QUANTITATIVE MICRO-PIXE COMPARISON OF ELEMENTAL DISTRIBUTION IN NI-HYPERACCUMULATING AND NON-ACCUMULATING GENOTYPES OF SENECIO-CORONATUS

The Ni hyperaccumulator, plant species Senecio coronatus (Thunb.) Harv ., Asteraceae is an example of plant adaptation mechanisms to differen t ecological conditions. This widespread species can inter alia be fou nd on serpentine outcrops and the genotypes growing in serpentine soil s show different ways of adaptation. The populations from two distant localities take up and translocate Ni in concentrations which are norm ally phytotoxic, while plants growing on a different site, in the vici nity of another hyperaccumulating species, absorb amounts which are ty pical for most of the plants found on serpentine soils. The NAC nuclea r microprobe was used to compare the distribution of Ni and other elem ents in selected organs and cells with simultaneous use of PIXE and pr oton BackScattering (BS). Quantitative maps of stems showed large diff erences in concentrations and distributions of major and trace element s. In hyperaccumulating genotypes Ni is present everywhere within stem tissues, but the highest concentrations were found in the epidermis, cortex and phloem. In non-accumulating plants Ni was concentrated in t he phloem. In the leaf epidermis Ni was concentrated in the cell walls for both accumulating and non-accumulating plants. These results sugg est that biochemical diversity is more than morphological, because inv estigated genotypes belong to the same taxon. (C) 1997 Elsevier Scienc e B.V.