THE EFFECT OF CALCIUM ON THE ABSORPTION OF POTASSIUM BY BARLEY ROOTS

Abstract

In a recent investigation (3) the absorption of potassium by excised barley roots was studied. It was proposed that, as a working hypothesis, the absorption of ions depended upon the presence of metabolically produced binding compounds. According to this idea, the absorption of a cation may be expressed as: M+ + HR = MR + H+, where HR is the metabolically produced binding compound. Studies of the absorption of potassium in the presence of H+ and other monovalent cations appeared to be consistent with the above hypothesis; that is, H* caused what appeared to be a reversal of the absorption reaction and pronounced competitive effects were noted between potassium and the other cations. On the other hand, in accordance with the observations of Viets (5), it was shown that the presence of calcium exerted a stimulating effect on potassium absorption. Since this calcium effect is in apparent conflict with the above hypothesis, a special study was made of the calciumpotassium relationship in absorption. The purpose of the present paper is to show that certain extensions of the theory of cation absorption appear necessary to explain adequately the behavior of calcium.