Phytohormones play an important role in the development and stress response of plants. Plants need to respond to a wide variety of environmental factors that can have a negative impact, but can also be positive. The former includes for instance wounding to which the plant reacts with the formation of protective substances against possible predators. Their synthesis is regulated by the phytohormone jasmonic acid (JA). Positive factors include arbuscular mycorrhizal (AM) fungi, which live in mutualistic symbiosis with the plant, helping to get nutrients from the soil. JA also has a regulating function in the establishment and development of an AM. Regarding the function of JA in plant developmental processes, we study the formation of the female flower organs of the tomato, since tomato plants, which are insensitive to jasmonic acid, are female sterile and are not able to form seeds. These approaches are complemented by the development of methods for a cell- and tissue-specific detection of jasmonates, thereby following different approaches to visualize JA using microscopic methods. In addition, we are interested in how the biosynthesis of JA, which occurs in two different plant organelles, the plastids and peroxisomes, is regulated.