Tissue Mn Research Articles

Slurry preparation by high-pressure homogenization for the determination of heavy metals in zoological and botanical certified reference materials and animal feeds by electrothermal atomic absorption spectrometry.

High-pressure homogenization was evaluated for the preparation of slurries suitable for the determination by ETAAS of Cr, Cu, Fe, Mn, Ni and Se in soft organ tissues (liver and kidney), certified reference materials of biological and botanical origin and animal feeds. Frozen fresh organ tissue, (2 g) or certified reference material or dried, ground plant material (0.1 g) was blended, at high speed with 20 ml of ethanol-water (1 + 9 v/v) containing 0.25% m/m of tetramethylammonium hydroxide and the resulting mixture was subjected to homogenization at 38.9 MPa. After four passes through the homogenizer, the resulting solution was suitable for analysis by ETAAS. Capping the flat valve head of the homogenizer with a ruby disc appreciably reduced (but did not eliminate) metal contamination introduced by the processing. Homogenization of botanical reference materials or dried animal feeds resulted in preparations with variable amounts of residual fibres and particulate matter in the resulting suspensions. Nonetheless, all the Cu and Mn and virtually all of the Fe had been transferred to the supernatant fraction and remained with that fraction for at least 10 d. The addition of EDTA to the solvent modestly increased the mobilization of Fe from the matrix but also increased the contamination from the homogenizer. The slopes of the calibration curves generated by the method of standard additions were not significantly different from those of calibration curves generated with aqueous standards in a homogenized blank indicating that there was no significant matrix effect for any of the analytes in the nine reference materials, liver or kidney or the five animal feed samples and that aqueous standards could be used to calibrate the instrumental response.

The impact of acid soil volume of reclaimed minesoils on plant growth in minilysimeters

ABSTRACT Limited data are available to assess the influence of randomly distributed acid soil, produced from acid forming materials (AFM), on growth and productivity of crops. This study evaluated the effect of amount and volume of acid soil on die growth of an acid tolerant plant (Coastal bermudagrass, Cynodon dactylon, L) and an acid intolerant plant (Yuchi arrowleaf clover, Trifolium vesiculosum, Savi.) in greenhouse lysimeters. Acid soil (pH=2·5) volumes up to 20 % for Yuchi arrowleaf clover and up to 40% for Coastal bermudagrass did not significantly decrease dry matter yield. Concentrations of Al and Mn in plant tissue of clover and bermudagrass were below the toxicity level. In the presence of randomly distributed acid soil, plant roots continued to elongate in non-acid soil, by evading localized areas of low soil pH. These results suggest that the federally mandated zero tolerance for AFM in the top 1.2 m of reclaimed lands may not be reasonable.

Supraoptimal Root-zone Temperature Influences the Medium Solution and Growth of `Helleri' Holly

Rooted cuttings of Ilex crenata Thunb. `Helleri' were grown for 12 weeks in pine bark with two root-zone temperature treatments (unheated or heated to 40C for 6 hours·day–1), two rates of limestone addition (0 or 6 kg·m–3), and three weekly N application rates (200, 400, or 600 mg·liter–1 as urea ammonium nitrate) in a factorial combination. Decreases in shoot and root dry weights due to root-zone heating (69% and 75%, respectively) or limestone addition (41% and 42%, respectively) were not influenced by N application rate. Effects of root-zone heating on medium solution characteristics, which differed in response to limestone addition, were similar for all N application levels. In unlimed pine bark at 400 mg N/liter, the pH and the NH4-N: NO3-N ratio were higher in the heated medium (5.5 and 1.15, respectively) than in the unheated medium (3.9 and 0.64, respectively) after 80 days, suggesting that 6 hours of daily exposure to 40C inhibited nitrification. The higher medium solution pH due to root-zone heating resulted in lower medium solution and shoot tissue Mn concentrations.

