Tropinone reductases (TR) are short-chain dehydrogenases/reductases participating in tropane alkaloid biosynthesis. TR genes were cloned from several tropane alkaloid containing Solanaceae. Based on DNA sequence similarity, 16 genes from Arabidopsis thaliana and 15 from Capsella rubella were annotated to code for TR-like enzymes (TRL). These Brassicaceae, however, do not contain tropane alkaloids. Another Brassicaceae, Cochlearia officinalis, contains the tropane alkaloid cochlearine as well as a tropinone reductase (CoTR), that reduces tropinone to pseudotropine and tropine. In this thesis the catalytic capacities of numerous TRL enzymes from A. thaliana and C. rubella were investigated. None of them reduces tropinone, but several low molecular ketones, among them aliphatic aldehydes, monoterpens, jasmonates, steroids and even flavonoids. Their exact metabolic role, is not known so far, but they have potential to serve as biocatalysts.