Wound-activated defense

From the large body of literature about chemical defense in the benthic environment (benthos the bottom of the sea and the littoral zones), only a few aspects can be highlighted here. The selection of examples from the benthos will focus on dynamic defense reactions including fast wound-activated and... 

Interestingly, the release of PUFAs without subsequent action of a lipoxygenase can act as a wound-activated defense diatom in rich fresh water biofilms. This reaction could be directly associated with a chemical defense against the grazer Thamnocephalus platyurus [78]. 

Scheme 14 The wound-activated transformation of halimedatetraacetate (48) to halimedatrial (50) and the unstable epihalimedatrial (51) increases the defensive potential of Halimeda spp.

The ability to respond so rapidly should be advantageous when herbivoregrazing is intense but extremely variable over short periods of time. The defense on demand could thus result in high levels of the defensive metabolites halimedatrial (50) and the unstable epihalimedatrial (51) only in the presence of actively feeding herbivores. Since grazing was also reduced significantly more by purified halimedatrial (50) than by halimedatetraacetate (48) this reaction fulfills all three criteria defined for a wound-activated defense (see above). 

The only known example of an activated defense in sponges arises from investigations of the defensive chemistry of Aplysina aerophoba. A wound-activated transformation of stored pro-toxins was found after disruption of compart-mentalization of this sponge [157,158]. 

A re-examination of the defensive chemistry of I marginata revealed that the tridentatols (85-88) represent the transformation products of less active sulfate ester storage forms (81-84) [161]. Crushing the tissue as an attacking predator would do results in the rapid conversion of the sulfate esters within seconds after wounding. This suggests that this reaction plays a role in a wound-activated defense. 

Plants respond to the mechanical or insect herbivore damage of their tissues." During herbivorous attacks, some plants emit a specific blend of volatiles, which may result in defense responses retarding development of the herbivores or attraction of herbivore enemies to feed upon them. In lima bean leaves, the spider mite-induced volatiles, as well as infestation and artificial wounding, activate the ethylene and JA signaling pathways. ... 

Recently, the activities of host defense peptides related to the resolution of infection have been suggested to result in part from nondirect antimicrobial activities. It has been postulated that immunomodulation may represent the primary action of these peptides in vivo as the immunomodulatory activities are retained under physiological conditions in contrast to the direct antimicrobial activities of most natural mammalian host defense peptides. These immunomodulatory activities include, but are not limited to, direct chemotactic activity, induction of chemokines and other immune mediators, stimulation of leukocyte degranulation and other microbicidal activities, effects on leukocyte and epithelial cell survival and apoptosis, stimulation of epithelial and endothelial cell proliferation, promotion of wound healing and angiogenesis, antiendotoxic and anti-inflammatory activities, and adjuvant fiinctions. These will be described in detail in the following sections and a summary is found in Table 1. 

Expression of peroxidases that catalyze crosslinking reactions can he induced by wounding or infection. Well-documented examples include the production of acidic peroxidase isoenzymes in woimded tissue of tobacco (132), potato (133), and tomato (134), and also in wheat plants infected with the powdery mildew fungus, Erysiphe graminis (135). It is known that peroxidase activity can be induced on wounding of horseradish leaves (56), but other mechanisms of defense in horseradish remain to be demonstrated. 

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