High V-PPase activity is beneficial under high salt loads, but detrimental without salinity

• Published in: The New phytologist Vol. 219; no. 4; pp. 1421 - 1432
• Main Authors: Graus, Dorothea, Konrad, Kai R., Bemm, Felix, Patir Nebioglu, Meliha Görkem, Lorey, Christian, Duscha, Kerstin, Güthoff, Tilman, Herrmann, Johannes, Ferjani, Ali, Cuin, Tracey Ann, Roelfsema, M. Rob G., Schumacher, Karin, Neuhaus, H. Ekkehard, Marten, Irene, Hedrich, Rainer
• Format: Journal Article
• Language: English
• Published: England New Phytologist Trust 01.09.2018; Wiley Subscription Services, Inc; John Wiley and Sons Inc
• Subjects: Acidification; Adenosine triphosphatase; Capacity; Cell death; Cell Death - drug effects; Cell Membrane - drug effects; Cell Membrane - metabolism; cell viability; Depolarization; Diphosphates - metabolism; electrodes; enzyme activity; functional properties; gene overexpression; Growth conditions; H-transporting ATP synthase; Hydrogen-Ion Concentration; hydrolysis; Hyperactivity; image analysis; Imaging techniques; Inorganic Pyrophosphatase - metabolism; Isoenzymes - metabolism; Leaves; Membrane potential; Membrane Potentials - drug effects; Mesophyll Cells - drug effects; Mesophyll Cells - enzymology; Necrosis; Negative feedback; Nicotiana - drug effects; Nicotiana - enzymology; Nicotiana benthamiana; pH effects; Photosynthesis; Plant Epidermis - cytology; Plant Epidermis - drug effects; plasma membrane; plasma membrane voltage; proton pump; proton pump currents; Proton Pumps - metabolism; proton-motive force; Protonmotive force; Protons; Pumping; Pyrophosphatase; Salinity; Salinity effects; Salinity tolerance; salt; salt stress; Salt tolerance; sodium; Sodium Chloride - pharmacology; Solute transport; Solutes; Stress, Physiological - drug effects; Transgenic plants; vacuolar pH; Vacuolar Proton-Translocating ATPases - metabolism; vacuolar proton‐ATPase (V‐ATPase); vacuolar proton‐pyrophosphatase (V‐PPase); vacuoles; Vacuoles - enzymology; salt; vacuolar proton-pyrophosphatase (V-PPase); cell death; vacuolar pH; vacuolar proton-ATPase (V-ATPase); proton pump currents; plasma membrane voltage
• ISSN: 0028-646X; 1469-8137; 1469-8137
• DOI: 10.1111/nph.15280

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 proton-pumping 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.