Iodide accumulation provides kelp with an inorganic antioxidant impacting atmospheric chemistry.
Brown algae of the Laminariales (kelps) are the strongest accumulators of iodine among living organisms. They represent a major pump in the global biogeochemical cycle of iodine and, in particular, the major source of iodocarbons in the coastal atmosphere. Nevertheless, the chemical state and biological significance of accumulated iodine have remained unknown to this date. Using x-ray absorption spectroscopy, we show that the accumulated form is iodide, which readily scavenges a variety of reactive oxygen species (ROS). We propose here that its biological role is that of an inorganic antioxidant, the first to be described in a living system. Upon oxidative stress, iodide is effluxed. On the thallus surface and in the apoplast, iodide detoxifies both aqueous oxidants and ozone, the latter resulting in the release of high levels of molecular iodine and the consequent formation of hygroscopic iodine oxides leading to particles, which are precursors to cloud condensation nuclei. In a complementary set of experiments using a heterologous system, iodide was found to effectively scavenge ROS in human blood cells.
Küpper
Frithjof C
FC
Scottish Association for Marine Science, Dunstaffnage Marine Laboratory, Oban, Argyll PA37 1QA, Scotland, United Kingdom. fck@sams.ac.uk
Carpenter
Lucy J
LJ
McFiggans
Gordon B
GB
Palmer
Carl J
CJ
Waite
Tim J
TJ
Boneberg
Eva-Maria
EM
Woitsch
Sonja
S
Weiller
Markus
M
Abela
Rafael
R
Grolimund
Daniel
D
Potin
Philippe
P
Butler
Alison
A
Luther
George W
GW
Kroneck
Peter M H
PM
Meyer-Klaucke
Wolfram
W
Feiters
Martin C
MC
D000975:Antioxidants / Q000378:metabolism*; D001272:Atmosphere / Q000737:chemistry*; D016166:Free Radical Scavengers / Q000378:metabolism; D006603:Hexuronic Acids / Q000494:pharmacology; D007454:Iodides / Q000378:metabolism*; D044423:Kelp / Q000378:metabolism*; D007795:Laminaria / Q000378:metabolism; D008954:Models, Biological; D010126:Ozone; D016897:Respiratory Burst; D013057:Spectrum Analysis; D013997:Time Factors
D000975:Antioxidants; D016166:Free Radical Scavengers; D006603:Hexuronic Acids; D007454:Iodides; C007896:guluronic acid; D010126:Ozone