Manganese and chronic hepatic encephalopathy

SummaryClinical observations and animal studies have raised the hypothesis that increased concentrations of manganese (Mn) in whole blood might lead to accumulation of this metal within the basal ganglia in patients with end-stage liver disease. We studied ten patients with liver failure (and ten controls) by magnetic resonance imaging (MRI) and measurement of Mn in brain tissue of three patients who died of progressive liver failure (and three controls) was also done.Whole blood Mn concentrations in patients with liver cirrhosis were significantly increased (median 34·4 μg/L vs 10·3 μg/L in controls; p=0·0004) and pallidal signal intensity indices correlated with blood Mn (Rs=0·8, p=0·0058). Brain tissue samples reveal highest Mn concentrations in the caudate nucleus, followed by the quadrigeminal plate and globus pallidus.Mn accumulates within the basal ganglia in liver cirrhosis. Similarities between Mn neurotoxicity and chronic hepatic encephalopathy suggest that this metal may have a role in the pathogenesis of chronic hepatic encephalopathy. Further studies are warranted because the use of chelating agents could prove to be a new therapeutic option to prevent or reverse this neuropsychiatric syndrome.

Effect of Root-media pH on Impatiens Shoot Micronutrient Concentrations

Impatiens were planted in media containing either hydrated or carbonate dolomitic lime and subirrigated for 17 weeks using four irrigation water qualities (IWQ) and three water-soluble fertilizers (WSF). Micronutrients (Fe, Mn, Zn, Cu, B, and Mo) were incorporated into all root media at planting with fritted trace elements (FTE 555) at 0.07 kg·m–3 and were added to all WSF treatments with a commercially available chelated material (Compound 111) at a constant 50 mg·liter–1. Root-medium pH obtained from the various IWQ/WSF solutions at 4, 8, 12, and 17 weeks after planting were used to determine relationships with shoot tissue micronutrient concentrations. Tissue Fe concentrations decreased linearly as root-media pH increased from 5.0 to 8.5. Below pH 5.0, the tissue Fe concentration increased at a rate indicating greater nutrient availability in the root medium. However, between pH 4.0 and 7.5, tissue Fe was within acceptable levels. A linear relationship also was found with tissue Zn and B, but without the rate increase below a pH of 5.0. Tissue Mn decreased to a minimum as the rootmedium pH increased from 4.0 to 6.0 and increased again as the root medium pH increased from 6.0 to 8.5. Tissue Mo concentrations increased as root medium pH increased. Tissue Cu concentrations were unaffected by medium pH.

Effect of soil Ph and nitrogen source on the nutrient status in peach: II. Micronutrients

Abstract The concentration of aluminum (Al), manganese (Mn), iron (Fe), zinc (Zn), and copper (Cu) in leaves, shoots, trunks, and roots, and the content of plant‐available Mn and Al in soil was examined after 13‐year treatments of soil pH and nitrogen (N) source in a peach orchard of North Carolina. Raising soil pH by liming tended to reduce soil Al content, but had no effect on soil Mn. Tissue Al and Mn level was decreased in high pH treatment. Poultry manure application resulted in the highest soil Mn content but the lowest soil Al. In comparison with calcium nitrate [Ca(NO3)2], ammonium sulfate [(NH4)2SO4] increased Al availability in soil while had little effect on soil Mn. Acid‐forming N, especially (NH4)2SO4, increased the concentration of tissue Al, Mn, Zn, and Fe. The plants treated with various basic N materials similarly contained lower levels of Al or Mn. Manure treatment resulted in high tissue Cu and Zn but low tissue Fe levels. Tissue Zn was low when mineral N sources containing calcium (Ca)...

Hepatic Concentrations of Zinc, Copper and Manganese in Infants with Extrahepatic Biliary Atresia

The objective of this study was to determine the concentration of Zinc (Zn), Copper (Cu) and Manganese (Mn) in hepatic tissue from extrahepatic biliary atresia (EHBA). Liver biopsy samples were obtained at time of portoenterostomy from 49 infants ages 1.1 to 20.7 months (median 2.1) with EHBA. Samples were dry ashed and analyzed by flame (Zn) or flameless (Cu and Mn) atomic absorption spectrophotometry. Hepatic Cu concentrations are physiologically elevated at birth and decline rapidly during the first 2 month of life, therefore only samples from 29 infants, ages greater than 8 weeks were considered for Cu. Concentrations (mg/kg dry weight, mean and range) were: Zn 142 (70-507), Cu 204 (19-570), Mn 9.1 (2.8-21.8) vs. literature controls in the same age range: Zn 262 (82-543), Cu 92, Mn 4.3 (3.3-11.5). No correlations were found between serum alkaline phosphatase, AST or total bilirubin and hepatic trace element concentrations, between trace element concentrations and age, or between Cu and Mn. Decreased bile flow with intrahepatic cholestasis may result in hepatic accumulation of Mn as well as Cu. The low hepatic Zn concentrations indicate the need for further study of Zn metabolism in this population.

