Abstract:Activity and cytochemical localization of polyamine oxidase （PAO, EC 1.4.3.4 ） were studied in the young seedlings ofKennong 4 of Glycine max （L.） Merrill. PAO activity was undetected in the seeds until 24 h after imbibition, and increased during seed germination. However, the activity in various organs was significantly different in distribution between the germinating seeds （after 72 h of imbibition） and the young seedlings （after 120 h of imbibition）. In the germinating seeds, PAO had the highest activity in radicles （5.17±0.91 U g-1 FW）, followed by embryonal axis, embryonic bud, and lowest in cotyledons （0.12±0.03 U g-1 FW）. In the young seedlings, PAO showed the maximum activity in hypocotyls （5.47±0.66 U g-1 FW）, followed by juvenile root, apical bud, and lowest in cotyledons （0.10±0.03 U g-1 FW）. The differences of PAO activity in distribution presumably had positive effects on seed germination as well as seedling morphogenesis. PAO localization was determined in various parts of the young seedlings by using a cytochemical technique and transmission electron microscope. PAO was present mainly on vacuole membrane in apical bud cells, cell wall of both cotyledons and hypocotyls as well as on its surface. In hypocotyls, PAO closely attached to the surface of cell wall, while in root cells, it appeared in cell wall, intercellular space, on cell membrane, and especially on vacuole membrane. The results confirmed that PAO widely spread in cell wall and intercellular space. Moreover, to the author＇s best knowledge, PAO was found on cell membrane and vacuole membrane for the first time.