PRETREATMENT OF PARSLEY SUSPENSION-CULTURES WITH SALICYLIC-ACID ENHANCES SPONTANEOUS AND ELICITED PRODUCTION OF H2O2

Suspension-cultured cells of parsley (Petroselinum crispum L.) were used to study the regulation of extracellular H2O2. After resuspension, the washed cells regulated the H2O2 concentration spontaneously to a constant level that was greatly increased when the cultures were pretreated for 1 d with salicylic acid (SA). The H2O2 level was further increased on addition of a fungal elicitor preparation, macromolecular chitosan, the sterol-binding polyene macrolide amphotericin B, the G protein-activating peptide mastoparan, or La3+. In all cases, this induced H2O2 burst was also greatly enhanced in cell suspensions pretreated with SA. Both the spontaneous and the induced H2O2 production were decreased by the protein kinase inhibitor K-252a. It is suggested that production of extracellular H2O2 occurs by an endogenously controlled plasma membrane enzyme complex that requires continuous phosphorylation for function and whose activity is increased by pretreatment of the cells with SA. This system can also receive various external stimuli, including those resulting from binding of fungal elicitor. SA can induce acquired resistance against pathogens. The conditioning of the parsley suspension culture by SA represents, therefore, a model for the long-term regulation of apoplastic H2O2 concentration by this signal substance, as suggested previously for the wound hormone methyl jasmonate.