Uptake Mechanisms for Metal and Organic Xenobiotics in Plants

Hot spots for heavy metal contamination of plants are the air, water, soil and sediments, and plants make use of the opportunity to enrich themselves in metals when their growth capacities allow this (Greger 2004). Whereas higher plants can take up metals from the air via shoots and leaves, entry via roots and rhizomes from the soil substrate predominates. Of course, heavy metals can be much more concentrated in soils than in water (Forstner 1979).

In any case, metal uptake through leaves and roots depends on the concentration of the metal in the medium. However, uptake does not increase linearly with the concentration of the metal in the medium. This is because metals are often present under bound conditions. The uptake efficiency is highest at lower concentrations, because the low metal concentration also minimises competition between the metal ions at the absorption (uptake) surface (Greger et al. 1991). The larger the root surface area available, the more effective the uptake of the metal ions. Competition for the metal ions between plants at the same location can also occur, reducing uptake efficiency (Marschner 1995).

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