Occurrence of mycosporine-like amino acids in the red-tide dinoflagellate Alexandrium excavatum: UV-photoprotective compounds?

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Abstract
Water extracts of the red-tide dinoflagellate Alexandrium excavatum grown at ''high'' light intensity (200 .mu.E m-2 s-1) show a broad absorbance maximum in the UV region of the spectrum (310-360 nm). Using TLC and reverse-phase HPLC a series of mycosporine-like amino acids have been characterized: mycosporine-glycine (.lambda.max = 310 nm), palythine (.lambda.max = 320 nm), asterina-330 (.lambda.max = 330 nm), shinorine (.lambda.max = 334 nm), porphyra-334 (.lambda.max = 334 nm), palythenic acid (.lambda.max = 337 nm) and the isomeric mixture of usujirene and palythene (.lambda.max = 359 nm). From the observed spectral changes during transference from ''low'' (20 .mu.E m-2 s-1) to ''high'' (200 .mu.E m-2 s-1) light intensities and vice versa, the series of compounds are supposed to be biogenically related to one another. The presence of these compounds in A. excavatum is discussed in relation to their possible role in the photoprotection to deleterious UV radiation.