The mechanism of iodide accumulation by the brown sea weed Laminaria digitata II. Respiration and iodide uptake

Abstract

Iodide absorption by fresh, summer Laminaria digitata frond was accompanied by about a 5 fold increase in the rate of O2 consumption. Between approximately 3 and 6 molecules of 02 were consumed for each iodide ion absorbed by the tissue and the respiratory quotient, whether measured in the presence or absence of iodide, lay between 0.9 and 1.1 (mean 0.94). It is argued that: (1) The iodide-stimulated respiration must occur principally near the surface of the frond, though this localization is not due to the limited diffusibility of 02. (2) Iodide absorption is connected with the oxidation of a carbohydrate-like compound or compounds. (3) The absorption of iodide is associated with a rate-limiting process for the oxidation of the compound or compounds. (4) Between 1 and 2 iodide ions are absorbed for each 6 carbon unit oxidized. (5) Probably only 1 or 2 reactions in the oxidation of each 6 carbon unit is involved in iodide absorption, 1 of these reactions being the rate limiting process governing the oxidation.