Iodine uptake in Laminariales involves extracellular, haloperoxidase-mediated oxidation of iodide |
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Authors: | F C Küpper N Schweigert E Ar Gall J-M Legendre H Vilter B Kloareg |
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Institution: | Centre d'Etudes Océanologiques et de Biologie Marine, CNRS, UPR 9042, F-29682 Roscoff, Brittany, France, FR Service de Médecine Nucléaire, CHU Morvan, F-29200 Brest, Brittany, France, FR Zurmaiener Stra?e 16, D-54292 Trier, Germany, DE
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Abstract: | Sporophytes of Laminaria digitata (L.) Lamour. were assayed for their content of accumulated iodine, which ranged from 0.4% of dry weight in adult plants up
to 4.7% for young plantlets. Sporophyte tissue from Laminaria saccharina (L.) Lamour. and L. digitata took up iodide according to Michaelis-Menten kinetics. Hydrogen peroxide and various substances known to interfere with oxidative
metabolism were shown to either inhibit or enhance the uptake of iodide, confirming that apoplastic oxidations play a key
role in iodide uptake in Laminaria. Consistently, iodide uptake was triggered in L. saccharina protoplasts by incubation in the presence of hydrogen peroxide. Similarly, the uptake of iodide was enhanced in L. digitata gametophytes by addition of haloperoxidase, suggesting that this enzyme catalyses the oxidation of iodide by hydrogen peroxide
and plays a key role in iodine uptake. Oxidative stress resulted in a marked efflux of the intracellular iodine. In both influx
and efflux experiments, a marked proportion (10–30%) of the tracer was not accounted for, indicating volatilisation of iodine.
The mechanism and possible functions of the accumulation of iodine by kelps are discussed.
Received: 11 February 1998 / Accepted: 18 June 1998 |
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Keywords: | : Apoplastic oxidative metabolism Haloperoxidase Hydrogen peroxide Iodine Laminaria |
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