Using 3-month-old seedlings of Kandelia obovata and Aegiceras corniculatum, we compared multiple signaling networks controlling K+/Na+ homeostasis in salt-secreting and non-secreting mangroves. K. obovata roots exhibited a higher capacity to extrude Na+ and take up H+ after exposure to 100 mM NaCl for 12 h compared to A. corniculatum. However, the salt-induced Na+/H+ exchange was inhibited by amiloride, a Na+/H+ antiporter inhibitor, and sodium orthovanadate, a H+-ATPase inhibitor, indicating that Na+ efflux resulted from active Na+ exclusion. Ca2+, H2O2, NO, and extracellular ATP (eATP) enhanced Na+ extrusion by 27-152% in the salinized roots of K. obovata and A. corniculatum. Moreover, eATP, H2O2, and Ca2+ interacted with each other to increase Na+ extrusion in the two species. However, the interactions between NO and other signals differed in the secretor and non-secretor mangroves. Under a saline environment, NO enhanced the Na+ efflux elicited by Ca2+ in A. corniculatum. In contrast, NO reduced the Na+ efflux elicited by eATP, H2O2, and Ca2+ in K. obovata. In the two mangrove species, salt caused a net K+ efflux, but it was markedly restricted by the K+ channel blocker TEA, indicating that the K+ efflux is mediated by K+-permeable channels. In A. corniculatum, Ca2+ interacted with H2O2, NO, and eATP to reduce the K+ loss during salt treatment, whereas eATP enhanced the inhibitory effect of H2O2, Ca2+, and NO on K+. efflux in the non-secretor K. obovata. Thus, species-specific salt signaling networks regulating root K+ and Na+ flux were established in the secreting and non-secreting mangroves. (C) 2014 Elsevier B.V. All rights reserved.
