Selenium and sulfur influences glucosinolate metabolism in hydroponically grown rapid cycling Brassica oleracea

Glucosinolates are sulfur-containing secondary plant metabolites commonly found in plants in the family Brassicaceae. The presence of selenium in soils can result in an accumulation of selenoamino acids, an increase in the uptake of sulfur, and an inhibition in the production of glucosinolates in Brassica species. This study was undertaken to determine the extent of selenium\u27s impact on selenoamino acid accumulation, sulfur uptake, and glucosinolate production in Brassica oleracea. Rapid cycling B. oleracea plants were grown hydroponically in half strength Hoagland\u27s nutrient solution with selenium treatments delivered as sodium selenate in concentrations of 0.0, 0.5, 0.75, 1.0, and 1.5 ppm. Elevated sulfur treatments of 37 ppm sulfate and 37 ppm sulfate/ 0.75 ppm selenate were incorporated to compare with selenium treatments. Plants were harvested and freeze-dried one to two days prior to anthesis. Selenium and sulfur content of plant tissue was determined by flame atomic absorption spectrophotometry and a Leco 232 S-determinator. Glucosinolate content of leaf tissue was determined by high performance liquid chromatography (HPLC). Selenium concentration in the nutrient solution was positively correlated with selenium and sulfur uptake in the plants. The sulfur concentration of plants exposed to selenium was equal to or greater than the sulfur concentration of plants exposed to elevated sulfur in the nutrient solution. In spite of higher sulfur concentrations, there was a statistically significant decrease in production of 5 of the 7 glucosinolates analyzed in selenium enriched plants. Plants in elevated sulfur treatments had higher glucosinolate production than selenium treated plants. These results suggest that selenium either up-regulates or prevents the down-regulation of sulfur uptake in B. oleracea. In addition, selenium\u27s presence within the plant seems to have a negative impact on the production of certain glucosinolates despite adequate availability of sulfur