Anion channel inhibitor NPPB-inhibited fluoride accumulation in tea plant (Camellia sinensis) is related to the regulation of Ca2+, CaM and depolarization of plasma membrane potential

Tea plant is known to be a hyper-accumulator of fluoride (F). Over-intake of F has been shown to have adverse effects on human health, e.g., dental fluorosis. Thus, understanding the mechanisms fluoride accumulation and developing potential approaches to decrease F uptake in tea plants might be beneficial for human health. In the present study, we found that pretreatment with the anion channel inhibitor NPPB reduced F accumulation in tea plants. Simultaneously, we observed that NPPB triggered Ca²⁺ efflux from mature zone of tea root and significantly increased relative CaM in tea roots. Besides, pretreatment with the Ca²⁺ chelator (EGTA) and CaM antagonists (CPZ and TFP) suppressed NPPB-elevated cytosolic Ca²⁺ fluorescence intensity and CaM concentration in tea roots, respectively. Interestingly, NPPB-inhibited F accumulation was found to be significantly alleviated in tea plants pretreated with either Ca²⁺ chelator (EGTA) or CaM antagonists (CPZ and TFP). In addition, NPPB significantly depolarized membrane potential transiently and we argue that the net Ca²⁺ and H⁺ efflux across the plasma membrane contributed to the restoration of membrane potential. Overall, our results suggest that regulation of Ca²⁺-CaM and plasma membrane potential depolarization are involved in NPPB-inhibited F accumulation in tea plants.