Web Figure 21.2.A
Structures of some naturally occurring cytokinins. Most plants have trans-zeatin as the principal free cytokinin, but dihydrozeatin and isopentenyl adenine (i6Ade) are also native plant cytokinins. Free cytokinins also include the ribosides and ribotides of zeatin, dihydrozeatin, and isopentenyladenosine, although these may be active as cytokinins by conversion to the respective bases. Free cytokinins from bacteria include 2-methylthio-cis-ribosylzeatin, as well as cis- or trans-zeatin, and their ribosides and ribotides.