Physiological and phytochemical aspects of ant plant mutualism Ant plant mutualism and the importance of ants as biotic defenders for these plants have been well studied in the last decades from an ecological perspective. However the knowledge about the underlying molecular mechanisms and the phytochemistry of ant plants is still scarce. Thus this dissertation aimed to study ant plant mutualism on a molecular level with a focus on defense related metabolism. Because most myrmecophytes are trees the Neotropical ant plant Tococa quadrialata as a fast growing shrub was chosen as a model species to explore the consequences of the mutualism and to characterize the response of myrmecophytes to herbivory in detail combining field studies and modern analytical techniques. I aimed to find out about (i) whether Tococa plants still possess chemical defenses against herbivores or entirely depend on the protection provided by their mutualistic ants. Special emphasis was placed on herbivore inducible defenses their regulation by phytohormones (ii) as well as the biosynthesis and role of the identified compounds (iii). For this purpose novel analytical methods were developed to detect defensive metabolites and responses. Additionally to obtain a holistic picture of this mutualism the general metabolism of ant plants and how it is affected by the presence or absence of ants was examined as well.