Glutamine Nitrogen And Ammonium Nitrogen Supplied As A Nitrogen Source Is Not Converted Into Nitrate Nitrogen Of Plant Tissues Of Hydroponically Grown Pak-choi (brassica Chinensis L.)

摘要

Many vegetables, especially leafy vegetables, accumulate NO_3~-(-N) in their edible portions. High nitrate levels in vegetables constitute a health hazard, such as cancers and blue baby syndrome. The aim of this study was to determine if (1) ammonium nitrogen (NH_4~+(-N)) and glutamine-nitrogen (Gln-N) absorbed by plant roots is converted into nitrate-nitrogen of pak-choi (Brassica chinensis L.) tissues, and (2) if nitrate-nitrogen (NO_3~-N) accumulation and concentration of pak-choi tissues linearly increase with increasing NO_3~(-N) supply when grown in nutrient solution. In experiment 1, 4 different nitrogen treatments (no nitrogen, NH_4~(-N), Gln-N, and NO_3~(-N)) with equal total N concentrations in treatments with added N were applied under sterile nutrient medium culture conditions. In experiment 2, 5 concentrations of N (from 0 to 48 mM), supplied as NO_3~(-N) in the nutrient solution, were tested. The results showed that Gln-N and NHj-N added to the nutrient media were not converted into nitrate-nitrogen of plant tissues. Also, NO_3~-N accumulation in the pak-choi tissues was the highest when plants were supplied 24 mM NO_3~-N in the media. The NO_3~(-N) concentration in plant tissues was quadratically correlated to the NO_3~- (-N) concentration supplied in the nutrient solution.