title: Calcium mediates root K+/Na+ homeostasis in poplar species differing in salt tolerance.
abstract: 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 Ca(2+) on ion fluxes were investigated in salt-tolerant poplar species, Populus euphratica Oliver and salt-sensitive Populus simonii x (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. Ca(2+) 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.
authors.affiliation: College of Biological Sciences and Technology, Beijing Forestry University, Beijing 100083, P.R. China.
authors.forename: Jian
authors.initials: J
authors.lastname: Sun
authors.forename: Songxiang
authors.initials: S
authors.lastname: Dai
authors.forename: Ruigang
authors.initials: R
authors.lastname: Wang
authors.forename: Shaoliang
authors.initials: S
authors.lastname: Chen
authors.forename: Niya
authors.initials: N
authors.lastname: Li
authors.forename: Xiaoyang
authors.initials: X
authors.lastname: Zhou
authors.forename: Cunfu
authors.initials: C
authors.lastname: Lu
authors.forename: Xin
authors.initials: X
authors.lastname: Shen
authors.forename: Xiaojiang
authors.initials: X
authors.lastname: Zheng
authors.forename: Zanmin
authors.initials: Z
authors.lastname: Hu
authors.forename: Zengkai
authors.initials: Z
authors.lastname: Zhang
authors.forename: Jin
authors.initials: J
authors.lastname: Song
authors.forename: Yue
authors.initials: Y
authors.lastname: Xu
mesh_terms: D002118:Calcium / Q000494:pharmacology*; D006706:Homeostasis; D007474:Ion Exchange; D007700:Kinetics; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D032107:Populus / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D011522:Protons; D055049:Salt Tolerance; D012964:Sodium / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology*; D013045:Species Specificity; D013312:Stress, Physiological
chemical_list: D011522:Protons; D012965:Sodium Chloride; D012964:Sodium; D011188:Potassium; D002118:Calcium