In plants, polyamines are catabolised by amine oxidases, which are present in different sub-cellular compartments. The chemical identity of AO-catalyzed reaction products depends on mode of polyamine oxidation, hydrogen peroxide representing a shared compound in all the AO-mediated reactions. It has been suggested that AO-mediated hydrogen peroxide production in the apoplast is involved in signalling pathways leading to stress and defence responses. Herein, a study on the physiological roles of cell wall-localized copper containing- (Cu)-AOs has been carried out. In Arabidopsis, ten putative CuAO genes have been identified, four of which (AtCuAO 1-4) encoding for proteins with a deduced extracellular localization. Insertional mutant lines for these genes were genotypically characterised by PCR, RT-PCR and Southern-blot analysis in order to identify the homozygous plants for single-locus T-DNA insertion and to confirm the absence of the full-length gene transcripts. Plant phenotype analysis revealed that methyl jasmonate (MeJA) treatments differently affects root growth of mutant and wild type plants, i.e. root growth of atcuao1 plants is less inhibited than wild type plants.