Toxic Effects of Heavy Metals on Germination and Physiological Processes of Plants
Pollution of the environment by toxic metals in recent years has accelerated dramatically due to rapid industrial progress. Heavy metals when taken up in amounts in excess of the normal concentration produce lethal effects on plants, on microbes, and dire
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Toxic Effects of Heavy Metals on Germination and Physiological Processes of Plants Parvaze Ahmad Wani, Mohammad Saghir Khan, and Almas Zaidi
Abstract
Pollution of the environment by toxic metals in recent years has accelerated dramatically due to rapid industrial progress. Heavy metals when taken up in amounts in excess of the normal concentration produce lethal effects on plants, on microbes, and directly or indirectly on the human health. Deleterious impact of metals on plants includes the reduction in germinability of seeds, inactivation of enzymes, damage to cells by acting as antimetabolites, or formation of precipitates or chelates with essential metabolites. Heavy metals also show unconstructive effects on other physiological processes like photosynthesis, gaseous exchange, water relations, and mineral/nutrient absorption by plants. These adverse effects may be due to the generation of reactive oxygen species which may cause oxidative stress. The impact of heavy metals on germination of legume seeds and different physiological events of plants with special reference to leguminous plants grown in distinct agroecological niches is highlighted.
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Introduction
Heavy metal pollution is one of the prime environmental problems that are caused due to the unabated, indiscriminate, and uncontrolled discharge of hazardous chemicals including heavy metals by different agencies into the environment (Fernandes and Henriques 1991; Cortes et al. 2003; Suciu et al. 2008; Navarro et al. 2008; Vaalgamaa and Conley 2008). Heavy metals released from such sources like metalliferous mining and smelting, use of chemicals in agricultural practices, and waste disposal and discharge of metals like cadmium, copper, chromium,
P.A. Wani (*) Department of Biological Sciences, College of Natural and Applied Sciences, Crescent University, Abeokuta, Ogun State, Nigeria e-mail: [email protected]; [email protected] A. Zaidi et al. (eds.), Toxicity of Heavy Metals to Legumes and Bioremediation, DOI 10.1007/978-3-7091-0730-0_3, # Springer-Verlag Wien 2012
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mercury, nickel, lead, etc., from other sources, when build up in soils, can generate damaging effects on various agroecosystems (Mcllveen and Nagusanti 1994) including plants (Stimpfl et al. 2006; Pandey and Pandey 2009; Stobrawa and Lorenc-Plucin´ska 2008; Wani et al. 2008a, b) and on animals and human health (de Vries et al. 2007; Lagisz and Laskowski 2008; Korashy and El-Kadi 2008) via food chain. In general, it is reported that heavy metals unfavorably affect about 12% of the world’s agricultural land (Moffat 1999). Even though some heavy metals like molybednium in low concentrations are required by plants to maintain its physiological functions (Hansch and Mendel 2009), the excessive accumulation of such metals in plant tissues can interfere and even disrupt the metabolic activities like photosynthetic and respiratory process, protein synthesis, and development of organelles of plants (Agarwala et al. 1995; Upadhyay and Panda 2009) includi
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