Potassium in Plants

Anna Amtmann, University of Glasgow, Glasgow, UK
Francisco Rubio, CEBAS‐CSIC, Murcia, Spain

Published online: May 2012

DOI: 10.1002/9780470015902.a0023737

Full Article on Wiley Online Library

Potassium (K) is an essential macronutrient for plants involved in many physiological processes. It is important for crop yield as well as for the quality of edible parts of crops, as it is also required in human nutrition. Although K is not assimilated into organic matter, K deficiency has a strong impact on plant metabolism. Plant responses to low K involve changes in the concentrations of many metabolites as well as alteration in the transcriptional levels of many genes and in the activity of many enzymes. Today, these changes can be studied with high throughput technologies that allow a quantitative description of metabolic responses to K deprivation at multiple levels. To ensure K nutrition, plant roots are endowed with high‐ and low‐affinity uptake systems, some of which have been identified and characterised over the last decades of research.

Key Concepts:

K is an essential macronutrient required for plant growth and development.
K deficiency affects many essential physiological and metabolic processes.
The K status determines the profile and distribution of primary metabolites in plant tissues.
K nutrition is closely related to sugar allocation, nitrogen assimilation and amino acid levels.
High‐throughput technologies allow researchers to determine simultaneously a large number of metabolites, transcript levels and enzyme activities in response to K supply.
K deficiency leads to build‐up of sugars, down‐regulation of nitrate uptake and synthesis of nitrogen‐rich amino acids.
Roots are endowed with high‐ and low‐affinity K uptake systems that ensure K nutrition in a wide range of external concentrations.
hak5 transporters mediate high‐affinity K uptake and akt1 channels mediate low‐affinity K uptake.
Under certain conditions akt1 channels can also mediate K uptake from very low concentrations.
Additional unidentified systems may also promote root K uptake.

Keywords: potassium; deficiency; metabolism; A. thaliana; uptake; abiotic stress

	Figure 1. Adequate K supply to food crops and grassland is important for many aspects of food production.
	Figure 2. The requirement of K for plant nutrition is based on many essential functions of K in plant physiology and metabolism.
	Figure 3. Example of data obtained in multi‐level analysis of the effect of K deficiency and K re‐supply on plant primary metabolism. A subset of reactions occurring in root cell cytoplasm, mitochondria and plastids of A. thaliana plants were quantified with respect to changes in metabolite concentrations (grey‐scaled bar graphs), transcript levels (blue for increase, red for decrease) and enzyme activities (green bar graphs) of important enzymes (purple). Bar graphs show data for plants grown in control conditions (left), K‐deficiency for 14 days (centre) and K re‐supply for 24 h (right). Transcript changes in response to K‐deficiency and re‐supply are shown above and below the enzymes respectively. Individual boxes represent individual genes encoding different enzyme isoforms. For details see (Armengaud et al., 2009).
	Figure 4. Model of how K affects primary metabolism in A. thaliana. Red colour indicates a decrease, blue colour an increase. Low K concentrations in the cytoplasm of root cells inhibit pyruvate kinase thus limiting the glycolytic flux of carbon leading to a build‐up of hexose sugars in roots (sink) with knock‐on affects on shoot hexose levels leading to feedback inhibition of photosynthesis. Root nitrogen metabolism adjusts to a low‐carbon situation by reducing nitrate uptake (down‐regulation of nitrate uptake transporters, NRT) and assimilation (down‐regulation of nitrate reductase, NR), and by increasing biosynthesis of amino acids (AA) with high N/C ratio. Protein production is maintained at the cost of carbon supply from organic acids, particularly malate, which is used to supplement the TCA cycle through increased activity of malic enzyme. Based on the results of (Armengaud et al., 2009).
	Figure 5. Root K acquisition in roots. Athak5 is the only system mediating K uptake at external concentrations below 10 μM, probably by K⁺–H⁺ symport. At higher concentrations, K uptake takes place also through the akt1 channel and between 10 and 200 μM both systems Athak5 and akt1 contribute to K acquisition. At external concentrations higher than 500 μM, akt1 is the only system mediating K uptake. Athak5 mediates the NH₄⁺‐sensitive component of K uptake and Atakt1 the Ba²⁺‐sensitive one. In the absence of Athak5 and Atakt1, unknown systems (?) mediate K uptake that is sufficient for plant growth at K concentrations higher than 1 mM.

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Further Reading
	book Nieves‐Cordones M, Alemán F, Fon M, Martínez V and Rubio F (2010) "K⁺ nutrition, uptake and its role in environmental stress in plants". In: Ahmad P and Prasad MNV (eds) Environmental Adaptations and Stress tolerance of Plants in the Era of Climate Change. New York: Springer.

Article Title:	Potassium in Plants
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Potassium in Plants

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