency, and Sirosal, a genotype intolerant to Mn deficiency, were then grown with 0, 10, 20, 50, 100, 200 or 800 μg Mn g−1 BRS and found to have critical shoot Mn concentrations of 17.7 (Salado) and 26.6 μg g−1 (Sirosal). The use of genotypes with high relative Mn deficiency tolerance is recommended to help improve sustainability of BRS revegetation as well as to improve productivity on Mn-fixing agricultural soils.

Role of leaf apoplast in silicon‐mediated manganese tolerance of Cucumis sativus L.

AbstractSilicon (Si) supplied as sodium silicate (1·8 mm) clearly decreased symptoms of manganese (Mn) toxicity in Cucumis sativus L. (cv. Chinesische Schlange) grown in nutrient solution with low to elevated Mn concentrations (0·5–1000 µm). Despite approximately the same total Mn content in the leaves, plants not treated with Si had higher Mn concentrations in the intercellular washing fluid (IWF) compared with plants treated with Si, especially in the BaCl2‐ and DTPA‐exchangeable fraction of the leaf apoplast. The Mn concentration of the IWF correlated positively with the severity of Mn‐toxicity symptoms and negatively with the Si supply. Furthermore, in Si‐treated plants less Mn was located in the symplast (< 10%) and more Mn was bound to the cell wall (> 90%) compared with non‐Si‐treated plants (about 50% in each compartment). Manganese present in Si‐treated plants is therefore less available and for this reason less toxic than in plants not treated with Si. It is concluded that Si‐mediated tolerance of Mn in C. sativus is a consequence of stronger binding of Mn to cell walls and a lowering of Mn concentration within the symplast. These results support the role of Si as an important beneficial element in plant nutrition.

Effects of silicon supply on apoplastic manganese concentrations in leaves and their relation to manganese tolerance in cowpea (Vigna unguiculata (L.) Walp.)

The effects of silicon (Si) supply on manganese (Mn) toxicity symptoms and Mn and Si concentrations in the leaf apoplast in a Mn-sensitive cowpea cultivar (Vigna unguiculata (L.) Walp. cv. TVu 91) were investigated in solution culture experiments. When 1.44 mM Si was supplied concurrently with 50 μM Mn, the Mn toxicity symptoms were clearly avoided without decreasing the total Mn concentration. On the other hand, the symptoms were not completely alleviated when the plants were pretreated with 1.44 mM Si and then exposed to 50 μM Mn without concurrent Si supply. Plants of both of these treatments exhibited lower Mn concentrations in the apoplastic washing fluids but higher amounts of adsorbed Mn on the cell walls than the plants treated with 50 μM Mn without Si supply. However, the difference in Mn concentration between plants with continuous and interrupted Si supply was not significant. Moreover, the Mn concentration in the apoplastic washing fluids of the plants with continuous supply of 1.44 mM Si and 50 μM Mn and not showing Mn toxicity symptoms was higher than that of the plants grown at 10 μM Mn without Si supply which showed distinct Mn toxicity symptoms. These results show that Si supply alleviates Mn toxicity not only by decreasing the concentration of soluble apoplastic Mn through the enhanced adsorption of Mn on the cell walls. A role of the soluble Si in the apoplast in the detoxicification of apoplastic Mn is indicated.

Effect of manganese on endomycorrhizal sugar maple seedlings

Manganese (Mn) toxicity may play an important role in the poor survival of seedlings in declining sugar maple (Acer saccharum Marsh.) stands in northern Pennsylvania. To determine the effect of Mn on the growth of sugar maple seedlings, 1‐year‐old seedlings inoculated with vesicular‐arbuscular mycorrhizal (VAM) fungi and growing in sand‐vermiculite‐peat moss medium were irrigated for 7 weeks with nutrient solution (pH 5) containing 0.1 (control), 1, 2, 4, 8, or 16 mg L−1 Mn. Total seedling dry weight was negatively correlated with Mn, becoming significantly different than the control at 2 mg L−1 Mn. Stem and root dry weight were reduced by lower Mn levels than leaf dry weight. Manganese had no effect on the root/shoot ratio. The concentration of Mn in roots and leaves increased as the level of Mn in the nutrient solution increased, with the concentration in the leaves 2.2‐ to 3.7‐fold greater than the concentration in the roots. Except for a reduction of P in the roots, Mn had little effect on the concentration of nutrient elements in the roots or leaves. Colonization of the roots by VAM fungi was increased by Mn, with a maximum percentage at 4 mg L−1 Mn. Manganese toxicity symptoms in the leaves, small discrete chlorotic spots, began to appear at 1 mg L−1 Mn. The sensitivity of sugar maple seedlings to Mn found in this study supports the hypothesis that Mn may affect regeneration in declining sugar maple stands. However, evaluation of the effects of Mn on seedlings in native soils under field conditions will be necessary before the role of Mn in sugar maple regeneration can be understood.

