Quantitative Estimation of Aluminium Toxicity in Cultured Tobacco Cells: Correlation between Aluminium Uptake and Growth Inhibition

The relationship between aluminium (Al) uptake and growth inhibitionwas studied in tobacco cells (Nicotiana tabacum L. cv. Samsun;nonchlorophyllic cell line) in suspension culture. Cells atthe logarithmic phase of growth were treated with 100 µMA1C1³ in modified Murashige-Skoog medium prepared without P_iand EDTA (pH 4.0) for up to 21 h. After treatment, the inhibitionof cell growth by Al was estimated from the growth of the Al-treatedcells relative to that of the control cells during post-treatmentculture. Neither Al uptake nor the inhibition of the growthoccurred with less than a 10-h exposure but then both parametersincreased rapidly, reaching maximum values after an 18-h exposure.When cells were treated with AlCl₃ at various concentrationsfor 18 h, the extent of growth inhibition was found to be afunction of the Al content of the cells. The dose-response curve(Al uptake versus growth inhibition) resembled the curve expectedfor "single-hit" kinetics. Extrapolation from the curve suggestedthat the uptake of 1 x 10¹¹ Al atoms per cell is the minimumdose that inhibits cell growth. Cells of stationary phase wereresistant to Al and did not take up Al, an indication that theuptake of Al depends on the active growth of cells. Resultsof several types of experiment (hematoxylin staining, washingwith chelators, digestion of cell walls) indicated that Al wasincorporated inside the cells. Together, therefore, our resultssuggest that the amount of Al absorbed by the cells is a determiningfactor in the inhibition of growth by Al. ¹Present address: Department of Biology, Faculty of Science,Hirosaki University Hirosaki, Aomori, 036 Japan