Biotic stresses such as infection by bacteria negatively affect plant growth and pose a severe threat to human food production. Improving our understanding of the immune systems of plants should help ensure food supplies in the years ahead. Bacterial infections induce Pattern-Triggered Immunity (PTI), a process in which plants perceive bacterial molecules and trigger an immune response. Mitogen- Activated Protein Kinase (MAPK) cascades are key players in this immunity process. Since the MAP Kinases (MPKs) 3/4/6 are mainly responsible for flg22- dependent phosphorylation events, we sought to find out how oxidation of MPK4 affects its ability to respond to stresses. Previous studies have shown varying kinase activity of MPK4 upon oxidation. Therefore, this project aims to provide an insight into the oxidative defense signaling mechanism of A. thaliana by investigating the role of MPK4 Cysteine181 in vitro and in vivo. Analysis of oxidation-mimicking as well as oxidation-dead mutants gave first hints that Cysteine181, which is located in the MPK4 substrate binding pocket, is a highly important regulatory residue of oxidative stress signaling by affecting MPK4 kinase activity and the activation of MPK3 and MPK6. Binding studies revealed that those events are due to sterical hindrance within the binding pocket of MPK4 and the blockage of upstream activator binding. The second part of this study characterizes compositional and post-translational changes of plant ribosomes during pathogen infection. Ribosomal proteins selectively participate in the formation of polysomes under different environmental and developmental conditions. However, the function of these changes still remains elusive. The current research project attempts to understand the plant ribosomal changes that occur upon exposure to bacterial pathogens. To observe ribosomal changes, A. thaliana plants were treated with a pathogen associated molecular pattern (PAMP), flg22. Mass spectrometric analysis identified quantitative changes of PAMP-induced ribosomal proteins in polysomes as well as changes in post-translational modifications. Spatial simulations of ribosomes revealed specific regions within the ribosomes to be PTI specific. This study demonstrates that MPK6 contributes to modification of P-stalk composition and phosphorylation status. The MPK6 mediated modifications may affect translation and in combination indicate a mechanism of PTI-related translational control.