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![Page 1: Iodide in kelp: an inorganic antioxidant in life impacting atmospheric chemistry Frithjof C. Küpper.](https://reader036.fdocuments.us/reader036/viewer/2022070401/56649f1f5503460f94c36f38/html5/thumbnails/1.jpg)
Iodide in kelp: an inorganic antioxidant in life impacting atmospheric
chemistry
Frithjof C. Küpper
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Biological model: Laminaria digitata (Phaeophyceae)
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Courtois, B. (lu par / read by
N. Clément), 1813:
Découverte d’une substance
nouvelle dans le Vareck.
Annales de Chimie 88, 304-
310
• Iodine as a novel chemical element was discovered in the ashes of Laminaria
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Iodine accumulation in Laminaria
• Laminariales (kelps) are a major biogeochemical pump of iodine!
Still unclear:
• Chemical form of accumulated iodine?
• Biological significance?
• Laminaria is the strongest iodine accumulator in life
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The Global Iodine Cycle
euphotic zone
kelp forestsand planktonic algae(accumulation of iodine, iodinated natural products)
IO3-
Nitrate reductase(phytoplankton, bacteria?)
I2, iodocarbons (R-I)(CH2I2, CHI3, CHI3 etc.)
iodine oxide (IO),
and: I-, IO3-, HOI
photolysis
“Iodovolatilisation”
IO provides condensationnuclei for cloud formation
precipitation
terrestrial runoff
diet
Thyroidlactoperoxidase-catalysedincorporation in thyroxine
fossil iodide / iodate deposits
dietarysupple-ments
fertilizers
Millions of years ago
deep waters
sedimentsR-I R + I-
H2S
Bacterial decomposition
IO3-
(predominantly) I-
(release of small amounts from POC)
I2, HOI
+ O2, O3 or H2O2
CH3I
+ organicmatter
I-
Adapted / modified from Feiters, Küpper & Meyer-Klaucke, 2005: J. Synchrotr. Radiation 12, 85-93
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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, 163-171
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Iodine accumulation in Laminaria
• Strong seasonality!
ArGall, E.; Küpper, F.C.; Kloareg, B., 2004: A survey of iodine contents in Laminaria digitata. Botanica Marina 47, 30-37.
Iodi
ne c
onte
nt (
% D
W)
0
1
2
3
Winter Spring Summer Autumn
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Iodine accumulation in Laminaria
• Accumulation in cortical tissues
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, 257-269.
(stipe section)
25 m
Particle-induced X-ray emissionElemental map of the meristoderm and outer cortes in a L. digitata stipe section
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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.
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Biological XAS at the EMBL Outstation, Hamburg
e+
synchrotron
whitebeam
Al foilslits 1
slits 2
focussingmirrororder sorting
double crystalmonochromator
(Si 111)
sample
ionizationchambers
I0 It
13 elementfluorescence
detector
calibrator crystal(Si 220) withscintillation
counters
monochromaticbeam
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Biological XAS at the EMBL Outstation, Hamburg
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Iodine XAS of Laminaria tissues
Iodide (I-) is the accumulated form of iodine in Laminaria!
(Iodine K-edge)
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Iodine metabolism and oxidative stress
• Iodine uptake requires low H2O2 levels (< 25 M)
• 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
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The oxidative burst in Laminaria• A key element in eukaryotic innate immunity
• Triggers in Laminaria: bacterial endotoxins (LPS), oligoguluronates (oligoalginates)
120 s
123
420 s
123
660 s
123
840 s
123
DCFH-DA : dichlorohydro-fluorescein diacetate
Küpper et al., 2001: Plant Physiology 125, 278-91
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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
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Cathodic stripping square wave voltammetry (CSSWV)
Strong iodide efflux upon oxidative stress
Oligoguluronate treatment
• No increased levels of oxidized or organic iodine species
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Scavenging of ozone (O3) by Laminaria
Laminaria thalli effectively scavenge ozone
When light is present: ultrafine particle formation
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Kelp forests contribute to aerosol formation
in the coastal environment
O’Dowd et al., 2002: Nature 417, 632-6
• Iodine oxides as condensation nuclei• “Particle bursts” in the coastal atmosphere
above kelp beds at low tide and high irradiance
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Kelp forests contribute to aerosol formation
in the coastal environment
O’Dowd et al., 2002:Nature 417, 632-6
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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)
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You can smell it!
I2 I2
Taynish National Nature Reserve, Argyll, Scotland, June 8, 2008