Figure 1.

Structures of cytokinins.

Adenine is the parent compound of naturally occurring cytokinins, though it does not activate cytokinin responses; the N⁶ position is indicated with an arrow. trans-zeatin is the most abundant cytokinin in Arabidopsis, and the free base as well as the riboside and ribotide forms are shown. Kinetin is an artificial, aromatic cytokinin and benzyladenine is an example of a naturally occurring aromatic cytokinin. Thidiazuron is a diphenylurea-type cytokinin.