To study the mechanism of aluminum toxicity in plant cells, the effects of aluminum on alkaline band formation were analyzed in the internodal cells of Chara. After cells were treated with AlCl
3, they were examined for their capacity to develop alkaline bands. Treating cells with AlCl
3 medium at pH 4.5 completely inhibited alkaline band formation. When either CaCl
2 or malic acid was added to the AlCl
3 medium(pH 4.5), it did not produce an ameliorative effect, whereas addition of both CaCl
2 and malic acid induced a significant ameliorative effect. It was found that treatment at pH 4.5 in the absence of AlCl
3 strongly inhibited alkaline band formation. This inhibition by the low pH(4.5) treatment was effectively ameliorated by CaCl
2. At higher pH(5.0), malic acid alone produced a significant ameliorative effect on aluminum inhibition of alkaline band formation, but CaCl
2 did not. Recovery from aluminum inhibition was also studied. When cells treated with AlCl
3 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 CaCl
2 was added to artificial pond water, cells recovered their alkaline band formation. It was concluded that one of the primary targets of aluminum is the plasma membrane and that aluminum affects the plasma membrane from the cell exterior at the beginning of the treatment(within 24 h). It was also suggested that the aluminum treatment impairs the HCO
3- influx mechanism but not the OH
- efflux mechanism.
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