Effect of cadmium on nitrogen fixing pea plants grown in perlite and vermiculite1

Abstract The effect of cadmium (Cd) on nitrogen (N2) fixing pea plants was studied. Perlite and vermiculite were compared as substrates in a hydroponic system where the plants were grown. In both experiments, there was no significant effect on nitrogenase activity when referred to fresh weight of nodules, but there was a reduction in the nodulation ratio (number of nodules developed per plant), even at low concentrations of available Cd. In plants grown in vermiculite, the nitrogenase activity expressed in terms of activity per nodule increased as Cd application increased; while in plants cultivated in perlite, that activity decreased when the applied Cd increased at the highest levels of Cd in the nutrient solution. Vermiculite had a significant interaction with the Cd in the nutrient solution, and therefore, we assume there was less Cd available to the plants than when perlite was used as the substrate. The loss of N2 fixation by the presence of Cd in plants grown in perlite has been related to a change in the distribution of manganese (Mn) in the plant tissues. There was a reduction of Mn content both in the root and nodules. The reduction was greater in the nodules, while the concentration of Mn increased in the shoot.

Intravenous manganese-mesoporphyrin as a magnetic resonance imaging contrast agent: An experimental model using VX-2 carcinoma in rabbits

We investigated the potential of manganese (III) mesoporphyrin (Mn-mesoporphyrin) as a hepatobiliary contrast agent for magnetic resonance (MR) imaging in rabbits given VX-2 carcinoma liver implants. Rabbits given VX-2 carcinoma liver implants (n = 8) were imaged before and after the intravenous (i.v.) administration of 0.04 mmol/kg Mn-mesoporphyrin. MR images were correlated with gross-specimen cross-sections. The distribution of Mn in various tissues following i.v. administration of 0.04 mmol/kg Mn-mesoporphyrin was determined using atomic absorption analysis. A standard panel of serum chemistries was followed over 7 days in six rabbits following this same dose of Mn-mesoporphyrin and compared with chemistries from two control rabbits. I.v. administration of 0.04 mmol/kg (25 mg/kg) Mn-mesoporphyrin resulted in improvement of tumor-to-liver contrast, with enhancement of normal liver (99.7 +/- 14.7%) and the gallbladder (442 +/- 116%), but not VX-2 tumor tissue (14.8 +/- 13.9%), (n = 8, p = .05). Analysis of tissue Mn levels 100 min after i.v. Mn-mesoporphyrin injection demonstrated preferential distribution of Mn to normal liver tissue (57.8 +/- 15.3 micrograms Mn/g) compared with VX-2 tumor (4.28 +/- 1.48 micrograms Mn/g). No significant change was found in the serum chemistries of six normal rabbits over a 7-day period after the i.v. administration of 0.04 mmol/kg Mn-mesoporphyrin. I.v. Mn-mesoporphyrin improved lesion-to-liver contrast because of preferential distribution of Mn-mesoporphyrin to normal liver parenchyma and bile.

The pigeon (Columbia livia) as a monitor for manganese contamination from motor vehicles

Methylcyclopentadienyl manganese tricarbonyl (MMT) is an organic derivative of manganese (Mn) used in unleaded gasoline in Canada since 1977. It has been suggested that the production of Mn3O4 resulting from the combustion of MMT may become one of the principal sources of manganese contamination in the urban environment. This research evaluates the feral pigeon (Columba livia) as a monitor of Mn contamination in rural (Lachute) and urban (Montreal) environments. Atmospheric Mn concentrations were measured over a 6-month period in the rural and urban areas. Twenty pigeons were captured in each area and the Mn concentrations of several tissues (liver, kidney, lung, pancreas, intestine, brain, down feathers, feces, whole blood, and blood serum) were measured by neutron activation. Biochemical profiles of the blood samples (total protein, aspartate aminotransferase, hematocrit, glucose, and uric acid) were also measured. Air particulate data showed significantly higher Mn levels (p 0.05) in the two groups of pigeons for all the tissues except liver (Lachute=2.42 ppm; Montreal=3.13 ppm) and feces (Lachute=32.2 ppm; Montreal=46.8 ppm); the urban pigeons had about 35% more Mn than the rural pigeons. Aspartate aminotransferase (AST) was also significantly different in the two groups. These results show the importance of the entero-hepatic cycle in the homeostasis of Mn in blood and other tissues. Since the excess of Mn in the feces and liver of the urban pigeons relative to the rural pigeons was similar to the excess Mn in urban air over rural air, pigeon feces and liver appear to be good biomarkers of Mn contamination. Although it is premature to associate this excess Mn with the combustion of MMT, these results nevertheless lead us to consider the pigeon as an interesting indicator of the potential risk to the ecosystem and to human health.

