Cellular compartmentation of nickel in the hyperaccumulators Alyssum lesbiacum, Alyssum bertolonii and Thlaspi goesingense

Nickel uptake and cellular compartmentation were investigated in three Ni h yperaccumulators: Alyssum bertolonii (Desv), Alyssum lesbiacum (Candargy) a nd Thlaspi goesingense (Halacsy). The three species showed similar hyperacc umulation of Ni, but T. goesingense was less tolerant to Ni than the two Al yssum species. An addition of 500 mg Ni kg(-1) to a nutrient-rich growth me dium significantly increased shoot biomass of all three species, suggesting that the Ni hyperaccumulators have a higher requirement for Ni than normal plants. Energy-dispersive X-ray microanalysis (EDXA) was performed on froz en-hydrated tissues of leaves (all species) and stems (Alyssum only). In al l species analysed, Ni was distributed preferentially in the epidermal cell s, most likely in the vacuoles, of the leaves and stems. In stems, there wa s a second peak of Ni in the boundary cells between the cortical parenchyma and the vascular cylinder. The non-glandular trichomes on the leaf surface s of the two Alyssum species were highly enriched with Ca, but contained li ttle Ni except in the base. In the leaves of T. goesingense, the large elon gated epidermal cells contained more Ni than the cells of the stomatal comp lexes. The role of cellular compartmentation in Ni hyperaccumulation is dis cussed.