To date, no biological mechanism has been elucidated for the uptake of noble metals nor has the form of accumulated Au inplants been studied. In general however, as indicated by Anderson et al. [20], plants accumulate Au because it is present in an available form in solution. Research on heavy metal uptake suggests rhizosecretion of biologically active compounds, i.e. organic acids (e.g. histidine), proteins (mainly phytochelatins and metallothionins),
isoflavonoids and enzymes, occurs in response to metal exposure [13,25–28]. These compounds may be responsible for the Au accumulation observed in MS and BJ in this work. Further biochemical and physiological studies are required on metal uptake,accumulation and sequestration in plants