Relative Abundance of Nickel in the Leaf Epidermis of Eight Hyperaccumulators: Evidence that the Metal is Excluded from both Guard Cells and Trichomes

Scanning electron microscopy combined with X-ray microanalysis was used to localize the sites of nickel accumulation on the leaf epidermis of eight nickel accumulators grown on ultramafic soils in Greece. In all species, nickel was excluded from guard cells, and in species possessing hairy leaves (seven out of eight) nickel was excluded from the hairs. In some species the metal was present in subsidiary cells, yet at low levels, while the sites of higher accumulation were epidermal cells away from stomata. Results indicate that nickel is not compatible with the functions and development of certain epidermal cell types.