NITROGEN-DIOXIDE FUMIGATION ALTERS THE GLUCOSINOLATE AND NITRATE LEVELS IN PAK CHOY (BRASSICA-CAMPESTRIS SSP CHINENSIS)

The influence of continuous short-term nitrogen dioxide fumigation on glucosinolate and nitrate-nitrogen levels in pak choy was investigated. Hydroponically grown seedling and commercially mature plants were exposed to increasing concentrations (0.6, 1.2, and 1.8 mul l-1) of nitrogen dioxide for 1, 3 and 5 days. Visual symptoms of NO2 fumigation included increased green leaf color and leaf distortion. The treatments altered the dry matter accumulation, total glucosinolate (GS) concentration and composition, and nitrate levels in plants. These changes depended on the stage of plant and tissue development, nitrogen dioxide concentration and exposure duration. Seven predominant glucosinolates were identified in pak choy with 1-methoxy-3-indolylmethyl-GS, 4-methoxy-3-indolylmethyl-GS, and 3-indolylmethyl-GS reported for the first time. In both seedlings and older plants, the proportion of indolyl-glucosinolates increased in response to increasing nitrogen dioxide concentration. The nitrogen dioxide treatments increased nitrate levels up to 21% in seedlings and 89% in older plant tissues. Variation in the total glucosinolate concentration and nitrate levels were not associated over the treatments. The implications of these findings on pak choy quality are discussed.