Oscillations of the Membrane Potential of Pulvinar Motor CellsIn Situin Relation to Leaflet Movements ofDesmodium motorium

Abstract

The ultradian rhythmic movement of the lateral leaflets of Desmodium motorium is accompanied by rhythmic changes of the extra- and intracellular electrical potentials in the pulvinus, which are measured in situ in the pulvinus against the bathing solution of the petiole. Extra- and intracellular potentials oscillate with 180'b0 phase difference to each other, as shown by simultaneous measurements of both types of potentials in the abaxial part of the pulvinus. Light-induced changes of these potentials move in opposite directions. The in situ membrane potential of the motor cells of the pulvinus was calculated from the difference between the extra- and intracellular potentials. It was found to oscillate between −136 and −36 mV, in phase with the intracellular and inverse to the extracellular potential. The phase relationship between the leaflet movement rhythm and the in situ membrane potential rhythm was as follows: downward movement is preceded and accompanied by a strong depolarization, upward movement by hyperpolarization. Our results suggest that membrane depolarization in pulvinar motor cells of Desmodium motorium drives and controls potassium efflux and hyperpolarization potassium influx via potassium channels.