Abstract
Chemical defense of the invasive red alga Gracilaria vermiculophylla has been studied and compared to that of the noninvasive but related Gracilaria chilensis. Both species rely on a wound-activated chemical defense that makes them less attractive to the herbivorous sea snail Echinolittorina peruviana. The chemical stress response of both species was monitored by LC–ESIMS-based metabolic profiling and revealed commonalities and differences. Both algae rely on a rapid lipoxygenase mediated transformation of arachidonic acid to known and novel oxylipins. Common products are 7,8-dihydroxyeicosatetraenoic acid and a novel eicosanoid with an unusual γ-lactone moiety. Several prostaglandins were predominantly formed by the invasive species. The role of some of these metabolites was investigated by surveying the attachment of E. peruviana on artificial food containing the respective oxylipins. Both algae species are defended against this general herbivore by 7,8-dihydroxyeicosatetraenoic acid, whereas the prostaglandins and the novel oxylipins were inactive at naturally occurring concentrations. The role of different oxylipins in the invasive potential of Gracilaria spp. is discussed.
Highlights
The red alga Gracilaria chilensis is native along the Chilean coast and is commercially farmed for the production of agar hydrocolloids [1]
As reported previously, wounding of G. chilensis triggers the pronounced formation of arachidonic acid derived oxylipins, including the most dominant 7,8-di-HETE (3) and 8-hydroxyeicosatetraenoic acid (8-HETE (4)) [3]
The chemical defense of Gracilaria spp. against E. peruviana is stimulated by tissue disruption and proceeds via the release of arachidonic acid derived oxylipins
Summary
The red alga Gracilaria chilensis is native along the Chilean coast and is commercially farmed for the production of agar hydrocolloids [1]. Recent work indicates that the invasive G. vermiculophylla relies on wound-activated transformations of arachidonic acid for its chemical defense. Bioassays with the generalist isopod grazer Idotea baltica, which is found in the areas in which G. vermiculophylla is invasive, revealed that among all the detected oxylipins a minor prostaglandin is responsible for the chemical defense [6].
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