Effects of temperature and dinitrophenol on the uptake of potassium and sodium ions in Ricinus communis roots

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Abstract
Detopped root systems of Ricinus communis plants were used for the study of the effects of temperature and DNP on the uptake of K and Na ions supplied as KNO3 and NaNO3. When K and Na ions were offered together in equivalent concentrations, the steady state uptake rates for K+ and Na+ at 23 to 25° gave a K+/Na+ ratio of 3. Increasing the Na+ concentration relative to K+ 3-fold did not alter the preferential uptake of K+. The uptake of K+ was more sensitive to temperature in the range 10 to 40° and to the application of DNP at 1.5x10-4 M than was the uptake of Na+. When NaNO3 was the only salt supplied Na+ uptake became more sensitive to DNP than when both K+ and Na+ nitrates were supplied. Prolonged application of DNP led to net K+ efflux from the roots, even when no K+ was being supplied to the roots. Net Na+ efflux under the influence of DNP occurred only in roots previously grown on Na-containing nutrient medium. The different responses of the K+ and Na+ uptake processes to temperature and DNP suggest the operation of different uptake mechanisms for K+ and Na+ These results have been considered in relation to the recent concept of dual mechanisms for the absorption of alkali cations by plant tissues.