Flavoenzyme involved in polyamine back-conversion (PubMed:24634478). Catalyzes the oxidation of the secondary amino group of polyamines, such as spermine, spermidine and their acetyl derivatives (PubMed:24634478). Substrate preference is spermine > spermidine > N(1)-acetylspermine > N(1)-acetylspermidine > norspermine > thermospermine (PubMed:24634478). No activity detected when putrescine is used as substrate (PubMed:24634478). May play a role in producing hydrogen peroxide for secondary wall thickening through lignin formation during anther development (Probable). H2O + O2 + spermine = 3-aminopropanal + H2O2 + spermidine H2O + N(1)-acetylspermine + O2 = 3-acetamidopropanal + H2O2 + spermidine H2O + norspermine + O2 = 3-aminopropanal + H2O2 + norspermidine H2O + O2 + spermidine = 3-aminopropanal + H2O2 + putrescine H2O + N(1)-acetylspermidine + O2 = 3-acetamidopropanal + H2O2 + putrescine H2O + O2 + thermospermine = 3-aminopropanal + H2O2 + spermidine Binds 1 FAD per subunit. Optimum pH is 7.0 with spermidine as substrate (PubMed:24634478). Optimum pH is 6.5 with spermine as substrate (PubMed:24634478). Optimum temperature is 37 degrees Celsius with spermidine as substrate (PubMed:24634478). Optimum temperature is 30 degrees Celsius with spermine as substrate (PubMed:24634478). Amine and polyamine degradation; spermidine degradation. Amine and polyamine degradation; spermine degradation. Specifically expressed during anther development, from the meiosis/tetrad pollen stage to the tricellular pollen stage, with a peak at the bicellular pollen stage. Belongs to the flavin monoamine oxidase family. Truncated N-terminus. Truncated N-terminus.