. Electrolytes in biological systems, incorporating papers presented at a symposium at the Marine Biological Laboratory in Woods Hole, Massachusetts, on September 8, 1954. Electrophysiology; Electrolytes; Electrolytes; Electrophysiology; Physiology, Comparative. io6 ELECTROLYTES IN BIOLOGICAL SYSTEMS Burk; 2) potassium competitively interferes with the absorption of Rb; j) ex- cept at high Na concentrations the interference of Na with Rb absorption is not competitive. Like K, Cs interferes competitively with Rb absorption; Li interference is not competitive and at low concentrations of Rb, a p
. Electrolytes in biological systems, incorporating papers presented at a symposium at the Marine Biological Laboratory in Woods Hole, Massachusetts, on September 8, 1954. Electrophysiology; Electrolytes; Electrolytes; Electrophysiology; Physiology, Comparative. io6 ELECTROLYTES IN BIOLOGICAL SYSTEMS Burk; 2) potassium competitively interferes with the absorption of Rb; j) ex- cept at high Na concentrations the interference of Na with Rb absorption is not competitive. Like K, Cs interferes competitively with Rb absorption; Li interference is not competitive and at low concentrations of Rb, a positive (accelerating) effect of Li on the rate of Rb absorption is observed. In an extension of this work to include the absorption of anions (14) the absorption of Br from solutions of KBr exhibited the same response to increas- ing concentrations of the salt. Interference by CI with Br absorption was com- petitive; NO3, on the other hand, did not compete for the halide binding • •Sr* 0 'Sr ^ Co 0 .M9 • ^ .--^ r \ \ \ \ Vs_ -§ W nutes e o -100 <^ 60 120 180 Fig. 2 FiG. 3 Figs. 2-3. Uptake and loss of labeled strontium by excised barley roots. Black circles and solid lines: roots in solutions of labeled strontium (Sr*). Open symbols and broken lines: roots in unlabeled solutions. Concentration of all salts: i mEq/1. PASSIVE EXCHANGE VS. ACTIVE TRANSPORT The assumption has been made above that the overall process of active ion absorption by plant roots is essentially irreversible. Hoagland and Broyer (23) found that barley roots do not lose significant amounts of K to distilled water and in the experiments of Broyer and Overstreet (9) only about 10% of pre- viously absorbed K was subject to ready loss through ion exchange. We recently obtained different results in a study of the absorption of alkaline earth cations by barley roots (17). The difference, however, is apparent rather than real. Figure 2 shows the time course of the absorption of Sr labeled with gj
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