Molecular mechanisms involved in caesium uptake and transport in land plants

Caesium (Cs) uptake in land plant is mainly carried out by potassium ion (K⁺) transport systems. Potassium ion uptake from the rhizosphere is regulated by two types of transport system, low affinity and high affinity transport systems, depending on the K⁺ concentration in soil solution, In both transport systems, there are several channels and transporters which mediate Cs⁺ transport also. In low affinity transport system, the inward-rectifying K⁺ and voltage-insensitive cation channels are involved in Cs⁺ uptake, while KUP/HAK/KT type transporters are the major Cs⁺ path in high affinity transport system. Within the plant body, Cs⁺ translocation is also mediated by outward-rectifying K⁺channels. In addition to these Cs⁺ and K⁺ competitive transport systems, recent studies reported novel Cs⁺ transport systems without changing K⁺ behavior in plant. In this review, Cs⁺ transport systems dependent/independent to K⁺ transport mechanisms are introduced. (author)