Impact, metabolism, and toxicity of heavy metals in plants

Abstract

Plants are sessile organisms, and in order to survive they have to combat with the surrounding environment. Due to the numerous anthropogenic activities, an excessive level of different heavy metals accumulates in the soil system. The uptake of eminent concentration of these metals is toxic for the living organisms existing in that region. The troubling impact of heavy metals on plants is associated with the deformed growth and development, ionic imbalance, reduced photosynthetic rate, degradation of photosynthetic pigments and chloroplast, alteration in elemental composition, and disturbed plant water relation. The influence of metal ion is more complex by interaction between different ions because a high level of one metal ion may interfere with the uptake and transport of others and disturb the nutritional composition of plants and induce toxic symptoms. Several mechanisms have been evolved by the plants to sustain suitable physiological concentrations of metal ions and to minimize exposure of cellular processes to toxic heavy metals. Plants exposed to toxic concentrations of heavy metals attempt to prevent entry of these metal ions in roots as well as translocation from root to aerial parts by restricting metal ions to the apoplastic region, binding them to the cell wall, extracellular chelation with root exudates, or by reducing long-distance transport. Once metals enter in the cell, several storage and detoxification strategies including metal transport, chelation, and sequestration into the vacuole take place to diminish the toxic effects. The entry and transport of heavy metal in plants, strategies of plants to overcome the lethal consequences, and the specific toxic effects of heavy metals on plants when exposed to metal-enriched environment are emphasized in this chapter.