Modification of the culture medium to produce aluminum toxicity in cell suspensions of coffee (Coffea arabica L.)

Coffee (Coffea arabica) plants are usually grown in soils containing high levels of organic materials. Under these conditions, aluminum (Al) is toxic because of the acidic nature of the soils. Al is the most abundant metal found in the earth's crust and occurs in a number of different forms in soil. In acid soils, Al toxicity is a global problem that limits crop productivity. A major problem in obtaining cellular lines displaying Al tolerance in culture is the composition of the medium. In the experiments presented here, we modified the composition of the culture medium for a C. arabica cell line to produce Al toxicity. Murashige-Skoog media was used, complete (MS) and half ionic strength (MSHIS), at either pH 5.8 or 4.3. We found that MSHIS and pH 4.3 provided the optimal conditions to obtain Al toxicity as measured by the ability to grow in a range of Al concentrations (25–1,000 µM). The lethal dose (LD50) under these conditions was 25 µM. The concentrations of free Al in the culture medium were corroborated by the fluorescent compound Morin. Al was found to enter the cell after 30 min, and the signal was then retained for up to 2 h.