Tuberization in Cassava (Manihot esculenta): Cytokinin and Abscisic Acid Activity in Tuberous Roots.

The nature and distribution of cytokinins and abscisic acid in tuberous roots of cassava (Manihot esculenta Crantz) was studied. Trans-ribosylzeatin, dihydrozeatin and trans-zeatin were tentatively identified as the major cytokinins in tuberous root extracts. Cytokinin activity was concentrated in the meristematic region of the secondary xylem and in the phloem. This suggests a role for cytokinins in the regulation of meristematic activity which is responsible for the growth of the tuberous roots. Some cytokinin activity which co-eluted with cytokinin glucosides was found in extracts from the phloem. Inhibitor activity which was tentatively identified as cis-abscisic acid was present in tuberous root extracts. The activity of this hormone did not vary greatly between the different tissues analysed.