Abamine (abscisic acid biosynthesis inhibitor with amine moiety) is abscisic acid (ABA) biosynthesis inhibitor targeting the oxidative cleavage reaction of 9-cis-epoxycarotenoids, which is catalyzed by 9-cis-epoxycarotenoid dioxygenase (NCED). To examine the effects of abamine during developmental stage, we compared the phenotype of abamine-treated Arabidopsis or cress seedlings grown in the dark with those of non-treated plants. In abamine-treated seedlings, hook formation was inhibited. It has been reported that this inhibition of hook formation is observed in ABA deficient mutant, aba2-2. These results suggest that the inhibition of hook formation induced by abamine should be due to ABA deficiency.