Relationship between intracellular pH and N metabolism in maize (Zea mays L.) roots |
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Authors: | Gerendás J Ratcliffe R G Sattelmacher B |
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Institution: | (1) Institute of Plant Nutrition and Soil Science, Christian-Albrechts-University, Olshausenstra·e 40, D-2300 Kiel, Germany;(2) Department of Plant Sciences, University of Oxford, South Parks Road, OX1 3RB Oxford, U.K. |
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Abstract: | In vivo
31P nuclear magnetic resonance (NMR) was used to characterize the effect of the N form (NO3 vs. NH4) and the external pH (4, 6, and 8), on the intracellular pH of root tips (0–5 mm) and root segments (5–30 mm). Ammonium-grown root tips were the most sensitive to changes in the external pH. In vivo
15N NMR was used to characterize the pathway of primary ammonium assimilation in the ammonium-grown roots and to compare the activity of the apical and more-basal root parts. The kinetics of 15NH4
+ incorporation showed that primary assimilation in both root tips and root segments followed the glutamine synthetase (GS) pathway. In agreement with the reported gradient of GS along the seminal root of maize, incorporation of label into glutamine amide was more rapid in tips than in segments. It is suggested that this higher GS activity increases the endogenous proton production and thus contributes to the greater dependence of the cytoplasmic pH on the external pH in the ammonium-treated root tips. |
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Keywords: | cytoplasmic pH NH4
+ assimilation 15N NMR N nutrition 31P NMR Zea mays L |
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