The tea plant is a fluoride (F) and aluminum (Al) hyperaccumulator. High concentrations of F and Al have always been found in tea leaves without symptoms of toxicity, which may be related to the special localization of F and Al in tea leaves. In this study, we for the first time determined the subcellular localization of F and Al in tea roots and leaves and provided evidence of the detoxification mechanisms of high concentrations of F and Al in tea plants. Results revealed that 52.3 and 71.8% of the total F accumulated in the soluble fraction of tea roots and leaves, and vacuoles contained 98.1% of the total F measured in the protoplasts of tea leaves. Cell walls contained 69.8 and 75.2% of the total Al detected in the tea roots and leaves, respectively, and 73.2% of Al sequestered in cell walls was immobilized by pectin and hemicellulose components. Meanwhile, 88.3% of the Al measured in protoplasts was stored in the vacuoles of tea leaves. Our results suggested that the subcellular distributions of F and Al in tea plants play two important roles in the detoxification of F and Al toxicities. First, most of the F and Al was sequestered in the vacuole fractions in tea leaves, which could reduce their toxicities to organelles. Second, Al can be immobilized in the pectin and hemicellulose components of cell walls, which could suppress the uptake of Al by tea roots.

The impacts of different ion channel inhibitors on the absorption and translocation of fluoride in tea plants were examined using the hydroponics method. The absorption of fluoride in tea plants increased after treatment with 0.5 mg/L water channel inhibitor (HgCl2), whereas no significant difference was demonstrated at concentrations of 2.0 and 10.0 mg/L HgCl2. Anionic channel inhibitors including NPPB and DIDS inhibited the absorption of fluoride in tea plants at concentrations of 10 and 20 μmol/L, respectively. When the concentration of NPPB in the solution was 10 μmol/L, the amount of fluoride accumulated in roots and in the whole tea plant were 135.44 and 356.22 mg/kg. These values were significantly lower (P < 0.01) than those in the control roots (340.36 mg/kg) and in the whole tea plant (758.19 mg/kg), respectively. At 20 μmol/L DIDS in the solution, the quantity of fluoride accumulated in the tea roots was 235.85 mg/kg, which was significantly lower (P < 0.01) than that in the control treatments (340.36 mg/kg). TEACl inhibited absorption of Al–F complexes in tea plants when the Al–F ratio was 1:2, but had no significant impact on the accumulation of Al–F complexes in tea plants when the Al–F ratio was 1:1. These results indicated that anionic and cationic channels may be important pathways for the entry of fluoride into tea plants.

Adsorption and desorption are important processes that influence the transport, transformation, and bioavailability of hexachlorobenzene (HCB) in soils. To examine the adsorption-desorption characteristics of HCB, equilibrium batch experiments were carried out using two soils (red soil and paddy soil) with different initial HCB concentrations (0.25, 0.50, 0.75, 1.00, 1.50, 2.50, 3.50, and 5.00 mg L−1) by using 0.01 mol L−1 calcium chloride as the background solution. The successive desorption experiments (48, 96, 144, 192, and 240 h) were conducted after each adsorption equilibrium experiment. The results revealed that adsorption and desorption isotherms of HCB on two soils were nonlinear, which can be best described by the Freundlich equation with the square of the correlation coefficient (r2) ranging from 0.97 to 0.99. Desorption of HCB from the two soils exhibited hysteresis at all HCB concentrations because the Freundlich desorption coefficients were always higher than the Freundlich adsorption coefficients. The hysteretic effect was enhanced with increasing initial HCB concentration, and positive hysteresis was observed at different concentrations.

Adsorption and desorption are important processes that influence the transport, transformation, and bioavailability of hexachlorobenzene (HCB) in soils. To examine the adsorption-desorption characteristics of HCB, equilibrium batch experiments were carried out using two soils (red soil and paddy soil) with different initial HCB concentrations (0.25, 0.50, 0.75, 1.00, 1.50, 2.50, 3.50, and 5.00 mg L−1) by using 0.01 mol L−1 calcium chloride as the background solution. The successive desorption experiments (48, 96, 144, 192, and 240 h) were conducted after each adsorption equilibrium experiment. The results revealed that adsorption and desorption isotherms of HCB on two soils were nonlinear, which can be best described by the Freundlich equation with the square of the correlation coefficient (r2) ranging from 0.97 to 0.99. Desorption of HCB from the two soils exhibited hysteresis at all HCB concentrations because the Freundlich desorption coefficients were always higher than the Freundlich adsorption coefficients. The hysteretic effect was enhanced with increasing initial HCB concentration, and positive hysteresis was observed at different concentrations.