Figure 2.

Schematic diagram showing the routes of NO₃¯ and NH₄ ⁺ sensing, transportation and accumulation in plants. The green dots and arrows denote the transport of NO₃¯ and the red dots and arrows indicates the transport of NH₄ ⁺ ions in plants. In the uptake process, NO₃¯ and NH₄ ⁺ enter the plant roots via NRTs and AMTs transporters respectively. For example, NRT1.1/NPF6.3/CHL1, AMT1.1 and AMT1.3 involved in the sensing of NO₃¯ and NH₄ ⁺ respectively. These transporter are localized in the plasma membrane of root cells. After uptake, NO₃¯ transported via NRT1.5/NPF7.3, NPF2.3, NPF2.4, NPF2.5 and NPF6.5 and NH₄ ⁺ via AMT1.1, AMT1.2 and AMT1.3 to the shoot through xylem. NRT1.5 is involved in NO₃¯ loading in the xylem, while as NRT1.8, NRT1.9 are involved in NO₃¯ unloading from the xylem. However, NRT1.7, NRT1.9 transport NO₃¯ into the phloem. Furthermore, NRT1.4/NPF6.2 and AMT1.3 mediates NO₃¯ and NH₄ ⁺ transport to the leaf/petiole. NO₃¯ accumulation within the leaf vacuole is mediated by NPF7.3, NPF5.12, and NRT2.7. AMT1.1, AMT1.2 and AMT1.3 mediates NH₄ ⁺ transoction from root to shoot. NRT1.6/NPF2.12, NPF7.9 and AMT1.1a, AMT1.4 is involved in the transportation of NO₃¯ and NH₄ ⁺ respectively in the seed where they accumulated in the vacuoles. NRT2.7 is a tonoplast transporter of embryo which regulates NO₃¯accumulation within seed vacuole. AMTs, ammonium transporters; Gla, glutamine; Glu, glutamate; GOGAT, glutamate synthase; GS, glutamine synthetase; NH₄ ⁺, ammonium; NiR, nitrite reductase; NO₃¯, nitrate; NR, nitrate reductase; NRTs, nitrate transporters; 2-OG, 2-Oxoglutarate.