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

作者：Schulze Lasse M; Britto Dev T; Li Mingyuan; Kronzucker Herbert J^*

来源：Journal of Experimental Botany, 2012, 63(7): 2479-2489.

DOI：10.1093/jxb/err419

• Barley
• compartmental analysis
• electrophysiology
• high-affinity Na+ uptake
• ion transport
• pharmacology
• potassium
• radiotracers
• salinity
• sodium

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 Na-24 and K-42, 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+, and Ca2+ suppressed Na+ transport biphasically, yielding IC50 values of 30, 10, and < 5 mu M, 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.

• 出版日期2012-4