Cytokinin biosynthesis in crown-gall tissue ofVinca rosea : The significance of nucleotides.

When care was taken to minimise the effects of phosphatase activity during extraction ofVinca rosea crown-gall tumour tissue, a large proportion of extractable cytolinin activity was present in the nucleotide fraction. Analysis using ion-exchange chromatography followed by enzymic or chemical degradation and subsequent identification of the biologically active material indicated that this activity was due to zeatin riboside 5'-monophosphate. This was also the major radiolabelled cytokinin formed when this tissue was supplied with [(14)C]adenine. The incorporation of radioactivity from [(14)C]adenosine into free cytokinins was also shown, but no incorporation of radioactivity was found when [(3)H]mevalonic acid lactone was supplied to this tissue under the same conditions. In parallel experiments using normal stem callus tissue ofV. rosea, no incorporation of [(14)C]adenine into free cytokinins was observed. The significance of these results is discussed in relation to a possible transfer-RNA-independent pathway of cytokinin biosynthesis, operating primarily at the mononucleotide level.