In view of the well-established role of protein kinase C effector element in signal transduction of animal systems, the possibility of diacylglycerol (DAG) and its analog 12-O-tetradecanoylphorbol13-acetate (TPA) having an effect on auxin-induced growih of com coleoptiles was explored. Both DAG and TP A were found to promote cell elongation in the coleoptile tissue_ Treatment of tissue with these protein kinase C-activating agents resulted in increase in the growth rate over the control by about 300%. When 1M was applied to TPA-pretreated coleoptiles. auxin effect appeared synergistic. Morever. coleoptile growth was found to be inhibited by staurosporine and methylated TPA, both of which are known to specifically inhibit protein kinase C. Electrophoretic and autoradiographic patterns of soluble proteins from the coeoptiles indicated that either 1M or TPA tereatment resulted in increased phosphorylation of certain proteins of 205 Kd. 66 Kd and 32 Kd in size. The results obtained from the present work suggest that protein kinase C may be associated with auxin action on cell elongation in the corn coleoptile segments.gments.