The amino acid cysteine was repeatedly shown to be implicated in the plants stress response. This project aims to elucidate which effect cysteine has on the proteome of Arabidopsis. Treatment of Arabidopsis thaliana seedling cultures with cysteine resulted in distinct proteomic changes. To further investigate on the role of cysteine metabolism and associated proteins during biotic stress, the proteomic response of Arabidopsis thaliana leaves inoculated with the plant pathogen Pseudomonas syringae pv. tomato DC3000 was monitored.