How high do ion fluxes go? A re-evaluation of the two-mechanism model of K(+) transport in plant roots

Plant Science : an International Journal of Experimental Plant Biology
Devrim CoskunHerbert J Kronzucker

Abstract

Potassium (K(+)) acquisition in roots is generally described by a two-mechanism model, consisting of a saturable, high-affinity transport system (HATS) operating via H(+)/K(+) symport at low (<1mM) external [K(+)] ([K(+)]ext), and a linear, low-affinity system (LATS) operating via ion channels at high (>1mM) [K(+)]ext. Radiotracer measurements in the LATS range indicate that the linear rise in influx continues well beyond nutritionally relevant concentrations (>10mM), suggesting K(+) transport may be pushed to extraordinary, and seemingly limitless, capacity. Here, we assess this rise, asking whether LATS measurements faithfully report transmembrane fluxes. Using (42)K(+)-isotope and electrophysiological methods in barley, we show that this flux is part of a K(+)-transport cycle through the apoplast, and masks a genuine plasma-membrane influx that displays Michaelis-Menten kinetics. Rapid apoplastic cycling of K(+) is corroborated by an absence of transmembrane (42)K(+) efflux above 1mM, and by the efflux kinetics of PTS, an apoplastic tracer. A linear apoplastic influx, masking a saturating transmembrane influx, was also found in Arabidopsis mutants lacking the K(+) transporters AtHAK5 and AtAKT1. Our work significantly revise...Continue Reading

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Citations

Mar 26, 2016·Frontiers in Plant Science·Ahmed M HamamHerbert J Kronzucker
May 18, 2016·Plant Science : an International Journal of Experimental Plant Biology·Raquel EstebanJose Fernando Moran
Jul 28, 2016·Frontiers in Plant Science·Manuel Nieves-CordonesFrancisco Rubio
Jan 18, 2018·Journal of Experimental Botany·Rubens Flam-ShepherdHerbert J Kronzucker
Apr 23, 2020·Physiologia Plantarum·Sahana BasuGautam Kumar
Aug 5, 2017·Frontiers in Physiology·Dekoum V M AssahaMahmoud W Yaish
Sep 25, 2018·Annals of Botany·Timothy J FlowersVadim Volkov
May 26, 2021·Journal of Plant Physiology·Dev T BrittoHerbert J Kronzucker
Jun 22, 2021·Frontiers in Plant Science·Shumei FangXilong Liang

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