INDUCTION OF ALKALINIZATION AND AN OXIDATIVE BURST BY LOW-DOSES OF CYCLOHEXIMIDE IN SOYBEAN CELLS

Soybean (Glycine max L. Merr.) Cell-suspension cultures inoculated wit h avirulent Pseudomonas syringae pv. glycinea bacteria generated a sus tained oxidative burst 3-6 h after the infection. The H2O2 production was not dependent on protein biosynthesis but, surprisingly, cyclohexi mide itself was a very strong inducer of the oxidative burst and of th e alkalinization measured in the cell culture medium. Both responses w ere activated in a very similar manner by inhibitors of protein phosph atases, implicating a phosphorylation change evoked by cycloheximide a s a trigger for the elicitation. The activation of the oxidative burst was totally blocked by the kinase inhibitor K252a. The alkalinization response preceded the oxidative burst. The generation of H2O2 deplete d the medium of H+ but the expected alkalinization of about one pH-uni t did not occur. The H2O2 production by the plasma membrane oxidase mu st therefore be charge-compensated, likely via H+-channel activity.