Identification of proteins involved in Hg–Se antagonism in water hyacinth (Eichhornia crassipes)
Different studies have established the presence of a proteinaceus complex involved in Hg–Se agonism/antagonism in plants. In order to identify proteins involved in this mechanism, water hyacinth plants were divided into groups and supplemented with Hg, Se and a Hg–Se mixture. Proteins involved were identified through a screening separation by SEC-ICPMS followed by SAX-ICPMS and then peptide mapping of selected fractions by nanoLC-ESI-ITMS2. Determination of total metal concentration showed that Se inhibits Hg translocation from roots to aerial compartments of the plant and that Se and Hg are antagonists to each other in terms of plant toxicity. In roots, stems and leaves Se was distributed mainly in two molecular mass fractions <670 kDa and ∼40 kDa, however, the proportion between these two fractions was inverted when Hg was co-administered. Hg throughout the plant was distributed in high and medium molecular mass compounds. Hg associated with molecules, ranging from <1.5 kDa to 15 kDa, was found in the root extract of Hg(II) supplemented plants, but was absent in the root extract of Se(IV) and Hg(II) supplemented plants. SAX showed that Hg and Se were mostly not associated with the same entity, since the complete overlapping of Hg and Se signals in all the peaks of SEC chromatograms was not observed. Changes in Se and Hg levels in water hyacinth were more evident in leaves in contrast to other compartments. Several proteins, possibly associated with either Se or Hg, were identified in roots, stems and leaves. Most of the identified proteins were associated with Hg and located in leaves, and these are associated specifically with chloroplast and mitochondria proteins, related to essential mechanisms in plants such as photosynthesis, carbon fixation and the electron transport chain.