Responses to Aluminium of Suspension-Cultured Tobacco Cells in a Simple Calcium Solution

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In a simple solution containing 3 mM CaCl_2 and 3% sucrose (pH 4.5), tobacco cells (Nicotiana tabacum L.) at the logarithmic phase of growth remained viable at least for 24h. In this medium, the toxic effect of aluminium (Al) on the plasma membrane was investigated for up to 24 h. After the addition of Al to the cell suspension, Al started to accumulate immediately in the cells, and a maximum value was observed at 9 h. Al induced callosed eposition, but did not enhance significantly the uptake of Evans blue (a nonpermeating dye), the peroxidation of lipids and the leakage of potassium (K) ions. Furthermore, the Al-treated cells were stained with fluorescein diacetate (FDA) as much as untreated control cells. These results suggest that the accumulation of Al does not damage the membrane. The addition of Fe(II) to the cells which had been exposed to Al for 12 h resulted in immediate lipid peroxidation and Evans blue uptake several hours later. A combination of Al and Fe(II) caused the K leakage, and enhanced the deposition of callose more than Al alone. These results suggest that the accumulation of Al sensitizes the membrane to the Fe(II)-mediated peroxidation of lipids, and that the Al-enhanced peroxidation of lipids is a direct cause of the loss of integrity of the plasma membrane (or cell death) in the Ca medium.
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