[On the light-dependent influx of ions in leaves of Elodea densa. Comparison of the influxes of K(+) and Cl (-) ions].

The light-dependent influxes of K(+) and Cl(-) in detached leaves of Elodea densa were measured using (36)Cl(-) and (42)K(+) or (86)Rb(+) as tracers.The K(+) and Cl(-) influxes were enhanced by light and also in the dark after a preillumination. The rate of influx decayed in the dark according to a first order reaction with a half-time of 25 or 27 sec.DCMU inhibits the light-dependent K(+) influx more severely in the presence of CO2 than in its absence in an atmosphere of N2 containing a trace of oxygen. This is similar to the effect of DCMU on the Cl(-) influx. CCCP(1), atebrin (quinacrine) and Dio-9 all affect the influx of K(+) and Cl(-) in a comparable way. CCCP exerts the strongest effect at low light intensities; atebrin and Dio-9 inhibit strongly even at high intensities when the ion influxes are light-saturated. The influence of these two inhibitors in attributed to an effect at the cellular membranes in addition to an effect on photophosphorylation. The effect of CCCP is ascribed to uncoupling of photophosphorylation, as photosynthesis is inhibited by about the same concentration as is ion influx.In far-red light the relative quantum yields of K(+) and Cl(-) influx drop to a similar degree as does the quantum yield of photosynthesis. Estimated values of the quantum requirement of ion influx are given. The quantum requirement in air is higher than in an atmosphere of N2. It is a function of ion concentration and is lower at higher external concentrations.The results indicate that the K(+) and Cl(-) influxes are partially coupled. The linkage of the ion influxes with the energy sources in the light and a possible contribution of a pseudocyclic photophosphorylation are discussed.