Abstract: The gene expression characteristics of glutamine synthetase（GS），glutamate synthetase （GOGAT），asparagine synthetase（AS）of‘M9T337’apple seedlings at different nitrogen levels（0.5，5 and 25 mmol ? L-1）were analyzed in hydroponic conditions. The results showed that，under low nitrogen stress treatment，the increase of GS gene expression in the underground part was significantly higher than that of GOGAT and AS，and the basic trend was up-regulated first and down-regulated later，and the expression levels of three genes in the overground part basically tended to be stable，and the expression of GOGAT in the root system basically tended to be not expressed after 1 d of low nitrogen treatment. With the increase of nitrogen level，the expression of GS and GOGAT genes in roots was up-regulated and then down-regulated，the expression of GS and GOGAT genes in leaves increased，and there was no significant difference in the change of AS. Under high nitrogen treatment，the gene expression of GS and GOGAT was inhibited，and the expression of GOGAT is extremely low in the root system，but the expression level in the overground part was significantly higher than that in the underground part. So，the AS and GS are involved in the response of apple root system to low nitrogen stress，and appropriate nitrogen level can induce the nitrogen metabolism key enzymes play a role in nitrogen metabolism circulation；however，high nitrogen level can inhibit the gene expression of nitrogen metabolism key enzymes in nitrogen metabolism，which had a negative effect on nitrogen metabolism in plants.

Key words: apple, rootstock, nitrogen metabolism, nitrogen supply level, gene expression