Seasonal Variations in Fig (Ficus carica L.) Leaf Nutrient Concentrations

Concentrations of N, P, K, Ca, Mg, B, Fe, Cu, Zn, and Mn in mature commercial fig (`Calimyrna'; `Sari Lop') leaves are presented throughout the growing season. These data can be used as preliminary norms for the interpretation of tree nutrient status for high-yielding commercial fig orchards. In comparison with other deciduous tree crops growing in the same regions {almond [Prunus amygdalus Batsch syn. P. dulcis (Mill) D.A. Webb], walnut (Juglans regia L.), peach [Prunus persica (L.) Batsch]}, productive fig trees have relatively low leaf N, P, and K concentrations (2.1%, 0.1%, and 1.0% dry weight, respectively) in July, although tissue Mn and Ca concentrations often exceed those typically found in other deciduous species growing in the same soils. Seasonal variations in fig leaf nutrient concentrations are similar to those of other tree crops. Marked declines in tissue K and N concentrations toward the end of the season may indicate a need for supplemental N and K fertilization in highly productive orchards. The potential for K deficiency in fig also is indicated by the generally lower leaf K concentrations in the low-vigor orchards examined.

Nutrient concentrations of foliage and soil in South-western Australia.

The element found in highest concentration in the shoots of the South-western Australian plants surveyed is N followed by K ≤ Ca ≤ Cl ≤ Mg ≤ P ≤ Mn ≤ Zn ≤ Cu. The oligotrophic families (mainly primitive Australian pioneer families Proteaceae, Casuarinaceae, Restionaceae and Epacridaceae) have the lowest nutrient concentrations. The nitrogen-fixing Mimosaceae and Papilionaceae have the highest N concentrations though the nitrogen-fixing Casaurinaceae have relatively low N concentrations. The native shrubs have lower tissue concentrations than the introduced species. Certain families possess a great variation in the concentration of tissue Mn (e.g. Proteaceae, Casuarinaceae) with certain individuals containing high concentrations compared to the average South-west Australian species. Increased amounts of soil nutrients can cause an increase in shoot concentration of the species found growing there, e.g. rich habitats (limestone heath) tend to have higher concentrations than those found on depleted habitats (sandplain heaths). There was no correlation found between shoot concentrations and mean annual rainfall.

Developmental patterns of aluminum in mouse brain and effects of dietary aluminum excess on manganese deficiency

Previous studies have shown that excess dietary Al during development can effect neurobehavioral measures and decrease tissue Mn of 21-day-old weanling mice without a corresponding increase in tissue Al concentrations. Al and Mn have similar tissue concentrations and similar affinities for transferrin, which is the major plasma transport protein for Al and Mn as well as Fe. In the present study, brain Al, Mn and Fe were studied at 6, 12, 18 and 24 days of age in offspring of Swiss Webster mice fed a semi-purified diet containing excess Al (Al[+], 1000 μg Al/g diet, Al as Al lactate), marginal Mn (mn[−], 3 μg Mn/g diet) or both excess Al and marginal Mn (Al[+]Mn[−]) from conception to day 24 postnatal (weaning on day 18). Brain Al concentrations were higher at 6 days of age than at later ages and were significantly elevated by the excess Al diet ( P = 0.017) but returned to control levels by weaning. Brain Mn concentrations increased from day 6 to day 24 and were lower in the Mn deficient groups ( P < 0.001) and also in the excess Al group ( P = 0.024) than in controls. Brain Fe concentrations were not influenced by diet. Similar patterns were seen in liver as in brain. The marginal Mn diet led to postnatal growth retardation which was more severe in litters of dams fed Al[+]Mn[−] diets than in litters fed Mn[−] diet. These data suggest that excess Al in diet can interact specifically with Mn metabolism during development.

