POLAR CURRENT PATTERNS IN THE LEAVES OF THE AQUATIC ANGIOSPERM ELODEA-CANADENSIS

The pattern and density of ionic currents near the surface of Elodea canadensis leaves were investigated using a 3-d recording vibrating probe. Positive current always entered the adaxial (upper) surface, and left the abaxial (lower) surface of mature leaves. Current densities ranged from 1 to 15μAcm-2 in leaves irradiated with white light submerged in artificial pond water of pH 8. When the pH of the medium was lowered from 8 to 6, a rapid, approximate 40% reduction in current density on both sides of the leaf occured. Within 15 min of turning the light off, the current at the surface almost vanished. After re-introducing light, current began to rise after 10 to 15 min. Immature leaves exhibited no polarity in the current pattern, i.e., inward and outward current was found on both surfaces. Immature leaves also produced less current than mature ones, and responded less strongly to darkness. The results support the conclusion that Elodea leaves pump H+ out at the lower surface, and leak OH- at the upper surface. The H+ current at the lower surface presumably facilitates the intake of carbon in form of CO2. © 1990 Springer-Verlag.