International Journal of Agriculture: Research and Review. Vol., 2 (3), 247-254, 2012 Available online at http://www.ecisi.com ISSN 2228-7973 ©2012 ECISI Journals tECISI EFFECT OF ZINC TOXICITY ON PLANT PRODUCTIVITY, CHLOROPHYLL AND ZN CONTENTS OF SORGHUM (SORGHUM BICOLOR) AND COMMON LAMBSQUARTER (CHENOPODIUM ALBUM) HASAN MIRSHEKALIL HASHEM HADI*29 REZA AMIRNIA2 AND HABIB KHODAVERDIL003 1- Former MS student of Agronomy, Faculty of Agriculture, Urmia University, Urmia, Iran. 2- Assistant Professor, Agronomy and Plant Breeding Department, Faculty of Agriculture, Urmia University, Urmia, Iran. 3- Assistant Professor, Soil Science Department, Faculty of Agriculture, Urmia University, Urmia, Iran. Corresponding author: HASHEM HADI, E-mail: hhadi52@gmail.com, Tel: +98-914-3224159 ABSTRACT: Zinc (Zn) as a heavy metal plays an important role in many biochemical functions of plants. However, the excess amount of zinc is one of the most important growth limiting factors in soils. In the present study, the effects of various concentrations of Zn on biomass, chlorophyll content, and Zn contents of Sorghum bicolor and Chenopodium album were studied at research field of Urmia University, Urmia, Iran, in 2011. The plants were grown in pots over a 3 month period in soils containing zinc concentration varying between 100.7, 300.7, 500.7, 900.7, 1300.7 and 2100.7 mgzii/kgsoil. At the end of growing season, plant height, chlorophyll a, b, and total chlorophyll content, biomass, Zn concentration in the plants and bio-available Zn of the soils were measured. Results indicated that, generally, with increasing Zn concentration in soil, plant height, content of a, b, and total chlorophyll and biomass were decreased significantly (r0.05). With an increase in soil Zn concentration, Zn in Common lambsquarter was increased up to a maximum of 1213 mg/kg (in concentration 2100 mgziiLkgsoil). The maximum Zn concentration in sorghum was 2538 mg/kg (in concentration 500 mgz1 /kgs01). In addition, there was significant correlation between NH4NO3- extractable soil Zn and response of plants to Zn pollution. Key words: Chenopodium album; phytotoxicity; Sorghum bicolor; Zn; Bio-availability; Biomass. INTRODUCTION Zinc (Zn) is one of the important elements of plant growth and development (Bonnet et al., 2000; Misraet al., 2005). Zn plays essential metabolic roles in the plant, of which the most significant is its activity as a component of a variety of enzymes, such as dehydrogenases, proteinases, peptidases, and phosphohydrolases (Clarkson and Hanson, 1980; Bowen, 1979). Zinc also plays a vital role in DNA and RNA metabolism, protein biosynthesis, and cytokinesis; it participates in chlorophyll synthesis and protects chlorophyll from decomposition, and it also influences nitrogen assimilation (Alekhina and Kharitonashvilli, 2005). However, high zinc concentrations, like other heavy metals, are toxic for plants (Zhao et al., 2003). Zinc toxicity in crops is far less widespread than Zn deficiency. However, Zn toxicity occurs in soils contaminated by mining and smelting activities, in agricultural soils treated with sewage sludge, and in urban and peri-urban soils enriched by anthropogenic inputs of Zn (Chaney, 1993). Toxicity symptoms usually become visible at [Zn] leaf > 300 mgzi, kg-1 leaf dry weight (DW), although some crops show toxicity symptoms at [Zn] leaf < 100 mgzi, kg-1 leafDW (Chaney, 1993; Marschner, 1995), and toxicity thresholds can be highly variable even within the same species. For example, [Zn] leaf associated with a 50% yield reduction in radish ranged from 36 to 1013 mgzi, kg-ipw (Davies, 1993). Zn toxicity symptoms include reduced yields and stunted growth, Fe-deficiency-induced chlorosis through reductions in chlorophyll synthesis and chloroplast degradation, and interference with P (and Mg and Mn) uptake (Foy et al., 1978; Chaney, 1993), And disturbance in the intensity of basic physiological processes, i.e., photosynthesis, respiration, and transpiration, and decrease of reproductive performance, too (Ali et al., 2000; Khudsar et al., 2004; Kholodova et al., 2005). Some plant species and genotypes have great tolerance to excessive amounts of Zn. The families Poaceae and Chenopodiaceae are of the most interest, because they include species that are able to grow at high zinc pollution (Likholat et