Se K X-ray absorption near-edge spectra of shoots of A. thaliana over-producing SMT and control plants. (A) Normalized spectra of different plant lines (filled circles), overlaid with the results of fitting each spectrum to a linear combination of spectra of standards (solid line). (B) Fit deconvolutions for two examples of the samples shown in A. Each panel shows the data and fit (as in A), the residual (dotted line beneath) and the spectra of standards scaled according to their contributions to the fit. The best fits were obtained using selenomethionine (RSeR), aliphatic selenonium (R3Se+), selenite (SeO32-) (all in aqueous solution) and elemental selenium (Se0). Other standards (not shown) were tested: aqueous selenate did not contribute to the fits, and dimethyl selenoxide gave poorer fits (as judged by the residuals) than the selenonium species. Note that selenomethioninine is chosen to be representative of RSeR species, and its spectrum is not reliably distinguishable from that of MeSeCys. (C) Chemical speciation of Se in planta in shoots of A. thaliana over-producing SMT and control plants. Se K X-ray absorption near-edge spectra were fit, as described in Figure 2, to produce quantitative data on the speciation of Se in shoots of A. thaliana. Total Se accumulation (Fig 1C) and percent speciation are combined to produce absolute concentrations of the various Se species.