Abstract Vacuolar NHX-type antiporters play a role in
Na?/K? uptake that contributes to growth, nutrition and
development. Under salt/osmotic stress they mediate the
vacuolar compartmentalization of K?/Na?, thereby preventing
toxic Na?K? ratios in the cytosol. Porteresia coarctata
(Roxb.) Tateoka, a mangrove associate, is a distant
wild relative of cultivated rice and is saline as well as
submergence tolerant. A vacuolar NHX homolog isolated
from a P. coarctata cDNA library (PcNHX1) shows 96 %
identity (nucleotide level) to OsNHX1. Diurnal PcNHX1
expression in leaves was found to be largely unaltered,
though damped by salinity. PcNHX1 promoter directed
GUS expression is phloem-specific in leaves, stem and
roots of transgenic plants in the absence of stress. Under
NaCl stress, GUS expression was also seen in the epidermal
and sub-epidermal layers (mesophyll, guard cells and
trichomes) of leaves, root tip. The salinity in the rhizosphere
of P. coarctata varies considerably due to diurnal/
semi-diurnal tidal inundation. The diurnal expression of
PcNHX1 in leaves and salinity induced expression in roots
may have evolved in response to dynamic changes in
salinity of in the P. coarctata rhizosphere. Despite high
sequence conservation between OsNHX1 and PcNHX1

http://link.springer.com/article/10.1007%2Fs11033-014-3848-4#page-1