Catalyzes the oxidation of cytokinins, a family of N(6)-substituted adenine derivatives that are plant hormones, where the substituent is an isopentenyl group. Cleaves zeatin, isopentenyladenine, isopentenyladenosine, zeatin riboside and cis-zeatin, but not dihydrozeatin, kinetin and benzylaminopurine. A + H2O + N(6)-dimethylallyladenine = 3-methyl-2-butenal + adenine + AH2 Competitive inhibition by phenylureas. Monomer. Expressed in immature kernels and unpollinated cobs. Weakly expressed in kernels harvested two weeks after anthesis. Glycosylated; with approximately 10 hexose residues per site. Belongs to the oxygen-dependent FAD-linked oxidoreductase family.