The Membrane Potential as Indicator for Transport and Energetic Processes of Leaf Cells of the Aquatic Plant Egeria densa I. Ion and Light Dependence and Reactions on Metabolic Inhibitors

Abstract

Summary Leaf cells of Egeria densa were investigated electrophysiologically in detail in order to employ the electric cell potential as sensitive parameter which reveals essential living processes such as transport and metabolism. Data obtained by membrane potential measurements and flame-photometry under various conditions were used for a numerical approximation of the Goldman-Hodgkinkatz equation. In comparison to other plants, Egeria cells possess a high membrane potential with a substantial light-dependent component. Darkness and inhibitors of photosystem II depolarize the membrane potential to the same extent. The ATPase inhibitors DCCD, DES and orthovanadate also led to depolarization but with different kinetics and amplitudes, suggesting unequal effectiveness of inhibition. The uncouplers CCCP and DNP depolarize the cell potential far below its dark level. Their depolarizing effect was accompanied by a rapid electrolyte leakage from the leaves indicating irreversible processes. In contrast to auxin, the phytoeffec or fusicoccin, hyperpolarizing the membrane potential in the light, abolished the depolarizing action of darkness and inhibitors but not that of uncouplers. The results confirm the sensitivity of the cell potential to changes of the environment and metabolic processes. However, the interpretation of the electric cell response has to be undertaken with precaution.