A pharmacological analysis of high-affinity sodium transport in barley (Hordeum vulgare L.): a 24Na+/42K+ study

Soil sodium, while toxic to most plants at high concentrations, can be beneficial at low concentrations, particularly when potassium is limiting. However, little is known about Na+ uptake in this ‘high-affinity’ range. New information is provided here with an insight into the transport characteristics, mechanism, and ecological significance of this phenomenon. High-affinity Na+ and K+ fluxes were investigated using the short-lived radiotracers 24Na and 42K, under an extensive range of measuring conditions (variations in external sodium, and in nutritional and pharmacological agents). This work was supported by electrophysiological, compartmental, and growth analyses. Na+ uptake was extremely sensitive to all treatments, displaying properties of high-affinity K+ transporters, K+ channels, animal Na+ channels, and non-selective cation channels. K+, NH4+NH4+, and Ca2+ suppressed Na+ transport biphasically, yielding IC50 values of 30, 10, and <5 μM, respectively. Reciprocal experiments showed that K+ influx is neither inhibited nor stimulated by Na+. Sodium efflux constituted 65% of influx, indicating a futile cycle. The thermodynamic feasibility of passive channel mediation is supported by compartmentation and electrophysiological data. Our study complements recent advances in the molecular biology of high-affinity Na+ transport by uncovering new physiological foundations for this transport phenomenon, while questioning its ecological relevance

Unravelling nutrient exchange in ectomycorrhizal symbiosis contributing to plant potassium nutrition

Unravelling nutrient exchange in ectomycorrhizal symbiosis contributing to plant potassium nutrition. 12th Congress of the International Plant Molecular Biolog

Venus Flytrap HKT1-Type Channel Provides for Prey Sodium Uptake into Carnivorous Plant Without Conflicting with Electrical Excitability

The animal diet of the carnivorous Venus flytrap, Dionaea muscipula, contains a sodium load that enters the capture organ via an HKT1-type sodium channel, expressed in special epithelia cells on the inner trap lobe surface. DmHKT1 expression and sodium uptake activity is induced upon prey contact. Here, we analyzed the HKT1 properties required for prey sodium osmolyte management of carnivorous Dionaea. Analyses were based on homology modeling, generation of model-derived point mutants, and their functional testing in Xenopus oocytes. We showed that the wild-type HKT1 and its Na+- and K+-permeable mutants function as ion channels rather than K+ transporters driven by proton or sodium gradients. These structural and biophysical features of a high-capacity, Na+-selective ion channel enable Dionaea glands to manage prey-derived sodium loads without confounding the action potential-based information management of the flytrap

Functional HAK/KUP/KT-like potassium transporter encoded by chlorella viruses

Chlorella viruses are a source of interesting membrane transport proteins. Here we examine a putative K+ transporter encoded by virus FR483 and related chlorella viruses. The protein shares sequence and structural features with HAK/KUP/KT-like K+ transporters from plants, bacteria and fungi. Yeast complementation assays and Rb+ uptake experiments show that the viral protein, termed HAKCV (high-affinity K+ transporter of chlorella virus), is functional, with transport characteristics that are similar to those of known K+ transporters. Expression studies revealed that the protein is expressed as an early gene during viral replication, and proteomics data indicate that it is not packaged in the virion. The function of HAKCV is unclear, but the data refute the hypothesis that the transporter acts as a substitute for viral-encoded K+ channels during virus infection