CHL1 Is a Dual-Affinity Nitrate Transporter of Arabidopsis Involved in Multiple Phases of Nitrate Uptake

• Published in: The Plant cell 1999-05, Vol.11 (5), p.865-874
• Main Authors: Liu, Kun-Hsiang, Huang, Chi-Ying, Tsay, Yi-Fang
• Format: Article
• Language: English
• Subjects: Animals; Anion Transport Proteins; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins; Biological Transport - drug effects; Carrier Proteins - genetics; Carrier Proteins - metabolism; Chlorates; Chlorates - pharmacology; Kinetics; Messenger RNA; Mutation; Nitrates; Nitrates - metabolism; Nitrogen; Oocytes; Plant cells; Plant growth; Plant Proteins; Plant Roots - drug effects; Plants; RNA, Complementary - metabolism; RNA, Plant - metabolism; Transgenic plants; Xenopus
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.11.5.865

Higher plants have both high- and low-affinity nitrate uptake systems. These systems are generally thought to be genetically distinct. Here, we demonstrate that a well-known low-affinity nitrate uptake mutant of Arabidopsis, chl1, is also defective in high-affinity nitrate uptake. Two to 3 hr after nitrate induction, uptake activities of various chl1 mutants at 250 μM nitrate (a high-affinity concentration) were only 18 to 30% of those of wild-type plants. In these mutants, both the inducible phase and the constitutive phase of high-affinity nitrate uptake activities were reduced, with the inducible phase being severely reduced. Expressing a CHL1 cDNA driven by the cauliflower mosaic virus 35S promoter in a transgenic chl1 plant effectively recovered the defect in high-affinity uptake for the constitutive phase but not for the induced phase, which is consistent with the constitutive level of CHL1 expression in the transgenic plant. Kinetic analysis of nitrate uptake by CHL1-injected Xenopus oocytes displayed a biphasic pattern with a Michaelis-Menten K m value of ∼50 μM for the high-affinity phase and ∼4 mM for the low-affinity phase. These results indicate that in addition to being a low-affinity nitrate transporter, as previously recognized, CHL1 is also involved in both the inducible and constitutive phases of high-affinity nitrate uptake in Arabidopsis.