Part D | 23
594 Part D Marine Algal Biotechnology
have to accumulate this element to such extreme levels? For this, it seemed crucial to first unambiguously
clarify the chemical speciation of accumulated iodine.
In fact, various and sometimes contradictory opinions
existed about the chemical state of iodine in Laminaria.
To this end, we used a non-invasive technique, X-ray
absorption spectroscopy, thus excluding the possibility of artifacts upon extraction [23.37]. This approach
revealed that the accumulated form is, indeed, iodide,
which is contained in a largely organic (rather than hydrated) environment. Upon oxidative stress such as an
oxidative burst [23.28, 38–40], a transition to a more
hydrated form occurs. Concomitantly, a strong efflux
of accumulated iodide occurs. Altogether and in light
of the hypothesis of Venturi [23.41], our results suggest that iodide serves the function of an antioxidant,
protecting the apoplast (cell wall space) of the cortical
cell layers. This constitutes the description of the first
inorganic and of the chemically simplest antioxidant
known from a living system [23.29]. Indeed, the reaction of iodide with the major reactive oxygen species
is both thermodynamically and kinetically favorable.
With the involvement of vanadium haloperoxidase and
in the absence of organic co-substrates, iodide effectively degrades H 2 O 2 (halide-assisted disproportionation of hydrogen peroxide). Furthermore, the millimolar
iodide levels on the Laminaria surface exposed at low
tide effectively scavenge atmospheric ozone, leading to
the release of I 2 – at rates up to about five orders of
magnitude higher than the combined iodocarbon emissions. These studies [23.16, 29] unambiguously clarify
the biochemical origin of particle-forming iodine oxides. Molecular iodine is photolyzed and further oxidized by ozone in the marine boundary layer, producing
hygroscopic iodine oxides. The latter form ultrafine
particles, leading to aerosol formation and establishing
a unique link between a biological antioxidant and climatic processes [23.30].
The current understanding of iodine metabolism is
summarized in Fig. 23.1. Using X-ray absorption spectroscopy in combination with other techniques, we have
recently demonstrated that bromide complements iodide as an antioxidant in particular with regards to
superoxide detoxification and that overall, its function
is more diverse than that of iodide in algal physiology [23.42].
In the 200 years since its discovery, research on iodine has developed into multiple areas of science, far
beyond marine algae where it was originally found and
beyond the scope of this chapter. In this context, we
would like to highlight a recent interdisciplinary review
article by an international consortium [23.43] that covers the many fascinating facets of iodine science and
applications ranging from the history of its discovery
to general, marine, atmospheric, environmental, radioand geochemistry, medicine and physiology, materials
science (in particular including semiconductors and solar cells), and organic synthesis.
References
23.1
L.R. McDowell: Iodine. In: Minerals in Animal and
Human Nutrition, ed. by L.R. McDowell (Academic
Press, San Diego 1992) pp. 224–245
23.2
L. Rosenfeld: Discovery and early uses of iodine,
J. Chem. Educ. 77(8), 984–987 (2000)
23.3
J. Wisniak: Bernard courtois – The discoverer of iodine, Educ. Quim. 13(3), 206–213 (2002)
23.4
F.C. Kelly: Iodine in medicine and pharmacy since
its discovery – 1811–1961, Proc. R. Soc. Med. 54, 831–
836 (1961)
23.5
B. Courtois: Découverte d’une substance nouvelle
dans le Vareck, Ann. Chimie 88, 304–310 (1813)
23.6
J.-L. Gay-Lussac: Sur la combinaison de l’iode avec
l’oxygène, Ann. Chimie 88, 319–321 (1813)
23.7
L.-J. Gay-Lussac: Sur un nouvel acide formé avec la
substance découverte par M. Courtois, Ann. Chimie
88, 311–318 (1813)
23.8
H. Davy: Some experiments and observations on
a new substance which becomes a violet coloured
gas by heat, Philos. Trans. R. Soc. 104, 74–93 (1814)
23.9
J.M. Synge: The Aran Islands (Maunsel, Dublin
1907)
23.10 N.N. Eschle: Ueber den Jodgehalt einiger algenarten, Z. Physiol. Chem. 23, 30–37 (1897)
23.11 M. Golenkin: Algologische Notizen 1, Das Vorkommen von freiem Iod bei Bonnemaisonia asparagoides, Bull. Soc. Imp. Nat. Mosc. 8, 257–270
(1894)
23.12 C. Sauvageau: Sur quelques algues floridées renfermant de l’iode à l’état libre, Bull. Station Biol.
d’Arcachon. 22, 3–43 (1925)
23.13 H. Kylin: Über das Vorkommen von Jodiden, Bromiden und Jodidoxydasen bei Meeresalgen, HoppeSeyler’s Z. Physiol. Chem. 186, 50–84 (1929)
23.14 P. Dangeard: Sur le dégagement de l’iode chez les
algues marines, C. R. Acad. Sci. Paris 186, 892–894
(1928)
23.15 G.B. McFiggans, H. Coe, R. Burgess, J. Allan,
M. Cubison, M.R. Alfarra, R. Saunders, A. SaizLopez, J.M.C. Plane, D.J. Wevill, L.J. Carpenter,
594 Part D Marine Algal Biotechnology
have to accumulate this element to such extreme levels? For this, it seemed crucial to first unambiguously
clarify the chemical speciation of accumulated iodine.
