Inhibition ofEnt-kaurene oxidation by cytokinins

Cytokinins, which have some structural similarities to ancymidol, a plant growth retardant, were tested for their effects on the cell-free oxidation ofent-kaurene. Results indicate that several cytokinins inhibit this reaction in microsomal extracts of liquid endosperm from immature wild cucumber seeds. N⁶-cyclohexanemethyladenine was the most active (inhibiting 50% of the controlent-kaurene oxidation at 2×10^–6 M). N⁶-isoamyladenine, N⁶-benzyladenine, N⁶-(²-isopentenyl)adenine and dihydrozeatin were active at successively higher concentrations. Zeatin, kinetin, adenine, N⁶-benzyladenosine, and N⁶-(isopentenyl)adenosine were inactive in this system.The basis for the inhibition ofent-kaurene oxidation by cytokinins may be similar to that of ancymidol: interaction with cytochrome P-450. A binding spectrum similar to that of ancymidol with cytochrome P-450 from wild cucumber endosperm microsomes was obtained with four active cytokinins. The cytokinin binding properties of this protein are currently under investigation.No metabolism of N⁶-benzyladenine could be detected under conditions in which the cytokinin inhibited the oxidation ofent-kaurene toent-kaurenol.This work was supported in part by National Science Foundation Grant PCM 7619279 and PCM 8016237, and a grant from Eli Lilly and Company.A portion of this work was presented as a poster paper at the Tenth International Conference on Plant Growth Substances, Madison, Wisconsin, USA, July 22–26, 1979.