[79]

MODIFICATION OF GRAVITROPIC RESPONSE AND GROWTH IN MAIZE ROOTS BY PHORBOL ESTERS.  Timothy J. Mulkey    Life Science Dept., Indiana State University, Terre Haute, IN  47809

   Phorbol esters have been shown to be activators and inhibitors of the second messenger signal transduction system in animal cells.  These compounds exhibit possible interactions with auxin and ethylene during elongation and the motor response of gravitropism in maize roots.  The tumor promoting agent 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and diacylglycerol (DAG) are known activators of Protein Kinase C (PKC) in a variety of animal models.  Staurosporine (STA) and phorbol 12-myristate 12-acetate-4-O-methyl ether (mTPA) inhibit or block activation of PKC in a wide variety of systems.  Treatment of primary roots of maize with PKC-activating agents results in a biphasic increase in elongation rates over the control by 100-200%; these treatments result in an increase in the degree of the gravitropic motor response and in the pattern of curvature.  The increase in elongation rate induced by PKC activating agents is blocked by pretreatment or reversed by post-treatment with STA.  Application of TPA (10^-6 M) to primary roots inhibited by high auxin concentrations (10^-6-10^-9 M) results in a recovery (20-100%) from inhibition of elongation.  STA (10 nM) inhibits promotion of elongation and slows the motor response in roots pretreated with AVG (aminoethoxyvinylglycine; 10^-6M) and exposed to auxin (10^-9-10^-11 M); these treatments do not prevent curvature but alters the resulting pattern of curvature.  Electrophoretic and autoradiographic patterns of soluble and membrane proteins from roots indicates that TPA and IAA treatment results in similar alterations of protein profiles and protein phosphorylation.

[