ALUMINUM ACTIVATES AN ANION CHANNEL IN THE APICAL CELLS OF WHEAT ROOTS

We describe an anion channel in the plasmalemma of protoplasts isolate d from wheat (Triticum aestivum L.) roots that is activated by aluminu m (Al3+), In the whole-cell configuration, addition of 20-50 mu M AlCl 3 to the external solution depolarized the membrane and activated an i nward current that could remain active for more than 60 min. The activ ation by Al3+ was rapid in 20% of protoplasts examined, whereas in ano ther 30% a delay of more than 10 min occurred after Al3+ was added, On ce the current was activated, changing the external Cl- concentration shifted the membrane reversal potential with E-Cl, showing that the ch annel is more selective for anions than cations (Ca2+, K+, tetraethyla mmonium(+)). The channel could be activated by Al3+, but not by La3+, and was observed in protoplasts isolated from the root apex but not in protoplasts isolated from mature root tissue. The anion channel antag onist niflumate inhibited the current in whole fell measurements by 83 % at 100 mu M. Outside out patch recordings revealed a multistate chan nel with single channel conductances of between 27 and 66 pS.