Arabidopsis NRT1.5 Is Another Essential Component in the Regulation of Nitrate Reallocation and Stress Tolerance1[W].

Nitrate reallocation to plant roots occurs frequently under adverse conditions and was recently characterized to be actively regulated by Nitrate Transporter!.8 (NRT1.8) in Arabidopsis (Arabidopsis thaliana) and implicated as a common response to stresses. However, the underlying mechanisms remain largely to be determined. In this study, characterization of NRT1.5, a xylem nitrate-loading transporter, showed that the mRNA level of NRT1.5 is down-regulated by salt, drought, and cadmium treatments. Functional disruption of NRT1.5 enhanced tolerance to salt, drought, and cadmium stresses. Further analyses showed that nitrate, as well as Na⁺ and Cd²⁺ levels, were significantly increased in nrtl.5 roots. Important genes including Na⁺ /H⁺ exchangerl, Salt overly sensitivel, Pyrroline-5-carboxylate synthasel, Responsive to desiccation29A, Phytochelatin synthasel, and NRT1.8 in stress response pathways are steadily up-regulated in nrtl.5 mutant plants. Interestingly, altered accumulation of metabolites, including proline and malondialdehyde, was also observed in nrtl.5 plants. These data suggest that NRT1.5 is involved in nitrate allocation to roots and the consequent tolerance to several stresses, in a mechanism probably shared with NRT1.8. [ABSTRACT FROM AUTHOR]