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. 1990 May;93(1):281–289. doi: 10.1104/pp.93.1.281

Evidence for Cotransport of Nitrate and Protons in Maize Roots 1

I. Effects of Nitrate on the Membrane Potential

Peter R McClure 1,2,2, Leon V Kochian 1,2, Roger M Spanswick 1,2, Jon E Shaff 1,2
PMCID: PMC1062500  PMID: 16667448

Abstract

The electrical response of nitrate-grown maize (Zea mays L.) roots to 0.1 millimolar nitrate was comprised of two sequential parts: a rapid and transient depolarization of the membrane potential, followed by a slower, net hyperpolarization to a value more negative than the original resting potential. The magnitude of the response was smaller in roots of seedlings grown in the absence of nitrate, but, within 3 hours of initial exposure to 0.1 millimolar nitrate, increased to that of nitrate-grown roots. Chloride elicited a separate electrical response with a pattern similar to that of the nitrate response. However, the results presented in this study strongly indicate that the electrical response to nitrate reflects the activity of a nitrate-inducible membrane transport system for nitrate which is distinct from that for chloride. Inhibitors of the plasmalemma H+-ATPase (vanadate, diethylstilbestrol) completely inhibited both parts of the electrical response to nitrate, as did alkaline external pH. The magnitude of the initial nitrate-dependent, membrane potential depolarization was independent of nitrate concentration, but the subsequent nitrate-dependent hyperpolarization showed saturable dependence with an apparent Km of 0.05 millimolar. These results support a model for nitrate uptake in maize roots which includes a depolarizing NO3−/H+ symport. The model proposes that the nitrate-dependent membrane potential hyperpolarization is due to the plasma membrane proton pump, which is secondarily stimulated by the operation of the NO3−/H+ symport.

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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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