Salt Uptake by Root Tissue Cytoplasm: the Relation Between Uptake and External Concentration

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Abstract
The proportion of a given length of bean root tissue which appears to reach the external concn. when placed in KC1 solns. (the apparent free space, =A.F.S.) increases as the external concn.is increased. The experimentally determined values of A.F.S. at various concns. of the medium fit the curves representing the quantitative relations between A.F.S. and the external concn. deduced by assuming a Donnan equilibrium between the root cell cytoplasm and the medium at each concn. Thus the expts. indicate the presence of non-mobile ions (probably anions) in the cytoplasmic phase. The concn. of these ions has been calculated to be of the order of 0.01 mol/l. for both bean and maize root cytoplasm. Mature cells seem to have a higher concn. than those less mature. The relation between uptake of KCl by bean root sections and the time of immersion was found to follow Fick''s law of diffusion. The apparent coefficient of diffusion for KCl in the tissue was calculated. A typical figure is 0.07 x 10-5 cm 2Sec-1, about 1/20 of the value for an aqueous soln. for the same concn. The results of these expts. are discussed in rela-tion to the few existing evaluations by other investigators of the non-mobile ion content of cell cytoplasm.

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