Intra-specific differences in nickel tolerance and accumulation in the Ni-hyperaccumulator Alyssum bertolonii

Populations of the serpentine-endemic nickel-hyperaccumulator Alyssum bertolonii from nine different outcrops were investigated for differences in their nickel tolerance and accumulation levels and shoot:root ratio of nickel concentration. Plantlets from the different populations were cultivated in hydroponics culture and subjected to a range of nickel concentrations. For populations of this obligate serpentinophyte, the results showed significant intra-specific differences in the degree of both nickel tolerance and nickel accumulation. Among populations there was no correlation between the patterns of shoot and root tolerance, whereas there was a clearly correlated pattern for root and shoot nickel accumulation. The populations of this hyperaccumulator showed a significant variation also in shoot:root ratio in nickel concentration, but there was no relationship between this trait and shoot nickel accumulation levels. Regarding the still obscure relationship between metal tolerance and hyperaccumulation, our results demonstrated a strong positive linear relationship between these two phenomena in the nickel hyperaccumulator Alyssum bertolonii.