Fluoride detoxification in tea plants depends on aluminium and localization in the epidermis

Tea (Camellia sinensis) is a hyperaccumulator of both aluminium (Al) and fluorine (F). While the formation of Al-F complexes has been proposed as a key mechanism for F detoxification and accumulation in tea, excessive Al and especially fluoride (F-) pose health risks to humans. In this study, we tested the hypothesis that Al3+ mitigates F--induced ionomic imbalance and that Al and F are spatially colocalized within tea tissues. Tea plants were grown hydroponically under different Al3+ and F- treatments, and elemental distributions were analysed using micro-particle-induced gamma-ray emission (micro-PIGE), micro-particle-induced X-ray emission (micro-PIXE), and low-energy X-ray fluorescence (LEXRF). Tea plants were highly sensitive to F- treatment, exhibiting leaf crinkling, chlorosis, and marginal necrosis; however, the addition of Al3+ markedly alleviated these symptoms by reducing F- translocation to the shoots. Ionomic profiling revealed that F- supply increased manganese (Mn) accumulation in both leaves and roots, whereas Al3+ supplementation mitigated F--induced Mn toxicity. Micro-PIGE mapping revealed co-localization of Al and F in leaf margins, particularly along fourth- and fifth-order veins. LEXRF analysis further showed that Al and F colocalized in the epidermis of leaves and roots, but not in the xylem of petiole or midribs. In root cortical cells, Al and magnesium (Mg) colocalized. These findings demonstrate that F- detoxification in tea is Al3+-dependent and occurs through the formation of Al-F complexes in the epidermis, providing a spatial framework for future mechanistic studies on Al-F interactions in tea.