Extracellular ATP, hydrogen peroxide, calcium and nitric oxide mediate root ion fluxes in Bruguiera gymnorrhiza subjected to salt stress
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Abstract
Using the non-invasive micro-test technique (NMT), the effects of extracellular ATP (eATP),
hydrogen peroxide (H2O2), calcium (Ca2 + ) and nitric oxide (NO) on root K+ /Na+ homeostasis were
investigated in a non-secretor mangrove species Bruguiera gymnorrhiza under short-term (ST, 24 hours)
salt stress (100 mmol/L NaCl). The experiments of NaCl and Mannitol in B. gymnorrhiza roots indicated
that there were mainly high ion-specific effects on NaCl-induced ion fluxes in roots. Salt stress resulted in
an increased Na+ efflux along the root axis of B. gymnorrhiza. However, the salt-enhanced Na+ efflux
was inhibited by amiloride, a Na+ /H+ antiporter inhibitor or sodium orthovanadate, a plasma membrane
(PM) H+ -ATPase inhibitor obviously, suggesting that the Na+ efflux was resulted from active Na+
exclusion. NaCl treatment caused an evident K+ efflux in B. gymnorrhiza, but it was significantly
restricted by the K+ channel blocker, TEA, suggesting that the K+ efflux was mediated by K+ permeable
channels. Exogenously applied eATP (300 mol/L), H2O2 (10 mmol/L), Ca2 + (10 mmol/L), or SNP
(NO donor, 100 mol/L) enhanced the salt-elicited Na+ efflux but reduced K+ efflux under ST
treatment. Under salt stress, H2O2 and Ca2 + showed a high capacity to exclude Na+ , while the inhibition
of K+ efflux was more pronounced by Ca2 + or NO application. In conclusion, our data revealed that
eATP, H2O2, Ca2 + , and NO upward regulated Na+ /H+ antiporter and H+ pump, an activity of Na+ /
H+ antiport system, which compelled the Na+ /H+ exchange across the plasma membrane and restricted
the K+ loss via depolarization-activated K+ channels simultaneously.
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