Abstract: The effects of root-zone hypoxia treatment on nitrogen metabolism in muskmelon seedlings were studied in a hydroponic culture system．The results showed that roo-zone hypoxia treatment NO₃ ^--N， NH₄⁺-N contents and NR activities in the roots and leaves all increased，the soluble protein contents decreased，the heat-stable protein contents in the roots increased．The increasing degrees in the roots were more than those of leaves．Under the hypoxia treatment，the decreasing degrees of NO₃ ^--N， NH₄⁺-N，soluble protein contents and NR activities of‘Gangqiang’were more than those of‘Xiyu 1’．It indicated that the higher contents of NO₃ ^--N， NH₄⁺-N，protein and NR activity played an important role in enhancing hypoxia resistance in muskmelon seedlings．

Key words: Muskmelon, Root-zone, Hypoxia treatment, NO₃ ^--N, NH₄⁺-N, NR, Protein