iodide in kelp: an inorganic antioxidant in life impacting atmospheric chemistry frithjof c. küpper
TRANSCRIPT
Iodide in kelp: an inorganic antioxidant in life impacting atmospheric
chemistry
Frithjof C. Küpper
Biological model: Laminaria digitata (Phaeophyceae)
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
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
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
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
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
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
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.
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
Biological XAS at the EMBL Outstation, Hamburg
Iodine XAS of Laminaria tissues
Iodide (I-) is the accumulated form of iodine in Laminaria!
(Iodine K-edge)
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
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
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
Cathodic stripping square wave voltammetry (CSSWV)
Strong iodide efflux upon oxidative stress
Oligoguluronate treatment
• No increased levels of oxidized or organic iodine species
Scavenging of ozone (O3) by Laminaria
Laminaria thalli effectively scavenge ozone
When light is present: ultrafine particle formation
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
Kelp forests contribute to aerosol formation
in the coastal environment
O’Dowd et al., 2002:Nature 417, 632-6
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)
You can smell it!
I2 I2
Taynish National Nature Reserve, Argyll, Scotland, June 8, 2008