Cytokinin Metabolism inPhaseolus vulgarisL.

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Abstract
A stable isotope dilution method employing a deuterium-labelled internal standard and combined gas chromatography-mass spectrometry has been used to quantify the accumulation of di-hydrozeatin-O-β-D-glucoside in the primary leaves of decapitated, disbudded bean plants. This cytokinin accumulated at a rate of 11 ng g−1 fr. wt. d−1 (eq. to an increase of 50 ng d−1 per leaf), reaching a maximum of c. 500 ng g−1 after 40 d from decapitation. This accumulation appeared to parallel the gradual increase in leaf fresh weight, and did not occur in detached leaves, in leaves of intact plants, or in leaves of plants that were decapitated but not disbudded. When secondary lateral buds were allowed to grow out from decapitated and initially disbudded plants, the levels of dihydrozeatin-O-β-D-glucoside in the primary leaves rapidly declined to a value similar to or lower than that found in leaves of intact plants. A similar decline in dihydrozeatin-O-β-D-glucoside levels was seen over 5 d in detached leaves of plants which had been decapitated and disbudded for 15 d; this effect was reduced but not prevented when the leaves were supplied with inorganic nutrients. These results are discussed in relation to the metabolism and distribution of cytokinins in the whole plant.