Abstract
In our previous study, we showed that 4 isoenzymes of cytosolic glutamine synthetase (GS1) are expressed in Arabidopsis roots, and that GS1;2 is the only isoenzyme whose transcript accumulates in response to high NH4+. These results suggest significance of GS1;2 in acclimation to high NH4+. In this study, we examined the roles of GS1;2 in root development of Arabidopsis in response to nitrogen sources.
When plants were grown on medium containing NO3- as the sole nitrogen source, the wild-type plants (WT) and gs1;2 mutants showed no differences in root development. By contrast, gs1;2 mutants developed shorter and smaller number of lateral roots (LRs) compared to WT plants when plants were grown on medium containing NH4+.
LR development is known to be regulated by auxin. To examine the effects of auxin on NH4+-induced LR development, roots of WT plants and gs1;2 mutants were treated with IAA. The number of LRs was significantly increased in WT plants, but not in gs1;2 mutants, when plants were grown on medium containing NH4+ and 10 nM IAA. The results suggested that gs1;2 mutants are desensitized to auxin and that the response of LRs to auxin is partly dependent on NH4+.
