A RICE MEMBRANE CALCIUM-DEPENDENT PROTEIN-KINASE IS INDUCED BY GIBBERELLIN

A rice (Oryza sativa) seed plasma-membrane calcium-dependent serine/th reonine protein kinase (CDPK) has been partially purified. Comparing r esults in seeds that were treated with and without the plant hormone g ibberellin (GA) for 10 min showed that rice CDPK was highly induced by GA. After separating solubilized membrane proteins by sodium dodecyl sulfate-gel electrophoresis, followed by renaturation, a radiolabeled phosphoprotein band of approximately 58 kD was detected, and it was ap parently produced by autophosphorylation. There are five aspects of th e rice CDPK that show similarity to mammalian protein kinase C (PKC) a nd to other plant CDPKs: (a) Histone IIIS and PKC peptide-ser25 (19-31 ) are phosphorylated by rice CDPK. (b) The phosphorylation reaction is strictly dependent on calcium. (c) The activity of the rice CDPK is i nhibited by either staurosporine or the PKC inhibitory peptide (19-36) . (d) Addition of calmodulin has no effect on the activity of the enzy me; however, the CDPK is inhibited by the calmodulin antagonists trifl uoperazine and W-7. (e) The rice CDPK reacts with a mammalian anti-PKC antibody in immunoblotting analysis. However, there is one major diff erence between the rice CDPK and other CDPKs: the rice CDPK is induced by GA, whereas no mammalian PKC or other plant CDPKs are known to be induced by any hormone.