Abstract: Two varieties of sunflower (Helianthus annuus) were used to testify the hypothesis that IAA induces or maintains high levels of ABA in plant tissue which are responsible for the inhibition of bud growth. Both the exogenous ABA treatment experiment and the endogenous ABA level detecting were carried out. The results showed that the ABA content in the node tissue and its changes were not correlated with the apical dominance of sunflower plants.