Abstract: Four pak—choi cultivars with diferent nitrate accumulation level were applied for explaining their genotypic variation in nitrate accumulation． Their dynamics parameters in nitrate uptaking ， Miehaelis constant(Km)，the maximum uptake Velocity(V )，nitrate content in nitrate maetabolie pool(MPs)and nitrate re．ductase activity(NRA)，were measured，results showed that Km and Vnmx，MPS，NRA varied greatly in diferent oak-choi cuhivars．But there was no relationship between nitrate content an d NRA，MPS． Th eir variation in
nitrate accumulation more resulted from their diferent uptake rate of nitrate than their NRA，M_lX5．

Key words: Pak-choi, Nitrate accum ulation, Absorption