Polyunsaturated aldehyde

Polyunsaturated aldehydes (PUAs) are a group of allelopathic chemicals typically associated with diatom-copepod predator-prey interactions.[1] These compounds are classified by an aldehyde group covalently bound to long carbon chains containing two or more carbon-carbon double bonds. Examples include isomers of heptadienal, octadienal, octatrienal, and decatrienal.[2]

Production by diatoms

Polyunsaturated aldehydes are oxylipins that are formed from lipids (specifically the fatty acid portion of lipids) when diatoms are exposed to environmental stresses. Stresses can include nutrient limitations, grazing by predators, and wounding.[3]

In particular, damage to diatom cells as a result of grazing by zooplankton invokes a chemical defense mechanism that produces PUA’s as secondary metabolites from fatty acids.[4] The production mechanism is as follows:

  1. Grazing by predators results in diatom cell membrane disruption.
  2. Enzymes (lipases) are produced in response to the damaged membranes. These enzymes make contact with newly freed phospholipids (from cell membranes) and catalyze the formation of polyunsaturated fatty acids.[5]
  3. The enzyme lipoxygenase then catalyzes the reaction of fatty acids to polyunsaturated aldehydes, which are then directly exposed to the grazing zooplankton.[6]

Thalassiosira rotula represents the most well-studied diatom species in terms of polyunsaturated aldehyde production. Wichard et al. determined that only 30% of PUA precursor molecules remain in T. rotula within minutes of cell membrane wounding, indicating a fast rate of response by diatoms to zooplankton grazing.[7]

PUA-producing diatoms

T. rotula has been known to produce many types of polyunsaturated aldehydes, including (2E,4E/Z)-hepta-2,4-dienal, (2E,4E/Z,7Z)-deca-2,4,7-trienal, (2E,4E/Z)-octa-2,4-dienal, and (2E,4E/Z,7Z)-octa-2,4,7-trienal. These particular aldehydes are also produced by Stephanopyxis turris and Skeletonema costatum in response to wounding.[7] Phaeocystis pouchetii and Skeletonema marinoi also produce various octadienal and heptadienal isomers.[8]

Effects on zooplankton

Copepods are known to be the primary consumers of diatoms in the water column and initiate the production of PUA upon grazing.[8] The consumption of PUA-producing diatoms by copepods has been shown to diminish their reproductive success. Specifically, female copepods that consume diatoms spawn eggs with low viabilities and offspring with high teratogenesis rates.[1] The compounds mainly act by preventing cell division and promoting apoptosis in copepod embryos,[9] though the mechanism behind this is still poorly understood.[8]

References

  1. 1 2 Miller, Charles B. Biological Oceanography. Malden, MA: Blackwell Pub., 2004. Print.
  2. ↑ Solomons, T. W. Graham., and Craig B. Fryhle. Organic Chemistry. Hoboken, NJ: John Wiley, 2008. Print.
  3. ↑ Schilmiller, Anthony L., and Gregg A. Howe. "Systemic Signaling in the Wound Response." Current Opinion in Plant Biology 8.4 (2005): 369-77. Web.
  4. ↑ Fontana, Angelo, Giuliana D'ippolito, Adele Cutignano, Antonio Miralto, Adrianna Ianora, Giovanna Romano, and Guido Cimino. "Chemistry of Oxylipin Pathways in Marine Diatoms." Pure and Applied Chemistry 79.4 (2007): n. pag. Web.
  5. ↑ Ribalet, François, Mauro Bastianini, Charles Vidoudez, Francesco Acri, John Berges, Adrianna Ianora, Antonio Miralto, Georg Pohnert, Giovanna Romano, Thomas Wichard, and Raffaella Casotti. "Phytoplankton Cell Lysis Associated with Polyunsaturated Aldehyde Release in the Northern Adriatic Sea." PLoS ONE 9.1 (2014): n. pag. Web.
  6. ↑ Barofsky, Alexandra, and Georg Pohnert. "Biosynthesis of Polyunsaturated Short Chain Aldehydes in the Diatom Thalassiosira Rotula." Org. Lett. Organic Letters 9.6 (2007): 1017-020. Web.
  7. 1 2 Wichard, Thomas, Andrea Gerecht, Maarten Boersma, Serge A. Poulet, Karen Wiltshire, and Georg Pohnert. "Lipid and Fatty Acid Composition of Diatoms Revisited: Rapid Wound-Activated Change of Food Quality Parameters Influences Herbivorous Copepod Reproductive Success." ChemBioChem 8.10 (2007): 1146-153. Web.
  8. 1 2 3 Lavrentyev, Peter, Gayantonia Franzè, James Pierson, and Diane Stoecker. "The Effect of Dissolved Polyunsaturated Aldehydes on Microzooplankton Growth Rates in the Chesapeake Bay and Atlantic Coastal Waters." Marine Drugs 13.5 (2015): 2834-856. Web.
  9. ↑ Miralto A, Barone G, Romano G, Poulet S, Ianora A, et al. (1999) The insidious effect of diatoms on copepod reproduction. Nature 402: 173–176
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