Characterization of fluoride uptake by roots of tea plants (Camellia sinensis (L.) O. Kuntze)

Tea plants (Camellia sinensis (L.) O. Kuntze) accumulate high fluoride in the leaves whereas the mechanism on its uptake is poorly understood. The measured F- uptake was compared to calculated uptake from transpiration rates assumuing no discrimination between F- and water to characterize the property of F- absorption by tea plant roots. The F- uptake was examined by depletion method under variable external F- concentrations, pH, temperature, relative air humidity, anion channel blockers and metabolism inhibitors in solution experiments. Measured F- uptake rates were significantly larger than those calculated from transpiration rates regardless of external F- concentrations, uptake durations, relative humidity, and solution pH. The measured and net F- uptake (subtracting that calculated from transpiration rate from the measured uptake) were reduced by low temperature and inhibited by anion channel and metabolism inhibitors anthracene-9-carboxylic acid (A-9-C), niflumic acid (NFA), and carbonylcyanide m-chlorophenylhydrazone (CCCP) but not by dihydro-4, 4' diisothiocyanostilbene-2, 2'-disulphonic acid (DIDS). The F- uptake showed biphasic response patterns, following saturable Michaelis-Menten kinetics in the range of low external F- (below 100 mu mol L-1) while increased linearly with external supply in the range of high concentrations. The uptake of F- by roots of accumulator tea plants was likely an active process and energy-dependent. This helps to explain why tea plants are able to accumulate considerably high F-.