Multiple signaling networks of extracellular ATP, hydrogen peroxide, calcium, and nitric oxide in the mediation of root ion fluxes in secretor and non-secretor mangroves under salt stress

Abstract 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. Ca 2+ , H 2 O 2 , NO, and extracellular ATP (eATP) enhanced Na + extrusion by 27–152% in the salinized roots of K. obovata and A. corniculatum . Moreover, eATP, H 2 O 2 , and Ca 2+ 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 Ca 2+ in A. corniculatum . In contrast, NO reduced the Na + efflux elicited by eATP, H 2 O 2 , and Ca 2+ 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 , Ca 2+ interacted with H 2 O 2 , NO, and eATP to reduce the K + loss during salt treatment, whereas eATP enhanced the inhibitory effect of H 2 O 2 , Ca 2+ , 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.