Discadenine (1), a self-spore germination inhibitor from the cellular slim mold Dictyostelium discoideum, is structurally related to the plant hormone cytokinin. This compound was synthesized from l-aspartic acid, and its activities were confirmed by three classical cytokinin bioassays as well as by using binding and activation assays with the Arabidopsis cytokinin receptors AHK3 and CRE1/AHK4.