Differential Cytokinin Structure-Activity Relationships in Phaseolus

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Abstract
The activities of eight cytokinins in promoting callus growth were tested in two Phaseolus genotypes, P. vulgaris L. var. Great Northern, and P. lunatus L. var. Kingston. The structural feature which contributes to the major genotypic difference in cytokinin structure-activity relationships is the presence or absence of a double bond at the 2,3-position of the isoprenoid N6 side chain. In Kingston, trans-zeatin was 3-fold more active than dihydrozeatin and 30-fold more active than cis-zeatin. The activities of N6-(Δ2-isopentenyl)adenine and N6-isopentyladenine were nearly the same. In Great Northern, however, dihydrozeatin was at least 30-fold more active than both trans-zeatin and cis-zeatin, and N6-isopentyladenine was 100-fold more active than N6-(Δ2-isopentenyl)adenine. The results suggest the possibility of employing cytokinin structure-activity relationships in distinguishing genotypic differences in cytokinin function and metabolism.

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