FUSICOCCIN BINDING TO ITS PLASMA-MEMBRANE RECEPTOR AND THE ACTIVATIONOF THE PLASMA-MEMBRANE H-ATPASE - IV - FUSICOCCIN INDUCES THE ASSOCIATION BETWEEN THE PLASMA-MEMBRANE H+-ATPASE AND THE FUSICOCCIN RECEPTOR()

Different approaches were utilized to investigate the mechanism by whi ch fusicoccin (FC) induces the activation of the H+-ATPase in plasma m embrane (PM) isolated from radish (Raphanus sativus L.) seedlings trea ted in vivo with (FC-PM) or without (C-PM) FC. Treatment of FC-PM with different detergents indicated that PM H+-ATPase and the FC-FC-bindin g-protein (FCBP) complex were solubilized to a similar extent. Fractio nation of solubilized FC-PM proteins by a linear sucrose-density gradi ent showed that the two proteins comigrated and that PM H+-ATPase reta ined the activated state induced by FC. Solubilized PM proteins were a lso fractionated by a fast-protein liquid chromatography anion-exchang e column. Comparison between C-PM and FC-PM indicated that in vivo tre atment of the seedlings with FC caused different elution profiles; PM H+-ATPase from FC-PM was only partially separated from the FC-FCBP com plex and eluted at a higher NaCl concentration than did PM H+-ATPase f rom C-PM. Western analysis of fast-protein liquid chromatography fract ions probed with an anti-N terminus PM H+-ATPase antiserum and with an anti-14-3-3 antiserum indicated an FC-induced association of FCBP wit h the PM H+-ATPase. Analysis of the activation state of PM H+-ATPase i n fractions in which the enzyme was partially separated from FCBP sugg ested that the establishment of an association between the two protein s was necessary to maintain the FC-induced activation of the enzyme.