Sodium Selenate Fertilisation Increases Selenium Accumulation and Decreases Glucosinolate Concentration in Rapid-cycling Brassica Oleracea

Glucosinolates (GSs) are S-containing compounds found in Brassica species and whose degradation products may provide protection against cancer. Sulphoraphane, a product of 4-methylsulphinylbutyl GS degradation, is a particularly potent inhibitor of anticarcinogenic detoxification enzymes. Selenium also has anticancer properties, and consumption of plants containing Se may be an effective way to increase dietary Se. Since plant uptake of Se and S is competitive, GS synthesis may be affected by Se fertilisation. The objective of this study was to determine how Se fertilisation of rapid-cycling B oleracea would affect Se and GS concentrations. Plants were grown in hydroponic solutions containing 0.0, 1.0, 2.0, 3.0, 6.0, 7.2 or 9.0 mg l⁻¹ Na₂SeO₄. Mineral and glucosinolate concentrations were measured in shoots harvested just before anthesis. Total GSs decreased from 5.84 µmol g⁻¹ (0.0 mg l⁻¹ Na₂SeO₄) to 1.90 µmol g⁻¹ (9.0 mg l⁻¹Na₂SeO₄). Levels of 4-methylsulphinylbutyl GS decreased 90% when Na₂SeO₄ fertilisation was increased from 0 to 1 mg l⁻¹, and remained low at higher Na₂SeO₄ concentrations. Shoot Se concentration was undetectable at 0.0 mg l⁻¹ Na₂SeO₄ and increased significantly with Na₂SeO₄ fertilisation. Although B oleracea may not simultaneously deliver high levels of dietary 4-methylsulphinylbutyl GS and Se, levels of other GSs with anticarcinogenic benefits may be beneficial even with Se fertilisation.