A Donnan relation between the medium and the outermost layer of the root or cell contents was supposed. Measurement of membrane potentials, indicating an unequal distribution of ions across the root wall, was the only practical way of showing its existence. Measurements of root potential in solutions of a broad pH range revealed the amphoteric nature of the root contents. The concentration of cell- bound (colloidal) ions, is the difference between the dissociated fractions of acid groups and of basic groups. This surplus varies with pH. If the constants K 1 and K 2 (concentration of cell-bound ions = K 1 log c H+ + K 2 ) are estimated, the concentration of fixed ions can be calculated for any pH. The adsorption capacities thus calculated with the prevailing pH values better approach the mineral contents in plant material than LUNDEG+RDH'S conclusion that a strongly acid component is present. The function of c H+ gradients in salt transport in an amphoteric system is also considered. Maximum accumulation of anions And cations takes place near the iso-electric pH. Three stages in the accumulation processes are distinguished: formation of organic acids in young tissue; accumulation of mineral anions from the medium; decrease of acidity, causing cation absorption and salt accumulation.
There are no comments yet. You can post the first one!
Post a comment
Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.