Blue Light Pulse-Induced Transient Changes of Electric Potential and Turgor Pressure in the Motor Cells of Phaseolus vulgaris L.

Blue light induces both depolarization of membrane potentialin the motor cell and turgor movement in the laminar pulvinusof bean plant. This paper describes the changes of electricpotential and turgor pressure induced in Phaseolus vulgarisL. by blue light pulses. A transient depolarization of membranepotential as large as 40 mV was induced by a short pulse of15 s blue light in motor cells of the laminar pulvinus. Thischange was not an action potential because of the absence ofa refractory period and threshold. The magnitudes of the responsewere dependent on the fluence of light. The response was long-lived,indicating that continuous input of light energy is not requiredfor a sustained response. The potential change was always followedby a transient turgor movement of the pulvinus. A molecular mechanism similar to a model postulated for theblue light response of stomata may operate in the motor cell.However, the direction of the electrical response to blue light(depolarization) in the motor cell was the opposite of thatin the guard cell (hyperpolarization). Turgor change of themotor cell by blue light was also opposite in direction (decrease). (Received February 19, 1988; Accepted June 28, 1988)