Integration of wound-induced intercellular signals and systemic molecular responses in sunflower and tomato

Locally applied damaging external stimuli trigger rapid and marked systemic physiological responses in higher plants. This implies the existence of intercellular signals transmitted throughout the plant. These phenomena have recently attracted considerable interest and sparked controversies. A computerized data acquisition system designed for continuous measurement of propagated intercellular signals in plants was assembled. Appropriate data acquisition and analysis software were written. Using this setup, data related to signalling in sunflower and tomato plants subjected to localized damaging stimuli were collected and analyzed. Advances in characterization and distinction of the two main types of electrical signals in plants (action potentials and variation potentials) were accomplished. Alterations in stem dimensions were also continuously monitored in order to gain understanding of the properties of wound-induced propagated hydraulic pressure wave signals. The hydraulic signals are rapid, massive, involve acropetal and basipetal mass flow, and may be correlated to propagated electrical responses. They precede the measured voltage fluctuations. Externally applied pressure mimics a wound-induced pressure surge and evokes propagation of variation potential throughout the plant. Understanding of the wound-induced intercellular signals created a basis for correlation of the signals with systemic molecular responses. Methods were refined for efficient analysis of gene expression in distant plant tissues. The kinetics of wound-induced systemic expression of proteinase inhibitor genes and calmodulin were determined, revealing the fastest reported transcript elevation. The expression of proteinase inhibitors and calmodulin was dependent on light intensity. Transcript elevation does not lead to concomitant accumulation of transcript into polysomes. The observed decrease in polysome levels and their altered potential for protein synthesis in vitro suggest marked translational wound responses. Transcription and translation are temporally uncoupled and there are probably additional mechanisms that regulate translation. Direct electrical induction of proteinase inhibitors expression was accomplished. Although novel and significant per se, this finding does not conclusively prove the functional significance of electrical signals in gene expression. Electrical stimulus-induced currents may be damaging the cells releasing compounds that induce proteinase inhibitors expression. Electrical stimulus-induced action potentials and systemic defense gene expression may therefore be two independent responses existing in parallel