Effect of Different Nitrogen–Sulfur Ratios on 2-Phenylethyl isothiocyanate (PEITC) Levels in Watercress

Abstract

A study was initiated to identify cultural conditions that optimize the production of important chemopreventive agents in watercress. Chemopreventatives are chemical compounds that reduce or prevent diseases such as cancer. Watercress (Nasturtium officinale) contains phenylethyl glucosinolate that, on hydrolysis, yields PEITC, and PEITC is one of the most-important anti-carcinogens among the cruciferous chemopreventatives tested. Watercress was grown in closed hydroponic systems containing 200 ppm nitrogen and either 64, 128, and 192 ppm sulfur to yield N:S ratios of 1:0.3, 1:0.6, and 1:0.9. The experiment was laid out as RCBD in the greenhouse with six replications. PEITC levels in leaf and stem tissue was assayed using gas chromatograph. After 36 days in the treatment solutions, watercress grown at a N:S ratio of 1:0.6 produced 90.1% and 65.3% (in repeated experiments) more PEITC than plants grown at a N:S ratio of 1:0.3. Plants grown in nutrient solution with a N:S ratio of 1:0.9 produced 57.4% and 24.2% greater PEITC than those grown with a N:S ratio of 1:0.3. Plants grown in a nutrient solution with a N:S ratio of 1:0.9 produced 17.2% to 24.2% less PEITC than those grown with a N:S ratio of 1:0.6. Leaves contained 54% to 70% more PEITC per unit dry mass than stems, suggesting that the leaf is the major site of synthesis and storage of PEITC.