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. 1992 Jun;99(2):456–463. doi: 10.1104/pp.99.2.456

Studies of the Uptake of Nitrate in Barley 1

IV. Electrophysiology

Anthony D M Glass 1,2, Jon E Shaff 1,2, Leon V Kochian 1,2
PMCID: PMC1080484  PMID: 16668907

Abstract

Transmembrane electrical potential differences (Δψ) of epidermal and cortical cells were measured in intact roots of barley (Hordeum vulgare L. cv Klondike). The effects of exogenous NO3− on Δψ (in the concentration range from 100 micromolar to 20 millimolar) were investigated to probe the mechanisms of nitrate uptake by the high-affinity (HATS) and low-affinity (LATS) transport systems for NO3− uptake. Both transport systems caused depolarization of Δψ, demonstrating that the LATS (like the HATS) for NO3− uptake is probably mediated by an electrogenic cation (H+?) cotransport system. Membrane depolarization by the HATS was “inducible” by NO3−, and saturable with respect to exogenous [NO3−]. By contrast, depolarization by the LATS was constitutive, and first-order in response to external [NO3−]. H+ fluxes, measured in 200 micromolar and in 5 millimolar Ca(NO3)2 solutions, failed to alkalinize external media as anticipated for a 2 H+:1 NO3− symport. However, switching from K2SO4 solutions (which were strongly acidifying) to KNO3 solutions at the same K+ concentration caused marked reductions in H+ efflux. These observations are consistent with NO3− uptake by the HATS and the LATS via 2 H+:1 NO3− symports. These observations establish that the HATS for nitrate uptake by barley roots is essentially similar to those reported for Lemna and Zea mays by earlier workers. There are, nevertheless, distinct differences between barley and corn in their quantitative responses to external NO3−.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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