title: Exogenous hydrogen peroxide, nitric oxide and calcium mediate root ion fluxes in two non-secretor mangrove species subjected to NaCl stress.
abstract: Using 3-month-old seedlings of Bruguiera gymnorrhiza (L.) Savigny and Kandelia candel (L.) Druce, we compared species differences in ionic homeostasis control between the two non-secretor mangrove species. A high salinity (400 mM NaCl, 4 weeks) resulted in a decline of the K(+)/Na(+) ratio in root and leaf tissues, and the reduction was more pronounced in K. candel (41-66%) as compared with B. gymnorrhiza (5-36%). Salt-altered flux profiles of Na(+), K(+), H(+) and Ca(2+) in roots and effects of exogenous hydrogen peroxide (H(2)O(2)), nitric oxide (NO) and Ca(2+) on root ion ﬂuxes were examined in seedlings that were hydroponically treated short term with 100 mM NaCl (ST, 24 h) and long term with 200 mM NaCl (LT, 7 days). Short term and LT salinity resulted in Na(+) efflux and a correspondingly increased H(+) influx in roots of both species, although a more pronounced effect was observed in B. gymnorrhiza. The salt-enhanced exchange of Na(+) with H(+) 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 active Na(+) exclusion across the plasma membrane. Short term and LT salinity accelerated K(+) efflux in the two species, but K. candel exhibited a higher flux rate. 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 channels, e.g., KORCs (outward rectifying K(+) channels) and NSCCs (non-selective cation channels). Exogenous H(2)O(2) application (10 mM) markedly increased the apparent Na(+) efflux and limited K(+) efflux in ST-treated roots, although H(2)O(2) caused a higher Na(+) efflux in B. gymnorrhiza roots. CaCl(2) (10 mM) reduced the efflux of K(+) in salinized roots of the two mangroves, but its enhancement of Na(+) efflux was found only in B. gymnorrhiza. Under ST treatment, sodium nitroprusside (SNP) (100 ∝M, an NO donor) increased Na(+) efflux at the root apex of the two species; however, its inhibition of K(+) loss was seen only in K. candel. Of note, NaCl caused an obvious influx of Ca(2+) in B. gymnorrhiza roots, which was enhanced by H(2)O(2) (10 mM). Therefore, the salt-induced Ca(2+) benefits B. gymnorrhiza in maintaining K(+)/Na(+) homeostasis under high external salinity.
authors.affiliation: College of Biological Sciences and Technology, Beijing Forestry University, Beijing 100083, PR China.
authors.forename: Yanjun
authors.initials: Y
authors.lastname: Lu
authors.forename: Niya
authors.initials: N
authors.lastname: Li
authors.forename: Jian
authors.initials: J
authors.lastname: Sun
authors.forename: Peichen
authors.initials: P
authors.lastname: Hou
authors.forename: Xiaoshu
authors.initials: X
authors.lastname: Jing
authors.forename: Huipeng
authors.initials: H
authors.lastname: Zhu
authors.forename: Shurong
authors.initials: S
authors.lastname: Deng
authors.forename: Yansha
authors.initials: Y
authors.lastname: Han
authors.forename: Xuxin
authors.initials: X
authors.lastname: Huang
authors.forename: Xujun
authors.initials: X
authors.lastname: Ma
authors.forename: Nan
authors.initials: N
authors.lastname: Zhao
authors.forename: Yuhong
authors.initials: Y
authors.lastname: Zhang
authors.forename: Xin
authors.initials: X
authors.lastname: Shen
authors.forename: Shaoliang
authors.initials: S
authors.lastname: Chen
mesh_terms: D002118:Calcium / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D043982:Rhizophoraceae / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology*
chemical_list: D009569:Nitric Oxide; D012965:Sodium Chloride; D012964:Sodium; D006861:Hydrogen Peroxide; D011188:Potassium; D002118:Calcium