SYSTEMIN INDUCES RAPID ION FLUXES AND ETHYLENE BIOSYNTHESIS IN LYCOPERSICON-PERUVIANUM CELLS

Suspension-cultured cells of Lycopersicon peruvianum L. reacted to the presence of mechanically damaged cells with a transient alkalinizatio n of their culture medium. This response resembled the alkalinization observed after treatment with fungal signal molecules such as chitin f ragments acid ergosterol or after application of the protein phosphata se inhibitor calyculin A. When compounds implicated in wound signallin g were tested, the 18 amino acid peptide systemin was found to be a po tent inducer of the alkalinization response, with a half-maximal activ ity at concentrations of similar to 100 pM. The decrease in extracellu lar H+ was paralleled by an increase of K+, and induction of both ion fluxes was blocked by the protein kinase inhibitor K-252a. Systemin al so caused rapid increases in the activities of 1-aminocyclopropane-1-c arboxylate (ACC) synthase and phenylalanine ammonia-lyase, two other r esponses commonly observed in cells treated with elicitors. The system in analogue systemin-Ala(17), a reported systemin antagonist in the in duction of proteinase inhibitors in tomato plants, provoked a much wea ker alkalinization response and did not induce ACC synthase at all. Wh en applied together with authentic systemin, this analogue antagonized induction of both responses, indicating that the perception system fo r systemin had very similar properties in the L. peruvianum cells as i n tomato plants. In conclusion, suspension-cultured L. peruvianum cell s provide a convenient and highly sensitive system to study elements o f wound response and, in particular, systemin perception.