Exploring Ni-accumulation in serpentinophytic taxa of Brassicaceae from Albania and Greece

The family Brassicaceae includes the highest proportion of Ni-hyperaccumulating plants in western Eurasia. Though increasingly relevant for scientific research and biotechnological applications, data about metal concentrations in native populations are still incomplete. The Balkan peninsula is a major diversity centre for Ni-hyperaccumulators due to the wide distribution of ultramafic soils across the area. Using Atomic Absorption Spectrophotometry and material from our field collections, we determined Ni concentration in 31 accessions of 22 taxa from nine tribes: Aethionemeae, Alysseae, Arabideae, Cardamineae, Coluteocarpeae, Erysimeae, Hesperideae, Iberideae and Isatideae. Results confirm that Ni-hyperaccumulation ability is phylogenetically restricted to Alysseae and Coluteocarpeae. Highest Ni-concentrations and bioaccumulation factors were found in Bornmuellera, Odontarrhena and Noccaea. Plants of the facultative serpentinophyte O. chalcidica from the type locality displayed shoot Ni levels > 2000 mu g g(-1) DW despite growing on non-ultramafic soils with low Ni. This resulted in a remarkably high bioaccumulation factor (91.7). High and low shoot Ni concentrations were instead detected in O. muralis accessions from serpentine and non-serpentine sites, respectively. Hyperaccumulation was confirmed in the endemic O. euboea, for which previous reports were contrasting. Shoot Ni concentration was negatively related to soil Ni concentration in non-accumulating taxa, suggesting efficient exclusion mechanisms on Ni-rich soils.