Y. Nishizaki et al., ACTION SPECTRUM OF LIGHT PULSE-INDUCED MEMBRANE DEPOLARIZATION IN PULVINAR MOTOR CELLS OF PHASEOLUS, Plant and Cell Physiology, 38(5), 1997, pp. 526-529
In addition to circadian changes in the membrane potential and leaf mo
vement, light applied to the pulvinus causes changes in both the membr
ane potential and the pulvinar movement in Phaseolus vulgaris L. Even
after a short pulse of light, a transient depolarization of the membra
ne occurs and leaf movement is observed. Decreases of turgor pressure
of the motor cells are always preceded by the depolarization. The dire
ction of the leaf movement can be explained by the decrease of turgor
pressure in the motor cells on the irradiated side of the pulvinus. Us
ing the Okazaki Large Spectrograph at the National Institute for Basic
Biology, we determined the action spectrum of the membrane depolariza
tion induced by light pulses (30 s) in motor cells of Phaseolus. The p
ulvinus was left exposed to air during measurement of the membrane pot
ential with microelectrodes. The action spectrum obtained was in the r
ange of 300 to 730 nm. It had the highest peak at 460 nm with lower pe
aks at 380 nm and 420 nm. Almost no sensitivity was observed at wavele
ngths shorter than 360 nm and longer than 520 nm. Red and far-red ligh
t had no effect on the depolarization of the motor cell. The features
of the action spectrum are almost the same as those of the Blue-Type r
esponse in plants.