TIME-RESOLVED ANALYSIS OF SIGNALS INVOLVED IN SYSTEMIC INDUCTION OF PIN2 GENE-EXPRESSION

The systemic induction of proteinase inhibitor genes in tomato plants is mediated either by electrical signals, hydraulic signals or chemica l messengers. In the present study we analyzed the effects of mechanic al wounding; heat treatment and electrical current application on wild -type tomato plants (Lycopersicon esculentum Mill. cv Moneymaker) and ABA-deficient mutants of tomato (sitiens). Kinetic studies revealed th at systemic Pin2 gene expression could be slightly induced by the fast transient membrane potential change which left the damaged leaf withi n 30-60s after wounding. Moreover, a signal leaving the damaged tissue between 2 and 4 minutes after wounding was responsible for a signific ant amplification of Pin2 gene expression. This signal could either be a decrease in turgor pressure, which occurred 3-4 min after treatment , or a slow electrical transient. In addition, mechanical wounding and electrical current seem to involve ABA to induce changes in membrane potential and to promote Pin2 gene expression. In contrast. heat trigg ers fast and slow electrical transients leading to an induction of Pin 2 gene expression within the plant independently of ABA. Turgor pressu re, in turn, is presumably adjusted in relation to ionic movements acr oss the membrane, elucidated by membrane potential recordings. In conc lusion, wound-induced changes in membrane potential seem to be depende nt on the endogenous level of ABA. These shifts in membrane potentials , in turn, are involved in regulation of turgor pressure within the pl ant.