Submitted to: American Society of Plant Physiologists Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 6/15/1999
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: The presence of Al3+ in the rhizosphere induces citrate efflux from Al- tolerant maize root apices, consequently chelating and reducing the Al3+ activity. The use of the patch clamp technique with protoplasts isolated from the terminal 5 mm of root apices allowed us to study the role of plasma membrane transport mechanisms involved in this specific response. .In the absence of Al3+, whole cell conductances were dominated by a K+ outward rectifying current, which was partially inhibited by lowering the extracellular pH. Addition of 12 uM Al3+ inhibited the remaining outward current and caused an immediate shift in the reversal potential to more positive potentials. Exposure to Al3+ frequently activated a small inward current which, at negative holding potentials, activated instantaneously and then partially deactivated with time. This current was frequently detected as individual single-channel events in the whole cell configuration. The current reversed near the theoretical potential for Cl- indicating that Cl- was the main ion permeating these channels, resulting in an Al-activated Cl- efflux. Membrane patches (outside out) isolated from protoplasts where the anion channel was activated by Al exposure revealed single anion channel activity, with a unitary conductance between 20 and 30 pS, and a high selectivity for anions over cations. The channel was inactivated when extracellular Al3+ was removed from the extracellular solution, and re-activated upon re-exposure to extracellular Al3+, suggesting that Al-activation of this channel is localized to the plasma membrane. This Al-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.