Uptake and translocation of cesium by Arabidopsis thaliana in hydroponics conditions: Links between kinetics and molecular mechanisms

- Parameters of Cs + uptake in A. thaliana under three different K+-supplies are given.
- Effects of K+ on Cs+ fluxes are discussed regarding properties of K+ transport systems.
- Both K+ and Cs+ external concentrations affect efficiency of Cs+ uptake.
- The root:shoot Cs+ concentration ratio is higher under low K+-supply.
- Role of HAK5 in Cs+ uptake is reduced when Cs+ external concentration increases.

Early studies have shown that cesium (Cs+) competes with the macronutrient potassium (K+) for uptake by plants. The present study investigates the effect of K+ supply on Cs+ uptake and translocation in Arabidopsis thaliana. Taking advantage of the frequent use of this model plant in previous molecular studies, we discuss the link between functional features described for transporters involved in K+ (and sometimes in Cs+) uptake and results obtained here in both Cs+ influx and accumulation experiments under different K+-treatments. In low K+ condition (10 μM), we observed that roots affinity for Cs+ increased significantly and Cs+ concentration in the external medium clearly affected the efficiency of Cs+ uptake. Our results are consistent with previous molecular studies indicating the role of the high-affinity K+ carrier AtHAK5 in Cs+ uptake under K+-deprivation. Further experiments show that the lack of AtHAK5 has no more effect on Cs+ uptake for external Cs+ concentration above 100 μM. We propose that non-selective cation channels, likely involved in Cs+ uptake under K+-sufficient conditions according to previous studies, could also mediate Cs+ uptake under K+-starvation and high Cs+ concentrations. Finally, evidences for Cs+ translocation mediated by K+ channels are discussed.