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Potassium transport and compartmentation in ....

Project: Research project (funded)Research

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Description

Potassium (K+) plays a number of important and interlinked functions: at the cell level these include protein synthesis, enzyme activation, photosynthesis and cytoplasmic pH homeostasis whereas at the whole plant level K+ is important in phloem transport, turgor regulation, and gas exchange through stomatal movements. To fulfil these roles, plants require large amounts of K+. The consequent need for K+ fertilisation, in agricultural settings, constitutes a major cost for agriculture.
In contrast to K+, Na+ is not essential for plants and can even be toxic. Indeed, its abundance leads to salinity stress, which results both from toxicity of Na+ per se (e.g., when this cation is accumulated in the cytosol) and from osmotic stress (e.g., in leaf cells due to Na+ accumulation in the leaf apoplast). Soil salinity affects over 20% of the world's cultivated land. Furthermore, growing demand on fresh water supplies and irrigation with lower grade water mean that soil salinisation and the resulting drought/osmotic stress will increase significantly in the near future, especially when combined with adverse climate change.
From the model species Arabidopsis we have learned that both the plasma membrane expressed HKT and the tonoplast expressed TPK transport systems play a role in Na+ and K+ homeostasis and thereby in tolerance to salinity and drought stress. We will characterise HKT and TPK transporters in cereals, by using patch clamp and two electrode voltage clamp to compare transport properties of barley and rice HKT and TPK transport systems with those of their orthologs in Arabidopsis. Real time PCR will be used and GUS-promoter lines will be constructed to study expression levels and patterns in a variety of K+, Na+ and drought conditions. Modulation of the expression levels of HKT and TPK transporters through overexpression using constitutive promoters or loss of function mutations will reveal the contribution of specific transporters to the uptake and compartmentation of K+ and Na+ in rice and barley. Lines altered in expression levels will be submitted to growth analyses, ion content analyses and grain yield assays to identify barley and rice genotypes with improved traits in low K+ environments and in response to salinity and drought stress.

Layman's description

Potassium (K+) is essential for plant growth. It is the most abundant cation in plant cells, where it plays a number of important and interlinked functions. At the cell level these include protein synthesis, enzyme activation, photosynthesis and cytoplasmic pH homeostasis, whereas at the whole plant level K+ is important in phloem transport, turgor regulation, and gas exchange through stomatal movements. To fulfil these roles, plants require large amounts of K+. The consequent need for K+ fertilisation, in agricultural settings, constitutes a major cost for agriculture.
In contrast to K+, Na+ is not essential for plants and frequently its abundance leads to salinity stress that affects over 20% of the world's cultivated land. Furthermore, growing demand on fresh water supplies and irrigation with lower grade water mean that soil salinisation and the resulting drought/osmotic stress will increase significantly in the near future, especially when combined with adverse climate change.
Salinity stress, drought stress and K+ nutrition are inextricably linked for example through competitive inhibition of K+ uptake in roots by Na+, through salinity induced drought stress (osmotic stress), or through the effects of K+ on water relations.
Based on data obtained from model species (mainly Arabidopsis thaliana), we propose to study these interactions in rice and barley in order to improve salt resistance, reduce K+ fertilisation input and to augment drought tolerance. The work will concentrate on two gene families involved in Na+ and K+ transport at respectively the plamamembrane (HKT family) and the vacuolar membrane (TPK family). Transport properties of native HKT and TPK transporters will be determined in both species using electrophysiological approaches. Along with such functional analyses, localisation of these transport systems in the plant and modulation of their expression levels (overexpression, loss of function mutation) will allow to decipher their function in the whole plant physiology, to identify key research in this field for improving plant K+ nutrition in low K+ soils and/or in the presence of high Na+ concentrations, and finally to develop barley and rice varieties with improved growth in presence of low K+ availability, high Na+ concentrations and drought conditions.

Key findings

1: We found that two rice TPKs target to different types of vacuole in rice, in spite of very similar sequence and transport properties. We showed that the distinct expression patterns are due to specific residues in the C-termini.

2: Our study on HvHKT2;1 is the first to give a detailed report on the role of HKT transporters in a salt tolerant plant. HKT2;1 overexpression improved barley salt tolerance.

3: An in depth patch clamp study of plant TPKs showed that these vacuolar channels are mechanosensitive and that they may constitute hitherto unknown vacuolar osmosensors.
StatusFinished
Effective start/end date1/09/0630/11/10

Award relations

Potassium transport and compartmentation in ....

Maathuis, F.

BBSRC: £396,871.00

1/09/0630/11/10

Award date: 1/09/06

Award: UK Research Councils

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