Induction of alkalinization and an oxidative burst by low doses of cycloheximide in soybean cells

Abstract

Soybean (Glycine max L. Merr.) Cell-suspension cultures inoculated with avirulent Pseudomonas syringae pv. glycinea bacteria generated a sustained oxidative burst 3–6 h after the infection. The H2O2 production was not dependent on protein biosynthesis but, surprisingly, cycloheximide itself was a very strong inducer of the oxidative burst and of the alkalinization measured in the cell culture medium. Both responses were activated in a very similar manner by inhibitors of protein phosphatases, implicating a phosphorylation change evoked by cycloheximide as 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 depleted the medium of H+ but the expected alkalinization of about one pH-unit did not occur. The H2O2 production by the plasma membrane oxidase must therefore be charge-compensated, likely via H+-channel activity.