title: The delivery of salts to the xylem. Three types of anion conductance in the plasmalemma of the xylem parenchyma of roots of barley.
abstract: To explore possible pathways for anions to enter the xylem in the root during the transport of salts to the shoot, we used the patch-clamp method on protoplasts prepared from the xylem parenchyma of barley (Hordeum vulgare L.) plants. K(+) currents were suppressed by tetraethylammonium or N-methylglucamine in the solutions in the pipette and the bath, and the permeating anions were Cl(-) or NO(3)(-). We recorded the activities of three distinct anion conductances: (a) an inwardly rectifying anion channel (X-IRAC), characterized by activation at hyperpolarization and open times of up to several seconds; (b) a quickly activating anion conductance (X-QUAC), important for anion efflux at voltages between -50 mV and the equilibrium potential of the prevailing anion; and (c) a slowly activating anion conductance (X-SLAC), activating above -100 mV. Both X-IRAC and X-QUAC were permeable for Cl(-) and NO(3)(-); X-QUAC was also permeable for malate. The occurrence of X-IRAC became more frequent with an increase in cytoplasmic Ca(2+), while the occurrence of X-QUAC decreased. Anion currents through X-SLAC, and particularly through X-QUAC, were estimated to be large enough to account for reported rates of xylem loading, which is in accordance with the notion that xylem loading is a passive process.
authors.affiliation: Albrecht-von-Haller-Institut für Pflanzenwissenschaften, Universität Göttingen, Untere Karspüle 2, 37073 Göttingen, Germany. sbs99bk@wye.ac.uk
authors.forename: B
authors.initials: B
authors.lastname: Köhler
authors.forename: K
authors.initials: K
authors.lastname: Raschke
mesh_terms: D000838:Anions / Q000378:metabolism*; D001692:Biological Transport; D001467:Hordeum / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism; D018408:Patch-Clamp Techniques; D018517:Plant Roots / Q000378:metabolism*; D011523:Protoplasts / Q000378:metabolism; D012492:Salts / Q000378:metabolism*
chemical_list: D000838:Anions; D007473:Ion Channels; D012492:Salts