The Movement of Rubidium Across the Root of Hordeum Vulgare (L)

Summary An automatic system is described for the continuous measurement of absorption and translocation of radioactive nuclides by living plants growing in a controlled environment. The system is suitable for studying the behaviour of nuclides emitting β particles in the energy band between 0.5 and 2.5 MeV. The reliability and precision of the system are discussed. Experiments on the absorption and translocation of 86Rb by 10‐14‐day‐old seedlings of barley are reported. It was found that when 86Rb was absorbed from 10−5 M 86RbNO3 the rate of movement into the shoot (translocation) increased with time, but that when absorption was from a higher concentration of RbNO3 a constant rate of translocation was observed after the initial rise during the first 3 hours. When radioactive seedlings were placed in an inactive 10−5 m RbNO3 solution no loss of 86Rb to the solution was detected, but 86Rb moved to the shoot, the decrease of 86Rb in the root following first‐order kinetics. When radioactive seedlings were transferred to a 10−4 m RbNO3 solution more complex kinetics of decrease in 86Rb in the root were observed. The findings are discussed and found to be compatible with a simple two‐compartment model of the root.