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

Suspension-cultured cells of parsley (Petroselinum crispum L.) were us ed to study the regulation of extracellular H2O2. After resuspension, the washed cells regulated the H2O2 concentration spontaneously to a c onstant level that was greatly increased when the cultures were pretre ated for 1 d with salicylic acid (SA). The H2O2 level was further incr eased on addition of a fungal elicitor preparation, macromolecular chi tosan, the sterol-binding polyene macrolide amphotericin B, the G prot ein-activating peptide mastoparan, or La3+. In all cases, this induced H2O2 burst was also greatly enhanced in cell suspensions pretreated w ith SA. Both the spontaneous and the induced H2O2 production were decr eased by the protein kinase inhibitor K-252a. It is suggested that pro duction of extracellular H2O2 occurs by an endogenously controlled pla sma membrane enzyme complex that requires continuous phosphorylation f or function and whose activity is increased by pretreatment of the cel ls with SA. This system can also receive various external stimuli, inc luding 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 substa nce, as suggested previously for the wound hormone methyl jasmonate.