Manganese Uptake and Toxicity in Solanum and Capiscum

1. Manganese Uptake and Toxicity in Solanum and Capiscum Randall Marshall, Kyle Moore, Dr. Jodi ShannDepartment of Biological Sciences, University of Cincinnati, Cincinnati, OH 45221 Methods and Materials Introduction Results Discussion • Plant Growth • Tomato (Solanum) and bell pepper (Capsicum) seeds were germinated in heat-treated potting soil. As soon as root systems were of sufficient size to allow handling (10-14 days after germination), seedlings were transferred to tubs containing Hoaglands(9)nutrient solution. This hydroponic solution provides all essential plant macro and micronutrients including Mn. Dilute Hoagland’s (¼ strength) was used until plants were 6 weeks old, then increased to full strength for the remainder of the study. All solutions were aerated. Plants were grown in a controlled environment room with supplemental lighting (12 h day length). • Manganese Treatments • Plants were first exposed to Mn as juveniles or as adults. Treatment levels were 50, 100, 200 (for Solanum only), or 300 µg/L (provided as manganese sulfate). Treatment solutions were periodically changed. Water was used to bring to tubs to volume between changes. • Harvest and Analysis • 45-75 days after germination, plants were removed from solution, the roots rinsed and soaked in DI water for 15 minutes to eliminate external mineral deposits, and tissues separated into roots, stems, and leaves. • Samples were then dried for one week at 75ºC, dry weights were taken, and plants reduced to ash in a muffle furnace for 8 hours at 500°C. Following ashing, tissue samples were treated with 2mL of 50% HCl, heated for 2 hours, and allowed to cool. Two 10mL measures of HNO3 were then used to suspend the tissue samples, and assist in gravity filtration. • Marietta Ohio Case Study Samples • Field soil samples were collected from Marietta, OH – a community that has been identified by the USEPA as having some of the worst “schoolyard” air levels (see figure 1). Over 95% of the air contamination is due to Mn. Soil was extracted (EPA method 3050)(5) and analyzed for total manganese on an Atomic Absorption Spectrometer (Perkin Elmer 3110). • All data was analyzed using JMP statistical software. In some communities, the use and release of manganese (Mn) by local industries has led to elevated levels in the environment and widespread distribution(1). Although Mn is an essential trace element for human health, exposure to excessive amounts is associated with toxic effects on the nervous system. Inhalation is the most common exposure, but recent studies have correlated elevated Mn in drinking water with decreased IQ in children. This is reminiscent of the effects of lead, and suggests the importance of evaluating all potential exposure pathways - especially those with the potential to put children at risk.  Food is a likely way that people may be exposed to environmental contaminants. In plants, Mn is an essential micronutrient involved in chlorophyll and respiratory enzyme formation. Phytotoxicitycan occur as a result of oxidative stress and the exclusion of other necessary nutrients(2) The goal of this study was to investigate the uptake and distribution of Mn in commonly consumed plants. There is concern that visible signs of damage or growth inhibition may not be present in plants capable of accumulating elevated amounts of manganese in their tissues. These high-manganese plants could then potentially find their way into human food supplies. Manganese, as expected for an essential nutrient, appears to have a significant stimulatory effect at lower concentrations and exhibit toxicity at higher concentrations in both Solanumand Capiscum, with mean plant mass reaching a maximum grown in 50ppm Mn growth media, and minimal mean mass in 300ppm Mn media as toxicity was exhibited (fig.2). Plant parts differed in Mn concentration, withroots being much higher than stems or leaves. Although tissue concentrations generally increased with exposure (treatment) levels, plant mass did not. Total accumulation by tomato (and to lesser extent by pepper) was actually a function of plant health and tissue concentration. It should be noted that plants grown at 50 µg/L did not display symptoms of toxicity. They did, however, accumulate significantly higher levels of Mn than plants grown in most other treatment levels. Soil sampled from the industrial site had very high levels of manganese compared to the exposure levels tested in the hydroponic cultures of this study. However, bioavailability in soil would likely be much lower. The much lower concentrations from the residentialarea sampledonly a short distance away suggests that the manganese may not be particularly mobile. Future work will investigate the general distribution of Mn in the actual soils and vegetation of Marietta. Environmental distribution will be determined, as will the historical levels at different depths in the soil profiles. Figure 2. Upper panel shows tomato and pepper growth in solutions containing Mn treatments. Areas of deficiency (yellow), and toxicity (red) are apparent. Lower panel shows a typical group of plants growing in low (left) to high (right) levels of Mn. References & Citations Soils Reveal Widespread Manganese Enrichment from Industrial Inputs. Herndon, Elizabeth N., Jin, Lixin and Brantley, Susan L. 2011, Environ. Sci. Technol. 45: 241–247. 3. Manganese Toxicity in a Hawaiian Oxisol Affected by Soil pH and Organic Amendments. Vega, Silvio, Silva, James A. and Hue, Nguyen V. 2001, SOIL SCI. SOC. AM. J., VOL. 65,, pp. p153-160. 4. Hoagland, D. I. and Arnon, D. I. The Water-Culture Method for Growing plants Without Soil. California Agriculural Experiment station circular #347. 1950. 5. EPA, USA. SW-846: Test Methods for Evaluating Solid Waste, Physical/Chemical Methods, Method 3050B: Acid Digestion of Sediments, Sludges, and Soils, 3rd edition. [Online] January 8th, 2008. Soil samples from a major industrial site in Marietta were determined to haveMnconcentrations from 9.5 to 13.75 mg/g. A residence across the street from the site had substantially lower soil Mn at 2.17µg/g. Figure 1. Warren Elementary School is located in Marietta OH.