Flavoenzyme involved in polyamine back-conversion (PubMed:20532512, PubMed:21081665). Catalyzes the oxidation of the secondary amino group of polyamines, such as spermine, spermidine and their acetyl derivatives (PubMed:20532512, PubMed:21081665). Substrate preference is N(1)-acetylspermine > spermine > spermidine (PubMed:21081665). Plays an important role in the regulation of polyamine intracellular concentration (Probable). Involved in abscisic acid-mediated developmental processes (PubMed:26310141). May contribute to nitric oxide-mediated effects on root growth (PubMed:26310141). H2O + O2 + spermine = 3-aminopropanal + H2O2 + spermidine H2O + N(1)-acetylspermine + O2 = 3-acetamidopropanal + H2O2 + spermidine H2O + O2 + spermidine = 3-aminopropanal + H2O2 + putrescine Binds 1 FAD per subunit. Amine and polyamine degradation; spermine degradation. Amine and polyamine degradation; spermidine degradation. Highly expressed in flowers and siliques. Also found in leaf and stem and in low levels in cotyledons, roots and in seedlings. By abscisic acid, jasmonate, salicylic acid, wounding and flagellin 22, a pathogen elicitor. Belongs to the flavin monoamine oxidase family.