HOW DOES ARMERIA-MARITIMA TOLERATE HIGH HEAVY-METAL CONCENTRATIONS

The perennial plant Armeria maritima ssp. halleri, growing on the copper-rich soil of a medieval mine dump, tolerates high heavy metal (HM) concentrations and accumulates e.g. 2000 (leaves) to 4000 (roots) times more copper in comparison to plants growing under normal conditions. For copper, as an example, the mechanisms of the HM-tolerance are discussed. The HM-tolerance of Armeria is the result of morphological differentiations and biochemical alterations. As measured by EDX analysis a great part of the copper in roots and leaves is retained in vacuoles of idioblasts (<<tannin cells>>) containing homogeneous or flaky precipitates of osmiophilic material. In the homogeneous precipitates, high copper concentrations can be measured. EELS spectra revealed that the copper in these vacuoles is chelated by polyhydroxy phenolic compounds. Moreover, a complex mixture of phenolic compounds from leaves and roots of Armeria can be separated by HPLC. Copper ions reaching the vascular bundle are translocated via the transpiration stream into the leaves and are excreted partly by salt glands on both leaf surfaces. Crystals on the surface of the leaves contain besides P, S, Cl, K and Ca large amounts of Cu and to a smaller extent Zn, Ni, Fe and Mn. A significant part of the copper in roots and leaves is found to be localized 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 bound preferentially to proteins, as determined by EELS. Obviously, the copper in the cytoplasm represents a stress situation for the cell, resulting in an expression of heat stress proteins (HSP).