Although the metabolism of phytochelatins and higher polyamines are linked with each other, the directrelationship between them under heavy metal stress has not yet been clarified. Two approaches wereused to reveal the influence of polyamine content on cadmium stress responses, particularly with regardto phytochelatin synthesis: putrescine pre-treatment of rice plants followed by cadmium stress, andtreatment with the putrescine synthesis inhibitor, 2-(difluoromethyl)ornithine combined with cadmiumtreatment. The results indicated that putrescine pre-treatment enhanced the adverse effect of cadmium,while the application of 2-(difluoromethyl)ornithine reduced it to a certain extent. These differences wereassociated with increased polyamine content, more intensive polyamine metabolism, but decreased thioland phytochelatin contents. The gene expression level and enzyme activity of phytochelatin synthase alsodecreased in rice treated with putrescine prior to cadmium stress, compared to cadmium treatment alone.In contrast, the inhibition of putrescine synthesis during cadmium treatment resulted in higher geneexpression level of phytochelatin synthase. The results suggest that polyamines may have a substantialinfluence on phytochelatin synthesis at several levels under cadmium stress in rice