Low iron supply aggravates manganese toxicity in zonal geraniums growing in soilless potting media

Zonal geranium (Pelargonium x hortorum) cultivars growing in soilless potting media based on Pinus radiata bark, and of pH 4.5–6.5, developed manganese (Mn) toxicity symptoms even though the medium contained only 26 mg‐kg‐1 total Mn. The toxicity was partly or wholly alleviated by increased iron (Fe) supply. Ferrous sulphate (7H2O) added to the medium before potting or weekly drenches with Fe chelates were effective, although the combination of the two tended to produce the best plants. Acidification of the medium caused by Fe‐stress is a major factor in mobilizing toxic levels of Mn from soilless media. While Fe supply had the major effect on the expression of Mn toxicity, this toxicity was produced in Pelargonium cultivars if water extracts (1:1.5 v/v) of the medium contained more than about 2 mg‐L‐1 Mn.

Influence of Soil Moisture Regimes on Subsequent Soil Manganese Availability and Toxicity in Two Cotton Genotypes

AbstractDifferential plant tolerance to high levels of Mn and effects of changing soil aeration on Mn availability and are major factors in the problem of Mn toxicity in acid soils. A pot study was conducted to evaluate the effects of temporary flooding or drying on Mn forms and toxicity during subsequent cotton (Gossypium hirsutum L.) growth. Two acid, high‐Mn Hapludalfs were incubated for 16 d in flooded, air‐dry, or moist conditions, then restored to field moisture content and planted with two cotton genotypes: C‐310,73‐307 (307, Mn‐tolerant) and C‐Sgl,70‐517 (517, Mn‐sensitive). After the incubation period, levels of exchangeable Mn in the Jackland soil (pH 4.8) were 9.0, 2.6, and 0.3 mmol kg2212;1, respectively, for flooded, air‐dry, and moist pretreatments. Corresponding values for the Myersville soil (pH 5.2) were only 4.4, 0.6, and 0.1 mmol kg2212;1. Three days after seedling emergence in the flooded pretreatment, exchangeable Mn declined to 4.4 mmol Mn kg2212;1 in the Jackland soil and 0.2 mmol Mn kg2212;1 in the Myersville soil. Manganese toxicity symptoms (crinkle leaf) for both cotton genotypes developed only on the Jackland soil, with severity of symptoms following the order: flood > air dry > moist. With both soils, flooding pretreatment decreased dry matter production; generally more for 517 than for 307. Tissue Mn concentrations were 20 to 50 times higher in leaves from Jackland soil compared to those from Myersville soil. Where flooding caused toxicity symptoms in both genotypes, lower exchangeable Mn was measured in pots growing Mn‐tolerant cotton. Differential Mn tolerance of cotton genotypes was not associated with differential Mn uptake or tissue concentration.

Manganese Oxidation Capacity of Homogenates of Cowpea [ Vigna unguiculata (L.) Walp.] Leaves Differing in Manganese Tolerance

Summary Dark-brown speckles on old leaves are manganese (Mn) toxicity symptoms in cowpea [Vigna unguiculata (L.) Walp)]. These speckles are deposits of brown substances found primarily in cell walls containing sensitivity Mn in an oxidized form, and their appearance is indicative of high Mn sensitivity of plant issue. In the present paper the hypothesis is tested that differences in leaf-tissue Mn tolerance owing to genotype, silicon (Si) concentration and leaf age are attributed to differences in Mn oxidation capacity of the leaf tissue. A Mn-sensitive and a Mn-tolerant cowpea genotype were precultured in complcomplete nutrient solution without and with Si (1400 μM) at optimum Mn supply (0.25 μM) for 17 days under controlled environmental conditions. Within 3 days of treatment with 10 μM Mn, Mn toxicity symptoms only appeared on older leaves of the Mn-sensitive genotype without Si supply. Homogenerates prepared from old and young leaves were incubated at 30 °C for 60 min either in the light or in the dark. Such homogenates had an extremely high potential to oxidize added and internal leaf Mn(II) in the light but not in the dark. Manganese oxidation could be described by enzyme kinetics with an apparent Km of approximately 0.5 mM Mn. Manganese oxidation capacity was higher in Mn-sensitive older leaves compared with Mn-tolerant younger leaves. However, no differences could be found between leaf tissues differing in Mn tolerance owing to genotype and Si status, which is not in aggrement with the working hypothesis. Therefore the results do not unequivocally support the hypothesis that high Mn leaf-tissue sensitivity is realted to high Mn(II) oxidation.

The influence of temperature on the accumulation and distribution of manganese in two cultivars of soybean (Glycine max [L.] Merr.)

