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Characterization of nitrite uptake in Arabidopsis thaliana : evidence for a nitrite‐specific transporter
Author(s) -
Kotur Zorica,
Siddiqi Yaeesh M.,
Glass Anthony D. M.
Publication year - 2013
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.12358
Subject(s) - nitrite , nitrate , transporter , biochemistry , arabidopsis , chemistry , arabidopsis thaliana , mutant , biology , gene , organic chemistry
Summary Nitrite‐specific plasma membrane transporters have been described in bacteria, algae and fungi, but there is no evidence of a nitrite‐specific plasma membrane transporter in higher plants. We have used13NO 2−to characterize nitrite influx into roots of Arabidopsis thaliana . Hydroponically grown Arabidopsis mutants, defective in high‐affinity nitrate transport, were used to distinguish between nitrate and nitrite uptake by means of the short‐lived tracers13NO 2−and13NO 3−. This approach allowed us to characterize a nitrite‐specific transporter. The Atnar2.1‐2 mutant, lacking a functional high‐affinity nitrate transport system, is capable of nitrite influx that is constitutive and thermodynamically active. The corresponding fluxes conform to a rectangular hyperbola, exhibiting saturation at concentrations above 200 μM ( K m = 185 μM and V max = 1.89 μmol g −1 FW h −1 ). Nitrite influx via the putative nitrite transporter is not subject to competitive inhibition by nitrate but is downregulated after 6 h exposure to ammonium. These results signify the existence of a nitrite‐specific transporter in Arabidopsis. This transporter enables Atnar2.1‐2 mutants, which are incapable of sustained growth on low nitrate, to maintain significant growth on low nitrite. In wild‐type plants, this nitrite flux may increase nitrogen acquisition and also participate in the induction of genes specifically induced by nitrite.