Aluminium alleviates fluoride toxicity in tea (Camellia sinensis)

Tea is a strong accumulator of both aluminium (Al) and fluoride (F). We tested the hypothesis that Al helps detoxify F in tea plants by forming Al-F complexes. Tea plants were grown hydroponically with a range of Al and F concentrations and in a soil pot experiment with amendments of NaF and acids. Growth and the uptake of F and Al were determined. Chemical species of F in the nutrient solutions and the cell saps of roots and leaves were determined by F-19 NMR. In hydroponic experiments, F inhibited the growth of new roots and shoot tips in the absence of Al in the nutrient solutions, whereas Al stimulated root growth and alleviated the toxicity of F. Aluminium generally increased F concentration in roots but decreased F concentration in leaves. Geochem-PC calculations and F-19 NMR showed the presence of AlF2+, AlF2 (+) and AlF3 (0) in the nutrient solutions when Al and F were present. Aluminium markedly decreased the NMR peak of free F in the cell saps from roots and leaves. An Al-F complex likely to be AlF2+ was detected in the leaf cell sap from the plants treated with both F and Al. In the soil pot experiment, F caused leaf necrosis when the leaf Al to F molar ratio was smaller than 1. Tea plants are sensitive to F toxicity in the absence of Al. Aluminium alleviates F toxicity in tea by forming Al-F complexes.