MEPS 279:297-303 (2004)  -  doi:10.3354/meps279297

Packaging of mycosporine-like amino acids in dinoflagellates

Isabelle Laurion1,2,*, Frédérick Blouin1,3, Suzanne Roy1

1Institut des Sciences de la Mer, Université du Québec à Rimouski, 310 Allée des Ursulines, Rimouski, Québec G5L 3A1, Canada 2Present address: Institut national de la recherche scientifique, Centre Eau, Terre et Environnement, 2800 rue Einstein, CP 7500, Ste-Foy, Québec G1V 4C7, Canada 3Present address: Centre de Recherche sur les Biotechnologies Marines, 265 2ième Rue Est, Rimouski, Québec G5L 9H3, Canada

ABSTRACT: Synthesis of mycosporine-like amino acids (MAAs) can significantly protect phytoplankton cells against damaging ultraviolet (UV) radiation, depending on the concentration, type and cellular distribution of these UV sunscreens. We addressed the hypothesis that MAAs are concentrated around UV-sensitive organelles for improved efficiency, thereby increasing their Œpackage effect¹. This was investigated for 2 species of MAA-producing dinoflagellates, with comparative analyses of a MAA-free diatom. Spectral absorbance of dinoflagellates suspended in their growth medium was relatively small throughout the MAA-absorbing region despite high concentrations of these compounds (determined by HPLC), suggesting that MAAs are highly packaged in intact cells. The measured in vivo absorbance of suspended and filtered phytoplankton cells revealed an extracellular release of water-soluble MAAs during freezing. The release of MAAs upon thawing enabled the calculation of an MAA packaging index based on the comparison between absorption characteristics before (MAAs inside cells in suspension) and after freezing (MAAs released from cells on thawed filters). Additionally, MAA packaging was evaluated from the reconstruction of absorption spectra from the individual MAA concentration. Consistent with our hypothesis, the results showed that UV absorption was up to 80% lower in the intact cells relative to the MAAs dissolved in solution. These results imply a high degree of MAA packaging in these dinoflagellates, that may increase the protection efficiency for specific cellular targets.

KEY WORDS: Package effect · Photoprotection · MAAs · UV-absorbing compounds · Bio-optics · Alexandrium tamarense

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