AUTHOR=Hamam Ahmed M. , Britto Dev T. , Flam-Shepherd Rubens , Kronzucker Herbert J. TITLE=Measurement of Differential Na+ Eﬄux from Apical and Bulk Root Zones of Intact Barley and Arabidopsis Plants JOURNAL=Frontiers in Plant Science VOLUME=7 YEAR=2016 URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2016.00272 DOI=10.3389/fpls.2016.00272 ISSN=1664-462X ABSTRACT=

Rapid sodium cycling across the plasma membrane of root cells is widely thought to be associated with Na⁺ toxicity in plants. However, the eﬄux component of this cycling is not well understood. Eﬄux of Na⁺ from root cells is believed to be mediated by Salt Overly-Sensitive-1, although expression of this Na⁺/H⁺ antiporter has been localized to the vascular tissue and root meristem. Here, we used a chambered cuvette system in which the distal root of intact salinized barley and Arabidopsis thaliana plants (wild-type and sos1) were isolated from the bulk of the root by a silicone-acrylic barrier, so that we could compare patterns of ²⁴Na⁺ eﬄux in these two regions of root. In barley, steady-state release of ²⁴Na⁺ was about four times higher from the distal root than from the bulk roots. In the distal root, ²⁴Na⁺ release was pronouncedly decreased by elevated pH (9.2), while the bulk-root release was not significantly affected. In A. thaliana, tracer eﬄux was about three times higher from the wild-type distal root than from the wild-type bulk root and also three to four times higher than both distal- and bulk-root fluxes of Atsos1 mutants. Elevated pH also greatly reduced the eﬄux from wild-type roots. These findings support a significant role of SOS1-mediated Na⁺ eﬄux in the distal root, but not in the bulk root.