Effects of Inhibitors on the Light-Induced Changes in Electric Potential in Pulvinar Motor Cells ofPhaseolus vulgarisL.

摘要

To analyze the mechanism of the light-induced changes in electric potential in motor cells of the pulvinus ofPhaseolus vulgarisL., inhibitors were applied to the pulvinus by the xylem perfusion method. The membrane potential was−60 to−80 mV, which indicated that the polarization was less than that of cells of a pulvinus in air. A pulse (30 s) of blue light (BL) induced transient depolarization of the membrane in the motor cells. Red light (RL) caused hyperpolarization of the membrane. The magnitude of BL pulse-induced transient depolarization was greater under the hyperpolarized state caused by the RL.The membrane was depolarized to−30 to−40 mV on perfusion with the respiratory inhibitor NaN3(1 mM) and a pulse of BL or irradiation with RL did not cause any change in the potential in the depolarized state. Hyperpolarization of the membrane by RL was inhibited by perfusion with DCMU (50μM), an inhibitor of electron transport in photosynthesis. However, the magnitude of the depolarization induced by the pulse of BL was not affected. Perfusion with a proton ionophore CCCP (100μM) depolarized the membrane and no change in the potential was induced by a pulse of BL or by RL in the depolarized state.The extent of the BL pulse-induced depolarization of the membrane was proportional to the magnitude of the membrane potential at the time of which the pulse of BL was applied. It is suggested that the active component of the membrane potential was inhibited by the pulse of BL. The experimental results further support the hypothesis that BL inhibits the activity of the proton ATPase and, thus, causes loss of the electrogenic component of the membrane potential of the pulvinar mo