Dynamics of selenium uptake and metabolism of organic selenium species in the leaves and seeds of Brassica napus L.
The essential micronutrient selenium (Se) is retained better in animal and human tissues in its organic forms while nonprotein selenoamino acids, such as selenomethylselenocysteine (SeMetSeCys), are considered as functional organic Se species. We studied the ability of oilseed rape Brassica napus to metabolize inorganic selenate/selenite (SeVI/SeIV) into various organic Se species, including SeMetSeCys. At 14 d after the inorganic Se application, 33% of the Se had accumulated as selenomethionine (SeMet) and 60% as SeVI, whereas no SeMetSeCys was detected. SeMet was the main organic Se species (53−94%) in seeds. Brassica napus selenocysteine methyltransferase (SMT) protein sequence revealed a substitution typical of nonaccumulators explaining the low SeMetSeCys accumulation. Brassica napus absorbs rapidly inorganic Se and converts it into organic Se forms, mainly SeMet, that are suitable for augmenting animal feed and thereby supplementing the human food chain in Se-deficient countries. In contrast, Se biofortification did not result in accumulation of the more valuable SeMetSeCys.