Department of Plant Sciences

Remobilisation of phosphate (Pi) within a plant is critical for sustaining its growth under external Pi fluctuation and for seed production. The barley transporter, HvPht1;6 has been implicated in Pi remobilisation. However, functional characterisation of HvPht1;6 and other known plant Pi transporters has been limited owing to the lack of a suitable expression system. In this report, we expressed HvPht1;6 in Xenopus laevis oocytes allowing the first detailed characterisation of a plant phosphate transporter. HvPht1;6 increased efflux of Pi near oocyte resting membrane potentials, dependent on external Pi concentration. Inward currents activated by negative membrane potentials were consistent with nH+:HPO42- (n>2) co-transport, and were dependant on Pi concentration gradient and pH. The large inward current (Pi influx) at -150 mV was also observed for other oxyanions including SO42- and NO3-. Inward and outward currents showed linear dependence on the concentration of external HPO42- and membrane potential, suggesting that HvPht1;6 may, in hyperperpolarised phloem cells, load Pi from the apoplast; and in depolarised cells, such as senescing mesophyll cells, unload Pi to the apoplast. The electrophysiological properties of HvPht1;6 are consistent with its suggested role in the remobilisation of Pi in barley plants. Our results demonstrate that using modified bath solution, X. laevis oocytes can be used for studies of electrophysiological properties of plant proton-coupled Pi transporters.