Allocation patterns of zinc and cadmium in heavy metal tolerant and sensitive Silene vulgaris

The allocation pasterns of Zn and Cd were studied in a tolerant and a sensitive ecotype of Silene vulgaris. Within mature leaves, the allocation pattern of Zn was similar to char reported earlier for Cd, with the highest concentrations found in the lower epidermis. Part of the Zn present in the leaf seemed to be bound to cell walls of the mesophyll tissue, which is different from the allocation of Cd. At low concentrations, both metals inhibited the growth of the sensitive plants, and the tolerant ecotype was also affected at higher concentrations and longer exposure times. However, Zn and Cd had different effects on morphological parameters such as root/shoot ratio and leaf thickness. The various metal concentrations found in the leaves of different ages could for the most parr be explained by these effects on plant growth. It is concluded that the allocation of metals in leaves of S. vulgaris can be largely explained by the different effects of the metals on plant growth and leaf morphology, and not primarily as a specific result of tolerance mechanisms.