Introduction Importance of Cadmium Accumulation in Plants

Certain heavy metals are well known to be essential microelements needed for plants to grow and complete their life cycle. Elevated concentrations of these metals, however, can be toxic and induce inhibition of various plant metabolic 

Most heavy metal resistant plants belong to the so-called excluders , they prevent the accumulation of heavy metals inside their tissues [5]. Metal exclusion can function in several different ways. The probably most simple way is a reduction of the unselective permeability of cells. This is typically reached by lignification of plant cell walls, and the enhancement of lignifying enzymes is a well-known response to cadmium toxicity [6]. In addition, exclusion can occur by precipitation 

To distinguish these very remarkable capabilities from the multitude of plant species that accumulate only a little Cd while being Cd-sensitive, but stiU are sometimes called Cd hyperaccumulators based on the old definition of Cd hyperaccumulation ( 100 ppm in shoot dry weight in the natural habitat [31]), it might be useful to re-define Cd hyperaccumulation as 500 ppm in shoots under enviroimientally relevant conditions with less than 20% growth reduction until the stage of maturity and a bioaccumulation coefficient 5 at a Cd concentration leading to 500 ppm in shoots. 

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