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KUPPER
A survey of iodine content in Laminaria digitataErwan Ar Gall | Frithjof C. Küpper | Bernard Kloareg Botanica Marina.February 2004, 47:1, pp 30-37 [abstract only]
"Laminaria digitata sporophytes sampled from eight European populations (five in Brittany, one in Helgoland, two in the Shetland Islands) were measured for their iodine levels. The average iodine contents were highest in late autumn and in winter (in the range 0.75–1.20% dw) and were lowest in summer (0.25–0.60%). Younger plants were richer in iodine, with maxima close to 5% of dry weight for plantlets. Tissue-specific differences in the rates of uptake of iodine correlated with haloperoxidase activity, but not with the iodine contents."
Iodine uptake in Laminariales involves extracellular, haloperoxidase-mediated oxidation of iodideF. C. Küpper, N. Schweigert, E. Ar Gall, J.-M. Legendre, H. Vilter, B. Kloareg Planta, Volume 207, Number 2 / November, 1998, 163-171. [abstract only]
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.
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