|MadSci Network: Botany|
Complete question: I am currently embarking on a school investigation into the affect of heavy metal compounds on plant development, specifically lead compounds with mung bean seeds. I am currently only looking at changes in dry mass compared to a control, but could also examine the affect on pigments (eg chlorophil) by paper chromatography. I would like to know if there is likely to be any affect with any heavy metals that would cause visible effects. Thanks for your help and time. Reply: Lead is usually not absorbed in large amounts by soil-grown plants. Also, the lead that is absorbed mostly remains in the roots. Lead toxicity in plants is not common under natural conditions but may be an indirect effect of the lead reducing uptake of other cations, especially calcium. Bergmann (1992) notes that lead toxicity may disrupt calcium metabolism. However, calcium deficiency does not usually result in chlorosis. Bergmann has photos of leaf chlorosis symptoms for toxicities of cadmium, zinc, copper and nickel. Heavy metals that most affect chlorophyll are the essential heavy metals, such as iron, copper, zinc and manganese. Deficiencies of these usually result in chlorosis. Iron deficiency is termed "iron chlorosis" because of its major effect on chlorophyll synthesis. Iron deficiency is easy to induce in plants grown in hydroponics (solution culture); houseplants work well and can lower the nutrient solution pH by 3 or 4 units when they become iron deficient (Hershey 1995). References Lead in the Home Garden and Urban Soil Environment Comparative Lead Uptake and Responses of Some Plants Grown on Lead Contaminated Soils Bergmann, W. 1992. Nutritional Disorders of Plants. New York: Gustav Fischer. Hershey, D.R. 1995. Plant Biology Science Projects. New York: Wiley.
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