Effect of HCO
-
3
concentration in the absorption solution on the energetic coupling of H+-cotransports in roots of Zea mays L. |
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Authors: | Valérie Toulon Hervé Sentenac Jean-Baptiste Thibaud André Soler David Clarkson Claude Grignon |
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Affiliation: | (1) Laboratoire de Biochimie et Physiologie Végétales (CNRS URA 573), ENSA-M INRA, F-34060 Monpellier Cédex 01, France;(2) Long Ashton Research Station, Department of Agricultural Sciences, University of Bristol, BS18 9AF Bristol, UK |
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Abstract: | The effect of HCO
3
-
on ion absorption by young corn roots was studied in conditions allowing the independent control of both the pH of uptake solution and the CO2 partial pressure in air bubbled through the solution. The surface pH shift in the vicinity of the outer surface of the plasmalemma induced by active H+ excretion was estimated using the initial uptake rate of acetic acid as a pH probe (Sentenac and Grignon (1987) Plant Physiol. 84, 1367). Acetic acid and orthophosphate uptake rates and NO
3
-
accumulation were slowed down, while 86Rb+ uptake and K+ accumulation rates were increased by HCO
3
-
. These effects were similar to those induced by 4-(2-hydroxyethyl)-1-piperazineethane sulfonic acid/2-amino-2-(hydroxymethyl)-1,3-propanediol (Hepes-Tris). They were more pronounced when the H+ excretion was strong, were rapidly reversible and were not additive to those of Hepes-Tris. The hypothesis is advanced that the buffering system CO2/H2CO3/HCO
3
-
accelerated the diffusion of equivalent H+ inside the cell wall towards the medium. This attenuated the surface pH shift in the vicinity the plasma membrane and affected the coupling between the proton pump and cotransport systems.Abbreviations FW
fresh weight
- Hepes
4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
- Jaa
acetic acid influx
- JK
+
K+ influx
- JPi
orthophosphate influx
- Mes
2-(N-morpholino)ethanesulfonic acid
- pCO2
CO2 partial pressure
- Tris
2-amino-2-(hydroxymethyl)-1,3-propanediol |
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Keywords: | Bicarbonate (root ion absorption) Energetic coupling Proton (cotransport excretion) Root (ion absorption) Surface pH Zea roots (ion absorption) |
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