Extracellular ATP mediates cellular K+/Na+ homeostasis in two contrasting poplar species under NaCl stress
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eATP mediates cellular K + and Na + homeostasis in two contrasting poplar species differing in salt tolerance.
Using the non-invasive micro-test technology (NMT), the effects of extracellular ATP (eATP) on salt-altered flux profiles of K+, Na+, and H+ were investigated in salt-tolerant poplar species, Populus euphratica and salt-sensitive P. popularis. A short-term NaCl (100 mM NaCl, 12 h) resulted in a Na+ efflux and a correspondingly increased H+ influx in P. euphratica cells, but the effect was not seen in P. popularis. ATP (50 μM) enhanced exchange of Na+ with H+ in salt-stressed cells of two species (6, 12 h), especially in P. popularis. However, the ATP-stimulated Na+ efflux and H+ influx were significantly inhibited by amiloride (a Na+/H+ antiporter inhibitor) or sodium orthovanadate (a plasma membrane H+-ATPase inhibitor), indicating that the ATP induction of Na+ extrusion resulted from an active Na+/H+ antiport across the plasma membrane (PM). NaCl accelerated K+ efflux in the two species, with a more pronounced effect in the salt-sensitive poplar. The salt-induced K+ efflux was markedly restricted by the K+ channel blocker, tetraethylammonium chloride, indicating that the K+ efflux is mediated by depolarization-activated outward rectifying K+ channels and non-selective cation channels. ATP benifited poplar cells, especially the salt-sensitive P. popularis, in maintaining K+ homeostasis under external salinity. This was likely the result of activated H+ pump in the PM, which restricted the K+ efflux through the inhibition of depolarization-activated K+ channels in both species. Na+ and K+ flux recordings revealed that non-hydrolysing analogues of ATP, αβ-meATP (50 μM), and ATPγS (50 μM) produced an effect similar to that of the hydrolysable form but with a more pronounced effect. However, ADP- and AMP-stimulated cells (50 μM) exhibited behaviors different from those invoked by ATP, αβ-meATP, and ATPγS treatments. eATP signalling in K+ and Na+ homeostasis was blocked by the antagonists of animal P2 receptors, PPADS, and suramin. Moreover, ATP-stimulated Na+ extrusion and reduction of K+ loss in NaCl-stressed cells were inhibited by LaCl3 (an inhibitor of Ca2+-permeable channels) and DPI (an inhibitor of PM NADPH oxidase), indicating that ATP signalling was mediated via second messengers, H2O2 and Ca2+, in the two poplars differing in salt tolerance.
KeywordseATP Salt stress signalling K+ flux Na+ flux H+ flux Populus euphratica Populus popularis Non-invasive micro-test technology (NMT)
The research was supported jointly by the National Natural Science Foundation of China (Grant Nos. 31270654, 31570587, 31200207, and 31200470), the Research Project of the Chinese Ministry of Education (Grant No.113013A), the key project for Oversea Scholars by the Ministry of Human Resources and Social Security of PR China (Grant No. 2012001), the Program for Changjiang Scholars and Innovative Research Teams in University (Grant No. IRT13047), the Program of Introducing Talents of Discipline to Universities (111 Project, Grant No. B13007), and Beijing Municipal Training Program of Innovation and Entrepreneurship for Undergraduates, Beijing Forestry University (Grant No. S201510022037).
Compliance with ethical standards
Conflict of interest
The authors declare no conflict of interest.
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