Timing of molecular events following elicitor treatment of plant cells

Extracellular products with elicitor activity from the bean pathogen Colletotrichum lindemuthianum induced a multiplicity of changes in bean suspension cells. An immediate increase in luminol-mediated chemiluminescence which peaked within 30 min indicated production of activated oxygen species. Shut down of synthesis of discrete proteins and enhanced synthesis of other proteins was apparent by 3 h. These differences in protein profiles between elicitor-treated and control cells were more pronounced by 6 h. Other changes at 4–6 h involved perturbations in membrane functions including lipid peroxidation, altered proton efflux and uptake of a vital stain, fluorescein diacetate as well as reduced activity of the extracellular enzymes peroxidase and β glucosidase. These changes coincide with an increase in electron paramagnetic resonance signal consistent with free radical accumulation. The accumulation of phytoalexins at 6–8 h after treatment suggests that phytoalexins do not account for either free radicals detected earlier by the electron paramagnetic resonance signals or altered plant membrane function. Our data suggest that altered protein expression may be triggered by free radicals connected to activated oxygen metabolism.