Physiological differences between cttokinins are well documented. An explanation for these differences is that cytokinins differentially regulate genes. Gene response has been analyzed in cell culture and organized tissue of Phaseolus vulgaris L. cv. Great Northern. Two novel cDNAs, L-221 and L-22, have been identified that are cytokinin responsive. In leaf tissue L-221 was repressed by zeatin, benzyladenine and thidiazuron at 50 μM. In suspension cell culture mRNA abundance of L-221 remained constant regardless of cytokinin treatment. By contrast, the abundance of L-22 mRNA was increased differentially by treatment with each of the 3 cytokinins in leaf tissue. Suspension cells analyzed for expression of L-22 after cytokinin treatment also showed differential gene expression. S-1 Nuclease Protection Assays revealed that gene expression is a transient phenomenon dependent upon the time of cytokinin application and cytokinin concentration. Callus bioassays showed that dihydrozeatin and O-glucosylzeatin gave greater responses than the co-application of zeatin and dihydrozeatin or zeatin and O-glucosylzeatin. The conjugate and the reduction derivative also gave greater responses than zeatin alone. Effects of dihydrozeatin and O-glucosylzeatin on gene expression will be reported.
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