Abstract
Photooxidations of protoplasmic droplets of Nitella were performed by crystal violet (C.V.), rose bengal (R.B.) and methylene blue (M.B.) from the inside or outside of the membrane. Various physical prop-erties of the droplet were examined. External treatment of the membrane by C.V. induced a temporary increase of resistance and a gradual depolarization of the membrane potential. Excitability disappeared after the depolarization, but the surface tension remained constant. Both membrane potential and resistance remained constant when the droplet was modified by C.V. from the inside, and the excitability was retained. Tension at the surface, however, decreased sharply by a factor of 100. Internal application of R.B. decreased resistance and depolarized the membrane potential by a maximum 20 mV. External treatment with R.B. caused a temporary decrease of resistance with depolarization by about 100 mV. Adsorption of M.B. on the surface membrane led to a decrease in resistance without changing the membrane potential under light illumination, and this was followed by abrupt depolarization. These results indicate that membrane potential and excitability of the protoplasmic droplet are governed largely by the structure at the outermost surface between the protoplasm and external solution and that the tension at the surface is maintained by the internal structure of the protoplasm.
