The effect of darkness on active and passive transport in Chara corallina

In Chara corallina, the membrane potential may stay much more negative than the equilibrium potential for potassium in the dark, indicating that the proton pump is operative. The high proton conductance which occurs at high external pH, as indicated by a high membrane conductance and a membrane potential near the equilibrium potential for protons, is not seen in the dark at pH 11. This effect is likely to be related to inhibition of photosynthesis since DCMU has the same effect. The effect is similar but not identical to the effect of a decreased internal pH.