Paris, May 6, 2008

Iodide build-up in brown algae influences the coastal climate

An international team(1) including Philippe Potin, a researcher at the Marine Plants and Biomolecules Laboratory (CNRS/Université Paris), has revealed the chemical form of iodide by using synchrotron rays. Iodide is used by large brown Laminaria algae (kelp) to store iodine(2) . The iodide (a simple, negatively charged ion) is released, in the event of stress, and acts as an antioxidant(3) - the first known inorganic agent in living organisms – protecting the alga from cell damage. The element, oxidized in the form of gaseous molecular iodine, participates in cloud formation and influences the coastal climate. The study has thrown light on algal defense mechanisms against stress factors, and is published on the website of the journal Proceedings of the National Academy of Science of the USA (PNAS).

Iodine, discovered in Laminaria two centuries ago by the French chemist Bernard Courtois, is an essential element for human beings, contributing, for example, to the smooth functioning of the thyroid. These algae are known for being the most efficient iodine accumulators on Earth, and for a long time they were the sole source of this widely used antiseptic. However, until now, the chemical form and the biological role of iodine in algae remained an enigma.

When kelp is subject to stress, in other words, when it generates free radicals from oxygen, it rapidly releases large quantities of iodine into the atmosphere. This is what happens, for example, during emersion at low tides when it is subject to dehydration, intense exposure to the sun and atmospheric ozone. Iodide – whose chemical form was identified here – detoxifies ozone and other forms of oxidants outside the cells, thus protecting the alga from cell damage. These reactions contribute to the formation of gaseous molecular iodine released into the air, producing condensation nuclei of water molecules and leading to cloud formation.

In a different context, kelp releases iodide into the sea after oxidant stress, which is part of its defense response to attacks by pathogens such as bacteria, viruses or fungi.

The unusual mechanisms involved in kelp’s protection against stress play a vital role in both iodide’s biogeochemical cycle on Earth and the destruction of ozone in the lower atmosphere. It is a positive element for our environment, as ozone is extremely harmful to human health.

Algues 1

© Pi Nyvall CNRS 2008 (this image can be obtained from the CNRS photo-library,

Photo 1 – a field of kelp (the species Laminaria digitata) emerges at low tide near Roscoff. These algae release iodide, consume ozone and form gaseous molecular iodine, which, when exposed to light, forms microscopic particles with ozone. They condense water molecules and lead to cloud formation.

Algues 2

© Pi Nyvall CNRS 2008 (this image can be obtained from the CNRS photo-library,

Photo 2 – emerged kelp at low tide near Roscoff.


1) This interdisciplinary study brings together contributions from CNRS, the United Kingdom, the Netherlands, Germany, Switzerland, the USA and EMBL (European Molecular Biology Laboratory).
2) Last February, a French consortium led by Philippe Potin within the framework of the interagency program on Environmental Nuclear Toxicology (CNRS-CEA-INSERM-INRA) revealed the location of this stock of iodide in kelp tissues and cells by using ionic microscopes and nuclear microprobes. Iodide is stored outside the cell, in the cell wall, which contains the enzymes and macromolecules involved in iodine accumulation and release mechanisms.
3) The antioxidant agents act against the free radicals generated from oxygen, which participate in cell ageing.


Frithjof C. Küpper, Lucy J. Carpenter, Gordon B. McFiggans, Carl J. Palmer, Tim J. Waite, Eva-Maria Boneberg, Sonja Woitsch, Markus Weiller, Rafael Abela, Daniel Grolimund, Philippe Potin, Alison Butler, George W. Luther III, Peter M. H. Kroneck, Wolfram Meyer-Klaucke, and Martin C. Feiters Iodide accumulation provides kelp with an inorganic antioxidant impacting atmospheric chemistry PNAS published May 5, 2008, 10.1073/pnas.0709959105 (Environmental Sciences-Social Sciences)
View web site

Verhaeghe E, Fraysse A, Guerquin-Kern J-L, Wu, T-D, Devès G, Mioskowski C, Leblanc C, Ortega R, Ambroise, Y, Potin P (2008). Micro-chemical imaging of iodine distribution in the brown alga Laminaria digitata suggests a new mechanism for its accumulation. J. Biol Inorg. Chem., 13: 257-69


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