Journal Article

Calcium mediates root K<sup>+</sup>/Na<sup>+</sup> homeostasis in poplar species differing in salt tolerance

Jian Sun, Songxiang Dai, Ruigang Wang, Shaoliang Chen, Niya Li, Xiaoyang Zhou, Cunfu Lu, Xin Shen, Xiaojiang Zheng, Zanmin Hu, Zengkai Zhang, Jin Song and Yue Xu

in Tree Physiology

Volume 29, issue 9, pages 1175-1186
Published in print September 2009 | ISSN: 0829-318X
Published online September 2009 | e-ISSN: 1758-4469 | DOI: http://dx.doi.org/10.1093/treephys/tpp048
Calcium mediates root K+/Na+ homeostasis in poplar species differing in salt tolerance

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Using the non-invasively ion-selective microelectrode technique, flux profiles of K+, Na+ and H+ in mature roots and apical regions, and the effects of Ca2+ on ion fluxes were investigated in salt-tolerant poplar species, Populus euphratica Oliver and salt-sensitive Populus simonii × (P. pyramidalis + Salix matsudana) (Populus popularis 35-44, P. popularis). Compared to P. popularis, P. euphratica roots exhibited a greater capacity to retain K+ after exposure to a salt shock (SS, 100 mM NaCl) and a long-term (LT) salinity (50 mM NaCl, 3 weeks). Salt shock-induced K+ efflux in the two species was markedly restricted by K+ channel blocker, tetraethylammonium chloride, but enhanced by sodium orthovanadate, the inhibitor of plasma membrane (PM) H+-ATPase, suggesting that the K+ efflux is mediated by depolarization-activated (DA) channels, e.g., KORCs (outward rectifying K+ channels) and NSCCs (non-selective cation channels). Populus euphratica roots were more effective to exclude Na+ than P. popularis in an LT experiment, resulting from the Na+/H+ antiport across the PM. Moreover, pharmacological evidence implies that the greater ability to control K+/Na+ homeostasis in salinized P. euphratica roots is associated with the higher H+-pumping activity, which provides an electrochemical H+ gradient for Na+/H+ exchange and simultaneously decreases the NaCl-induced depolarization of PM, thus reducing Na+ influx via NSCCs and K+ efflux through DA-KORCs and DA-NSCCs. Ca2+ application markedly limited salt-induced K+ efflux but enhanced the apparent Na+ efflux, thus enabling the two species, especially the salt-sensitive poplar, to retain K+/Na+ homeostasis in roots exposed to prolonged NaCl treatment.

Keywords: K+ flux; NaCl; Na+/H+ antiport; Populus euphratica; Populus popularis; the scanning ion-selective electrode technique; X-ray microanalysis

Journal Article.  7152 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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