A conserved Arg in OsSUT1 is crucial for sucrose-induced currents. (A) Arg188 in OsSUT1 is conserved in all three types of SUTs. (B) Substrate-induced currents in oocytes expressing OsSUT1 wild type or Arg188 mutants at pH 5.6. The currents were induced by 30 mM sucrose, β-phenyl-glucoside, or glucose, at −118 mV. Error bars indicate SE (n=3). (C) Oocyte expressing OsSUT1(R188K) shows block of inward leak currents by 30 mM sucrose. Currents were measured in Na ringer or K ringer (Na-free) at pH 5.6, and a holding potential of −40 mV. Results in C are from one oocyte that is representative of four experiments. Pipette potential was zeroed when bath solutions were changed.