The use of micro-energy dispersive X-ray fluorescence spectrometry (μ-XRF) combined with a multivariate approach to determine element variation and distribution in tobacco seedlings exposed to arsenate

Here, we present a new scheme of analysis combining micro-energy dispersive X-ray fluorescence spectrometry (μ-XRF) with a multivariate approach that allows to establish the inter-correlation of multiple elements and their elemental map in plants. The main advantage of this procedure is that XRF spectral profiles can be analysed directly, by means of principal component analysis (PCA), allowing a quick interpretation of the results. Furthermore, this analysis requires small amounts of plant material and can be performed in whole individual seedlings in the hydrated state without chemical extraction. With this technology, we determined the distribution of arsenic (As) and the variation and spatial distribution of multiple elements in whole tobacco seedlings grown in the presence of different arsenate concentrations. We observed that As is detectable mainly in roots, primarily in the basal part, but also in the root apex in seedlings grown in the highest arsenate concentration. The low rate of As translocation from roots to shoots and the significant increase in S are consistent with previous evidence showing that As is retained in roots by forming complexes with thiol peptides. We also found a significant non-linear increase in P, as arsenate is taken up by phosphate transporters and induces the expression of genes encoding them. A decrease in Mn, Fe and Zn proportional to the accumulation of As and in the same tissues, suggests a competition of these elements with As for cellular transporters.