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Allosteric Regulation of Potassium Uptake in Plant Roots

Allosteric Regulation of Potassium Uptake in Plant Roots In uptake experiments from nutrient solutions containing 2.0 mM K+ labelled with 86Rb+, the relationship between potassium uptake efficiency and internal potassium concentration of the roots, (K+)i was found to be partly sigmoidal for intact plants of spring wheat (Triticum aestivum L.), glasshouse cucumber (Cucumis sativus L.), birch (Betula verrucosa Ehrh.), lingonberry (Vaccinium vitis‐idaea L.), Scots pine (Pinus silvestris L.) and Norway spruce (Picea abies (L.) Karst.), The results were interpreted in terms of sigmoidal enzyme kinetics for allosteric regulation. Hill plots of the data gave straight lines at specific (K+)i intervals for the species. The slopes of the lines are the Hill coefficient, which could be regarded as a measure of the minimal number of allosteric sites. The Hill coefficient varied between ‐ 14.4 and ‐ 15.9. When divided by four, these values are fairly consistent with those in the literature. It is suggested that four active uptake sites interact with four groups of allosteric sites, each group containing four such sites, or that one active uptake site interacts with all the allosteric sites. Thus the results are evidence that the mechanism regulating K+ uptake is basically similar for the investigated plants. It is the interval of (K+)i mediating highly negatively cooperative allosteric regulation that differs among species. For some of the species, n decreased from about 15 and approached unity at high (K+)i values. This may indicate that only few sites are still available, making cooperativity unimportant. Alternatively high vacuolar (K+)i concentrations may give rise to an incorrect evaluation of data from Hill plots, since the cytoplasmic K+ content likely regulates the allosteric mechanism. Moreover, it is suggested that gene‐controlled carrier synthesis is responsible for the varying maximum K+ uptake efficiency among species. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Physiologia Plantarum Wiley

Allosteric Regulation of Potassium Uptake in Plant Roots

JENSÉN, PAUL; PETTERSSON, SUNE
Physiologia Plantarum , Volume 42 (2) – Feb 1, 1978
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References (31)

Publisher
Wiley
Copyright
Copyright © 1978 Wiley Subscription Services, Inc., A Wiley Company
ISSN
0031-9317
eISSN
1399-3054
DOI
10.1111/j.1399-3054.1978.tb02549.x
Publisher site
See Article on Publisher Site

Abstract

In uptake experiments from nutrient solutions containing 2.0 mM K+ labelled with 86Rb+, the relationship between potassium uptake efficiency and internal potassium concentration of the roots, (K+)i was found to be partly sigmoidal for intact plants of spring wheat (Triticum aestivum L.), glasshouse cucumber (Cucumis sativus L.), birch (Betula verrucosa Ehrh.), lingonberry (Vaccinium vitis‐idaea L.), Scots pine (Pinus silvestris L.) and Norway spruce (Picea abies (L.) Karst.), The results were interpreted in terms of sigmoidal enzyme kinetics for allosteric regulation. Hill plots of the data gave straight lines at specific (K+)i intervals for the species. The slopes of the lines are the Hill coefficient, which could be regarded as a measure of the minimal number of allosteric sites. The Hill coefficient varied between ‐ 14.4 and ‐ 15.9. When divided by four, these values are fairly consistent with those in the literature. It is suggested that four active uptake sites interact with four groups of allosteric sites, each group containing four such sites, or that one active uptake site interacts with all the allosteric sites. Thus the results are evidence that the mechanism regulating K+ uptake is basically similar for the investigated plants. It is the interval of (K+)i mediating highly negatively cooperative allosteric regulation that differs among species. For some of the species, n decreased from about 15 and approached unity at high (K+)i values. This may indicate that only few sites are still available, making cooperativity unimportant. Alternatively high vacuolar (K+)i concentrations may give rise to an incorrect evaluation of data from Hill plots, since the cytoplasmic K+ content likely regulates the allosteric mechanism. Moreover, it is suggested that gene‐controlled carrier synthesis is responsible for the varying maximum K+ uptake efficiency among species.

Journal

Physiologia Plantarum – Wiley

Published: Feb 1, 1978

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