Effects of aluminum on plasma membrane as revealed by analysis of alkalineband formation in internodal cells of Chara coralline

To study the mechanism of aluminum toxicity in plant cells, the effects of aluminum on alkaline band formation were analyzed in the internodal cells o f Chara. After cells were treated with AlCl3, they were examined for their capacity to develop alkaline bands. Treating cells with AlCl3 medium at pH 4.5 completely inhibited alkaline band formation. When either CaCl2 or mali c acid was added to the AlCl3 medium (pH 4.5), it did not produce an amelio rative effect, whereas addition of both CaCl2 and malic acid induced a sign ificant ameliorative effect, It was found that treatment at pH 4.5 in the a bsence of AlCl3 strongly inhibited alkaline band formation. This inhibition by the low pH (4.5) treatment was effectively ameliorated by CaCl2. At hig her pH (5.0), malic acid alone produced a significant ameliorative effect o n aluminum inhibition of alkaline band formation, but CaCl2 did not. Recove ry from aluminum inhibition was also studied. When cells treated with AlCl3 at pH 4.5 were incubated in artificial pond water, they could not recover the capacity to develop alkaline band. When either malic acid or CaCl2 was added to artificial pond water, cells recovered their alkaline band formati on. It was concluded that one of the primary targets of aluminum is the pla sma membrane and that aluminum affects the plasma membrane from the cell ex terior at the beginning of the treatment (within 24 h). It was also suggest ed that the aluminum treatment impairs the HCO3- influx mechanism but not t he OH- efflux mechanism.