Abstract: The content and the different dynamic of endogenous hormones in spur terminal buds，young leaves and fine roots during the bud differentiation of ornamental crabapple in different juvenile lengths has been measured by ELISA for probing how the ornamental crabapple flower bud differentiation is effected by endogenous hormones and for using the resources to shorten the juvenile lengths. The results demonstrated that the similar endogenous hormones contents and trend between the precocious plants and grafted mature plants. The IAA contents in the apical buds and roots decreased first and reached the minimum value in the early September during the process of flower bud differentiation. It was lower than the immature plants. The contents of IAA in the mature materials in leaves were higher than the immature one. The contents of GAs in apical buds increased first and then decreased to the minimum value in the early August. It was down to the lowest in the mature and also in the immature materials in the September. The contents of GAs in leaves of mature materials stayed at a low level in most of the time. The contents of GAs in the root were contrary to it was in the apical buds. The contents of endogenous hormones were higher and showed the highest range ability in mature materials than in precocious one. The ABA contents in buds of the mature materials were fluctuated in 160–170 ng · g^-1FW and immature individuals were always less than 160 ng · g^-1FW. The similar trend of ABA contents was showed in leaves and roots，increased first and then decreased gradually and reached the minimum level in the early September finally. The opposite results were discovered in roots. Mature varieties have a high ratio of ABA/GAs and ZR/GAs than more immature variety in buds and leaves，and contrast in the root.

Key words: precocious crabapple, juvenile stages, endogenous hormone, floral bud differentiation