Elemental mapping using PIXE shows the main pathway of nickel movement is principally symplastic within the fruit of the hyperaccumulator Stackhousia tryonii

Ashwath, N ORCiD: 0000-0002-4032-4507; Walsh, KB ORCiD: 0000-0002-3033-8622Metal concentrations within reproductive tissues of metallophytes are rarely reported. Here, the spatial distribution of nickel (Ni) within the fruits (seeds) of the Ni hyperaccumulator Stackhousia tryonii was investigated. Two microanalytical techniques, energy dispersive x-ray spectrometry (EDXS) and nuclear microprobe (micro-proton-induced x-ray emission spectrometry; micro-PIXE) were employed for qualitative and quantitative assessment, respectively, of localized Ni, within the fruits of S. tryonii The results were compared with quantitative analysis made using inductively coupled plasma-optical emission spectrometry (ICP-OES). Nickel analysis made using micro-PIXE was consistent with bulk (ICP-OES) analysis (at 1800 μg g − 1 d. wt), however, a beam resolution of approx. 2 × 2 μm 2 allowed tissue localization. Nickel was partitioned to the fruit wall (pericarp) (4433 μg g − 1 ), while endospermic and cotyledonary tissues possessed little Ni (309 and 182 μg g − 1 d. wt, respectively). This distribution is consistent with the interpretation that principal pathway of Ni movement within the fruit is symplastic rather than apoplastic (as the filial generation lacks symplastic connection with the parent)