| Popis: |
The mechanisms of radiocesium uptake and accumulation have been studied, from a physiological point of view, in Riccia fluitans . There are two mechanisms of radiocesium uptake in this plant. One takes place when the external potassium concentration is above 0.1 mM. In this case, the uptake kinetic is linear, and the transport system exhibits a low affinity for cesium. Radiocesium enters the cells through potassium channels, the electrochemical potential gradient for this ion being the driving force. A second mechanism is developed in plants adapted to low or very low concentrations of potassium (less than 0.1 mM). The uptake kinetic is hyperbolic and exhibits a great sensitivity for cesium. This mechanism is carrier-mediated, protons probably being the driving ions, and takes place against the electrochemical gradient for potassium and cesium. |