Alfalfa responses to foliar and soil applications of manganese

Abstract Manganese (Mn) deficiency often occurs in crops grown on well‐limed sandy soils of the Atlantic Coastal Plain region of the United States. This study was conducted to compare the responses of established alfalfa (Medicago sativa S.) to various application methods of manganese sulfate (MnSO4) fertilizer. Experiments conducted in farmers’ fields at three New Jersey locations determined the effects of applied Mn on forage yield, tissue Mn concentration, and leaf chlorophyll meter readings. An untreated control was compared to the following treatments: foliar Mn applied once before each harvest, foliar Mn applied twice before each harvest, and a one‐time broadcast Mn application in April Or May at 22.4 kg Mn/ha to the soil surface. The rate of foliar Mn used in 1990 was 1.12 kg Mn/ha and in 1991 was 0.56 kg Mn/ha at each treatment time. Forage yield increases were greater with foliar than soil‐applied Mn but there were no differences between foliar‐applied Mn treatments. Total seasonal forage yields ...

Blueberry Germplasm Screening at Several Soil pH Regimes. II. Plant Nutrient Composition

Seedlings from crosses among Vaccinium corymbosum L., V. angustifolium Ait, and V. corymbosum/V. angustifolium hybrid-derivative parents, and micropropagated `Northblue', `Northsky', and `Northcountry' plants, were grown for 2 years at Becker, Minn., in low (5.0) and high (6.5) soil pH regimes. Nutrient composition expressed as a concentration and total content was determined for P, K, Ca, Mg, Fe, Mn, Zn, Cu, and B in the aboveground portion of the plant. Except for Fe, the pH regime effects on aboveground plant nutrient concentration and total content were much larger than population or population × pH regime interaction effects. Population × pH regime interactions were detected for all nutrients expressed as a concentration, except for P. Generalizations about plant performance and nutrient concentration of the plant could only be made in the context of a given pH regime. At low pH, P and Mn tissue concentrations increased and Ca, Mg, and B concentrations decreased as the percentage of lowbush ancestry increased. At high pH, K, Cu, and B concentrations decreased as the percentage of lowbush ancestry increased. Overall plant performance on the higher pH soils appeared to be positively correlated to aboveground tissue concentrations of Mn, K, and Cu. When expressed as total content, population × pH regime effects were only significant for tissue Mn. Differences in total nutrient content attributed to soil pH were primarily related to differences in plant dry weight.

Cadmium-zinc interaction in maize grown on sewer water irrigated soil

Abstract Zinc fertilization in soil may ameliorate the negative health effects of Cd in crops. Therefore, a screenhouse experiment was conducted to study the effect of Cd (0, 5, 10, 25, and 50 mg Cd kg‐1 soil) as influenced by Zn (0, 5, 25, and 50 mg Zn kg‐1 soil) on dry matter yield of maize (Zea mays L.) and tissue concentration and uptake of Cd, Zn, Mn, Cu, N, P, and K. Application of Cd to soil decreased dry matter yield significantly at all concentrations of Zn. Addition of Zn to soil, however, did not affect yield at any concentration of Cd. Increasing concentrations of Cd in the soil increased the tissue concentration and uptake of Cd more in presence than in the absence of soil‐applied Zn, indicating that Zn application could not override the toxic effect of Cd. Concentration of N, P, K, Zn, Cu, and Mn in maize tissue increased with the application of Cd to soil. The uptake of these elements by maize decreased, except that of N and Mn which recorded an increasing trend up to 10 mg Cd kg‐1 soil tre...

Heavy-metal accumulation by Fucus ceranoides in a small estuary in north-west Spain

Concentrations of Fe, Al, Mn, Cu, Ni, Co, and Zn were measured in Fucus ceranoides and F. vesiculosus from Pontedeume, a small estuary on the northwest coast of Spain, affected by mining activities upstream and by sewage discharge to the estuary itself. Plants were collected from two intertidal levels at each of six locations, each sample eventually consisting of the homogenized tissues of ten individuals. Tips and thalli were analysed separately. By using these methods, it was found that three or four samples were sufficient to detect differences between means for different sites of 50% for all the metals considered except Cu, the high variability of which made eight samples necessary in order to detect differences of 100%. It was demonstrated that the contribution of particulate matter not removed during washing prior to analysis is significant only in the cases of Fe, Al and Cr. Mn and Co, and, to a less but still considerable extent, Ni and Zn, were found to be greatly enriched in the algae studied. Concentrations in mature tissues were higher than in apices for all the metals studied except Cu, for which there were no significant differences between the two tissues. The vertical position on shore did not affect apical metal concentrations but showed correlations with Mn, Co, Ni, Zn and Cu in mature tissues. Possible reasons for these correlations are discussed.

