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 trichomes and in developing stomata of young growing leaves. Strong expression in stipules and in the root cap, but not detected in the root meristem. High expression in stomatal meristemoids, but ceased during the differentiation of guard cells. Belongs to the oxygen-dependent FAD-linked oxidoreductase family.