Hydrogen Suifide Mediates Root K~+/Na~+Homeostasis In Poplars Under NaCl Stress

Soil salinization is serious environmental problem that restricts the development of agriculture and forestry in our China. Improving salt-resistance of crop and woody plants has received much attention for many years. Increasing evidence shows that hydrogen sulphide (H2S) functions as a signaling molecular contributing to mediations of multiple physiological processes. However, the mechanisms for H2S control of ion homeostasis under salt stress are largely unknown.Using the Non-invasive Micro-test Technique (NMT), we investigated the effects of exogenous NaHS (a H2S donor) on root ion fluxes in a salt-tolerant poplar species, P.euphratica, and salt-sensitive poplar spcies, Populus simonii·(P. pyramidalis+Salix matsudand){Populus popularis35-44, P. popularis), after exposure to salt shock (100mmol L-1NaCl), and short-term stress (24h,50mmol L-1NaCl), and long-term salt treatment (5d,50mmol L-1NaCl). NaCl treatment caused a net K+efflux in roots of the two poplars. However, the salt-induced K+efflux was markedly restricted by NaHS (50μmol L-1) irrespective of the duration of salt exposure, shock or short-term stress. Moreover, the NaHS-enhanced Na+efflux was obviously inhibited by amiloride (a Na+/H+antiporter inhibitor) or sodium orthovanadate (a plasma membrane H+-ATPase inhibitor), indicating that the Na+efflux resulted from an active Na+exclusion across the plasma membrane. Our flux data showed that enhancement of H2S on Na+/H+antiporting and restriction of K+were more pronounced in the salt sensitive species, as compared to the salt-resistant poplar, P.euphratica. We concluded that the beneficial effects of H2S are presumably due to the upward regulation of Na+/H+antiport system (H+pump and Na+/H+antiporter), which drives the Na+/H+exchange across the PM, and simultaneously restricts the K+efflux through depolarization-activated channels.