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We show that the pH dependence of the base-catalysed exchange rate of the ammonium ion provides a basis for discriminating between the cytoplasmic and vacuolar pools of ammonium in plant tissues. In vivo, (14)N-nuclear magnetic resonance spectra were recorded with and without (1)H-decoupling and information on the subcellular distribution of NH 4 (+) was obtained from a lineshape analysis of the (1)H-coupled spectrum. We applied this method to maize (Zea mays L.) root tissues and found that: (i), the cytoplasmic ammonium concentration was low, which was in accord with the large activity of glutamine synthetase present in the roots; and (ii), inhibition of glutamine synthetase with methionine sulphoximine increased the cytoplasmic ammonium concentration, and led to the appearance of ammonium in the xylem sap.

Original publication

DOI

10.1007/BF00197734

Type

Journal article

Journal

Planta

Publication Date

02/1991

Volume

183

Pages

359 - 367