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. 1988 Nov;88(3):605–612. doi: 10.1104/pp.88.3.605

Charge Balance in NO3−-Fed Soybean

Estimation of K+ and Carboxylate Recirculation

Bruno Touraine 1, Nicole Grignon 1, Claude Grignon 1
PMCID: PMC1055632  PMID: 16666356

Abstract

Soybeans (Glycine max L. Merr., cv Kingsoy) were grown on media containing NO3− or urea. The enrichments of shoots in K+, NO3−, and total reduced N (Nr), relative to that in Ca2+, were compared to the ratios K+/Ca2+,NO3−/Ca2+, and Nr/Ca2+ in the xylem saps, to estimate the cycling of K+, and Nr. The net production of carboxylates (R−) was estimated from the difference between the sums of the main cations and inorganic anions. The estimate for shoots was compared to the theoretical production of R− associated with NO3− assimilation in these organs, and the difference was attributed to export of R− to roots. The net exchange rates of H+ and OH− between the medium and roots were monitored. The shoots were the site of more than 90% of total NO3− reduction, and Nr was cycling through the plants at a high rate. Alkalinization of the medium by NO3−-fed plants was interrupted by stem girdling, and not restored by glucose addition to the medium. It was concluded that the majority of the base excreted in NO3− medium originated from R− produced in the shoots, and transported to the roots together with K+. As expected, cycling of K+ and reduced N was favoured by NO3− nutrition as compared to urea nutrition.

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Selected References

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