Abstract
Cytosolic glutamine synthetase (GS1) catalyzes the first step of NH4+ assimilation in the roots of higher plants. Four GS1 isoenzymes, AtGLN1;1-1;4 were expressed in Arabidopsis roots, and can be classified into two groups by the affinity to NH4+. High-affinity GS1, AtGLN1;1 was induced in the epidermis by nitrogen deprivation. However, low-affinity form, AtGLN1;2 was significantly up-regulated by NH4+. Gln accumulation was reduced in the AtGLN1;2 mutant roots under NH4+-sufficient condition. On the other hand, two high-affinity GS1, OsGLN1;1 and OsGLN1;2 were abundantly expressed in rice roots. The transcripts of both GS1 isoenzymes showed reciprocal responses to NH4+ supply in the surface cell layers of roots. Taken together, individual GS1 is strictly regulated by gene expression and post-translation level to adapt the nitrogen environment.
