MEPS 247:43-50 (2003)  -  doi:10.3354/meps247043

Laminaria saccharina photosynthesis measured in situ: photoinhibition and xanthophyll cycle during a tidal cycle

François Gévaert1,*, Anne Créach1, Dominique Davoult2, Aline Migné3, Guy Levavasseur2, Pierre Arzel4, Anne-Catherine Holl1, Yves Lemoine1

1UMR CNRS 8013 ŒELICO¹, Equipe de Cytophysiologie Végétale et Phycologie, Université des Sciences et Technologies de Lille, Bât SN2, 59655 Villeneuve d¹Ascq Cedex, France
2UMR CNRS 7127, Université de Paris VI, Station Biologique, 29682 Roscoff Cedex, France
3IFR-101, Laboratoire d¹Hydrobiologie, Université de Paris VI, 12 rue Cuvier, 75005 Paris, France
4Laboratoire côtier DRV/RH, IFREMER, Centre de Brest, BP 70, 29280 Plouzané, France

ABSTRACT: Photosynthetic activity in thalli of Laminaria saccharina (Lamouroux) was followed in situ in the upper subtidal zone of a Northern Brittany rocky shore (Roscoff, France), using a submersible pulse amplitude modulated (PAM) fluorometer. Two fluorescence parameters, the effective quantum yield of photosystem II (ΦPSII) and the relative electron transport rate (rETR), were estimated at various stages of a tidal cycle from 10:00 to 18:30 h, and different light conditions due to variations of water depth and position of the sun. The ΦPSII decreased strongly during the ebb tide, essentially due to a drop in the maximal fluorescence level for light-adapted samples (Fm¹). This was the result of increasing non-photochemical quenching (NPQ). Algae totally recovered during the rising tide, indicating that no significant photosynthetic damage occurred at ebb tide. L. saccharina responded to high light stress with photoprotective processes such as the xanthophyll cycle. The de-epoxidation ratio (DR) (i.e. conversion of violaxanthin into antheraxanthin and zeaxanthin) increased during the ebb tide and decreased during the rising tide. However, in spite of the development of a photoprotective mechanism, the overall photosynthetic activity (rETR) declined strongly at the highest irradiance level. This result indicates that primary production levels have been overestimated in the past.

KEY WORDS: Laminaria saccharina · Photoprotection · Xanthophyll cycle · Chlorophyll fluorescence · Diurnal tidal cycles · Diving PAM

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