Ca2+ and CaM are involved in Al3+ pretreatment-promoted fluoride accumulation in tea plants (Camellia sinesis L.)

Tea plant (<em>Camellia sinensis</em> (L.) O. kuntze) is known to be a fluoride (F) and aluminum (Al³⁺) hyper-accumulator. Previous study showed that pre-treatment of Al³⁺ caused a significant increase of F accumulation in tea plants. However, less is known about the intricate network of Al³⁺ promoted F accumulation in tea plants. In this study, the involvement of endogenous Ca²⁺ and CaM in Al³⁺ pretreatment-promoted F accumulation in tea plants was investigated. Our results showed that Al³⁺ induced the inverse change of intracellular Ca²⁺ fluorescence intensity and stimulated Ca²⁺ trans-membrane transport in the mature zone of tea root. Also, a link between internal Ca²⁺ and CaM was found in tea roots under the presence of Al³⁺. In order to investigate whether Ca²⁺ and CaM were related to F accumulation promoted by Al³⁺ pretreatment, Ca²⁺ chelator EGTA and CaM antagonists CPZ and TFP were used. EGTA, CPZ, and TFP pretreatment inhibited Al³⁺-induced increase of Ca²⁺ fluorescence intensity and CaM content in tea roots, and also significantly reduced Al³⁺-promoted F accumulation in tea plants. Taken together, our results suggested that the endogenous Ca²⁺ and CaM are involved in Al³⁺ pretreatment-promoted F accumulation in tea roots.