In synchronously cultured tobacco cells (Nicotiana tabacumcv. Xanthi), the incorporation of U-14C-adenosine into butanol-soluble cytokinins in vivo was studied. The radioactivity was incorporated into zeatin, ribosylzeatin, isopentenyladenosine and glucosylzeatin after 20 min. The radioactive cytokinins were identified by thin-layer chromatography and high performance liquid chromatography. From the short time course of the incorporation of14C-adenosine into butanol-soluble cytokinins, the presence of the following biosynthetic pathway in vivo was suggested: adenosine is convered into isopentenyladenosine and then into zeatin via ribosylzeatin. The biosynthetic pathway of free cytokinins in vivo is compared with that in vitro.
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