Observations on the subcellular distribution of the ammonium ion in maize root tissue using in-vivo14N-nuclear magnetic resonance spectroscopy

✍ Scribed by R. B. Lee; R. G. Ratcliffe

• Publisher: Springer-Verlag
• Year: 1991
• Tongue: English
• Weight: 961 KB
• Volume: 183
• Category: Article
• ISSN: 0032-0935
• DOI: 10.1007/bf00197734

✦ Synopsis

We show that the pH dependence of the basecatalysed exchange rate of the ammonium ion provides a basis for discriminating between the cytoplasmic and vacuolar pools of ammonium in plant tissues. In vivo, 14N-nuclear magnetic resonance spectra were recorded with and without IH-decoupling and information on the subceltular distribution of NH2 was obtained from a lineshape analysis of the tH-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.