Movement of signals or cues, presumably chemical, among individual plants or plant parts. These chemical cues are a consequence of damage to plant tissues and stimulate physiological changes in the undamaged “receiving” plant or tissue. There are very few studies of this phenomenon, and so theories of its action and significance are fairly speculative.
Plants produce a wealth of secondary metabolites that do not function in the main, or primary, metabolism of the plant, which includes photosynthesis, nutrient acquisition, and growth. Since many of these chemicals have very specific negative effects on animals or pathogens, ecologists speculate that they may be produced by plants as defenses. Plant chemical defenses either may be present all of the time (constitutive) or may be stimulated in response to attack (induced). Those produced in response to attack by pathogens are called phytoalexins. In order to demonstrate the presence of an induced defense, the chemistry of plant tissues or their suitability to some “enemy” (via a bioassay) must be compared before and after real or simulated attack. Changes found in the chemistry and suitability of control or unattacked plants when nearby experimental plants are damaged imply that some signal or cue has passed from damaged to undamaged plants. Controlled studies have shown that responses in undamaged plants are related to the proximity of a damaged neighbor. See Allelopathy, Phytoalexin, Plant metabolism