Some plants of the genus Alyssum are able to accumulate nickel(II). It has been observed that increase in nickel content is accompanied by an increase in the level of malonic and malic acids in the leaves [1]. Indeed crude extracts obtained from the leaves showed the presence of the nickel salts of the above mentioned acids. However, it has been shown these plants also contain a considerable amount of free amino acids, which in principle should also act as ligands of the nickel(II) ion [2]. R. J. P. Williams has suggested that only the presence of ligands containing nitrogen donors can explain the selective uptake for example of nickel(II) over cobalt(II) [3]. We decided therefore to study the mechanism of uptake, transport and accumulation of metal ions by these plants, using the copper(II) ion as a probe. This is because the copper(II) ion can be studied trough ESR, a technique which can be applied directly to whole samples (roots, leaves, plants etc.) thus avoiding the formation of artefacts. When the cut roots of the plant are introduced for 1′ into a 10 −4 M CuSO 4 solution and washed with distilled water the spectrum 1a is observed (Fig. 1). ▪ This spectrum can be interpreted as the superimposition of the isotropic spectrum of freely rotating aqueous copper(II) with an anisotropic spectrum typical of immobilized copper(II) [4]. This spectrum does not change with time even if the roots are kept in water. If however the roots of an entire plant are immersed in distilled water after the treatment with CuSO 4, the spectrum 1a changes with time (1b, 1c, 1d) showing the progressive formation of a copper(II) complex with low molecular weight. The spectrum 1d is also found in the leaves indicating that this is the medium through which copper(II) is transported across the plant. The g iso = 2.13 and A iso = 80 × 10 −4 cm −1 values are consistent with the presence of nitrogen atoms among the donors. This complex is fairly stable as it is also found in crude extracts of the plant and this might provide a possible way for its isolation. Preliminary experiments indicated that this complex does not migrate under electrophoresis. This complex could represent a 1:2 copper(II) amino acid complex. Studies are in progress in order to isolate and characterize this species (or mixture of species). We also studied the absorption of other metal ions by these plants and we found that the uptake follows the order Cu Zn Ni Co Mn Cr. All these metals behave competitively toward Ni(II) indicating a common uptake pathway at least at the level of the roots (Fig. 2). ▪