D-serine- andp-fluorophenylalanine-resistant mutants ofPhyscomitrium patensare defective in amino acid uptake

Two amino acid analogue-resistant lines of Physcomitrium (formerly Physcomitrella ) patens, DSR8 and PFR4 , are resistant to a range of D-amino acids and an inhibitory concentration of L-lysine. Both are defective in the uptake of [ 35 S]-L-methionine. Uptake by the wild-type line is pH-dependent (decreasing with raised external proton concentrations) and is depressed by dinitrophenol and by ammonium ions. We discuss the possible involvement of an active proton-general amino acid antiport pump in the plasma membrane.