1 Review: Mechanisms of ammonium toxicity and the quest for tolerance Raquel Esteban a* , Idoia Ariz b , Cristina Cruz b , Jose Fernando Moran a a Institute of Agrobiotechnology, IdABCSICUPNAGovernment of Navarre, Avda. de Pamplona 123; E31192 Mutilva, Navarre, Spain b Faculdade de Ciências, Centro Ecologia Evolução e Alterações Ambientais, Universidade de Lisboa, 1749016 Lisboa, Portugal *Author for correspondence: Jose Fernando Moran Phone: (+34) 948168000; Fax: (+34) 948 232191; email: jose.moran@unavarra.es Running title: ammonium toxicity and tolerance © 2016. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/