title: Measurement of Differential Na(+) Eﬄux from Apical and Bulk Root Zones of Intact Barley and Arabidopsis Plants.
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 (24)Na(+) eﬄux in these two regions of root. In barley, steady-state release of (24)Na(+) was about four times higher from the distal root than from the bulk roots. In the distal root, (24)Na(+) 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.
authors.affiliation: Canadian Centre for World Hunger Research, University of Toronto Toronto, ON, Canada.
authors.forename: Ahmed M
authors.initials: AM
authors.lastname: Hamam
authors.affiliation: Canadian Centre for World Hunger Research, University of Toronto Toronto, ON, Canada.
authors.forename: Dev T
authors.initials: DT
authors.lastname: Britto
authors.affiliation: Canadian Centre for World Hunger Research, University of Toronto Toronto, ON, Canada.
authors.forename: Rubens
authors.initials: R
authors.lastname: Flam-Shepherd
authors.affiliation: Canadian Centre for World Hunger Research, University of Toronto Toronto, ON, Canada.
authors.forename: Herbert J
authors.initials: HJ
authors.lastname: Kronzucker
keywords: Arabidopsis thaliana; SOS1; barley; compartmental analysis; distal root; eﬄux; salinity stress; sodium