Catalyzes the oxidation of cytokinins, a family of N(6)-substituted adenine derivatives that are plant hormones, where the substituent is an isopentenyl group. A + H2O + N(6)-dimethylallyladenine = 3-methyl-2-butenal + adenine + AH2 A number of isoforms are produced. According to EST sequences. Expressed in the developing leaf petioles and in the rib zone of the axillary shoot meristems. In roots, expressed in the vascular cylinder within the root apical meristem and only faintly detectable in the differentiated root. Expressed in young developing stamen primordia and later confined to the central part of growing anthers. Before and during pollination, restricted to the maturing pollen grains. Belongs to the oxygen-dependent FAD-linked oxidoreductase family.