Coupling of Proton Fluxes in the Polar Leaves of Potamogeton lucens L

An attempt has been made to quantify the light-induced H⁺ effluxand influx observed in polar leaves of Potamogeton lucens.Theseproton fluxes are spatially separated. The H⁺ efflux, mediatedby a plasmalemma bound H⁺ –ATPase, occurs across theplasmamembrane at the morphological lower epidermis and is accompaniedby an H⁺ influx (or OH^– efflux) at the upper side oftheleaf. As a result, these leaves exhibit a remarkable pH–polarityin the light. The pH near the lower epidermis may drop to avalueas low as 3.5, while a pH of about 10.5 can be observed at theupper epidermis. Obviously this phenomenon requires theco–ordinationof transport processes in the different cell layers of the leaftissue. These observations led to quantitative studies oftherelation between the H⁺ fluxes at either plasmalemma. Thesefluxes were calculated from the pH values recorded at twodistancesfrom the leaf surface. Although the H⁺ influx always exceededthe efflux, a coupling between the transport processesacrosseither plasma membrane became evident from the time–coursesof the two fluxes. Key words: Potamogeton lucens, proton flux, flux coupling, pH–;polarity