Phytochelatin-based complexes bind various amounts of cadmium in maize seedlings depending on the time of exposure, the concentration of cadmium and the tissue

The aims were to determine the quantities of tissue cadmium (Cd) bound in maize (Zea mays ) roots through phytochelatin-based complexes with changes in time of exposure, the concentration of Cd, the part of the primary root system, and the status of the complexes in shoots. Six buffer extractions solubilized most tissue Cd and a rapid small-scale gel filtration resolved the buffer soluble Cd into high and low molecular weight Cd-binding complexes. Six buffer extractions, rather than one, effectively represented high and low molecular weight phytochelatin-based Cd-binding complexes. The low molecular weight complex predominated in root apices and after 1 d of 3 mum Cd; the high molecular weight complex predominated in mature root parts and after 2 d of exposure. More tissue Cd was bound by both complexes with increasing time of exposure and concentration of Cd. Buffer extracted less Cd from shoots than roots and phytochelatin-based complexes bound less shoot Cd (29% vs 88%). The phytochelatin-based complexes are in a dynamic state dependent on the treatment and they function to bind variable amounts of tissue Cd.