Plants are sessile organisms, anchored to the ground through the root system for acquisition of nutrients and water, and thus are devoid of any possible avoidance mechanism to prevent injuries caused by chewing insects or larger herbivores. For defence, plants are endowed with pre‐existing physical barriers that limit damage, such as the cuticle, and hardened, woody covers that may succesfully withstand the aggression of small herbivores, or else have trichomes, thorns and other specialized organs that may further restrict pest access to the more nutritious parts of the plant. Once an injury occurs though, there is no possibility of mobilizing specialized cells devoted to wound healing such as in mammals, as plant cells are encapsulated inside rigid walls. Plants have thus evolved towards the capacity of making each cell competent for the activation of defence responses which largely depend on the transcriptional activation of specific genes. These wound‐activated responses are directed to healing of the damaged tissues and to the activation of defence mechanisms that prevent further damage. Most of the induced responses occur in a time window between a few minutes to several hours after wounding, and include the generation/release, perception and transduction of specific signals for the subsequent activation of wound‐related defence genes. Proteins encoded by those wound‐inducible genes may play one of the following functions: (i) repairing of damaged plant tissue; (ii) producing substances that inhibit growth of the predator insect, i.e. those lowering the digestibility of the plant tissue or producing a toxin; (iii) participating in the activation of wound defence signalling pathways; or (iv) adjusting plant metabolism to the imposed nutritional demands.
A localized injury activates defence mechanisms throughout the plant both in the tissues directly damaged (local response) and in the non‐wounded areas (systemic response). Whilst healing or reparation of damaged tissue is a function related to locally activated responses, herbivore deterring defences are deployed both locally and systemically. Wound‐activated local and systemic responses include metabolic changes and induction of gene expression, but only damaged tissues also undergo a severe disorder of cellular structures, associated with de‐compartmentalization and release of stored material, and a drastic loss of water. This review will focus on what is currently known about the signals that are produced and mobilized in the wounded plant, on the different transduction pathways activated by these wound signals and, finally, on the results that the activation of defence gene expression has on the injured plant. The potential and perspectives of the studies on wound signalling for the improvement of plant resistance against pests and pathogens will also be summarized. Copy and pasted 1 of many papers on this subject.