Absorption of Trimethylselenonium by Plants 1

The trimethylselenonium ion (TMSe⁺) is an important urinary Se metabolite. As an aid to evaluating its role in the natural cycling of Se, these plant studies concerning its uptake from soils or from nutrient solution and its metabolism were undertaken. Wheat (Triticum aestivum L.) and alfalfa (Medicago sativa L.) were grown on Dalton and Lima loam soils (coarse — silty, mixed, mesic Aeric Fragiaquert and fine-loamy mixed, mesic Glossoboric Hapludalf) containing no added Se or added Na₂SeO₃, Na₂SeO₄, or TMSe⁺, with and without a 4-month storage period prior to planting. Wheat only was grown in a separate experiment on Cecil (a clayey, haolinitic, thermic Hapludult) and Lakeland (thermic, coated Typic Quartzipsamment) soils containing similar amounts of these added Se compounds. The Se contents of the wheat and alfalfa grown on the TMSe⁺-treated Luna and Dalton soils were much lower than for the Na₂SeO₃ or Na₂SeO₄ treatments, barley exceeding that for the untreated control. With the Cecil and, especially, the Lakeland soils the Se content of the wheat was considerably above that for the untreated control, greater than that for the Na₂SeO₃ treatment, but considerably less than that for the Na₂SeO₄ treatment. TMSe⁺ added to nutrient solutions was readily absorbed and translocated to the leaves and stems but not the grain of wheat. At concentrations providing 3 mg Se/liter or more of nutrient solution, it caused signs of toxicity resembling those caused by similar concentrations of Se as Na₂SeO₄. Studies on the chemical form of the Se in the wheat suggested that, except for some volatilization, the TMSe⁺ absorbed was not metabolized.