HOW DOES ARMERIA-MARITIMA TOLERATE HIGH HEAVY-METAL CONCENTRATIONS

The perennial plant Armeria maritima ssp. halleri, growing on the copp er-rich soil of a medieval mine dump, tolerates high heavy metal (HM) concentrations and accumulates e.g. 2000 (leaves) to 4000 (roots) time s more copper in comparison to plants growing under normal conditions. For copper, as an example, the mechanisms of the HM-tolerance are dis cussed. The HM-tolerance of Armeria is the result of morphological dif ferentiations and biochemical alterations. As measured by EDX analysis a great part of the copper in roots and leaves is retained in vacuole s of idioblasts (<<tannin cells>>) containing homogeneous or flaky pre cipitates of osmiophilic material. In the homogeneous precipitates, hi gh copper concentrations can be measured. EELS spectra revealed that t he copper in these vacuoles is chelated by polyhydroxy phenolic compou nds. Moreover, a complex mixture of phenolic compounds from leaves and roots of Armeria can be separated by HPLC. Copper ions reaching the v ascular bundle are translocated via the transpiration stream into the leaves and are excreted partly by salt glands on both leaf surfaces. C rystals on the surface of the leaves contain besides P, S, Cl, K and C a large amounts of Cu and to a smaller extent Zn, Ni, Fe and Mn. A sig nificant part of the copper in roots and leaves is found to be localiz ed in cell walls, in the cytoplasm, in the stroma of the plastids and in the chromatin of the nuclei. In these compartments the copper is bo und preferentially to proteins, as determined by EELS. Obviously, the copper in the cytoplasm represents a stress situation for the cell, re sulting in an expression of heat stress proteins (HSP).