31P nuclear magnetic resonance evidence for differences in intracellular pH in the roots of maize seedlings grown with nitrate or ammonium

Abstract

Summary 31 P nuclear magnetic resonance (NMR) spectroscopy was used to measure the cytoplasmic and vacuolar pH values in maize ( Zea mays ) root tissues from seedlings grown in nutrient solutions at different pH values with either nitrate or ammonium as the source of nitrogen. The nitrogen form had little effect on intracellular pH at pH 6, but differences were found at pHs 4 and 8 with the largest effects occurring in root tips with ammonium supply. Intracellular pH in roots was regulated more tightly in the nitrate grown plants than in the ammonium grown plants and it was concluded that the influx of free ammonia at pH 8 and the unfavourable energetics of H + excretion at low external pH were responsible for this difference.