It has been shown that tomato (Lycopersicon esculentum) plants respond to flame wounding and electrical stimulation by a rapid (15 min) and systemic up-regulation of proteinase inhibitor (pin) genes. To find other genes having a similar expression pattern, we used subtractive cDNA screening between flamed and control plants to select clones up-regulated by flame wounding. We report the characterization of one of them, a chloroplast mRNA-binding protein encoded by a single gene and expressed preferentially in the leaves. Systemic gene expression in response to flaming in the youngest terminal leaf exhibited three distinct phases: a rapid and transient increase (5-15 min) in transcript accumulation, a decline to basal levels (15-45 min), and then a second, more prolonged increase (60-90 min). In contrast, after a mechanical wound the rapid, transient increase (5 min) was followed by a rapid decline to basal levels but no later, prolonged accumulation. In the petiole, the initial flame-wound-evoked transient increase (15 min) was followed by a continuous decline for 3 h. The nature of the wound signal(s) causing such rapid changes in transcript abundance is discussed in relation to electrical signaling, which has recently been implicated in plant responses to wounding.

Localized wounding of one leaf in intact tomato (Lycopersicon esculentum Mill.) plants triggers rapid systemic transcriptional responses that might be involved in defense. To better understand the mechanism(s) of intercellular signal transmission in wounded tomatoes, and to identify the array of genes systemically up-regulated by wounding, a subtractive cDNA library for wounded tomato leaves was constructed. A novel cDNA clone (designated LebZIP1) encoding a DNA-binding protein was isolated and identified. This clone appears to be encoded by a single gene, and belongs to the family of basic leucine zipper domain (bZIP) transcription factors shown to be up-regulated by cold and dark treatments. Analysis of the mRNA levels suggests that the transcript for LebZIP1 is both organ-specific and up-regulated by wounding. In wounded wild-type tomatoes, the LebZIP1 mRNA levels in distant tissue were maximally up-regulated within only 5 min following localized wounding. Exogenous abscisic acid (ABA) prevented the rapid wound-induced increase in LebZIP1 mRNA levels, while the basal levels of LebZIP1 transcripts were higher in the ABA mutants notabilis (not), sitiens (sit), and flacca (flc), and wound-induced increases were greater in the ABA-deficient mutants. Together, these results suggest that ABA acts to curtail the wound-induced synthesis of LebZIP1 mRNA.

In Bidens pilosa (cv. radiata), a non-injurious stimulus induces a local and transient change in membrane potential, and an injurious stimulus induces a transmitted electrical signal described as the combination of an action potential and a slow wave. We have studied calmodulin gene expression after these stimuli. When the stimulus is non-injurious, calmodulin mRNA accumulation is only increased in the stimulated region. In contrast, when the stimulus is injurious, mRNA accumulation takes place in both wounded and distant, unwounded tissue. We propose that the slow wave plays a role in the long-distance transmission of a woundinduced information in plants.

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In Bidens pilosa L. (var. radiatus), wounding of both cotyledons induces the inhibition of hypocotyl growth. This morphogenic response occurs only if plantlets have been tranferred 24 h before from a non‐permissive (ion‐rich) to a permissive (deionized water) incubation medium. We have defined three kinds of experimental conditions where the wound‐response depends on the ionic content of the incubation medium: (1) permissive, allowing inhibition of hypocotyl growth; (2) non‐permissive, leading to storage of the wound signal; and (3) conditions required to recall the stored wound signal. Under these three experimental conditions, the accumulation of two stress‐related genes, tch1 (calmodulin) and hsp70, was investigated using northern blots of poly(A)+ and polysomal RNA. Under permissive conditions the wound response was characterized by a marked increase in tch1 and hsp70‐like poly(A)+RNA and by a slight association of these mRNAs with polysomes, 30 to 60 min after mechanical perturbation. In contrast, under non‐permissive conditions, we only observed a decrease in the accumulation of the two transcripts incorporated into polysomes. Under conditions that allow expression of the previously‐stored wound signal, we showed an increase in transcript accumulation (hsp70‐like gene) or an increase in the level of mRNA associated with polysomes (tch1‐like gene). These results suggest that transcriptional and post‐transcriptional regulation may occur at least at the level of transcript incorporation into the polysomes. This mechanism would be involved both after the immediate wound response and during the storage of the wound information.