Endogenous jasmonates (plant hormones) and synthetic derivatives were synthetized to study different aspects of plant signaling. In a first study, new evidence of the close relationship between the Ca2+- and JA- signaling pathways is provided. It is reported that the antibiotic neomycin selectively blocks the Ca2+ elevation induced by oral secretions of Spodoptera littoralis larvae and consequently inhibit the accumulation of the active jasmonate JA-Ile in the leaves of Arabidopsis thaliana plants. A second study uses a fluorinated mimic of the JA precursor OPC-8:0 as a molecular probe to study its metabolism in planta. The fluorinated compound and derived metabolites can be detected by UHPLC-MS/MS easily. The fluorinated OPC-8:0 can be translocated from damaged to undamaged systemic leaves. This result suggests that OPC-8:0 ─ in addition to JA and JA-Ile ─ may also contribute to propagate the mobile signal which induces systemic defense responses in plants. The third case of study reports on the possibility of manipulating the JA-signalling pathway by modifying the endogenous ligand JA-Ile. Based on the crystal structure of the JA-Ile receptor, two JA-Ile derived macrolactones were prepared. Both synthetic lactones induce nicotine accumulation to a similar extent as MeJA does in Nicotiana attenuata leaves. Finally, the JA-Ile inactivation mechanism upon ω-hydroxylation is investigated by using a chemical approach. It was found that impaired activity of 12-OH-JA-Ile is likely due to steric hindrance caused by the ω–OH. Furthermore, a convenient synthesis of 12-modified jasmonates is described. The methods discussed in this Dissertation should complement established molecular biology techniques to study plant physiology. New knowledge of the molecular mechanism of JA-Ile signalling ─ from early events like Ca2+-induced JA-Ile burst, until late events like the switch-off of the jasmonate signal ─ is presented.