
%0 Journal Article
%A McPharlin, IR 
%A Bieleski, RL 
%T P<sub>I</sub> Efflux and Influx by P-Adequate and P-Deficient <I>Spirodela</I> and <I>Lemna</I>
%J Functional Plant Biology
%D 1989/10/01
%V 16
%N 5
%P 391-399
%K 
%R https://doi.org/10.1071/PP9890391
%U https://www.publish.csiro.au/paper/PP9890391 
%X Net Pi influx by P-adequate (+P) and P-deficient (-P) Spirodela and Lemna plants was determined by gross PI influx and PI efflux. Rates of PI influx (gross) and PI efflux were sensitive to both internal [P] and external [PI]. The different responses of these two fluxes to external [PI] resulted in their rates converging at low external [PI], from PI efflux being 9-10% of gross PI influx at 1000 µM PI to being over 70% at low (1 µM) external PI in + P plants. At very low external Pi (0.34 µM, 0.22 µM Pi for + P Spirodela and Lemna, respectively), rates of gross Pi influx and Pi efflux were assumed to be either equal or zero (referred to as the equilibrium [Pi]ext), such that net Pi influx was zero. There was assumed to be insufficient Pi diffusing to the carrier site on the root surface at very low external [Pi] (i.e. equilibrium [Pi]ext) for the phosphate pump to operate and Pi influx was zero. P deficiency resulted in a simultaneous reduction in rates of Pi efflux and an increase in gross Pi influx such that the equilibrium [Pi]ext was reduced 3-4 times (0.8, 0.07 µM Pi for -P Spirodela and Lemna respectively) compared with +P plants. Some of the limitations of Pi diffusion to the carrier sites in P-adequate plants are overcome as internal [P] decreases during P deficiency. As a consequence the ability of Spirodela and Lemna to extract Pi from solution during P deficiency was considerably greater than for plants with adequate P status.    Inhibitors of metabolism (low temperatures, arsenate, azide, cyanide and CCCP) reduced rates of gross Pi influx but increased rates of Pi efflux such that net Pi influx was reduced. These findings are discussed in relation to previous work on the kinetics of Pi influx in - P versus + P plants and the role of changes in membrane potentials in the enhancement of Pi influx and reduction of Pi efflux capacity in P-deficient Spirodela and Lemna. 
