Article,
High V-PPase activity is beneficial under high salt loads, but detrimental without salinity
New Phytologist, (2018)
DOI: 10.1111/nph.15280
Abstract
* The membrane-bound proton-pumping pyrophosphatase (V-PPase), together with the
V-type H+-ATPase, generates the proton motive force that drives vacuolar membrane solute
transport. Transgenic plants constitutively overexpressing V-PPases were shown to have
improved salinity tolerance, but the relative impact of increasing PPi hydrolysis and protonpumping
functions has yet to be dissected.
* For a better understanding of the molecular processes underlying V-PPase-dependent salt
tolerance, we transiently overexpressed the pyrophosphate-driven proton pump (NbVHP) in
Nicotiana benthamiana leaves and studied its functional properties in relation to salt treatment
by primarily using patch-clamp, impalement electrodes and pH imaging.
* NbVHP overexpression led to higher vacuolar proton currents and vacuolar acidification.
After 3 d in salt-untreated conditions, V-PPase-overexpressing leaves showed a drop in
photosynthetic capacity, plasma membrane depolarization and eventual leaf necrosis. Salt,
however, rescued NbVHP-hyperactive cells from cell death. Furthermore, a salt-induced rise
in V-PPase but not of V-ATPase pump currents was detected in nontransformed plants.
* The results indicate that under normal growth conditions, plants need to regulate the
V-PPase pump activity to avoid hyperactivity and its negative feedback on cell viability.
Nonetheless, V-PPase proton pump function becomes increasingly important under salt stress
for generating the pH gradient necessary for vacuolar proton-coupled Na+ sequestration.
