Simulating the Mineral Environment of Aluminium Toxic Soils in Plant Cell Culture

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Abstract
The development of a medium for studying aluminium toxicity in plant cell cultures is described. To prevent the precipitation of Al added to the standard cell culture medium, it was necessary to lower the phosphate concentration from 1250 mmol m−3to 10 mmol m−3, and the pH from 5.8 to 4-0. Two additional modifications were the use of unchelated iron and a reduction in the calcium concentration from 3.0 mol m−3 to 0.1 mol m−3. Since the gelling properties of agar are inhibited at pH 4.0, cells were cultured on filter paper supported by polyurethane foam sturated with liquid medium. The only limitation to the growth of plated Nicotiana plumbaginifolia Viv. cells on the modified medium was the reduced phosphate concentration. This was partly overcome by ‘preloading’ the cells with phosphate prior to each experiment. In addition, the filter paper with adhering cells was transferred to fresh medium every second day to replenish phosphate, and to re-establish the initial pH of4.0 (which otherwise drifts upward). With the modified medium, Al toxicity was observed in plated N. plumbaginifolia cells at both 200 mmol m−3 and 400 mmol m−3 Al. There was no toxicity at these Al concentrations when the normal phosphate concentration or pH were restored to the modified medium. Partial alleviation of Al toxicity occurred with restoration of the normal calcium concentration or chelated iron. Chelation of Al with citrate or EDTA also mitigated Al toxicity. In additon to Al toxicity, the modified medium should also prove useful for studying other metal toxicities in plant cell culture.