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Plant Physiol, January 2001, Vol. 125, pp. 292-305
A Patch-Clamp Study on the Physiology of Aluminum Toxicity and
Aluminum Tolerance in Maize. Identification and Characterization of
Al3+-Induced Anion Channels1
Miguel A.
Piñeros and
Leon V.
Kochian*
United States Plant, Soil, and Nutrition Laboratory, United States
Department of Agriculture, Agricultural Research Service, Cornell
University, Ithaca, New York 14853
The presence of Al3+ in the rhizosphere induces citrate
efflux from the root apex of the Al-tolerant maize (Zea
mays) hybrid South American 3, consequently chelating and
reducing the activity of toxic Al3+ at the root surface.
Because citrate is released from root apical cells as the deprotonated
anion, we used the patch-clamp technique in protoplasts isolated from
the terminal 5 mm of the root to study the plasma membrane ion
transporters that could be involved in Al-tolerance and Al-toxicity
responses. Acidification of the extracellular environment stimulated
inward K+ currents while inhibiting outward K+
currents. Addition of extracellular Al3+ inhibited the
remaining K+ outward currents, blocked the K+
inward current, and caused the activation of an inward Cl
current (anion efflux). Studies with excised membrane patches revealed
the existence of Al-dependent anion channels, which were highly
selective for anions over cations. Our success in activating this
channel with extracellular Al3+ in membrane patches excised
prior to any Al3+ exposure indicates that the machinery
required for Al3+ activation of this channel, and
consequently the whole root Al3+ response, is localized to
the root-cell plasma membrane. This Al3+-activated anion
channel may also be permeable to organic acids, thus mediating the
Al-tolerance response (i.e. Al-induced organic acid exudation) observed
in intact maize root apices.
1
This work was supported by the U.S. Department
of Agriculture National Research Initiative (grant no. 96-35100-3213
to L.V.K.).
*
Corresponding author; e-mail lvk1{at}cornell.edu; fax
607-255-2459.
© 2001 American Society of Plant Physiologists
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