1. an inorganic antioxidant in life impacting atmospheric chemistry
Iodide in kelp:
an inorganic antioxidant in life impacting atmospheric chemistry
Frithjof C. Küpper

2. Biological model: Laminaria digitata (Phaeophyceae)

3. Iodine as a novel chemical element was discovered in the ashes of Laminaria
Courtois, B. (lu par / read by N. Clément), 1813:
Découverte d’une substance nouvelle dans le Vareck.
Annales de Chimie 88,

4. Iodine accumulation in Laminaria
Laminariales (kelps) are a major biogeochemical pump of iodine!
Laminaria is the strongest iodine accumulator in life
Still unclear:
Chemical form of accumulated iodine?
Biological significance?

5. The Global Iodine Cycle
iodine oxide (IO), and: I-, IO3-, HOI
Thyroid lactoperoxidase-catalysed incorporation in thyroxine
IO provides condensation nuclei for cloud formation
photolysis
precipitation
I2, iodocarbons (R-I)
(CH2I2, CHI3, CHI3 etc.)
diet
CH3I
“Iodovolatilisation”
fertilizers
dietary supple- ments
kelp forests
and planktonic algae
(accumulation of iodine, iodinated natural products)
euphotic zone
+ organic matter
Nitrate reductase
(phytoplankton, bacteria?)
I2, HOI
IO3- I-
terrestrial runoff
+ O2, O3 or H2O2
deep waters
IO3- (predominantly)
I- (release of small amounts from POC)
fossil iodide / iodate deposits
H2S
Bacterial decomposition
Millions of years ago
R-I R + I-
sediments
Adapted / modified from Feiters, Küpper & Meyer-Klaucke, 2005: J. Synchrotr. Radiation 12, 85-93

6. Iodine accumulation in Laminaria
Requirement of an intact cell wall (apoplast)
Role of hydrogen peroxide and haloperoxidases in iodine uptake
Iodine efflux upon oxidative stress
Küpper, F.C.; Schweigert, N.; ArGall, E.; Legendre, J.M.; Vilter, H.; Kloareg, B., 1998: Iodine uptake in Laminariales involves extracellular, haloperoxidase-mediated oxidation of iodide. Planta 207,

7. Iodine accumulation in Laminaria
Strong seasonality!
Iodine content (% DW) 1 2 3
Winter Spring Summer Autumn
ArGall, E.; Küpper, F.C.; Kloareg, B., 2004: A survey of iodine contents in Laminaria digitata. Botanica Marina 47,

8. Iodine accumulation in Laminaria
Accumulation in cortical tissues
(stipe section)
25 mm
Particle-induced X-ray emission
Elemental map of the meristoderm and outer cortes in a L. digitata stipe section
Verhaeghe, E.F.; Fraysse, A.; Guerquin-Kern, J.-L.; Wu, T.-D.; Devès, G.; Mioskowski, C.; Leblanc, C.; Ortega, R.; Ambroise, Y.; Potin, P., 2008: Microchemical imaging of iodine distribution in the brown alga Laminaria digitata suggests a new mechanism for its accumulation. Journal of Biological Inorganic Chemistry 13,

9. Iodine accumulation in Laminaria
Techniques used in this study:
GC/MS
Gas-phase particle counters
Cathodic stripping square wave voltammetry (CSSWV)
X-ray absorption spectroscopy using synchrotron radiation (XAS)
etc.

10. Biological XAS at the EMBL Outstation, Hamburg

11. Biological XAS at the EMBL Outstation, Hamburg

12. Iodine XAS of Laminaria tissues
(Iodine K-edge)
Iodide (I-) is the accumulated form of iodine in Laminaria!

13. Iodine metabolism and oxidative stress
Iodine uptake requires low H2O2 levels (< 25 mM)
Higher concentrations of H2O2 result in iodine efflux
Oxidative stress in Laminaria:
Oxidative (respiratory) burst – a defense reaction
Desiccation, high temperatures, high irradiance and exposure to atmospheric oxidants at low tide

14. The oxidative burst in Laminaria
A key element in eukaryotic innate immunity
Triggers in Laminaria: bacterial endotoxins (LPS), oligoguluronates (oligoalginates)
120 s 1 2 3
420 s 1 2 3
660 s 1 2 3
840 s 1 2 3
DCFH-DA : dichlorohydro- fluorescein diacetate
Küpper et al., 2001: Plant Physiology 125,

15. Monitoring the iodine pool during the oxidative burst in Laminaria with XAS
EXAFS: Oxidative stress results in a change of the solution environment of accumulated iodide (towards an aqueous, hydrated form)
XANES: No changes in the redox state of iodine – only iodide is detectable

16. Cathodic stripping square wave voltammetry (CSSWV)
Oligoguluronate treatment
Strong iodide efflux upon oxidative stress
No increased levels of oxidized or organic iodine species

17. Scavenging of ozone (O3) by Laminaria
Laminaria thalli effectively scavenge ozone
When light is present: ultrafine particle formation

18. Kelp forests contribute to aerosol formation in the coastal environment
Iodine oxides as condensation nuclei
“Particle bursts” in the coastal atmosphere above kelp beds at low tide and high irradiance
O’Dowd et al., 2002: Nature 417, 632-6

19. Kelp forests contribute to aerosol formation in the coastal environment
O’Dowd et al., 2002: Nature 417, 632-6

20. Kelp iodine emissions into the coastal atmosphere
“Iodovolatilisation” discovered in 1920s by Kylin and Dangeard: I2 detected with starch paper
J. Lovelock, 1973: Discovery of methyl iodide emissions from seaweeds
B. Alicke et al., 1999: High IO levels above kelp beds at low tide
L.J. Carpenter et al., 2000: CH2I2 main species emitted by Laminaria (total iodine emissions: 0.09 – 0.5 pmol g FW-1 min-1)
This study: High I2 fluxes due to reaction of O3 with I- on seaweed surface (130 pmol g FW-1 min-1)

21. You can smell it! I2
Taynish National Nature Reserve, Argyll, Scotland, June 8, 2008