Intercellular communication in plants: electrical stimulation of proteinase inhibitor gene expression in tomato

Abstract.

Tomato (Lycopersicon esculentum L.) plants accumulate proteinase inhibitor ( pin) mRNA in response to various stimuli in leaves distant from those treated. Most earlier work suggests that the intercellular wound signals are chemical; we have tried to determine whether electrical or hydraulic signals can also evoke systemic pin expression. We used a mild flame to evoke a hydraulic signal and its local electrical aftermath, the variation potential (VP), and an electric stimulus to trigger an action potential. Under medium light, wounding evoked a 3- to 5-fold systemic increase in pin mRNA within 15 min, suggesting involvement of a rapidly transmitted signal. Wounding also triggered a transient systemic increase in calmodulin (cal ) mRNA, under medium light conditions. Wounded plants exhibited electrical responses (VP) and yielded 5-to 15-fold increases in pin mRNA within 1 h. Electrically stimulated plants that transmitted an action potential to the analyzed leaf exhibited similarly large, rapid increases in pin transcript. Plants which generated no signal had unchanged levels of pin mRNA. Thus, in addition to the previously shown chemical signals, both hydraulically induced VPs and electrically induced action potentials can elicit systemic pin expression.