PLANT PHYSIOLOGY , Vol 113, Issue 4 1419-1426, Copyright © 1997 by American Society of Plant Biologists
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CELL BIOLOGY AND SIGNAL TRANSDUCTION |
Characterization of a Light-Controlled Anion Channel in the Plasma Membrane of Mesophyll Cells of Pea
JTM. Elzenga and E. Van Volkenburgh
Department of Botany, University of Washington, P.O. Box 351330, Seattle, Washington 98195 (J.T.M.E., E.V.V.)
In leaf mesophyll cells of pea (Pisum sativum) light induces a transient
depolarization that is at least partly due to an increased plasma membrane
conductance for anions. Several channel types were identified in the plasma
membrane of protoplasts from mesophyll cells using the patch-clamp
technique. One of these was an anion channel with a single-channel
conductance of 32 picasiemens in symmetrical 100/100 KCl solutions. In
asymmetrical solutions the reversal potential indicates a high selectivity
for Cl- over K+ at high cytoplasmic Cl-. At negative membrane voltages the
channel openings were interrupted by very short closures. In the open
channel conductance several substrates were identified. At a cytoplasmic
negative logarithm of Ca concentration higher than 6.3, no channel openings
were observed. When the protoplast was illuminated in the cell-attached
configuration, at least one channel type had a higher opening probability.
This channel can tentatively be identified as the above-described anion
channel based on conductance and the characteristic short closures at
negative membrane potentials. This light activation of the 32-picasiemen
anion channel is a strong indication that this channel conducts the
light-induced depolarizing current. Because channel activity is strongly
Ca2+-dependent, a role of cytoplasmic Ca2+ concentration changes in the
light activation of the conductance is discussed.
