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Phaseolus seedlings (Phaseolus vulgaris L.) in light conditions were treated with 2 different concentrations of 2 heavy metals, mercury (0.05 mM and 0.4 mM) and chromium (0.5 and 1.0 mM). Mercury was given in the form of HgCl2 and chromium was given in the form of K2Cr2O7. | Turk J Biol 29 (2005) 15-21 © TÜB‹TAK Effects of Mercury and Chromium on Peroxidase and IAA Oxidase Enzymes in the Seedlings of Phaseolus vulgaris Nayna G. PARMAR, Sumitra V. CHANDA Department of Biosciences, Saurashtra University, Rajkot 360 005 - INDIA e-mail: sumitrachanda@yahoo.com Received: 13.02.2004 Abstract: Phaseolus seedlings (Phaseolus vulgaris L.) in light conditions were treated with 2 different concentrations of 2 heavy metals, mercury (0.05 mM and 0.4 mM) and chromium (0.5 and 1.0 mM). Mercury was given in the form of HgCl2 and chromium was given in the form of K2Cr2O7. Peroxidase activity was measured with 4 different hydrogen donors (ferulic acid, caffeic acid, pyrocatechol and pyrogallol). Both mercury and chromium inhibited root and hypocotyl length. The inhibition was about 50%-80%, depending on the concentration of the heavy metal. Peroxidase and IAA oxidase activities showed a clear inverse relation with growth. Seedlings treated with a lower concentration of mercury had similar activities to those treated with higher concentrations of chromium. The role of peroxidase and IAA oxidase activities in defense mechanisms in response to heavy metal toxicity is discussed. Key Words: chromium, mercury, metal toxicity, peroxidase activity, defense mechanism Introduction Peroxidases are of immense importance in a variety of cellular functions such as lignification, suberization, cell elongation, growth, regulation of cell wall biosynthesis and plasticity (1-3). Peroxidases are commonly classified as cytoplasmic or wall bound (ionically or covalently). In some instances, disease-specific isoperoxidases have been seen to appear in infected tissues (4) and these individual isozymes of peroxidase may have unique functions. Heavy metals are known to cause irreversible damage to a number of vital metabolic constituents and important biomolecules. They also cause irreversible injury to the plant cell wall and cell membrane. Trace elements are necessary .
