Broomrape Species Parasitizing (Brassicaceae) Individuals Act as Nickel Hyperaccumulators.

The elemental defense hypothesis supports that metal hyperaccumulation in plant tissues serves as a mechanism underpinning plant resistance to herbivores and pathogens. In this study, we investigate the interaction between and broomrape parasitic species, in the light of the defense hypothesis of metal hyperaccumulation. Plant and soil samples collected from three serpentine sites in Lesbos, Greece were analyzed for Ni concentrations. and were found to infect . In both species, Ni concentration decreased gradually from tubercles to shoots and flowers. Specimens of both species with shoot nickel concentrations above 1000 mg.kg were found, showing that they act as nickel hyperaccumulators. Low values of parasite to leaf or soil nickel quotients were observed. growing on a serpentine habitat but not in association with had very low Ni concentrations in its tissues analogous to excluder plants growing on serpentine soils. Infected individuals showed lower leaf nickel concentrations relative to the non-infected ones. Elevated leaf nickel concentration of individuals did not prevent parasitic plants to attack them and to hyperaccumulate metals to their tissues, contrary to predictions of the elemental defense hypothesis.