ABSTRACT
Cytokinin metabolites are structurally similar to, and presumably derived from, free bases. Metabolites were discovered in feeding studies with radiolabeled free cytokinins and were named in reference to the parent compound, such as zeatin riboside or dihydrozeatin riboside. This chapter reviews key properties of known enzymes involved in cytokinin metabolism and discusses the possible significance of these enzymes in cytokinin action and plant development. The importance of those enzyme-catalyzing steps in common with adenine metabolism is more difficult to fathom, since they have broad substrate affinity and are expected to utilize adenine cytokinins as substrates. The work represents the first isolation of cytokinin genes from plants and demonstrates the feasibility of using zeatin-specific enzymes to study the genetics of cytokinin metabolism. Perhaps additional attention should be focused on the demanding, but effective, approach of isolating cytokinin-specific enzymes to provide more definitive answers.
