Systemin activity

Fig. (1). The wound response in tomato plants. Tomato plants respond to wounding with the transcriptional activation and accumulation of Systemic Wound Response Proteins including defense proteins, proteolysis-associated proteins, signaling-associated proteins, and proteins of yet unknown function in plants defense. The change in gene expression can be monitored on SDS-PAGE gels. In comparison to control plants (I), treatment with systemin (II), or overexpression of the prosystemin cDNA (III) leads to the accumulation of SWRPs (arrowheads) and the downregulation of other, unidentified proteins (triangles). The figure was modified after [13].

Progress was made possible by use of a different source for membrane preparations. It had been shown by Felix and Boiler [26] that cell suspension cultures of a wild tomato species (Lycopersicon peruvianum) give a characteristic response to systemin. After addition of systemin an alkalinization of the culture medium was observed paralleled by an efflux of K+. Systemin also caused an increase in the activities of 1-... 

Systemin exerts its biological activity at extremely low concentrations (fmol/plant). Therefore, in analogy to animal systems, proteases have to be postulated that inactivate systemin and clear the system from residual active hormone. Experimental data indeed support the existence of such enzymes. Felix and Boiler observed that the transient nature of systemin-triggered alkalinization response in L. peruvianum cells is due to proteolytic inactivation of systemin rather than desensitization of the perception system [26]. Inactivation of systemin was, in fact, observed in... 

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