The Wound Response in Tomato Involves Rapid Growth and Electrical Responses, Systemically Up-Regulated Transcription of Proteinase Inhibitor and Calmodulin and Down-Regulated Translation

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Localized heat wounding of tomato plants triggered rapid changes in growth and in electrical activity. The growth alterations were manifested as a transient increase in growth (petiole elongation), followed by a massive, long-lasting growth reduction. The electrical potential changes consisted of a wave of depolarization and re-polarization, i.e., a variation potential (VP). The tissue deformation apparently resulted from a pressure surge rapidly transmitted through the xylem, and preceded the changes in electrical potential. Externally-applied pressure mimicked flame wounding by triggering an electrical response resembling a VP. Our findings suggest that the VP results from a pressure surge in the xylem causing change in activity of mechanosensitive ion channels or pumps in adjacent living cells. The ensuing ion fluxes evoke plasma membrane depolarization, monitored extracellularly as a VP. Wounding also evoked a systemic decrease in polysomes, as well as a decrease in their protein synthesizing capacity in vitro. Very little of the newly-synthesized proteinase inhibitor (pin) and calmodulin (cal) mRNA was recruited into polysomes during the first hour following wounding. Since the VP appearance in distant tissue preceded the systemic molecular responses, the VP might be the long-distance signal up-regulating transcription of proteinase inhibitors and calmodulin, and down-regulating translation.