Accumulation and distribution of manganese in soybeans (Glycine max [L.] Merr. cvv. Lee and Bragg) grown over a range of manganese concentrations from 0 to 275 8m in solution culture were studied at four day-night temperatures ranging from 20-15�C to 33-28�C in growth cabinets. High levels of solution manganese (275 8m ) produced symptoms of manganese toxicity and reduced yields of both varieties with the symptoms and yield reductions being more severe on Bragg than Lee. Increasing the day-night temperatures from 20-15�C to 33-28�C increased the ability of both cultivars to tolerate high concentrations of manganese in solution but there was no indication of any effect of temperature on the differential tolerance of the two cultivars. At high managanese concentrations in solution, high temperatures increased the rate of absorption by roots and total plant uptake of manganese, but there was no effect on the concentration of manganese in the plant tops. Total leaf concentration increased markedly while stem concentration were reduced at high temperatures. Young leaves contained lower concentrations of manganese than older leaves at all temperatures. While the concentration of manganese in the youngest expanding leaf decreased slightly as temperatures were raised from 20-15�C to 28-25�C, there was no significant difference in concentrations at 20-15�C and 33-28�C. These results suggest that the increased tolerance of soybeans to high manganese supply was not due to growth dilution in young tissues.

Effect of manganese toxicity on growth and N2 fixation in groundnut, Arachis hypogaea

SummaryThe development of manganese (Mn) toxicity symptoms and its effects on the growth, nodulation, and nitrogen fixation of groundnut genotypes were examined using a quartz‐sand/solution culture system. The 11 genotypes tested all accumulated considerable concentrations of manganese (1.04–3.07 mg g‐1dry matter) when supplied with 15 μg Mn ml‐1of nutrient solution daily. Toxicity symptoms differed between genotypes: some showed no visual effects, some produced marginal leaf spots, and others developed marginal leaf spots coupled with an inward rolling of the margins of the younger leaves. The growth of one genotype (ICG 5394) grown with inorganic nitrogen as its source of N was more severely affected by Mn toxicity than when dependent on symbiotic fixation for its nitrogen.

Identification of Manganese Toxicity and Magnesium Deficiency on Melons Grown in Low-pH Soils

Abstract Field-grown muskmelons (Cucumis melo var. reticulatus Ser.) and watermelons [Citrullus lanatus (Thunb.) Matsum and Nakai] are sensitive to nutrient stress induced by low-pH soils. Severe foliar injury observed on melons grown in low-pH soils was caused by toxic levels of Mn and/or deficient levels of Mg in the leaf tissue. Manganese toxicity symptoms in muskmelons develop as chlorotic spotting on the adaxial surface of older leaves, with water-soaked rings around necrotic spots on the abaxial surface. In watermelons, Mn toxicity develops initially on older leaves as black-brown speckling on the abaxial leaf surface. Severe vein browning develops with age. Magnesium deficiency develops first on mature muskmelon and watermelon leaves as an interveinal bronzing, followed by a necrosis and browning of the interveinal tissue. Muskmelons are more sensitive to both Mn toxicity and Mg deficiency than are watermelons.

Effect of Magnesium and Manganese Nutrition on Muskmelon Growth and Manganese Toxicity

Abstract Muskmelons (Cucumis melo L.) ‘Harvest Queen’ were grown in sand culture to evaluate the response to Mn toxicity as affected by solution concentration of Mn and Mg. Manganese toxicity symptoms were developed as water-soaked spots, necrotic spots, and necrotic lesions, which were most severe on the lower mature leaves. Leaves developed toxicity symptoms when they contained ≥900 μ-g·g-1 Mn. Increased levels of Mg in the nutrient solution alleviated symptoms of Mn toxicity, decreased Mn concentration in shoot and root tissues, and increased growth of muskmelon plants. The reduction in Mn toxicity was brought about by reduced root absorption of Mn at high Mg supply.

Effect of Magnesium and Manganese Nutrition on Watermelon Growth and Manganese Toxicity

Abstract Watermelon [Citrullus lanatus (Thunb.) ‘Sugar Baby’ was grown in sand culture to evaluate Mn uptake as affected by solution concentration of Mn and Mg. Manganese toxicity symptoms were developed first on the lower mature leaves as small, distinct, blackish-brown speckling on the lower leaf surface that progressed to extensive vein browning and necrotic lesions. Leaves developed toxicity symptoms when they contained ≥1325 mg·liter−1 Mn. Growth was reduced at Mn concentrations in nutrient solution ≥22.5 mg·liter−1. Development of Mn toxicity symptoms was delayed with increasing Mg concentrations in solutions. Increasing Mg concentration in solution to 48 or 96 mg·liter-1 reduced Mn composition and Mg uptake per unit root surface at 2 and 30 mg·liter-1 Mn in solution, but had no effect at 60 mg·liter-1 Mn in solution.