Identification of glutamine synthetase (GS) and glutamate synthase (GOGAT) responsible for assimilation of exogenous NH₄⁺ in Arabidopsis root

Abstract

Primary ammonium assimilation into glutamine and glutamate is carried out by the GS/GOGAT cycle. In Arabidopsis, GS and GOGAT are coded by 9 isoforms gene families (GS1;Gln1;1-1;5, GS2; Gln2, Fd-GOGAT; Glu1, Glu2, NADH-GOGAT; Glt1).
In the present study, we identified the molecular species of GS and GOGAT responsible for assimilation of NH₄⁺ in roots. Real-time PCR analysis showed that levels of Gln1;2 and Glt1 mRNA were specifically increased following supply of NH₄⁺. In addition, these genes mainly expressed in epidermis or cortex cells that play important roles in absorption of NH₄⁺. These results strongly suggest that most of the absorbed NH₄⁺ can be assimilated to glutamine and glutamate by the NH₄⁺ inducible Gln1;2/Glt1 system at the surface of Arabidopsis root.