Influence of sulphur fertilization on speciation of small water-soluble sulphur compounds and selenium uptake in garlic

Garlic is known for its high sulphur content and for its ability to metabolize selenium. We studied the influence of sulphur fertilisation (0.1, 0.5, 2mM SO4 2 ) in hydroponically grown garlic on Se uptake (7.8 mg Se/L for 24 h) and the influence on small water-soluble S and Se species. Beside total S and Se in root and bulb, acid soluble S and Se species were identified and quantified. Roots of control plants contained more sulphur than Se treated plants, showing that short-term exposure to Se has generally a negative impact on S-content in roots. Se uptake by roots was highest in plants grown at low S-fertilisation. Bulbs on the other hand showed the opposite trend, with high S-fertilisation plants having higher Se accumulation. The main Se-species in roots were N-acetyl-selenocystathionine and Se-Met. Bulbs contained generally less acid-extractable Se than roots and this was present mostly in form of Se-Met.This experiment shows that the metabolism of small acid-extractable Se and S compounds is interlinked. Considering garlic as nutritional supplement to increase Se-uptake it seems that the application of increased S-fertilisation in addition to the exposure to inorganic Se would improve the transport of Se into the edible bulb and therefore produce a more valuable crop.