Cytokinin Biosynthesis in Cultured Rootless Tobacco Plants

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Abstract
Biosynthesis of cytokinin in shoots was examined by growing rootless tobacco (Nicotiana tabacum) plants in vitro. The rootless plants were originated by culturing tobacco callus on a high cytokinin-low auxin medium to induce the formation of plantlets which were then grown on medium without exogenous cytokinin and auxin. The rootless plants supplied with [14C]adenine synthesized ethanol-ethyl acetate-water-soluble radioactive components, portions of which had the same chromatographic and electrophoretic mobilities as N6-(.DELTA.2-isopentenyl)adenine, N6-(.DELTA.2-isopentenyl)adenosine, 6-(4-hydroxy-3-methyl-2-butenylamino)purine and 6-(4-hydroxy-3-methyl-2-butenylamino)9-.beta.-D-ribofuranosylpurine. The total amount of these 4 major cytokinins was estimated to be present at a concentration of 14-23 nmol/kg of rootless plant. Apparently adenine serves as a precursor of the purine moiety of cytokinin molecules and the cytokinin biosynthetic sites are also located in the shoot in addition to the presumed root sites.