Involved in cytokinin biosynthesis. Catalyzes the transfer of an isopentenyl group from dimethylallyl diphosphate (DMAPP) to ATP, ADP and AMP. GMP, IMP, CMP or UMP are not used as substrates. AMP + dimethylallyl diphosphate = diphosphate + N(6)-(dimethylallyl)adenosine 5'-phosphate ADP + dimethylallyl diphosphate = diphosphate + N(6)-(dimethylallyl)adenosine 5'-diphosphate ATP + dimethylallyl diphosphate = diphosphate + N(6)-(dimethylallyl)adenosine 5'-triphosphate Optimum pH is 6.0-9.0. Expressed in roots, stems, leaves and cones. Belongs to the IPP transferase family.