Iodine in seaweeds -- two centuries of research
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| Abstract |
This paper provides a historic overview of the research on iodine in seaweeds, starting with historic uses of iodine-containing seaweeds in ancient China and Greece. Iodine as a novel element was discovered by Courtois in Napoleon-era France. This triggered research on the chemical properties of the novel element and also started an iodine-producing seaweed industry. However, iodine-containing seaweeds did not receive much academic attention until the end of the nineteenth century, when the release of molecular iodine from red algae was discovered, followed by similar findings in brown algae (kelp) three decades later. The 1950s saw the rise of studies of iodine uptake in kelp, based on the availability of radioactive iodine isotopes. Since the 1970s, a wealth of studies has investigated the emission of iodo- and other halocarbons from seaweeds and their role in the atmospheric and marine environments. Our group has addressed the physiology and biochemistry of iodine uptake in Laminaria since the 1990s. This has established the involvement of both hydrogen peroxide and vanadium haloperoxidases in the process and led to the finding of iodine efflux upon oxidative stress. X-ray absorption spectroscopy identified the accumulated form as iodide, constituting an antioxidant protecting the cell wall space and surface of kelp against oxidative stress. Iodide in Laminaria constitutes the first inorganic and chemically simplest antioxidant known from a living system. Upon exposure to atmospheric ozone, this leads to the emission of molecular iodine and, together with high irradiance, to the formation of ultrafine particles. |
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