Application of micro-pixe and energy dispersive x-ray microanalytical techniques for localization of nickel within fruits of the Ni-hyperaccumulator Stackhousia tryonii Bailey (Stackhousiaceae)

Two micro-analytical techniques, viz. scanning electron microscope-energy dispersive X-ray microanalysis (SEMEDXMA) and micro-PIXE (micro-proton-induced X-ray emission spectrometry), were employed for qualitative and quantitative assessment (respectively) of Ni localization within the fruits of a Ni hyperaccumulator plant (S. tryonil). Most Ni translocated to the fruit was localized in the pericarp (4430±670 g-1), while endospermic and cotyledonary tissues contained comparatively much less Ni, at 310±40 and 180±45 Ni g-1 dry weight, respectively. These results suggest that Ni moved symplastically within the fruits of S. tryonil. Nickel concentration of fruits, determined using micro-PIXE (1400 g-1 dry weight), was in general agreement with that measured by ICP-OES (inductively-coupled plasma optical emission spectrometry) (at 1800 g-1 dry weight), indicating that micro-PIXE can be relied upon for quantitative analysis of metals within various plant tissues.