ABSTRACT
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 escaping mechanism to prevent injuries caused by insects and other herbivores. However, plants are endowed with preexisting physical barriers that limit damage, such as the cuticle and hardened woody covers that may successfully 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 there is no possibility of mobilizing specialized cells devoted to wound healing such as in mammals, as plant cells are encapsulated inside rigid walls. However, plants have the capacity of making each cell competent for the activation of defense responses, which largely depend on the transcriptional activation of specific genes. These wound-activated responses are directed to heal the damaged tissues and to the activation of defense mechanisms that prevent further damage. Much research has been focused in recent years on the interactions that occur among insect herbivores, plant pathogens, and their hosts. This research has revealed many interesting and valuable responses that are used by plant to limit damage that can occur from insect feeding and pathogen infection (1-6). In addition, tritropic interactions show the ability of many plants to bring on additional forces to combat herbivore attack, in the form of herbivore parasitoids (7). Most of the induced responses occur in a time window between a few minutes to several hours after wounding, and include the generation, perception, and transduction of specific signals for the subsequent activation of wound-related defense genes. Proteins encoded by those wound-inducible genes may have one of the following functions: (a) repair of damaged plant tissue; (b) production of substances that inhibit growth and development of the insect pest, i.e., those lowering the digestibility of the plant tissue or producing a toxin; (c) participation in the activation of wound defense signaling pathways; or (d) adjustment of plant metabolism to the imposed nutritional demands (4).