The influence of manganese supplementation on seizure onset and severity, and brain monoamines in the genetically epilepsy prone rat

Human and experimental animal studies suggest a relationship between low Mn status and seizures. The genetically epilepsy prone rat (GEPR), which has low tissue Mn levels, was studied in the context of Mn supplementation. Manganese was provided at 45 μg/g diet (control) or 1000 μg/g diet (supplemented) to dams during pregnancy and lactation, then to the offspring after weaning. Offspring were tested for seizure susceptibility as young adults; tissue trace elements, brain monoamines and brain glutamine synthetase activity were measured as endpoint biochemical indices. Supplementation, although developmentally encompassing and highly effective in elevating tissue Mn levels, had no effect on seizure latency or severity. Similarly, brain monoamine concentrations and glutamine synthetase activities were resistant to Mn supplementation. Notably, the GEPR was confirmed to have low whole brain glutamine synthetase activity. These findings suggest that seizure activity in the GEPR does not stem from an increased nutritional/metabolic need for Mn.

COPPER TOXICITY IN RICE

Long-term experiments (30 days) were carried out with rice in solution culture containing varying concentrations of Cu in an attempt to examine the threshold toxic concentration of this metal and its effects on Mn and Fe concentration in plant tissues. Cu concentration by rice roots (Oryza sativa L.) consisted of two distinct accumulation phases: a slow phase, in solution containing up to 0.01 mg/L, and a rapid phase above this concentration. In both phases the net absorption rate, as measured by Cu concentration in the roots, increased with metal concentration in the culture solution, but the increase was much faster in the second phase. Total Cu tissue concentration showed little variation between normal tissue and that clearly showing initial symptoms of the metal toxicity. Cu toxicity, as expressed by reduced root length, appeared to be a direct result of the accumulation of excess Cu in total tissues, the average concentration being 35.1 μg/g (dw) Cu at threshold toxicity. With respect to the effects of excess Cu on Mn and Fe concentrations, it was observed that while Mn and Fe concentrations in the shoot decreased at solutions of Cu concentrations above 0.05 mg/L, in the root these metals showed different patterns, with Fe concentration decreasing above 0.05 mg/L Cu and Mn concentration showing no defined trend. It is suggested that Cu affects Mn and Fe net translocation by different mechanisms, having the X coefficient for Mn and Fe values of 0.995 and 0.581, respectively.

The effects of excess manganese on photosynthetic rate and concentration of chlorophyll in Triticum aestivum grown in solution culture

Manganese toxicity, which involves a broad array of physiological responses, has been identified as an important factor limiting plant growth on acid soils. In the experiments reported here, we examined the toxic effects of Mn on chlorophyll content, photosynthesis and respiration in two cultivars (Norquay and Columbus) of Triticum aestivum (wheat) which differ in tolerance of Mn. When grown over a range of concentrations of Mn (0–1 000 μM), the Mn‐tolerant cultivar maintained higher rates of photosynthesis and respiration, and higher concentrations of chlorophyll a and chlorophyll b, than did the Mn‐sensitive cultivar, despite greater accumulations of Mn in leaf tissues. After 5 days growth with 1 000 μM Mn in solution, the photosynthetic rate fell to 25% of control in the sensitive cultivar and to only 75% of control in the tolerant cultivar. The concentration of chlorophyll a fell to 50% of control in the sensitive cultivar, but did not differ from control in the tolerant cultivar. Greater effects were seen on concentrations of chlorophyll b. which fell to 35% and 55% of control in the sensitive and tolerant cultivars, respectively. Rates of photosynthesis decreased in both cultivars as concentrations of chlorophyll decreased; however, the photosynthetic rate per unit chlorophyll remained constant or increased in the tolerant cultivar and decreased in the sensitive cultivar as concentrations of Mn in solution increased. Thus, in the sensitive cv. Columbus, Mn seemed to have a toxic effect on both chlorophyll content and photosynthesis per unit chlorophyll. In the tolerant cv. Norquay, the only clear effect of Mn was a reduction in chlorophyll content, although direct inhibition of photosynthesis could not be discounted.