Selenomethionine semet

All of the commercial standards of selenium species used in the experiments (Na₂SeO₃ (Se(IV)), Na₂SeO₄ (Se(VI)), selenomethionine (SeMet), methylselenocysteine (MeSeCys), and selenocystine (SeCys₂)) were purchased from Sigma-Merck (Steinheim, Germany). selenomethionine oxide (SeMetO) was synthesized based on the previously described method [43 (link)]. Briefly, 1.00 mL of 30% (v/v) H₂O₂ was added to 10.0 mL of an acidic solution of selenomethionine (10.00 mg L ⁻¹).
The standards of polyphenolic compounds such as catechin, epicatechin, and epigallocatechin gallate, as well as the standards of green tea and black tea, were purchased also from Sigma-Merck (Steinheim, Germany).
For mobile-phase preparation, methanol hyper grade for LC-MS LiChrosolv was purchased from Merck (Darmstadt, Germany), and water was obtained from a Mili-Q water purification system (Millipore, Bedford, MA, USA).

All chemicals were of analytical grade and were used without further purification. Nitric acid (V) 65 %, hydrochloric acid 37 %, internal standard (yttrium), and multielemental ICP MS standard solutions were obtained from Merck (Merck, Germany). Water for the analysis was obtained from the Milli-Q System (Millipore, USA).
Sodium selenite (Na₂SeO₃), sodium hydrogen selenite (NaHSeO₃), sodium selenate (Na₂SeO₄), and sodium-ammonium selenate (NaNH₄SeO₄) were obtained from Sigma, Germany. Selenomethionine (SeMet) and selenomethylselenocysteine (SeMetSeCys) were purchased from Sigma (USA). l-γ-Glutamyl-Se-methylseleno-l-cysteine (γ-glutamyl-SeMetSeCys) was obtained from PharmaSe Inc. (USA). Selenomethionine-Se-oxide (SeMetO) was achieved by adding an excess of oxidizing agent, 1 mL of 30 % (v/v) H₂O₂, to a 10-mL aliquot of a 0.1 mol/L HCI solution of selenomethionine (1 mg Se/L) and left overnight in the dark. Chemicals used for Knop’s medium, Ca(NO₃), KNO₃, KH₂PO₄, KCl, MgSO₄, EDTA-Fe, were obtained from POCH (Poland).
The reference material BCR-402, white clover, with a certified total selenium content of 6.70 ± 0.25 μg/g, was obtained from the European Commission Joint Research Centre, Institute for Reference Materials and Measurements, Belgium.

Four-week-old wheat seedlings were transferred to pots (one plant per pot) containing 1 L of aerated uptake solutions, which were composed of normal nutrients and different species of Se (5 μmol), including Selenite, selenate, SeMet and SeOMet. Each treatment had three replicates. The pH of these uptake solutions was buffered to 6.0 with 2 mmol MES. After treatment for 24 h, the seedling roots were rinsed with deionized water three times and then transferred to 150 mL ice-cold desorption solutions (1 mmol L⁻¹ CaSO₄ + 1 mmol L⁻¹ K₂HPO₄, 2 mmol L⁻¹ MES, pH 6.0) for 15 min to remove the Se and other ions adsorbed on the root surface. After desorption, the wheat plants were rinsed thoroughly with deionized water and then separated into shoots and roots, weighed, frozen in liquid nitrogen, powdered and analyzed for total Se contents. Selenite, selenate and Selenomethionine (SeMet) were obtained from Sigma-Aldrich (St Louis, MO, USA). Selenomethionine-oxide (SeOMet) was prepared according to Larsen et al. (2004) [26 (link)].