Abstract
Rice (Oryza sativa L.) plants possess three homologous but distinct genes for cytosolic glutamine synthetase (GS1), i.e. OsGS1;1, OsGS1;2 and OsGS1;3. Both OsGS1;1 mRNA and OsGS1;2 mRNA were detected in roots, leaf sheaths, leaf blades, and spikelets. However, the OsGS1;3 mRNA was only detectable in spikelets. OsGS1;1 knockout mutants caused by insertion of endogenous retrotransposon Tos17 showed severe retardation in growth rate under NH4+-containing hydroponic solution. Tos17-mediated mutants for OsGS1;2 and OsGS1;3 were recently identified. Their characteristics will be discussed.