| Abstract: | A simple expression has been derived to predict the rate ofnet K uptake into exponentially growing plants of Lemna minor.Net uptake predictions are in good quantitative agreement withmeasurements of ‘steady-state’ K influx, indicatingthat, in the ‘steady state’, K movements in theplant are essentially undirectional and that efflux is small.This close matching of inward K movement to the demands of theexpanding tissue is temporarily disturbed if plants are transferredto media of different K status. Uptake rates in the ‘step-up’are initially enhanced and then fall gradually towards a new‘steady-state’ rate. In contrast, the ‘step-down’causes an initial depression of uptake and then rates increasegradually towards the new ‘steady-state’ rate. Itis argued that these changes in uptake rates are associatedwith alterations in the cytoplasmic K content. |
