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Waves. © INRA, Foucaud-Scheunemann Catherine

How phytoplankton rule the oceans

Photosynthesis is a unique biological process that has permitted the colonization of land and sea by plants and phytoplankton respectively. While the mechanisms of photosynthesis in plants are well understood, scientists are only now beginning to elucidate how the process developed in phytoplankton. In collaboration with scientists from several countries1, researchers from the Cell and Plant Physiology Laboratory (CNRS/CEA/UGA/INRA)2, the Institut de Biologie Structurale (CNRS/CEA/UGA), the LEMMA Advanced Electron Microscopy Laboratory (CEA/UGA)3, and the Laboratory of Membrane and Molecular Physiology of the Chloroplast (CNRS/UPMC) have proposed a structural model of the photosynthetic process in phytoplankton, based on studies of the diatom Phaeodactylum tricornutum. Their findings are published in Nature Communications on June 20, 2017.

Updated on 07/28/2017
Published on 06/20/2017

Photosynthesis is a remarkable mechanism for the transformation of light energy into chemical energy. Two miniature photochemical power plants make it possible: photosystem I (PSI) and photosystem II (PSII). But ideal conditions demand that PSI and PSII be kept apart, to avoid any “short circuits” that would make photosynthesis less effective. In plants, the two photosystems are separated by structures (see image A) that do not seem to exist in phytoplankton (see image B). But then how can phytoplankton be responsible for half of all photosynthesis on our planet?

By adapting different high-resolution cellular imaging methods to Phaeodactylum tricornutum, the researchers were able to create a 3D model of the photosynthetic system in diatoms (see image C). They detected microscopic subdomains, permitting separation—as in plants—of the two photosystems for greater efficiency. These findings explain how diatoms may account for approximately 20% of all oxygen production on Earth, and why they have thrived in the oceans for about 100 million years.

The researchers are continuing to develop their 3D model of diatom photosynthesis, which should enable them to understand how these unicellular organisms may adapt to the effects of climate change.  

Top left: plant leaves. Top right: cultured cells of the diatom Phaeodactylum tricornutum.. © CNRS, Pascale Martinez
Top left: plant leaves. Top right: cultured cells of the diatom Phaeodactylum tricornutum. © CNRS, Pascale Martinez

Image A: Electron micrograph of a plant chloroplast revealing its internal structure of grana (shown in yellow), where PSII predominates, and lamellae (shown in green), where PSI is concentrated. This organization is not found in diatoms (see image B).

Image B: Micrograph of P. tricornutum cell showing photosynthetic membranes that are not organized into grana.

Image C: This 3D reconstruction of the photosynthetic membranes reveals membrane subdomains allowing for physical separation of PSI (outside; green) and PSII (inside; yellow) units. The white arrow
points to bridges connecting these subdomains, for maximum photosynthetic yield.

1The French teams worked together with researchers from ETH Zurich (Switzerland) and the University of Konstanz (Germany).
2This is a unit of the Biosciences and Biotechnology Institute of Grenoble (CEA BIG).
3This is a unit of the Institute for Nanosciences and Cryogenics (CEA INAC).

Contact(s)
Scientific contact(s):

Press Relations:
INRA News Office (33 (0)1 42 75 91 86), CNRS press officer - Alexiane Agullo (33 (0)1 44 96 43 90 )
Associated Division(s):
Plant Biology and Breeding
Associated Centre(s):
Auvergne-Rhône-Alpes

Reference

Serena Flori, Pierre-Henri Jouneau, Benjamin Bailleul, Benoit Gallet, Leandro F.Estrozi, Christine Moriscot, Olivier Bastien, Simona Eicke, Alexander Schober, Carolina Río Bártulos, Eric Maréchal, Peter G. Kroth, Dimitris Petroutsos, Samuel Zeeman, Cécile Breyton, Guy Schoehn, Denis Falconet, and Giovanni Finazzi. Plastid thylakoid architecture optimises photosynthesis in diatoms. Nature Communications, 20 June 2017. DOI: 10.1038/NCOMMS15885