In order to investigate whether phospholipase C (PLC) activity in oat celIs is regulated by Gprotein, we have characterized PLC in plasma membranes of oat tissues. To identify the purified plasma membrane,

-stimulated,

-dependent ATPase activity was measured. The activity of ATPase was shown to be proportional to the concentration of membrane protein. To examine the PLC activity regulated by G-protein, we used the inside-out and outside-out plasma membrane mixture isolated from the oat cells. The plasma membrane mixture showed higher PLC activity than the one of the outside-out plasma membrane. This suggests that PLC activity is located at the cytoplasmic surface of plasma membrane. PLC activity in plasma membrane mixture was dependent on

with maximum activity at 100

and it was inhibited by 1 mM EGTA. Using Sep-pak

Plus QMA chromatography, we found that inositol 1,4,5-trisphosphate (

) was produced in the presence of 10

. The PLC activity in the membrane was enhanced by an activator of G-protein (

) and not by an inhibitor (

). This indicates that a G-protein is involved in the activation of PLC in the plasma membrane of oat cells.