In fact, various and sometimes contradictory opinions
existed about the chemical state of iodine in Laminaria.
To this end, we used a non-invasive technique, X-ray
absorption spectroscopy, thus excluding the possibility of artifacts upon extraction [23.37]. This approach
revealed that the accumulated form is, indeed, iodide,
which is contained in a largely organic (rather than hydrated) environment. Upon oxidative stress such as an
oxidative burst [23.28, 38–40], a transition to a more
hydrated form occurs. Concomitantly, a strong efflux
of accumulated iodide occurs. Altogether and in light
of the hypothesis of Venturi [23.41], our results suggest that iodide serves the function of an antioxidant,
protecting the apoplast (cell wall space) of the cortical
cell layers. This constitutes the description of the first
inorganic and of the chemically simplest antioxidant
known from a living system [23.29]. Indeed, the reaction of iodide with the major reactive oxygen species
is both thermodynamically and kinetically favorable.
With the involvement of vanadium haloperoxidase and
in the absence of organic co-substrates, iodide effectively degrades H 2 O 2 (halide-assisted disproportionation of hydrogen peroxide). Furthermore, the millimolar
iodide levels on the Laminaria surface exposed at low
tide effectively scavenge atmospheric ozone, leading to
the release of I 2 – at rates up to about five orders of
magnitude higher than the combined iodocarbon emissions. These studies [23.16, 29] unambiguously clarify
the biochemical origin of particle-forming iodine oxides. Molecular iodine is photolyzed and further oxidized by ozone in the marine boundary layer, producing
hygroscopic iodine oxides. The latter form ultrafine
particles, leading to aerosol formation and establishing
a unique link between a biological antioxidant and climatic processes [23.30].
The current understanding of iodine metabolism is
summarized in Fig. 23.1. Using X-ray absorption spectroscopy in combination with other techniques, we have
recently demonstrated that bromide complements iodide as an antioxidant in particular with regards to
superoxide detoxification and that overall, its function
is more diverse than that of iodide in algal physiology [23.42].
In the 200 years since its discovery, research on iodine has developed into multiple areas of science, far
beyond marine algae where it was originally found and
beyond the scope of this chapter. In this context, we
would like to highlight a recent interdisciplinary review
article by an international consortium [23.43] that covers the many fascinating facets of iodine science and
applications ranging from the history of its discovery
to general, marine, atmospheric, environmental, radioand geochemistry, medicine and physiology, materials
science (in particular including semiconductors and solar cells), and organic synthesis.
References
23.1
L.R. McDowell: Iodine. In: Minerals in Animal and
Human Nutrition, ed. by L.R. McDowell (Academic
Press, San Diego 1992) pp. 224–245
23.2
L. Rosenfeld: Discovery and early uses of iodine,
J. Chem. Educ. 77(8), 984–987 (2000)
23.3
J. Wisniak: Bernard courtois – The discoverer of iodine, Educ. Quim. 13(3), 206–213 (2002)
23.4
F.C. Kelly: Iodine in medicine and pharmacy since
its discovery – 1811–1961, Proc. R. Soc. Med. 54, 831–
836 (1961)
23.5
B. Courtois: Découverte d’une substance nouvelle
dans le Vareck, Ann. Chimie 88, 304–310 (1813)
23.6
J.-L. Gay-Lussac: Sur la combinaison de l’iode avec
l’oxygène, Ann. Chimie 88, 319–321 (1813)
23.7
L.-J. Gay-Lussac: Sur un nouvel acide formé avec la
substance découverte par M. Courtois, Ann. Chimie
88, 311–318 (1813)
23.8
H. Davy: Some experiments and observations on
a new substance which becomes a violet coloured
gas by heat, Philos. Trans. R. Soc. 104, 74–93 (1814)
23.9
J.M. Synge: The Aran Islands (Maunsel, Dublin
1907)
23.10 N.N. Eschle: Ueber den Jodgehalt einiger algenarten, Z. Physiol. Chem. 23, 30–37 (1897)
23.11 M. Golenkin: Algologische Notizen 1, Das Vorkommen von freiem Iod bei Bonnemaisonia asparagoides, Bull. Soc. Imp. Nat. Mosc. 8, 257–270
(1894)
23.12 C. Sauvageau: Sur quelques algues floridées renfermant de l’iode à l’état libre, Bull. Station Biol.
d’Arcachon. 22, 3–43 (1925)
23.13 H. Kylin: Über das Vorkommen von Jodiden, Bromiden und Jodidoxydasen bei Meeresalgen, HoppeSeyler’s Z. Physiol. Chem. 186, 50–84 (1929)
23.14 P. Dangeard: Sur le dégagement de l’iode chez les
algues marines, C. R. Acad. Sci. Paris 186, 892–894
(1928)
23.15 G.B. McFiggans, H. Coe, R. Burgess, J. Allan,
M. Cubison, M.R. Alfarra, R. Saunders, A. SaizLopez, J.M.C. Plane, D.J. Wevill, L.J. Carpenter,