Photosynthetic pigments of oceanic Chlorophyta belonging to prasinophytes clade VII
Résumé
The ecological importance and diversity of pico/nano-planktonic algae remains poorly studied in marine waters, in part because many are tiny and without distinctive morphological features. Amongst green algae, Mamiellophyceae such as Micromonas or Bathycoccus are dominant in coastal waters while prasinophytes clade VII, yet not formerly described, appear to be major players in open oceanic waters. The pigment composition of 14 strains representative of different sub-clades of clade VII was analyzed using a method that improves the separation of loroxanthin and neoxanthin. All the prasinophytes clade VII analyzed here showed a pigment composition similar to that previously reported for RCC287 corresponding to pigment group prasino-2A. However we detected in addition astaxanthin for which it is the first report in prasinophytes. Among the strains analyzed the pigment signature are qualitatively similar within sub-clades A and B. In contrast, RCC3402 from sub-clade C (Picocystis) lacks loroxanthin, astaxanthin and antheraxanthin, but contains alloxanthin, diatoxanthin and monadoxanthin, that are usually found in diatoms or cryptophytes. For sub-clades A and B, loroxanthin was lowest at highest light irradiance suggesting a light–harvesting role of this pigment in clade VII as in Tetraselmis.
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