Electrostatic Association and Donnan Phenomena as Mechanisms of Ion Accumulation

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Abstract
Excised roots of barley (Hordeum vulgare cv. ''Campana'') were incubated for periods up to 24 hr. in salt solutions of various concentrations and ion accumulation was determined at various time intervals. The data were consistent with the existence of 2 components of ion uptake, one accounting for ion uptake from solutions below 1 mM and both components contributing to uptake from solutions of concentrations higher than 1 mM. It is proposed that organic and amino acids play an important role in ion accumulation by providing nondiffusible charges which may bind or retain inorganic ions within the cell. Ions would enter the cell by diffusion or exchange from salt solutions of low concentration and become associated with nondiffusible organic ions, principally organic and amlno acids. The electrostatic association between inorganic and organic ions would maintain a gradient and diffusion-exchange would occur until equilibrium between the cell and the external solution was reached. It is proposed that the additional component of ion uptake which becomes important at salt concentrations higher than 1 mM is a result of diffusion of neutral salts according to Donnan phenomena. Ion uptake by this proposed mechanism would not necessarily involve the action of carriers.