Nitrate transfer and remobilization in leaves
Three nitrate transporters have been shown to be involved in nitrate transfer and/or redistribution to the phloem from xylem or source nitrate-containing tissues: NPF2.13/NRT1.7, NPF1.1/NRT1.12, and NRT1.2/NRT1.11 (Iqbal et al., 2020). In particular, it has been recently shown that NPF2.13/NRT1.7 is essential for remobilization of nitrate from old leaves to deliver nitrate into the phloem, making it available for new, developing leaves and enhancing nitrogen use efficiency (Chen, Chen, Tseng, & Tsay, 2020). NPF1.1/NRT1.12 and NPF1.2/NRT1.11 have been found to be involved in the transfer of xylem nitrate to phloem in the petiole thereby facilitating nitrate remobilization from mature (old) leaves to young leaves (Hsu & Tsay, 2013).