Energization of potassium uptake in Arabidopsis thaliana |
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Authors: | Frans J M Maathuis Dale Sanders |
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Institution: | (1) Department of Biology, University of York, YO1 5DD York, UK |
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Abstract: | Plant roots accumulate K+ from micromolar external concentrations. However, the absence of a firm determination of the trans-plasma-membrane electrochemical gradient for K+ in these conditions has precluded an assessment of whether K+-accumulation requires energization in addition to the driving force provided by the inside-negative membrane electrical potential (Em). To address this question unequivocally, we measured Em, and the cytosolic and external K+-activities in root cells of Arabidopsis thaliana (L.) Heynh. cv. Columbia in conditions in which net K+-accumulation occurs at low external K+ (10 M). In these conditions, net K+-uptake was about 0.1 mol · (g FW)-1 · h-1, Em varied between-153 and -129 mV and the cytosolic K+-activity, determined with K+-selective electrodes, was 83 ± 4 mM. These values yield an outwardly-directed driving force on K+ of at least 6.5 kJ · mol-1. Only if external potassium is raised to the region of 1 mM does Em become sufficient to drive net K+-accumulation. It is therefore concluded that at micromolar external K+-activities which prevail in most soils, K+-uptake cannot be solely energized by Em — as exemplified by a channel-mediated mechanism. The nature of the energization mechanism is discussed in relation to processes operating in fungal and algal cells.Abbreviations and Symbols AAS
atomic absorption spectrometry
- Em
membrane potential
-
electrochemical potassium gradient
- F
Faraday constant (96500 C · mol-1)
We thank Peter Barraclough, Roger Leigh, David Walker and Tony Miller (Rothamsted Experimental Station, Harpenden, UK) for helpful discussions. Financial support was provided by the Agricultural and Food Research Council (Grant PG87/529). |
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Keywords: | Arabidopsis Ion-selective electrode Membrane potential Potassium uptake Ion channel |
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