MEPS 292:139-146 (2005)  -  doi:10.3354/meps292139

Comparison of photosynthetic responses in diploid and haploid life-cycle phases of Emiliania huxleyi (Prymnesiophyceae)

Aude Houdan1, Ian Probert1, Kees Van Lenning2, Sébastien Lefebvre1,*

1Laboratoire de Biologie et Biotechnologies Marines, Université de Caen, Esplanade de la Paix, 14032 Caen Cedex, France
2Institut de Ciències del Mar, CMIMA, Passeig Marítim 37–49, 08003 Barcelona, Spain
*Corresponding author. Email:

ABSTRACT: Emiliania huxleyi is a ubiquitous coccolithophore, capable of forming large blooms. This species presents a digenetic heteromorphic life cycle, the non-motile diploid phase typically bearing coccoliths and the flagellated haploid phase being non-calcified. Oxygen production rates at different irradiances of both phases were studied in mid-exponential and transitional growth phases in cultures grown under identical conditions. There were no significant differences in basic photosynthetic parameters (αchl a , maximum light utilization coefficient; Pchl amax, the light-saturated maximal rate of photosynthesis; Ek, the light-saturation parameter) between the 2 life-cycle phases; however, whereas the diploid phase did not exhibit photoinhibition at irradiances up to 1000 µmol photons m–2 s–1, photoinhibition was recorded in the haploid phase above 400 to 500 µmol photons m–2 s–1 and photosynthetic rate decreased to ca. 75% of Pmax at 1400 µmol photons m–2 s–1. The 2 phases cultured under identical (non-saturating in terms of light) conditions did not present any significant differences in pigment content. These results are discussed in an ecological context. The lack of photoinhibition could confer a competitive advantage on the diploid stage, notably in a turbulent environment. For the haploid stage, the occurrence of photoinhibition may indicate niche separation (spatial and/or temporal) relative to the diploid phase.

KEY WORDS: Emiliania huxleyi · Coccolithophore · Life cycle · Haplo-diploid · Photosynthesis · Pigments

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