Regulation of Nectar Secretion and Volatile Emission in Plants bei Jasmonates
Inducible indirect defences of plants include secretion of extrafloral nectar (EFN) and emission of volatile organic compounds (VOC), which are essential to attract plant defenders. Although the regulation of these defences is understood to be controlled by jasmonates (jasmonic acid, JA and related compounds), fundamental questions such as the ecological and evolutionary constraints that were involved shaping these traits and the evolutionary trajectory of the underlying signalling pathways remain unresolved. The focus of this thesis is to illuminate these questions from various angles using different model systems particularly selected to address each individual question. The first aim was to understand the spatial distribution of these indirect defences in the light of plant defence theories. It was found that defences are allocated in proportion to the value of the respective plant part for future fitness in Phaseolus lunatus and Ricinus communis. Next, the temporal pattern in EFN secretion was investigated. In lima bean, it was revealed that JA-regulated EFN secretion depends on the ambient light regime and is mediated by the formation of the amino acid conjugate, JA-Ile. To find parallels in the regulatory process of nectar secretion, the role of jasmonates in floral nectar (FN) secretion was explored as a next step and it was shown that JA treatment can trigger higher FN secretion in Brassica napus. Finally, the regulation of indirect defences was studied in the fern species Pteridium aquilinum to compare the ecological function and signalling pathways with known regulatory process in more derived plant species. The results obtained suggest a different and yet unclear ecological function of EFN and a very different signalling pathway for the emission of VOCs and EFN secretion in P. aquilinum.