Effect of Selenium on Glucosinolate and Isothiocyanate Concentrations in Arabidopsis thaliana and Rapid-Cycling Brassica oleracea

Brassica vegetables play a unique nutritional and sensory role in human diets around the world. Their characteristic flavors come from the break down products of glucosinolate (GS) compounds, a large group of nitrogen (N) and sulfur (S) containing glucosides. Glucosinolates are hydrolyzed by myrosinase to isothiocyanates (ITCs) which are biologically active. Mounting evidence of this process is of scientific interest due to the potential for high consumption of Brassica vegetables containing several GSs and their respective hydrolysis products that are associated with cancer chemoprevention. Glucosinolates are sulfur-rich hydrophilic, nonvolatile plant secondary metabolites; and. over the past few decades, their importance has increased following discoveries of their hydrolysis products, ITCs, as potential anticarcinogens. The importance of selenium (Se) to human health has increased in recent years due its antioxidant potential and cancer suppression properties. Recent studies have demonstrated that certain Se containing compounds like Se-methyl-Se-Cysteine and Se-methionine are effective chemoprotective agents, reducing the incidence of breast, liver, prostate, and colorectal cancers in model systems. Brassicaa species are able to hyperaccumulate selenium at concentrations of up to 10-15 mg Se·g-¹ dry weight in their shoots while growing on naturally-occurring soils containing only 0.2-10 mg Se·kg-¹. The non-specific integration of Se into the S assimilation pathway enables the plant to metabolize selenoamino acids, selenocysteine and selenomethionine, into proteins. The process is believed to be the major contributor of Se toxicity in plants. The ability of hyperaccumulators to accrue and tolerate high concentrations of Se is thought to be associated with a distinct metabolic capacity that enables the plants to convert these selenoamino acids into non-protein amino acids.