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

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.