The previous report (Chung and Lee, 1992) in our laboratory demonstrated that the protein kinase C (PKC) activator, TPA, promotes the elongation of corn coleoptiles significantly. To understand the role of TPA on the growth, substrates of PKC were investigated using PKC partially purified from soybean by DEAE-52 cellulose column. The enzyme activity increased about 5-fold in the presence of $Ca^{2+}$, phosphatidylserine and diolein compared with that in the absence of these reagents. Phosphorylation of both cytosol and membrane proteins by the purified PKC increased in the presence of $Ca^{2+}$ compared with that of EGTA treatment. However, the phosphorylation did not increase markedly by treatment with TPA or phosphatidylserine and diolein in the presence of $Ca^{2+}$ compared with $Ca^{2+}$ alone. The decrease, in phosphorylation of 100, 61 and 43 Kd proteins of the cytosol, and 140, no, 66, 47 and 32 Kd membrane proteins in hypocotyls, and 140, no, 66, 47, 33, 31 and 16 Kd membrane proteins in the root was observed in the presence of PKC inhibitor staurosporine (5T A). These results suggest that subatrates of PKC in soybean may be 110, 63 and 41 Kd proteins of the cytosol, and 140, 110, 66, 47 and 32 Kd membrane proteins in the subapical region of the hypocotyl, and 140, 110, 66, 47, 33, 31 and 16 Kd membrane proteins of the root.e root.