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 ni ckel accumulators grown on ultramafic soils in Greece. In all species, nick el was excluded from guard cells, and in species possessing hairy leaves (s even 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 o f higher accumulation were epidermal cells away from stomata. Results indic ate that nickel is not compatible with the functions and development of cer tain epidermal cell types. (C) 2000 Annals of Botany Company.