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A Procedure for Control of pH in Cation Uptake Studies with Excised Barley Roots¹

ABSTRACT

A procedure for the control of pH of salt solutions in cation uptake studies with excised roots is described. Through the addition of small increments of an anionic exchange resin in OH^- form during the absorption period, it was possible to maintain the pH at a desirable physiological level and within quite narrow limits. Whole excised barley roots exhibited maximum K⁺ absorption activity when pH of solutions was resin-controlled. The rapid change in external cation concentration which occurs in high root-to-solution ratio experiments is not accompanied by a reduction in uptake rate between the first and sixth hour. Good reproducibility was observed with this procedure not only between replicates but also with different batches of roots.

Potassium absorption by whole excised roots and shorter root segments cut from the same barley root culture was compared. With the whole excised roots as a control, the amount of K⁺ absorbed at the end of 6 hours was reduced by 12% for 3-cm. segments and by 25% in the case of 1-cm. segments. Any apparent advantage of cutting roots into short segments to achieve greater homogeneity of subsamples is out-weighed by a lowered net cation absorption capacity.

¹ Contribution from the Plant Nutrition Laboratory, Department of Botany, The University of Michigan, Ann Arbor, Paper No. 36. This work was supported by research grant GM-07339-02 from the National Institutes of Health, U. S. Public Health Service.

² Research Associate and Professor of Botany, The University of Michigan, respectively.

Received for publication December 3, 1962. Accepted for publication February 22, 1963.