Figure 2.

Proposed biosynthetic and metabolic pathway for cytokinins.The proposed biosynthesis of zeatin tri-/diphosphate in Arabidopsis is shown on the left side of the figure. Both ADP and ATP are likely substrates for the plant IPT enzyme, and these and their di- and tri-phosphate derivatives are indicted together (e. g. ATP/ADP). The biosynthesis of cytokinins in bacteria (e.g. Agrobacterium) is compared next to it. Several possible modifications and the degradation of zeatin are shown on the right side. The diagram only depicts reactions that are described in the text; cytokinin metabolism is more complex than the pathways shown (see Mok and Mok, 2001). See text for more details.