Electric Potential Differences in Bean Roots and Their Relation to salt uptake

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Abstract
Characteristic changes of p.d. with time were obtained when a root tip taken from dist. water was dipped in 0.01[image] KCl followed by 0.0001[image] KCl, indicating an increase of concn. in the root tissue while in the first soln. and then a decrease while in the more dilute soln. When excised root tips which had been in dist. water were immersed in 0.01[image]KCl, conductivity measurements showed a mean initial uptake of 0.13 x 10-5 g. mol./g. of tissue. An approx. equal amt. of salt left the roots if they were then transferred to 0.0001[image] KCl. The region of the tissue to which the electrolyte has access by diffusion, called the "apparent free space," is calculated to be 13% for the material used. Approx. 10 of the 13% is likely to be protoplasm. The evidence supports the hypothesis that electric p. d.''s between young root tissue and surrounding electrolytes are the result of differential mobility of cations and anions in the protoplasmic phase of the epidermal cells. It is concluded that the properties of the protoplasm/environment boundary to not include high resistance to ion diffusion. It is possible that protoplasm contains a certain concn. on non-mobile anions resulting in a Donnan distribution of ions between this phase and the surrounding soln. Ways of testing this hypothesis are suggested.

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