Alexandrium

Figure 1. Structures of the twelve saxitoxins found in Alexandrium sp.

Gymnodinium catenatwn, first recognized as a cause of toxicity in an outbreak in Mazatlan (43,44), lacks a theca but otherwise bears some resemblance to the catenate Alexandrium species. It has now been recognized as a source of PSP in Spain (45), Portugal (46), Venezuela (A. La Barbera-Sanchez, personal communication), Tasmania (47), and Japan (48),... 

Figure 7A. The toxigenic dinoflagellate Alexandrium sp. from Southeast Alaska. Two vegetative cells of clone EC06, from Elfin Cove. Bar is 30 xm. Photomicrography by R. A. Horner.

Figure 8. Origins of Alexandrium cultures used for the analyses of toxin composition summarized in Table I. Data from Ref. 10.

Table I. Toxin Composition of Alexandrium from the Northeast Pacific...

As discussed above, there is the possibility that toxigenesis in Alexandrium is not intrinsic but due to symbionts. Whichever proves to be the case, the observed patterns of toxin composition, whether they are for the dinoflagellate itself or the isolated assemblage of dinoflagellate and symbiont, are a basis for recognizing and distinguishing the regional populations. 

Sensitivity of bivalves to the saxitoxins appears to be more general than has been recognized. Shellfish that contain levels of the saxitoxins that make them dangerous for human consumption can seldom be distinguished visibly from those that are safe. Nevertheless, detailed study has shown (64 R. Mann and S. Hall, unpublished results) that Alexandrium cells have significant effects on bivalve responses, presumably due to the contained saxitoxins. 

Agelasine, 320 Aiptasia pallida, 304,310 Aiptasia species, toxic protein, 321 Aiptasiolysin, 304,310 Alexandrium dinoflagellates clones, 36,38-3 saxitoxin source, 21 toxicity, 36... 

Some dinoflagellates of the genus Alexandrium produce neurotoxic compounds known as paralytic shellfish poisoning (PSP) toxins. Because these toxins can contaminate filter-feeding shellfish they may threaten public health and create economic problems for fisheries. PSP-toxins include at least a dozen saxitoxins, neosaxitoxins, and gonyautoxins (Scheme 1). 

Wyatt, T. and Jenkinson, I.R. (1997). Notes on Alexandrium population dynamics. Journal of Plankton Research 19 551-575. 

Rapid-acting paralytic neurotoxins that blocks transient sodium channels and inhibits depolarization of nerve cells. They are some of the causative agents of paralytic shellfish poisoning (PSP). They are obtained from dinoflagellates (Gonyaulax spp., Alexandrium spp.) and cyanobacteria (Anabaena circinalis). 

The paralytic shellfish toxins (PSTs Fig. 5.2a) include saxitoxin (STX) as well as STX analogs such as neo-saxitoxin (neo-STX), gonyautoxin (GTX), and the decar-bamoyltoxins (Sivonen and Jones 1999). These molecules are of particular concern in marine systems, where they have been implicated in human deaths following the consumption of contaminated seafood (Van Dolah 2000). The causative agents in those cases are several genera of marine dinoflagellates that are common components of red tides (e.g., Alexandrium sp. Homer et al. 1997 Van Dolah 2000). 

Colin SP, Dam HG (2002) Latitudinal differentiation in the effects of the toxic dinoflagellate Alexandrium spp. on the feeding and reproduction of populations of the copepod Arcatia hudsonica. Harmful Algae 1 113-125... 

Caretto JI, Lutz VA, De Marco SG, Carignan MO (1990) Fluence and wavelength dependence of mycosporine-like amino acid synthesis in the dinoflagellate Alexandrium excavatum. In Graneli E, Edler L, Sundstrom B, Anderson DM (eds) Toxic marine phytoplankton. Elsevier, Amsterdam, pp 275-279... 

Several phenolic acids and many nonspecific allelopathic conditions have been shown to alter the mineral content of plants, and certainly phenolic allelochemicals may perturb cellular functions in a number of ways that are of importance to plant nutrition (34,35). However, raising fertility does not always suppress allelopathic inhibition, and the interrelationships between these two factors are still not clear. Bhowmik and Doll (36) showed that allelopathic inhibition of corn and soybeans by residues of five annual weeds was not alleviated by supplemental nitrogen or phosphorus. Similarly, an increase in fertilizer did not overcome inhibition of corn by quackgrass or circumvent the autotoxicity of berseem clover Trifolivm alexandrium L.) (37,38). Even when raising nutrient levels releases Inhibition, it does not mean that allelopathy was inoperative under the original conditions. These instances simply illustrate the importance of the Interaction of the two stress conditions. 

Anderson, D.M. Scholin, C.A. (1997) Genetie markers derived from rRNAs and their use in deteetion of Alexandrium species of dinoflagellates associated with red tides. US Patent 5,582,983. Chem. Abstr., 1997, 126, 101706k. 

Kodama, M. Sato, S. Sakamoto, S. Ogata, T. (1996) Occurrence of tetrodotoxin in Alexandrium tamarense, a causative dinoflagellate of paralytic shellfish poisoning. Toxicon, 34, 1101-5. 

Murakami, M. Okita, Y. Matsuda, H. Okino, T. Yamaguchi, K. (1998) From the dinoflagellate Alexandrium hiranoi. Phytochemistry, 48, 85-8. 

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