XVI International Botanical Congess

In this study, We demonstrate that CHL1 is a dual-affinity nitrate transporter. A deletion mutant chl1-5 was demonstrated to be defecive in hgih-affinity nitrate uptake. This observation was upheld by a chlorosis test on wild type and chl1-5 at 10 uM chlorate. A transgenic plant expression 35S-CHL1 cDNA in the deletion background showed a recovery in uptake. This observation is further supported by the uptake assay using HPLC in the hetero-expression system of Xenopus oocytes. Both low- and high-affinity uptake activity were observed in CHL1-injected oocyte.Kinetic analysis of nitrate uptake of CHL1-injected Xenopus oocytes displayed a biphasic pattern with a Km calue of ~50 uM for the high-affinity phase and ~4 mM for the low-affinity phase. These results indicate that CHL1 is also involved in both the inducible and constitutive phases of high-affinity nitrate uptake of Arabidopsis.