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.

Populus euphratica HSF binds the promoter of WRKY1 to enhance salt tolerance

“…The pattern of Na + flux in herbaceous species differs from that in woody plants. Our previous studies showed that root Na + flux was constant in P. euphratica and mangrove [35,36,41,42], because the roots of these woody plants were large and could accumulate large amount of salt ions.…”

Sodium efflux in plant roots: What do we really know?

“…In addition, the Na + -specific microelectrode cocktailsin these procedures are still relatively new, and can pose problems including insufficient discrimination between Na + and similar ions such as K + (Shabala et al. 2005a,b;Cuin et al, 2011;Jayakannan et al, 2011;Lu et al, 2013).…”

NaCl-elicited, vacuolar Ca2+ release facilitates prolonged cytosolic Ca2+ signaling in the salt response of Populus euphratica cells

“…6-8). It has been repeatedly shown that Ca 2+ could maintain cellular K + /Na + homeostasis by enhancing Na + exclusion and minimizing K + loss in herbaceous species [87,88] and woody plants [29,30,39,[89][90][91]. In this study, the salt-induced enhancement of Na + /H + exchange and the transcription of genes that encoded a PM Na + /H + antiporter (SOS1) and a PM H + -ATPase (PMA) were markedly inhibited by antagonists of IP 3 and cADPR, neomycin and nicotinamide (Figs.…”