PHYTOCHELATINS AS BIOMARKERS FOR HEAVY-METAL STRESS IN MAIZE (ZEA-MAYS L) AND WHEAT (TRITICUM-AESTIVUM L) - COMBINED EFFECTS OF COPPER AND CADMIUM

Heavy metal contaminated soils often show increased levels of more tha n one metal, e.g. copper (Cu), cadmium (Cd), zinc (Zn), lead (Pb) or n ickel (Ni). In case such soils are used for crop production, predictio n of yield reduction or quality decline due to heavy metals in the soi l is inadequate when based only on chemical soil analysis. The use of biomarkers such as phytochelatins (PC), non-protein thiols specificall y induced in plants upon exposure to heavy metals, may be an additiona l tool or diagnostic criterion in heavy metal research and in practice . In the present work, Cu and Cd uptake and induction of PC synthesis are studied with hydroponically grown maize and wheat plants exposed t o mixtures of the two metals. We observed a close positive relationshi p between the concentrations of Cd and PC in the plant shoot material. A decreased shoot concentration of Cd after addition of Cu, due to me tal competition at common root absorption sites, coincided with lower shoot PC levels. Also differences in metal uptake and xylary metal tra nsport among the two plant species were reflected in corresponding dif ferences in PC concentration. The observed direct relationship between shoot PC concentration and the degree of metal-induced growth inhibit ion makes the use of PC promising for the purpose tested for.